View Full Version : 18C performance manifold help

South Island
09-27-2013, 01:56 PM

I have once again become a Donzi owner. I just bought a lower hour one owner 1994 18C with 32 hours on it. The old owner installed selectable exhaust and I would like to install a brand of performance manifolds.

My question is what brand and will they fit with the selectable exhaust?


09-27-2013, 03:50 PM
Before you plunk down $$$ do some research, in a very high percentage of the installs there was little to no gains, for many it was a total waste of $$$. But many like to open the engine box to show folks something that looks cool but does not really work. That being said if you intend on some decent engine mods, then you will see some benefit even then not as much as you think. For about the same $$ slap a shorty on it and get decent speed gains!

Just Say N20
09-27-2013, 04:16 PM
Congratulations! Nice looking boat.

+1 on what MOP said. You will spend a lot to get some bling. Period. Performance manifolds on a stock engine will not improve performance at all.

It boggles my mind. 1994 boat, 32 hours = 100 minutes of use PER YEAR.

Carl C
09-27-2013, 05:14 PM
That's a beauty! Congrats. Ditto on the exhaust though. I spent nearly $5,000 for CMI Sportubes for my old 496 and saw ZERO gain.

09-27-2013, 05:21 PM
Not all risers will be in the right position to be connected to your diverters.
The riser tails might be too long.
Measure carefully before investing.

09-27-2013, 05:59 PM
Brad, congrats on your purchase! I just picked up a 1994 as well. Just got here today. Lenny told me you might be around.

Ed Donnelly
09-27-2013, 06:05 PM
That's one purty looking Donzi ..Ed

Too many good looking Donzis going to B.C.

Pat McPherson
10-01-2013, 04:13 PM
Nice boat! Same colors as my 22. There are aluminum versions of the stock Merc manifolds and risers that will save you weight. I think GLM makes them.
As the others have said, a stock smallblock will not gain much with aftermaket exhaust.
I've gained 100-200rpm on 454 and 502 mag engines using Stainless Marine.