[MariahMX20]

i have a 91 mx20 with a omc ford h.o. 5.0 and i purchased a 4 barrel intake and marine carb to throw on it. is this going to actually help me performance or just kill my fuel consumption?

[Z 202]

Both.

Honestly though, I don't know how much performance gain you will see on a 5.0, though if you have a matching intake it may make the whole thing breathe a bit better. Typically a 4 barrel setup really shows gains when pumping air into big blocks. My 5.7L came with a Rochester 4 bbl, and it drinks the gas pretty good at WOT. Then again it hops up on plane real fast! At mid range rpms it's actually fairly reasonable on gas. I doubt the "pleasure cruising" fuel economy is any worse than it's 2 barrrel counterpart.

[MariahMX20]

right now i can get the boat up to around 50 give or take, do you think i will get much more out of her with anything performance wise i might do? the thing will take off and plane right out with 5-6 people and a cooler or 2. i am also running a 21 pitch prop rather then the 19 it came with. i just hate watching my dads stingray barrel past me and his buddies behind him, i would like to hang with them even thought their boats do 65-70

[Z 202]

Is your prop stainless or aluminum?

Mine does between 53 and 55 mph at WOT on a crappy 21p 3 blade aluminum.

I've heard opinions both ways on 4bbl conversions. Some people claim big gains in performance, others only a few mph. I do know one thing: unless you repower to something huge, you're never gonna run 65 - 70.

[MariahMX20]

i do not expect 65-70 at all, 55-58 would be super but i dont expect it. both of my props are stainless.

[Z 202]

Well if you've already bought it, I vote for putting it on!

See what I did there?

[moondance100]

MX20, I don't think that 4bbl is going to give you any measureable performance gains. My old boat was a 20' with a 350 4bbl merc, I had a buddy with roughly the same size boat and a 350 2bbl volvo (same engine). He'd pull me out of the hole while my small block was still trying to digest all that the qjet was sending to it, then I'd catch him at mid range and it was nip and tuck to the top end, which was about 52 on flat water.

What rpm's are you turning at 50? Keeping the same prop and drive configurations, you're going to have to turn approximately another 100 rpm for each mph gained. If you're turning 4600-4800 @ WOT now, then to hit 55, you're talking about 5100-5300. Think about that 17 yr old small block ford back there working for ya! The only thing worse than being passed by your dad's Stingray is having him pull you home after your 5.0 bombed itself at 5300 rpm!

Good luck either way dude!!