bikepilot

I need to replace the manifolds and risers on my 1995 Cobalt 272 due to age and fix up the silent choice mechanism. The boat has the original 454 Mag MPI motor with Corsa Silent Choice Exhaust. Also, the Corsa setup isn't switching--something's wonky with the harness and, I think, one solenoid.

Not sure if this matters, but the transom exhaust exits are almost flush with the back of the transom on the exterior, have rubber flapper covers and have internal butterfly-like things that appear to be there to help prevent reversion. These are near the exit.

I'd very much appreciate input as to what would be the simplest approach to fix both. My inclination is to find new solenoids/harness for the Corsa setup and source manifolds/risers that will work with that stock setup and be an upgrade in weight, looks, and performance (CMI E-tops? EMI Thunder or similar?). I've run the boat with the exhaust routed through the prop and out the back. It runs dramatically better (~+400 rpm) out the back but is pretty obnoxious so don't want to do that all the time.

I'd love to gain a little performance and loose a little weight in the process. The boat is used for running around Tampa Bay (salt water), pulling a tube/skiers, and mostly island/sand bar hopping. Not a serious go-fast setup and I'd like something that'll last and not be too high maintenance. There are some lovely CMI e-tops in the swap shop here, but I haven't figured out yet how or if they'd link up to what I've already got...

Under the hatch:


An idea of riser height:


Left side



Shifter brackets, etc.


Right side



Thanks very much!

(PS, I'm aware that there are many items other than exhaust that need to be addressed that are viable in this pictures--haven't had the boat long and am working on getting it all fixed up).

dereknkathy

first off those are stainless risers. so you could do with new manifolds and reuse those. are the GLM's alum or iron? replace with alum manifoldsand you pick up 50 to 70 lbs loss in rear of the boat. so if not interested in ultimate performance, 500 for a pair of stock manifolds compared to 2 grand for exotic stuff...do the math. plus you are sure it fits existing steup.

cig20

iTrader: (1)

i have a set of used fresh water merc manifolds and riser if interested

tunertech

you can pickup at set of fresh water MERC upper an lower take offs for about 350.00 plus freight... all day long. I have a set if interested.

Call Jim at corsa..... they have a retor kit for about 400 that upgrade both selanoids and the harness to low voltage.. works 100% better

dereknkathy

i don't understand why they don't use engine vacuum to close the diverters. would be fully automatic. hit throttle, vacuum drops, the thru-hull opens. go back to idle. vacuum pulls diverters shut for thru-prop...

bikepilot

Thanks, had no idea the risers were stainless. I do like the idea of dropping some weight off the boat so will be shopping for aluminum manifolds.

Griff

You are not going to find aluminum manifolds that work with your stock risers.
I would look for a set of 496mag exhaust. They flow better and are lighter.

Knot 4 Me

+1 on the 496 take-offs. All years are stainless risers but only the early motors (2001 - sometime in 2004?) are aluminum manifolds.

575cat

Ck out CP performance they have alum & cast stock replacements as well as others . just purchased the cast kit manifolds ,risers,bolts , gaskets 560. + shipping mistake whole kit 539.00 + shipping

Baja226sport

iTrader: (28)

GLM makes big block aluminum manifolds that are a direct replacement for stock, they have the same bolt pattern/water ports as the mercruiser risers. They are about $220 a piece new.