Desperate for Mechanical Insight

[Rusten]

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 .

[Catdog1]

Sorry,

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.

[Catdog1]

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

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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 @[email protected]. Thanks, Brian Raymond.

[Rusten]

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!

[Rusten]

On the topic of timing, I had also found the following, which is very nice:
http://www.marinemechanic.com/site/page229.html

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

[Ktn_cmu]

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...

Kyle

[Catdog1]

OK.

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

[Rusten]

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!
-Rusten

[Catdog1]

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.

[lowdrag]

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.