Merc 7.4l 454 Gen 4 to 5 interchangeable?

[thormx11]

I do not know much about engine internals (which is why I am always here!) but the engine in question I am talking about they replaced the cam, heads, lifters, intake, and carb going from 330hp to 560 hp on the dyno. The entire kit was $3600 if I remember right.

I am sure the marine carb/intake/exhaust would restrict the numbers quite a bit on that setup though.

 

[thormx11]

But would that be a viable option for my boat? Somebody has already swapped the gen 4 engine into it before. I do not know how it worked for the boat though.

My current boat (1995 Century Arabian 240) only came from the factory with a 7.4/bravo 1 but when I got the boat it had a ~2000 5.7/alpha 1. The boat handles great for me, gets on plane quickly and tops out around 48 mph. For as heavy as that boat is I believe it works well, and could only imagine how it handled with a 7.4.

 

[Scott Danforth]

I do not know much about engine internals (which is why I am always here!) but the engine in question I am talking about they replaced the cam, heads, lifters, intake, and carb going from 330hp to 560 hp on the dyno. The entire kit was $3600 if I remember right.

I am sure the marine carb/intake/exhaust would restrict the numbers quite a bit on that setup though.

to get that on a dyno is one thing. however you have to add lots of duration with lots of overlap to the cam....... all top end power, no lower RPM power and it would suck water up your exhaust and hydrolock your motor in a boat once you tried starting it. again, you have to understand maximum duration of a cam in a boat, especially with wet exhaust.

personally, I would talk to your local machine shop and build a motor.

 

[thormx11]

Would a gen VI l29 engine from a 1ton truck swap over with my accessories? No matter which way I go I will need a new carb (was thinking edelbrock 1410) and could swap the cam before I put it in the boat.

 

[Scott Danforth]

Yes. I would look at a new comp cams XM284HR

 

[Tail_Gunner]

Yes. I would look at a new comp cams XM284HR

You need to sneak around and take a look at what the guy vortecpro is doing with 454's...450 hp with peanut heads.

Vortecpro 454 Peanut Port Engine Build And Drag Test

www.chevelles.com

 

[Scott Danforth]

here is real world dyno readings of a stock L29 and the comp XM284HR

How to Pick Up Big Power On a Junkyard 454 With a Simple Cam Swap

It was time to dig into the internals and make some power the old-fashioned way with a cam swap on our junkyard 454 engine.

www.superchevy.com

 

[alldodge]

Can also just leave the truck cam in the motor

 

[thormx11]

I may have to stick with the truck cam. According to that article you also have to change the valve springs and retainers. Also it looks like most of the HP gain is outside of the WOT throttle range of the boat which is 4200-4600 I believe? Maybe that range is for the stock engine only though and would change?

 

[Scott Danforth]

I may have to stick with the truck cam. According to that article you also have to change the valve springs and retainers. Also it looks like most of the HP gain is outside of the WOT throttle range of the boat which is 4200-4600 I believe? Maybe that range is for the stock engine only though and would change?

the 4200-4600 RPM limit is because of the stock valve train. your outdrive is limited to 5500 RPM in stock configuration

a big block can spin 6000 RPM all day long if you want it. however you have to have the right valve train among other things.

 

[thormx11]

I picked up a used L29 from a 2000 silverado. I will be leaving it stock for now, minus a new intake & carb. I am planning to go with a Edelbrock 1410 but am having trouble figuring out which intake I should go with. I have found two cast iron ones (part# 333841 & 14087487) but am not sure if they will fit. Or would a cheaper aftermarket aluminum intake work? It will be raw water cooled with freshwater only.

 

[alldodge]

Being Fresh water you could go with aluminum

 

[thormx11]

What intake should I look for? Most of the aluminum intakes are showing for yaer through 1995, none later.

 

[alldodge]

I believe the heads should be rectangular ports and not oval. Can you verify?

 

[thormx11]

I do not have a picture of the heads and I am away from the shop right now. I did grab the casting number yesterday though. The head # is 10141279

 

[alldodge]

That clears it up, you have oval port vortec heads
Here is one which will work

Edelbrock 2561 and carb adapter 2732
Edlebrock shows out of stock, but places like summit racing and others indicate they do have them. I would call before placing order

https://www.edelbrock.com/performer-rpm-q-jet-marine-intake-manifold-2561.html

 

[thormx11]

Those coated ones are nice but are more than I am wanting to spend right now. I was looking more for a standard automotive one in the ~$200 range.

Something like this Speedmaster from Summit, but it is showing application years up to 1990 only. https://www.summitracing.com/parts/sdm-1-147-016/applications

 

[alldodge]

You can use an auto one, but even fresh will corrode it over time. Will take a while but will work.
The Edelbrock 7161 is $327
Or Weiand Stealth 8019 is $281
Both at Summitt. Look for 16 bots on the intake

​

 

[thormx11]

The 16 bolts is one of the things that was throwing me off. I believe I only took out 12 bolts (6 each side) when removing the stock GM intake off the engine, but thats not to say there were not the extra holes that weren't used.

 

[Scott Danforth]

Unless you have a heat exchanger, run a marine intake or a cast iron intake.

AD is right, even in fresh water, aluminum intakes corrode

I am running an oval port RPM airgap on my BBC, however I am running a HX.

The marine intake with dual alloy castings are a necessity.