4.3L boat upgrade

Lenten · **Joined:** Sun Apr 22, 2012 4:27 pm **Posts:** 3

I have 2 boats, 1 with a 99 mercruiser 4.3l 4bbl carb. the other a 91 4.3l OMC 2bbl carb. I want to use the parts from the 99 on the 91. the compression is low on the 99 and the 91 is all good but a lot slower. Does anybody know what parts I should salvage of the 99 to make the 91 faster? Thanks for any help you guys can provide!

Borchik · **Posted:** Sun Apr 22, 2012 5:31 pm

your higher horsepower is mostly due to the part that has low compression....if you just want to swap parts around you are not really going to find any better performance.

LouC · **Posted:** Sun Apr 22, 2012 5:55 pm

Well the 99 is probably feels faster by virtue of having a 4bbl carb, but the problem is that the 91 is a pre Vortec, the 99 is a post Vortec (new cylinder head design) and to put the 4 bbl carb on the 91 you'd of course have to swap the intake manifolds. The pre Vortec and post Vortec use different heads and different manifolds. So while you might be able to put the 4 bbl on the 91, you'd have to get the old style manifold for the 4 bbl carb.

Lenten · **Joined:** Sun Apr 22, 2012 4:27 pm **Posts:** 3

Thanks for the reply's. Will the newer heads fit on the older block? The 91 is a lot nicer and newer boat. But the other has a HO 99 mercruiser. The 99 was great before the cylinders and rings got damaged. All other parts on the 99 motor is good.

LouC · **Posted:** Mon Apr 23, 2012 12:23 am

Lenten wrote:

Thanks for the reply's. Will the newer heads fit on the older block? The 91 is a lot nicer and newer boat. But the other has a HO 99 mercruiser. The 99 was great before the cylinders and rings got damaged. All other parts on the 99 motor is good.

I know a balance shaft was added at around the same time, and that might change things. Go over to http://www.iboats.com and ask on the i/o forums, there are some very good techs over there who will know....

ric · **Posted:** Mon Apr 23, 2012 6:31 am

Vortec 4.3 long blocks are like $800, just buy another.

Lenten · **Joined:** Sun Apr 22, 2012 4:27 pm **Posts:** 3

Does anybody know where to get a 91 OMC 4bbl manifold that would hold up good to salt water? Thanks for the help.

ric · **Posted:** Sun Aug 12, 2012 11:01 am

Ebay. Mercruiser 4.3 4bbl non vortec manifolds are everywhere cheap. Mercruiser/omc/volvo/whatever doesn't matter they're all the same.

www.iFourWinns.com

4.3L boat upgrade

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