Desperate for Mechanical Insight

[Catdog1]

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.

[Rusten]

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

[Catdog1]

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.

[Catdog1]

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.

[Jerensen]

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.

Jerensen

[Bobby]

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?

[Catdog1]

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]

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.

[Rusten]

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/f...n&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.
-Rusten

[Catdog1]

Pretty interesting, yes.

Which crate engine, exactly, did this guy utilize?