awesomecat26

can anyone offer there opinion on this one 1996 L29 vortec engine with zz 502 cam 224 iin 234 ex @.050 527lift world products intake 850 holley cmi headers it wont seem to pull upstairs it is in a 26' awesome thundercat trying to pull a 26 bravo 1 4blade can only get 4200rpm and 53mph tried smaller prop but seen the same mph at a higher rpm ,4800

PatriYacht

Do you have any signs of detonation? Vortec cylinder heads have small chambers and are prone to detonate in marine engines. Try better gas and turn your timing back to about 32 total.

Madmax

I agree with what PatriYacht says. Turn back your timing to about 30-32 degrees.

I also think you have a pretty bad mismatch, personally. A single plane intake prob isn't the best for that combo, and an 850 holley is prob a lil big. An Edelbrock performer RPM, with a 750 holley would most likely work better. I ran about the same motor combo only with the 454HO cam, and it would also lay down at 4200. I was never sure if the heads were the restriction, or the cam, but it did the same thing. Good luck.!

kenny v

I would have to agree with the mismatch theory.The zz502 cam is probably alittle big for the L29 heads as well as the 850 carb.I dont think the heads can flow what the rest of the engine needs.Just my opinion.

GOODT

have to agree with patri check total timing at about 3000 rpms should be about 32*

KAAMA

iTrader: (1)

At first glace your combo doesn't seem to be way out of order to me, but I am really not sure. I'm not real familiar with the Vortec stuff for marine use. I have always heard it said that the performance of an engine is in the combination. Call JimV, he knows quite a bit about what a head for offshore marine use should do. His number is: 616-735-0800

PatriYacht

Those aren't the best flowing heads. The Merc 454/420hp cam had more duration and lift. Generally, if you have less flow in the heads, you make up for it by increasing duration. So, I don't think the cam is too big. I do agree the manifold is not the best. An Air Gap is about the best for that size engine. I doubt if changing the carb to a smaller one will help at higher rpms. Make sure it's jetted correctly. Running lean or rich will kill a lot of power.

Pat McPherson

There is a fellow on this board running a similar combo (L-29 454 with ZZ502cam) with good success.
I would guess you have a timing or carb problem...

awesomecat26

intake is a duel plane world products 180 intake .timing is at 32 degrees .I'm going to try a 750 holley this weekend and see what that does thanks for the comments