5.7 to 7.4...hopefully

[harveycrew]

Hello All,<br />Questions of the day pertaining to engine swapping.<br />1) Will a 7.4 bolt in where a 5.7 is with no problem? <br />2) Will the exhaust manifold, risers, elbows, starter, and flywheel from the 5.7 fit onto the 7.4?<br />3) Will the Alpha 1 handle the new power without any problem? <br />4) Are the electronics from the 5.7 interchangeable to the 7.4?<br /><br />Just FYI, I have a 1995 5.7L/350. Thunderbolt IV. The current power is good but I need to step up with out having to buy a new boat. Call the present one a "labor of love." It is a 25'2" Cuddy cabin. What kind of top end hp can I expect? <br /><br />Thanks in Advance

 

[DJ]

Re: 5.7 to 7.4...hopefully

Harvey,<br /><br />I can say with certainty that the parts listed in # 2, won't swap.<br /><br />The Alpha drive is "marginal" behind a 7.4, in my opinion.

 

[magster65]

Re: 5.7 to 7.4...hopefully

Yeah, what DJohns said. I looked in my merc. manual, it says the base timing is different but doesn't give details about the timing curve.

 

[Bondo]

Re: 5.7 to 7.4...hopefully

Harvey,<br />To answer all your questions.......<br />1) NO...<br />2) NO....<br />3) NO.....<br />4) NO......<br /><br />Sorry, but Nothing in your present set-up is any Good for what you want.....

 

[harveycrew]

Re: 5.7 to 7.4...hopefully

Thanks All. I guess all good dreams must come to an end. I'll have to settle with my 5.7.

 

[Albe]

Re: 5.7 to 7.4...hopefully

I heard that you can find an exact replacement engine from Marine Power. They seem to have complete engine packages that will bolt on including the wiring. Good luck.

 

[Lake Rat]

Re: 5.7 to 7.4...hopefully

Even though a 7.4 won't bolt right in, you still have a few options for more cubic inches in displacement! Consider a 383 "stroker". It consists of a 5.7 block (350 Chevy) with a replacement crankshaft with a 3.75" stroke. Stock 5.7 stroke is 3.48" The added stroke helps produce more torque. Several sources for these and other large displacement small blocks can be found in magazines. Some popular choices- Super Chevy Magazine, Hot Rod, Car Craft, Chevy High Performance. Please E-mail me if I can be of help! John

 

[horndog]

Re: 5.7 to 7.4...hopefully

bolting a big block to a small block setup doesn't work even in the auto world. <br /><br />Stroker motor sounds good! I have seen stroked chevy 350s and they fly! Seem the strokers in 383 and 388.

 

[magster65]

Re: 5.7 to 7.4...hopefully

Our local prop guy has a 383 stroker in his 25' Pachanga. It goes 80 mph (gps). No kiddin'!

 

[mkast]

Re: 5.7 to 7.4...hopefully

I replaced a 260 hp 350 cu in with a 330 hp 454 cu in. The boat is a 23 footer, weighs 2650 empty. Changed the gear ratio in the drive to 1.32 to 1. Bellhousing fit, starter, exhaust manifolds, holley carb and water pump came from EBay. Bought the flywheel from Chevy. Modified the engine coupler to work with the new flywheel. Used the 350 ignition on the big block. Had to buy an engine power steering bracket from Mercruiser. Risers fit with a longer hose from Napa. I'll be the first to tell you no to put a big block on an Alpha drive, unless your boat is light enough. Alpha was rebuilt with the late model gears and shaft. I'm using a two speed prop. Drive is holding up well, no WOT standing starts.