Fountaineer

I'm currently running a 509 Blower motor and using Gil Offshore Exhaust manifolds in my single engine Fountain 29.

Has anybody had experience with changing to headers from a "standard type" exhaust manifold. Perfomance increase, etc? I'm wondering if is worth it.

fountaindriver

I changed from Gil Offshore style headers to CMI headers a few years ago on a 32 Fever with 525 SC's. I did not pick up any speed or any noticeable performance gains.

Fountaindriver

epeek

Thats my take, no difference between good manifolds
and headers,except on very large H.P. applications

Fountaineer

Thanks guys. I think you just saved me some $$$

Helmwurst

Probably pick up some noise or even a ticket. Those "dry" Gils are plenty loud. My basic understanding is that with a blower you won't see a significant gain to justify the expense. Merc ran those Gils on evrything except the big 540's up until just a few years ago. Big reason was to cut down on reversion on big cam motors.
Built a couple of 454's with 525 cams N/A and extensive head work, running Big Guns, no water problems here.
Anyone else want to chime in here??

bryanspeedracer

Helmwurst,

I will. I have gills on 468 with 990 heads/cch 296 (.553/.571;236/246) AED/Holley carbs. What intake should I look for. I've heard Victor Jr. is a good bet. Don't want to steal the thread...

bob

There have been quite a few threads over the last couple years here on this subject. I think you will find that on a 500 hp engine, at 5000-5300 a set of Eickert or individual runner CMI's -Stellings will make 20-30 hp more than a Gill. As the rpm goes up the difference gets more dramatic. Hot Boat back in Jan 97 did a series of tests on various pipes that was interesting.

Helmwurst

bryanspeedracer: I would run any high rise Performer or Chevy style Alum intake that has a divider down the carb bore unless you are running over 5800-6000 RPM. These will build more torque between idle and that kind of top RPM's.
Bob: agree with you on the HP gains on the true header style exhaust, but if he already has the gils, why not use them? 25 HP will not get you anything except burn more fuel

mcollinstn

exhaust scavenging is an issue on 500 to 800 horse NA motors. Eickerts or long runner Sport Tubes will return more power than a dump style manifold or shorty header.

Supercharging changes that. You don't need to tune the exhaust, you only need to provide a way for it to get out.

NA it matters.
SC bigger is better.