Performance questions on 4.3L OMC

[SmurfOnAScarab]

As some of you read in the other post, that I had a destroyed engine on my hands. Well after the block gets cleaned up I want to give her a little more power. I haven't really done many V6 marine engines, I pretty much stay with BB.

Here is what I was thinking, someone shoot me some tips if you have any.

I am going to rebuild the bottom end, maybe with a little better pistons and bump compression a little bit. I have a set of 03 Vortec CNC Ported heads, going to run an edelbrock ported intake, and edelbrock 600cfm carburetor.

Just wondering what you guys think this might do for me, and what would be a good camshaft of choice?

Or will I just be wasting my time with the stock exhaust manifolds as a restriction?

Thanks in advance!

 

[mthieme]

Re: Performance questions on 4.3L OMC

I've never built up a 4.3 although I have one in my Searay and also have a spare which needs to be rebuilt. I was thinking of doing just a little bit more to the spare similar to you. Nothing radical, but if I can get another 10 knots out of the boat without sticking a V8 in, it would be nice.
I have seen performance manifolds. They are available.
Keep us up to date as work progresses. There are a lot of 4.3's out there.

 

[Tail_Gunner]

Re: Performance questions on 4.3L OMC

I have tried for a year or two looking for performance upgrades's that would be both reasonably priced and effective on a 4.3 vortec. In the end i have come to the final conclusion that a 5.7 litre motor would be by far more cost effective.....more than probably cheaper.....and quite easly getting you 300hp with far less modifications and work. By the time youve finished a 4.3 and maybe getting 260hp you will have spent a lot of coin. Aka carb's.. cam... heads....ahh then you have to exhaust that whole process...Then its time for new risers and open exhaust...Big buck's. And sound like a roaring bumble bee

 

[SmurfOnAScarab]

Re: Performance questions on 4.3L OMC

Yeah, I also have a few 350s sitting around. I was just going to play with the 4.3 I think.

I do need some exhaust options. Does anyone make marine headers, or are performance manifolds my only option?

thanks for the replys.

 

[SmurfOnAScarab]

Re: Performance questions on 4.3L OMC

Has anyone ever taken the stock manifolds and ran them through hull? That would definitely free up some flow issues not having it run out of the drive anymore.

 

[mtnrat]

Re: Performance questions on 4.3L OMC

I am pretty sure the 4.3 cannot flow enough to be restricted by through leg exhaust. A 350 is likely not hampered until the engine exceeds 375-400 hp.

 

[MikDee]

Re: Performance questions on 4.3L OMC

Here's some decent factory camshafts for the 4.3V6 (non balance shaft)
I believe the L-79, or L-82 V6 version of this cam is the same as the stock hi-perf 350/290hp V8 cam:

http://www.gmpartsdirect.com/performance_parts/store/catalog/Category.jhtmlCATID=304.html

 

[MikDee]

Re: Performance questions on 4.3L OMC

Here's a link to some aftermarket cams for the 4.3V6, but if you have a later balance shaft engine, all those here have at least .500" lift, the Vortec heads have to be machined as they only go to approx. .480" lift, or you can use the beehive springs, with thinner retainers:

http://www.compcams.com/Technical/CamHelp/Default.asp

 

[Bondo]

Re: Performance questions on 4.3L OMC

Has anyone ever taken the stock manifolds and ran them through hull?

Ayuh,... Sure have....

All it'll get you is NOISE....

The source of the Restriction is the common chamber manifolds....

Thru-hulls are No Help...

Now,... If you found some True Headers,.... Then maybe thru-hulls might Help...