View Full Version : Desperate for Mechanical Insight

08-03-2004, 08:27 PM
Hi group,
I'm in a world of trouble and I desperately need some advice. After attempting to call the only Moomba mechanic (the only one within two-plus hours of my house) for over *two months*, I finally had to resort to using a conventional mechanic who is very familiar with the Chevy 350, in hopes fixing my Moomba's Indmar 350 Carb engine. That went very badly and now I'm stuck with a new engine that doesn't work - not sure what to do next.

Some background: After I purchased a 2000 Kanga w/94 hours, my engine overheated in *less* than an hour. It appeared that something may have been stuck in the cooling system, but it was too late once I realized it was running over it's heat threshold. I wound up with water in the oil, etc (cracks heads from what I understand). I immediately called the local Moomba tech, no return call ... Local Indmar techs - two disconnected lines, one (MasterCraft specialists) didn't call back.

My only option was to try a conventional automobile mechanic who did a lot of work with similar engines. He purchased a new Chevy 350 Vortec that according to him is identical to the Indmar (as far as the basic block/heads that he was using), then he used all of the existing marine parts from the Indmar to outfit the engine.

When all of this was done, the engine seemed to run fine (out of the water at least) -- just one problem. To this day, I can't get the engine over 3,600 - 4,000 RPM (depending on the day). I attempted to take the engine back to him on four separate occasions and he swears up-and-down it runs perfect. Without a load (out of the water), we've rev'ed it over 5,000 without a problem, every time. Yet as soon as the boat hits the water, I cannot get any top-end. Wondering if it wasn't able to push the shaft, I attempted to align the shaft to the .002 required by Moomba; however, that didn't give me any added speed. The prop and all other parts are the same parts that worked great on the original engine. After reading this forum, I had him set the timing to 10 BTDC @ 850 RPM as recommended here for more WOT -- but this didn't help. He checked/adjusted the carb several times, but he claims it's running fine.

I've spent literally weeks trying to comb this forum for something that might give me an idea -- but I can't find anything similar to my circumstance.

Unfortunately, I'm not mechanically inclined and I have a new Moomba I purchased that I have yet to be able to use for fear I may be jeopordizing the engine in the present running condition. Most recently, the mechanic doesn't want to work on the boat because he swears it runs fine. Essentially I'm stuck with a very large, pretty paperweight.

My question is two fold: One, does anyone have *any* idea what the problem might be -- why I can't get more than 4,000 RPM on a good day - from a new engine ... Two, does anyone have a recommendation for a marine mechanic somewhere near West Palm Beach, Florida?

Thank you in advance for *ANY* suggestions!

08-04-2004, 01:33 AM

I'm not going to pretend that I have the answer but....... in order for an engine to run it needs compression, spark, fuel and air. If these four things are present in correct supply it will run.
I'm sure you've tried everything. However in going over your story you said that you were able to get 5000 rpm at the shop but not on the water...right? I'm wondering if there was any difference between how this was done? For example I have a strong hunch that the engine cover was open when the mechanic got the 5000 rpm.....but on the water the cover is normally down. If this is true it sounds like the engine is starving for air. Check the carburetor and make sure the butterfly valve is wide open at full throttle. Also check to make sure that nothing is blocking the air intake vents on the engine housing. The lack of air would cause the symptoms you have experienced.

As for timing you can always try advancing or retarding the timing to see if that helps but it sounds like you've already tried that.

good luck

08-04-2004, 10:27 AM
Hi Jerensen,
Thanks so much for the reply.

I think I explained the problem incorrectly. I don't believe the difference is a running condition/change, but that the engine can't get up over 3,500-4,000 RPM when there is a *load* applied (when it's pushing through the water as opposed to out-of-gear). In other words, I can take it out-of-gear and run it over 5,000 RPM when in the water -- I just can't get it to rev when actually pushing the prop. This is why I thought it may be an alignment issue and I spent some time making sure the alignment is 100%. I can hand-turn the prop very easily, so I don't think that is stopping it.

It runs at exactly 160 degrees at all times, oil pressure at about 70 psi when it gets going in the 3,500 RPM range.

I think the engine probably gets air okay. I've been testing it with the entire engine case/back panel removed. If I understood what could make an engine rev fine, but not push a load, then I might have a better idea - but the mechanic says that could be anything and he doesn't want to work with it again. I've read up on changing carburators -- if I can't find someone to fix the boat, I may just try to add a new carburator on my own, even though the mechanic says it won't do anything.

I wonder if any Indmar mechanics in Florida might have those computer diagnostic systems -- perhaps that would help get to the bottom of the problem.

Thanks again for your suggestions,

james yarosz
08-04-2004, 10:36 PM
Did the mech. change the cam,and/or intake manifold when he changed engines?

08-05-2004, 12:09 AM
Hi James,
Thank you for the reply.

The mechanic utilized the cam shaft included with the new 350 Vortec (non marine) engine, which as I understand is slightly different from the "Marine" version of this same engine. I asked the mechanic if this could be related to the current problem. He explained that this could not be the cause of more than 300 RPM difference, maximum, in his opinion. He said that if we were comparing a non-Marine Chevy 350 alone to the Marine 350 Vortec, it would be a significant difference; however, the difference between a non-Marine 350 *with* Vortec heads as a "Crate" engine that is a higher performance specimen, this is an insignificant difference in comparison to the Marine version. Do you have any evidence to help me explain that he is misguided in his thinking / possibly get him to install the cam from my original Indmar 350?

I am going to ask him about the Intake Manifold tomorrow. He used just about everything from the Indmar outside of the block/heads, so I'm guessing the Intake Manifold is the original from the Indmar. Can you help me understand the significance of this / the issues if this was/was not replaced?

Thanks so much,

08-05-2004, 02:34 AM
Can you get indmar on the phone and ask them to define some of the differences?

They may go deeper than you think. The automobile engine may be designed to redline at 4000 rpm or so.... there should be a dyno curve available for the crate engine that would define the horsepower / torque / rpm curve.

I'm very surprised about the heads being the same. I also thought the main and connecting rod bearings were toleranced differently on the marine engine, for different lubrication characteristics. The car engine uses 5 W oil, the marine version uses 20 W oil. If you are using 20 W in this crate engine, and its not toleranced for it, you may be starving for lubrication and compression at top end.... you really have got to find somebody that knows what indmar does inside these motors.

The marine service for a motor is considered to be extremely stressful, far more stressful on a motor than the typical automotive application... that's why I think indmar bullet-proofs the lower-end internals....again, you need to check. The parts guy at my dealer said the indmar is close to the auto crate motor, but on cross examination he has absolutely now experience or data to make that claim. Plus, he's wrong 85% of the time about Moomba parts. Frustrating, but unfortunately par for the course in the marine retail world.

I'm also surprised you'd ever rev the engine that high. Have never had our Outback above 4500 and rarely above 4200. Its a ski boat, designed for about 40mph top speed, and can go for many outings, many days, not exceeding 35 mph or roughly 3800 rpm.

So, check those expectations that you have about performance. Be cautious on the top end. Dangerous place to be messing around.

08-05-2004, 02:43 AM
Camshaft and intake ... yes, that could definitely be a difference. Should be able to ( very carefully ) remove the marine camshaft, get a part number, get a part number from the specifications on the crate motor, and compare the camshafts. Should be able to find performance curves on each of them also.

Just be sure to let us all know what you find. This whole topic is an area a lot of us have wondered about.

Indmar internal information seems hard to come by, maybe they try to keep the internal specifications "trade secret" in order to protect their niche. The last thing they want is marine engines replaced with less expensive crate engines. The key is figuring out what they have optimized internally in the marine engine over the years. Again, dig deep here. You may have to call big boat places on the coast to get real marine mechanics. Surely you could go down a phone list and eventually find somebody experience.

I can't believe this topic hasn't been searched out before in a google search....

08-05-2004, 03:17 AM

Here's one link that gives general reference to cams and heads.

No mention at all of engine internals...

08-05-2004, 04:43 AM
4th post. Sorry, can't edit others to add stuff.

OK. Its 4:30 in morning and I've been researching on the net for 2 hours.

According to what I'm reading ( and its mostly all third party stuff ), the marine application requires a motor rated for continuous duty. A totally different service factor than automotive. They are designed with higher quality pistons forged and/or with high silicone content that don't expand as much with heat build-up, different internal tolerances, very different cams and heads.

Basically, the marine version is an engine with parts that are heavy duty, similar to the way you would build a hot rod motor, to allow wide open throttle WOT, allow tolerances to remain proper for oiling while heat builds up, and generally to have a very, very different torque curve.

The automotive application is comparitively light-duty. Not a continuous service factor.

If you selected a truck-version of the automotive crate motor, you may be in better shape, especially as you change the cam. Truck motors are supposedly more robust, but apparently not so robust as a marine motor.

No matter what, unless you've bought a special duty, bulletproof crate motor, running at high rpm is going to be dangerous. And continuous full power starts, like needed for slalom, are going to take their toll.

Pratically speaking, trying to salvage some boating season, remaining questions are can you find a way to baby the thing and still have fun and how long will the motor it last. 1 year? 3?

08-05-2004, 01:15 PM
Prior to writing this reply, if anyone else has ANY suggestions -- please let us know. Despite the depth and value of this thread, I still don't have anything to put my finger on the prolem. This post discusses the finer points between two engines, however, I'm still left without an idea of what could cause my 350 Vortec to run at 4,000 RPM (or less) under load when it runs perfectly fine at 5,000 RPM out-of-gear.

First, to James-
Yes, the Intake Manifold (which is branded w/Indmar logo) is the same as the Indmar, attached to the new block. The carbs, water pump, ignition system, harmonic balancer, etc (essentially all "marine" upgraded parts on the engine) remain the original parts from Indmar. The mechanic says he only replaced the block/heads with the new Chevy 350 Vortec.

Hi Catdog-
Thanks for all of your replies. You've always been a great help when I've had questions on the forum. I've included answers to all of your points; however, consider that I am a software developer and not mechanically inclined. This is a disclaimer I may be way off ;-).

Regarding the top-end speed, consider that 4,000 is the *MAX* I can ever run the engine as it sits -- and often it won't run over 3,500. Typically it runs at 4,000 for two minutes, then makes a bogging sound and drops to 3,500. I am primarily a slalom skier, running the boat at 3,600-3,900 through the course and presently, the boat won't offer this power. On the same note, I'm *not* worried about running the boat at high speeds, such as 5,000 RPM - not at all. I'm far more worried about why the boat is running so much slower and whether this means that I'm hurting the engine by running it at all. I am so worried about this that I will not run the boat for more than five minutes -- I *only* run it for testing purposes. I haven't skied once since March -- when I sold my former boat and bought the Moomba.

First - regarding the differences between the marine/conventional "crate" engines: I did a lot of research after my mechanic purchased the non-marine engine despite my requesting him to purchase the marine version at MichiganMotorz or Discount Marine (both have very good pricing on Indmar replacement 350 Vortec marine engines). I was furious when I found out he purchased the standard engine, but the more research I did -- not to mention the fact that I couldn't get a marine mechanic to call me back and he was my only option -- I decided not to make a big deal of his action. In my research I found the same link you mentioned, plus many definitive "features" lists for marine engines. After speaking to Michigan Motors for about 20 minutes, I received a complete overview of differences -- and from what they explained, the cam is about the only significant/operational difference operationally speaking, unrelated to corrosion prevention/etc. At the end of this post, I'll list the full set of upgrades included with the marine version of the engine. Despite the cam and other less significant differences, the core engine appears to be 100% identical. They both have the same RPM top-end (both rated 330HP at 5,000 RPM - at the crank), etc.

Regarding the performance curve of the marine v. conventional cam for a 350 engine, I cannot locate that data. I also cannot determine what specifically is different between the two camshafts. I do believe they are both hydraulic roller cams (although not being mechanically inclined, this doesn't mean much to me) - and that is the extent of what I can find. The specs for the OEM motor that Indmar builds from are located on GM's site from what I understand. The PDF is here: http://www.gm.com/automotive/gmpowertrain/engines/vortec/apps/marine/5700_brochure.pdf

This may not be correct; however, I did find two specifications that may hold true:
Marine Cam: Lift .474” I, .474” E. Duration @ .050: 210° I, 214° E
Standrd Cam: Lift .435” I, .460” E. Duration @ .050: 212° I, 222° E

Regarding the difference in oil - if I understand correctly, the lower viscosity is the minimum, in other words, the number of viscosity while running cold while the higher number is at "operating temperature". Since the thermostat keeps the engine running at 160, the oil is always at the operating temperature viscosity (e.g. on a 20w-40, the oil would run at 40 and the 20 is a moot specification). In short, if I run a 20w-40 or a 5w-40, the engine would effectively be running the same weight at 160 degrees, regardless of which I used. Of course I could be wrong.

Regarding the two engines being engineered with different qualities of steel/forging/etc -- although I am not experienced in this, the facts appear to speak differently that what you've suggested. None of the documentation or feature-lists for the Marine engines includes such data. The marine engines have better paint, some brass parts, etc. Other than those minor differences, plus the more substantial upgrades in camshaft and intake manifolds (which is preserved from my original engine, so this shouldn't be an issue), there is never anything in black-and-white backing up the claim of a different engine. From what I understand they are made from the same parts/same facility in Mexico.

All of this does raise one interesting point. Indmar's website says that timing cannot be set using "conventional" methods. Does anyone know what it cannot be set using conventional timing methods? I ask because I'm fairly sure this is how my timing was set, with a conventional timing gun on the first plug (did I say that correctly?). Additionally, it appears that cams have to be adjusted in relation to timing/etc. Could this be an issue relating to a unique method required to time the engine and/or a cam adjustment?

Thanks again for all of your suggestions,

08-05-2004, 08:30 PM
Agree with about everything both of you are saying.

Found that load is the issue also.

Load breaks-down further, not to the physical "block" or carcass, but to the rating of the short block, which is the block containing the pistons, crank, bearings etc. They need to operate at a higher heat due to full-load operation for long times. Pistons need to be toleranced to accept expansion, simultaneously, pistons need to be made of different materials to prevent expansion. Net result is the ability to operate at higher core temperature. Yes, the thermostat still reads 160, but the internal temperatures are indeed higher --- so the parts need to be chosen accordingly --- when runnning the engine at high load / high rpm ( that's the part that's different for a boat vs a car ).

Based upon what I found, it looks like power curve for the automotive engine can be changed via cam and head-flows/valve size to approach the marine torque/power/rpm curves, but the duty factor on all the other parts probably won't provide longevity.

Regarding the drop in rpm at skiing speeds... am not sure. Time it and tweak it. But I'm afraid Inliner's point will prevail. ( glad we are not talking about redline operation.)

Your other instincts are correct about the thread, we are not marine engine internal specialists. I'm a chem engineer and I build old car motors on the side, but I have no data about marine engine construction that is pure and factual. I know how pistons are chosen for the duty, and I know that performance engine internals are selected for the specific application. And the automobile block is the plain jane version of all this. Hot rodders beef up parts for reasons. Internal operating temperatures are different than temperature measured in the water stream by the thermostat and sensors.

What happened was clearly against your instructions, so don't take any of our speculation personally here, and recognize we aren't experts... just want to give you a sounding board. Want to give you some information that you can use to further quiz the experts... once you find them.

08-06-2004, 02:46 AM
Hi Catdog-
Thanks again for the reply (thanks to Inliner as well). I certainly don't mind criticism whatsoever, please don't take my reply to suggest that. Rather, I hoped to shed some empirical data to further hone in on the problem / continue to receive ideas.

On that note, and to reply to both you and Inliner, I absolutely understand the load requirements on a marine engine. I think it is clear that the engine in a boat (particularly a ski boat) can't be compared with a car engine, from the perspective of the workload, and I definitely don't disagree with anything you are saying in theory.

With that said, I'm still hoping to seek out additional ideas. While I certainly see the "marine v. conventional engine" issue as one very likely cause of this problem, I am not sold on that being the end-all, for a couple reasons... First, the empirical data shows that there isn't a difference in torque, horsepower, quality of metals/forging, etc. If two engines have equivalent torque and utilize the exact same parts from the same facility (again, this is black-and-white evidence) - we're talking only about the block/head here, there just isn't anything to suggest that there is some mysterious, almost intangible marine component missing from the crate 350 Vortec that prevents it from outputting the torque specified. Now if other numbers were equal and the torque was different, I would agree. Or if I weren't losing 1,700 RPM to something that essentially can't be described (you have to admit, for a loss of 1,700 RPM, there should be at least a difference in torque rating, some serious difference in the heads that would show up in the manufacturers own specifications, etc. Comparing the GM specs, this is not present. Second, the way in which the engine "bogs" -- it almost sounds as if the fuel pump or carburator isn't supplying enough to power the engine. The mechanic suggested that he thought this was not the problem, but had I received advice on this forum to the contrary, I was considering buying a new carburator and fuel pump on the small chance it would work, even though it could be money wasted.

Finally, since the camshaft does indeed appear to be different and because there exists this statement against setting the timing using a conventional manner, I thought at a minimum I could *start* here. If I learn the proper way to set the timing, and possibly how this relates to the unique marine cams, maybe I could get a bit further. Even if it turns out that there is some unwritten difference between GM's marine and non-marine blocks, at least I would still be improving my situation by learning what needs to get done with timing, etc.

More importantly, if someone happens onto this thread that knows a reliable Indmar/Moomba mechanic in South Florida, one that will call me back, that would be ideal!

Does this make more sense?

On a separate note, I promised a list of differences between engines. The following is what I understand to be the *complete* list of alterations to the "marine" version of the 350 Vortec Carburated engine. PLEASE - if you have evidence I am wrong, let me know.

* Marine cam shaft
* VORTEC aluminum High Rise intake manifold (brass lined)
* Marine circulation pump
* Marine harmonic balancer
* Marine 14" fly wheel
* Marine Gaskets
* Corrosion resistant urethane paint
* Bronze freeze plugs
* Stainless valves
* Marine Brackets

08-06-2004, 03:40 AM
Maybe there is some sort of motor protection logic built into the wiring. Indmar makes some reference in the owners manual that overheating will force the engine into a mode where 4 cylinders shut down and pump only air and limit rpm to 2000 so you can get back to the dock. I think its only the EFI engines, though.

Anyway, you are asking good questions about timing and spark, maybe there is an electronic timing advance circuit in the motor that is getting way out-of-whack when this motor is revving at the loads of moving the boat at speed. The camshaft installed, combined with the huge overload, causes an electronic timing correction outside the actual ability of the firing cycle. ( with the street cam it is not set-up to give the torque you need at that speed and load ) Try this avenue.

Regarding the internals, I'm seeing mixed things on the net. Generally, my takeaway is that the marine unit by design has internals that the typical mechanic won't understand as being all that different, but really are. No data. Need GM or Indmar engineer to clarify it.

08-06-2004, 04:05 AM
www.gm.com/automotive/gmpowertrain/ engines/vortec/news/press19.htm

This marketing press release implies same internals.

If so, that's a great answer.

Lets keep digging; marketers can spin stuff, perhaps they're not above clouding the "standard of identity" of what "Vortec engine" means.

08-06-2004, 04:24 PM
Hey gang,
This is all very interesting and you can cut my rope but I agree with Rusten, you can talk all you want about automobile engines verse marine engines and work loads. The bottom line is that if a 350 votec street engine and a marine 350 vortec engine with the same horsepower and torque rating will provide exactly the same pulling power depending on gear ratios added or subtracted! Come on! Torque is torque!
If I extrapolate what I’m hearing ….some of you are telling me that a marine 350 vortec engine placed in a car will outperform …. have more pulling power than its original 350 vortec street engine? Are we serious? We’d better tell the guys and gals at the track I’m sure they’d love to hear this.

A steel can opener doesn’t open a can any faster than an aluminum pull tab but you can use it more than once…right? “Hardened” pistons do not provide anymore compression than their”weaker brothers” they just will not last as long under punishment. Bore, stroke, and compression ratio is still bore, stroke, and compression ratio.

The vortec engine that Rusten currently has in his boat should provide exactly the same power as a 350 marine vortec. Durability is not really the issue here.

I still say it has to have something to do with fuel, spark or air mixture.
Check the fuel pump pressure. (3 – 7) psi
I really doubt that the carburetor is a problem. You have not gone to a higher compression ratio or changed the fuel needs in any way. If idle system seems okay with no complaints and you’ve commented that it revs up fine in neutral….the carburetor is not the problem save your money.]
Check the timing.
If need be set the timing by hand under load…out on the lake. This engine isn’t breathing properly if it’s choking down. If this doesn’t solve the problem I have a hunch Catdog may be on to something with the electronic timing advance circuit not working properly.
Could it be that the street cam and the electronic advance are out of sinc and when the cam rpm calls for the advance, the circuit is not delivering the proper advance for this particular cam?

After all, the electronics were set up for the Indmar marine engine (and cam), right?
The only basic internal difference is the cam grind. Right?
You’re trying to use the same electronics and they may need to be recalibrated to provide the top end performance you’re looking for.

If this were the old ignition system with a mechanical distributor you’d pull the distributor and put it on a distributor machine and check the point gap, dwell and spring tension that control the spark advance system at the specified rpm.
At what rpm does this street cam call for advance to kick in? Is this being correctly provided electronically?
I’m not that familiar with electronic ignition but seems like this may need to be reset electronically.


08-06-2004, 05:23 PM
I am not a mechanic but have read this thread with a great deal of interest. If the problem is RPM why don't you simply try a smaller (lower pitch) propeller?

08-07-2004, 03:43 AM
Your right --- same is same on output. Two issues here --- achieving output and longevity. We started answering one question, and brought up the other, bigger question in the process. Got it.

I also surmise that the first answer is rooted in wrong cam and heads for marine, plus timing that can't possibly be adjusted to make the engine deliver even moderate rpm at the huge load of a boat. That stuff is a fact for crate auto versus boat motors. Example for me is pulling my boat and trailer uphill with my chevy truck. Foot to the floor, 4th gear, rpm just bogs and slows, downshift, same, downshift again, same ( if hill is really high )..... running the boat at skiing speeds is an application equivalent to steep uphill towing. Doesn't seem possible, but it is. Needs different cam and heads to pull faster uphill. Yes, a prop change might help, like a downshift, but before he tries that he should try to work it out in the motor.

Marine engines have never been set-up for same torque/hp curve as automotive. Thats clear on many mentions of the topic here on a net search. And, most of the crate blocks on the GM web sight clearly say not for marine use ( I'm talking short blocks, without the explosion proof electrical stuff even in the equation ). If Rusten can link that kind of disclaimer to his motor, he may have a different path he can follow.

Now, Vortec. Vortec I'm learning is a brand name. Within "Vortec" engines of the same displacement there appear to be very different set-ups for light truck versus marine versus industrial. The marketing press releases don't come-out and say the duty factor is higher for marine and industrial applications, and so internals need to stand-up to higher internal heat and longer exposure to stresses, so the truck version isn't the toughest version of Vortec. That's what it looks like, reading between the lines of all the press releases and magazine articles I can find on the net the last few days. They do reference boat and truck as two totally different markets, and that R&D/racing from one market is feeding advances in the other market. But they never say that the truck version is not set-up or tweaked for marine stresses. .

Theory now, marketers want to control the message. Vortec is being "branded" as tough enough for trucks with multimillion dollar ad campaigns. They don't want to cloud the message with "but the boat version is tougher". That, I'm pretty sure, is why we can't find the details about differences in the pistons, tolerancing, etc.
They don't want us to find the differences. I think that would confuse the truck buyers and endanger their branding concept. Plus, they consider the underlying engineering tweaks to be proprietary.

I hope the differences don't end up being significant, and that Rusten will work through the torque/rpm issue, or,

that he proves that the wrong short block has been installed for the application and its not fixable --- so the mechanic swaps it for him. Just trying to help nail the details down once and for all.

Really just want to complete that chart of Rusten's about what is different, Vortec marine vs Vortec automotive. Not sure where to get the information. Want to believe the internals are the same, but can't be sure yet.

Sorry, Rusten, for continuing to drive ideas without data. I hope we prove I've gone overboard.

james yarosz
08-08-2004, 09:33 AM
Rustin,beibg a Ford man I don't know much about "Chevys",but I have a friend who does.(GM engineer,hot rod guy).He says there are no internal differences in the two engines,and your problem lies elsewhere.Why would it turn 4000 rpm one day,and 3500 the next? My 03 LS only turns 4100rpm. JMO.

08-09-2004, 05:10 PM
This has developed into a very interesting thread! Thanks again to everyone who can contributed so far.

First – to CatDog’s first reply: I absolutely agree that, contrary to a simple carbureted engine, the EFI engine is very likely to have some proprietary logic relating to the ignition/etc and be more significantly altered from the conventional engine. That makes perfect sense with an EFI engine, even considering how naive I am about all of this. I’ve also found some collateral indicating this logic (a host of press releases for Indmar’s 1998 “new” engine line-up). Regarding the continued thread about the basic 350 Carbureted Vortec engine block/heads being different, there just isn’t any empirical data showing up to suggest so.

I should also mention that my thinking in this regard is related to my 20 minute conversations with both people from DM and Michigan Motorz (the two largest resellers I could find of Marine OEM engines). I made the assumption that if there was something to tout about a marine block and the reason an automobile block wouldn’t work, the guys selling the marine blocks would know! This is the manner in which I assembled the differences I included above. Additionally, it’s not like a marketing person to under-emphasize the features/upgrades, and because we can’t find such features listed in the marketing text, I’m further lead to believe there isn’t something we are missing (outside of what we’ve discussed) in the case of this Chevy 350 Vortec-to-Marine 350 Vortec Carburated, Block/Heads alone.

With that said, take a look at the bottom of this post for some interesting notes about cam differences.

To Jerensen – Thanks very much for the reply. Great analogy regarding torque v. integrity and it confirms what I had hoped. I am going to check the fuel pump pressure in-line and I’m going to try another carburetor, just to see whether it makes a difference. Because this could be an issue relating to a component that was fried when I overheated the original engine, I’m basing this test on the idea that it could be related to the secondary pump on the carburetor just as easily as the fuel pump.

To Bobby’s reply about the prop – the problem is not that the engine can’t drive the prop, it’s that the engine is not performing correctly. This could lead to more significant problems down the line if not addressed now. Further, although I could reduce the size of the prop, it still wouldn’t increase the overall output. On this note, any idea where people find things like prop specs for our boats other than on this forum? In other words, do you know whether Moomba sells some sort of comprehensive manual, something like a “Chilton’s Guide” for our boats? For specific CNC measurements (not rounded like the old-style measurements from what I understand), I have written down 13x12, 0.80 cup, 1” LH turn. Is that correct for the Kanga/Outback w/350 Carb?

In my travels and attempts to learn of the performance curves for the Marine cam, I found a very helpful site I thought you all might find interesting: “SkiBoatHelp.com – Drive Train Forum” here: http://www.skiboathelp.com/cgi-bin/forumdisplay.cgi?action=topics&forum=Technical+-+Drivetrain&number=1

Specifically, I think you will find this quote (in reply to my question regarding the Indmar 350 cam) very interesting:

Qutoe: camshafts ground for marine use have a couple more degrees of lobe separation (difference between centerline of In. and Ex.) than their automotive counterparts. You can't dial this in by degreeing the camshaft. It is ground in. A wider lobe separation does two things that are favorable in an engine used in a boat. #1 - it prevents the engine from sucking water into the heads and cylinders should something go wrong in your exhaust manifolds. #2 - it gives your engine a broader torque curve.

Thanks again for everyone’s input.

08-09-2004, 09:15 PM
Pretty interesting, yes.

Which crate engine, exactly, did this guy utilize?

08-10-2004, 03:39 AM
Hi Catdog-
Not sure what you mean or which "guy"? The quote was in reply to my question on the Indmar 350 cam performance curve. As far as the crate engine utilized by my mechanic, it was a post-97 generation GM Vortec 350 directly from a Chevrolet dealer. This is a "four bolt" if memory serves, which is different from earlier models of the 350 Vortec, which were eigh bolt, there was one other moderate difference I cannot recall, but it was required to match the blocks precisely. Of course I could have this backwords ;-).

08-10-2004, 08:35 AM

Was referring to your mechanic, earlier post.

Following one of your original thoughts: is the crate motor valid for the application?

If you have a part number for the crate motor, or other ID ( may be on new oil pan, bar code with numbers ) then we can check to see if it is considered not valid for your marine application. But as thoroughly as you are searching, I bet you've probably done this already.

Rusten, the Vortec is indeed just a platform in marketing terms, advertised for auto, marine, and industrial applications as you know, and each application is indeed set up differently. The industrial vortec is cammed for 1800 rpm constant top speed at which it delivers its full hp. It has different internals including pistons. The marine version we've determined is also cammed differently and has a different set of curves than the auto version. The curves you posted earlier from GM Vortec Marine lliterature are prefaced with "varies by application". But I suspect you saw that, too

Even the auto version is cammed differently for different trucks.

I guess you either have to prove that the crate motor is not recommended for marine or else assume its ok and start making cam changes and see what happens.

The auto aftermarket parts guys like edelbrock and federal mogul can probably help you, also, on cams and bearings and pistons questions... maybe you can dial through to one of their technical applications specialists.... companies like this have to have guys who live to answer interesting cross-applications questions like yours.

Glad you picked IT for a living and not mechanics, aren't ya, by now!

By the way, completely blew my knee out this weekend on the water. My boat and ski are surplus now. So, your fighting to get onto the water and I'm wishin I never went.

08-10-2004, 01:21 PM
Found this post in archives here, response to question of how to set timing on a 5.7 V8 replacement engine, carb:

Boat Boy
Posts: 211
Joined: August 31 2002, 02:27 Posted on: 08-30-02 21:53:33


In order to bring the motor back into base time, jump the bare end of the timing shunt wire (the black one on the plug in on the backside of the distributor) to the pos. cable on the starter. this will take the motor to base timing, and slightly increase the rpm's. Hook up the timing light with the magnetic pick up on the #1cyl, and proceed to set your timing @10degrees BTDC. Once completed, disconnect jumper wire. If you should have further questions, please contact me @techservice@skierschoice.com. Thanks, Brian Raymond.

08-10-2004, 02:16 PM
Very sorry to hear about that Catdog. I do know how you feel - I went eight years without being able to ski. I wish I had stuck with some derivative; it’s the best workout I’ve found. Good luck with finding something to continue.

Regarding the engine, I don’t have the specific part number, but the mechanic did consider this when picking the crate engine. From what I understand, they are identical in torque/horsepower, displacement, etc -- as mentioned earlier in the thread. He looked up the particular variation of the engine Indmar utilizes and went from there. This is what I was referring to when mentioning a post-97 350 Vortec engine (Gen III, I believe). This was the “Corvette” engine.

After much additional searching, I am every more confident on the differences being no further than those I’ve included and the engine in my boat being the same block/heads. Therefore, I’m more interested at looking to different angles at this point.

Any ideas on the Moomba manuals, is something like this offered? Or the prop sizes?

Best of luck with your recovery!

08-10-2004, 02:19 PM
On the topic of timing, I had also found the following, which is very nice:

I also read around the 'net that the Indmar 350 should be at 8 degrees BTDC between 500-800, although Brian recommends 10 degrees.

08-10-2004, 02:53 PM
I'd guess it is fuel. It takes a lot more fuel to run an engine at 4,000 rpm's under load than it does to do the same free. What if you run your boat out on the water and when it does it's thing, try pouring a little fuel in the top, or spraying some starter fluid in the carb, or best, a spray bottle of raw premium. If it runs better for that moment...fuel starvation is your problem...


08-10-2004, 07:47 PM

Check out page 4 of this pdf. The ECM for this application appears to control fuel pump output with engine load sensing. This type of situation could be causing your abrupt shift in output, consistent in a way with the above post about fuel starving.

Moomba should be able to tell you what ECM features are included in your original wiring harness set-up, which I think you are still using?

http://www.industrial-irrigation.com/Vortec PDF Brochures/IndustrialEFI.pdf

08-10-2004, 08:26 PM
Hi Catdog,
I am still using all original parts including ignition; however, I'm not aware of any ECM type of component on a Carburated engine -- at least I haven't seen anything to indicate there is more to it than just the standard ignition. I know that when I read Indmar press on the EFI's this type of functionality is included; however, I've never read anything similar regarding the carburated engines. Do you have a similar engine and noticed something along these lines? I will ask my mechanic tomorrow if he knows about this component.

Regardless of that, it is very interesting reading!

08-10-2004, 11:34 PM
Not certain, that's why when I saw this reference to ECM's with limited functions carburetted Vortec that I thought the Moomba set-up might have one.

Only historical post on ECM I've found here is the case where an EFI boat owner sent his ECM back to Moomba for reprogramming.

If it is ECM, then cam and ECM likely must match. Algorithms for these things tend to be proprietary and therefore functionality is hard to define.

Again, not an expert.

08-11-2004, 04:45 AM
After reading all of this, the big things I noticed were the benifits of the marine cam listed in a previous post. The benefit of having a broader torque curve seems like a big thing to me. Sounds like the marine cam will produce more torque higher in the rev range where your new engine seems to be falling flat. The motor gets to a certain rev limit where the application with the street cam can no longer produce enough torque to push a boat. Just my .02.

08-17-2004, 07:15 PM
OK, Rusten, we realize this thread got repetitive ( where my replies were concerned ) and we didn't nail down some causes.

Did you get resolution in another way?

08-17-2004, 08:20 PM
Hi Catdog-
I have an urgent medical matter with a family member that has required me to leave my home/boat for a couple weeks. As soon as I return I am going to try the alternate carburator and test the fuel pump. Then I'm going to update the thread.

Thank you for checking in. Hope your knee is feeling better,

10-12-2004, 06:26 PM
After taking the boat out of storage as a result of two hurricanes that have caused damage to our house, I'm finally focusing on repairing the Moomba again. As a refresher, the engine maxes out at 3,500 RPM for about 10 seconds, then drops down to 3,000 RPM *maximum* at Wide Open Throttle.

Yesterday I replaced the carburator, but that didn't do the trick.

Next I plan on replacing the fuel pump, but I'm not sure of the correct PSI / GPH. The Carter replacement seems to be two different GPH strengths.

I'm also going to try a new ignition system, as that seemed to get fouled up as a result of floods in the first hurricane. It's not terrible, but I think an electronic ignition would be a nice upgrade. Anyone have any ideas/opinions on the options?

Catdog - how is your knee coming?

Thank you all,

10-13-2004, 08:11 PM
Thanks, knee is better, but still a bit weak. Was a badly sprained MCL ( inner tendon ). Glad I had a lifejacket on when I fell in between the dock and the boat.

Am wanting to hear the final diagnosis on the replacement engine. I'm still voting camshaft / timing & ECM, but I'm merely a backyard mechanic. Good luck. Sorry about the hurricanes.

10-16-2004, 06:18 PM
Has anyone suggested cheking the fuel tanl if the sock in the tank is dirty trhe engine would run fine till a load is put on it

10-28-2004, 09:34 AM
Has the fireing order been checked? Whe have ran into this exact problem after working on our engine a few times, and it was the firing order. It runs fine until under load, then the engine boggs. Due to the fact you aren't running on all holes!

Didn't read all the pages (too man), just a suggestion.