GM Marine L29 swap

[Larry]

I just scored a complete brand new marine variant (Mercruiser MPI) L29 454 fuel injection manifold with the fuel rail, injectors, throttle body, etc to bolt on to my crate 454HO in my 78 K10. It is complete and even powder coated per marine specs. The Ebay god was good to me.

 

Being that GM Marine stuff (Mercruiser, Volvo, etc) do not have emission controls (no EGR, etc)…or limited emissions controls, I am thinking of running a Mercruiser marine wiring harness, ECM and calibrations apposed to using an automotive PCM from a L29 C/K truck. The automotive L29 only produced 290 HP while the same engine in marine form produced 340 HP running on OBD I data. There is a sea of more power available with marine.

 

I realize that most of the board members on this forum are not into retrofitting newer powertrains into 20 plus year old trucks but have any of you ran across any decent websites or forums that mention success stories of using marine goodies for automotive retrofitting. I know LS1tech.com is pretty good but they don’t seem to deal with much marine stuff since the LS1 style engine has not been used in any marine applications until very recently. I also have friends at GM Powertrain but they are pretty well seperated from marine activity.

 

The thing that scares me about marine stuff is it is related to a BOAT (Bring Out Another Thousand).

[ezstriper]

not sure of all the issue you will face, but one I've seen is the early merc units would start in cold weather, I guess they figured no body would be boating when it got cold but we do and several boats in my marina will not start when the temp drops, they may have fixed the problem by now, Rob

[builderpaul]

Old (carborated) boat engines made great truck motors. They delivered lots of low end torque (not much highend though).

The additional HP is do to different engine internals. (cam) Not sure if you will gain anything with just the top end. I can see the electronics as being a problem. Boats operate under very different conditions. (Lower RPM with much more throttle and constant speed.)

As mentioned the cold start may be a problem.

To keep engine bay temps low most boats operate at a lower coolent temp. (mine runs at 140)

I also don't know about deceleration. Cars programming cuts fuel at deceleration (high vaccum) boats never incounter deceleration so I dont know how a boat program would handle this. You may be better to use the truck program.

Keep us posted.

[AmericanMuscle]

If you want to stick with the MerCruiser wiring harness and MEFI engine computer (which is the way I would go), I would acquire the cam MerCruiser put in that engine so it matches the ECM calibration. If you have the L29 GM intake, this was a 310hp engine offering from MerCruiser. This package would work well in a car. The air/fuel ratio in a marine engine is a little richer than what it is in a truck engine, so it will drink a little more gas, but you will find the throttle response is much better. Until somewhat recently, marine engines don't have to pass emissions, so the calibration was able to be richer.

 

MerCruiser installed a two-piece bread box style intake on their 454 MAG (385hp) and 502 MAG (415hp). If you want to make this kind of power, I'd suggest not using the GM L29 intake. I've seen the MAG intake systems for sale on Ebay before at reasonable prices.

 

The MerCruiser wiring harness is going to be much less complicated and you won't have to mess with emissions stuff. I would definitely go this route rather than mess with GM's factory wiring system.

 

Good luck!

[ManyCamaroz]

One thing to keep in mind is that a boat engine is under constant strain and is designed to accomodate that condition. Basically it's like a truck that never quits climbing a hill and never reaches the top.

 

As far as the HP rating the HP for the boat is probably measured at the flywheel and the truck is measured at the rear wheels.

[AmericanMuscle]

One thing to keep in mind is that a boat engine is under constant strain and is designed to accomodate that condition. Basically it's like a truck that never quits climbing a hill and never reaches the top.

 

As far as the HP rating the HP for the boat is probably measured at the flywheel and the truck is measured at the rear wheels.

 

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Your right that a boat engine is designed to sustain a constant, heavy load. There isn't a time when the engine isn't working (such as going down a hill in a truck), except when it's idling. For that reason an engine using a computer system calibrated for a marine engine isn't going to be as finely tuned for part throttle operation as a factory GM system, but I'd be willing to bet it still runs very well. I know a guy who put a 502 Mag MPI MerCruiser (415hp) in an older muscle car and used the MerCruiser wiring harness and computer, and it ran like awesome. Marine engines are typically tuned to seek a constant Air/Fuel ratio (such as 13.0:1) under all conditions, which is partly why the throttle response is typically much better on a marine engine than on a car engine. A car engine may have an Air/Fuel range of 16:1 while idling to 12.5:1 under a heavy load. A marine engine will be sitting idling at 13:1 and under a heavy load still at 13:1. With that being the case, the only variable changing is ignition timing. A truck engine is trying to seek a preset A/F ratio and a specific ignition timing degree based upon the load your putting on the engine. If you've ever looked at air/fuel tables and ignition timing tables that are programmed into an engine computer, you'll know what I'm talking about. There are a lot of values the engine is engine computer is using to provide just the right amount of air, fuel, and ignition timing.

 

Horsepower for boat engines and car/truck engines are both measured at the flywheel.