evile1003

im Building a 383 for a 21 foot wellcraft i have all forged bottom end with h beam rods 3.750 stoke already. planning on buying comp xm270hr cam with afr210 cc eliminator heads. i will be running wet exhaust so im looking for some input on whats the best exhaust system to run and will i be able to clear tall valve covers so i can run stud girdles.. thanks for any help

Cory H

Might consider dropping down to 195ish cc heads to keep some good velocities moving and pick up some torque. 210cc more if an rpm head and you won't likely be turning the rpm to benefit from the bigger head.

Cory H

Compare flow numbers with that relatively small cam and you might find the smaller head flows better at those valve lifts.

Trash

Two points:

I concur with Cory, go with AFR 195s instead or something equivalent, especially with that cam.

Stud girdles are unnecessary for this application. Run the stock style Merc exhaust with 4" thru hull and you will be fine. If running a roller rocker you may need a double thick head gasket to clear the rocker nut with stock valve covers.

evile1003

can i throw more cam at it without having to worry about reversion i want to get every pony i can out of it. looking for the biggest performance from 3-6 and i plan on at least running aluminum exhaust with stainless risesrs if yall have any preferences..

Ryan00TJ

iTrader: (8)

Search my username Ryan00TJ. You'll find alot of info that might help ya. I ran a 234/240 .580/.568 112+4 Cam Motion hyd roller in my 383 with AFR 190 heads. I ran dry to the transom exhaust and it was around 22" mixing farther back than stock to prevent reversion. In a nutshell mix the water in as far back as possible.

Trash

Ryans size cam is about as big as you would want to go, and he had some tweaked exhaust work to make it happen.

NHGuy

If you use roller rockers, which is important with extra lift, you can cut away some of the inner structure of the factory valve covers to make room. Or you can get taller or more open covers and then you need to get a little creative with some of the bracketry if you are running an alpha shift plate and remote oil filter.
I think Trash meant you'd need double valve cover gaskets not double head gaskets.

Build your motor for .040 quench distance and it will run hard. I have 9.85:1 static and it's fine. The dynamic is well within a normal ratio. I think it came out way down around 8:1.dynamic. My cam is only 218 @ 50 and has .565/.570 lift at the valves. Dart Iron Eagle small port heads. I bought EMI exhaust with 3"extra height and water entry back 5" in front of the transom. No reversion, but it's kinda loud.
I wish I had seen Ryan's idea for duration before I borrowed CFM's part #. Mine is a Comp 268 XFI which is intended for car efi. It happens to have marine tolerant lsa and centerline.

Trash

I did mean valve cover gasket. Sorry for the confusion.

evile1003

I was looking at the 16" emi system would that be enough to get into a cam like ryans. my exhaust outlets are right above the waterline right now. I was thinking with the tube style risers I could probably clear tall fabricated valve cover with parameter bolt am I wrong with that idea I don't really want to double gasket or cut covers out