Upgradin from 454 to 502 HELP

[23check]

For straters not even sure what 454 I got in there now.. I was thinking it was a gen 4 but was told I would need a new rect. port intake manifold but when I pulled it off it has rect. ports which means 454 HO correct? Was absoulutley nothing wrong with the 454 just wanted some power without building for reliability reasons.. So I just purchased a 502 marine crate from 1800runsnew. Wanting to know recommendations on upgrades to 502 Intake, carb, etc. I currently have elderbrock rpm performer intake which i will prob use. Carb that was on 454 is 4150 750cfm holley double pumper. I was told it wasn't big enough for 502? That I should upgrade to 800cfm. Also i know what the coast guard says but is it necessary to have a marine carb? All input will be apprectiated!! Plan on doing the swap this weekend

Thanks
TJ

[beamrverbeek]

just make sure that the ports are the same size so you dont get unwanted turbulance. also the 502 will run best on more cfm. we have a 501 bbc that has a 1050 cfm just make sure you jet it so its happy and you should be fine. the 750 will make it very snapy on start off but it wont want to rev out like it should. nascar runs vary small carbs on there motors but they are very much moddified and cost lotsa $$$. we have the rpm manifold also and it seems to do just fine, turns 6500 on top with good bottom. just my .02 if it helps:)

[Raceman]

I upgraded one of my Pachangas from a 330 horse 454 to a marine 502 when the 502's first came out. I bought the complete motor in a crate from Merc, and it came with the dual plane high rise intake that was very similar to the old GM high perf intake like came on the 396/375 AND 427/425 engines, except it had the bronze inserts in the water jackets. I like this design intake and think it's a good choice for marine application with the 502. I agree that a little more than 750 CFM is a good idea on this engine, but don't think it'll make night and day difference. It's been over 15 years now, but I think I ran the Quadrajet from the 454 on the 502 when I first put it in. I don't know the CFM, but some of the old Q-jets were either 800 or 850.

If you're running a holley the marine carb is a good idea for several reasons. The vent tubes are curved to dump back over into the venturis if a carb floods over and the bowl gaskets are different and don't dry and leak like the old style automotive ones do. Of course both of these mods can be done to a non marine carb without too much trouble.

There's no reason to turn that motor over upper 4's, or 5K flat at WOT. The boat will run faster at that RPM, and of course the engine will last longer and use less fuel. Anything more and the camshaft that comes in it is way off the curve.

I'd bet a parts wanted ad here, or maybe a listing in Stern drive parts would cough you up a GM high perf intake, but if your 454 is a rect. port marine engine that's what would have come on it from the factory. I've never run a Performer on a BB Chevy, so don't know exactly how it reacts, but like carb size doubt that it's a very big difference. The 502 in stock form is a great upgrade from the 454. From my 330/454 it put about 10 MPH on the boat with all stock components including exhaust manifolds, and only a prop change.

[23check]

cool man thats what im looking for about 10 12 mph's gonna be right around under 30 over 80!!!! I bought the holley 800 cfm marine carb and the elderbrock 800cfm polished from summit... When i get em I'm gonna see how hard it will be to make the mods to the elderbrock cause it's a great lookin carb but if it's too much ill use the holley... whichever i don't use is getting sent back.. The only thing im really concerned about is boat is a 89 and I have no idea what the drive has been through so I guess we will see if she holds together lol

[Greg Moss]

cool man thats what im looking for about 10 12 mph's gonna be right around under 30 over 80!!!! I bought the holley 800 cfm marine carb and the elderbrock 800cfm polished from summit... When i get em I'm gonna see how hard it will be to make the mods to the elderbrock cause it's a great lookin carb but if it's too much ill use the holley... whichever i don't use is getting sent back.. The only thing im really concerned about is boat is a 89 and I have no idea what the drive has been through so I guess we will see if she holds together lol
Be careful if you use that boat in the salt water. That automotive intake doesn't have the brass inserts in the water passages and will corrode threw very fast in the salt water. If you ride in even brackish water you need to find the intake Raceman is talking about.