imco powerflow exhaust ?
 

anybody have experience with this set up on efi motors? was told by a reputable calif. performance
shop that they have tried all different types of exhaust systems on customers boats and hands down
imco power flow on stock efi engines made the biggest gains ! ( 3-5 mph). could this be possible ? iv'e read here on oso that exhaust as a general rule don't get you much top end speed .

most of these aftermarket companies do little or no actual testing on a boat, be careful. most cannot prove any gain in hp or speed. consider CMI or lightening, real headers. most others are just a slicked up log style manifold.

I can't speak for EFI motors.... But I installed IMCO Powerflow exhaust & risers on my 454Mag Carb.... 24' Superboat.... NO other changes.... everything else the same... 300rpm & 5 mph better!..... Thats the truth... the whole truth... and nothing but the truth.... ;)

I have the Powerflow exhaust mainfolds on my 1999 454 MAG/MPI. A friend has the exact same boat and engine without the Powerflows, and there is MAYBE a 1 MPH difference. They won't do much to give you more top end. However, if you ever have plans to add a blower, they are a must have item.

Laveyman - Could it be you're up against the Rev limiter? Prior to the IMCO installation I ran about 4700-4750.... after 5050.... I have heard that any aftermarket exhaust shows its biggest gains on the old 454Mag Carbs.... but no S^$%.... I picked up a good 300rpm's!

GRH did you retune the engine fuel Mix? timing?
K&N?

WWW - I honestly didn't change anything BUT the exhaust manifolds and risers.... I intentionally had timed, tuned, set up the boat best I could ..... Then changed the manifolds.... I try never to change more then one thing at a time.... combining changes doesn't tell you which one worked best... we all know that.... the manifolds were a grand slam on my boat!

IMCO manifolds
 

Gents,

For what it's worth, we have had some good luck and seen positive results anytime we have added EMI or IMCO manifolds to a boat.

With and EFI motor I always suggest reprogramming the ECU, and adding a larger flame arrestor.

My .02 cents,

Don Baca

I always thought if you changed the exhaust or put bigger air filters on that u had to check the fuel mix & timing, you know too lean or too rich
more air in and out is usually to lean? right

Any experiences with Stainless Marine exhausts? Heard that GM tested these and found them very effective.

You're right of course about the exhaust allowing you to push more air through..... i didn't expirience a lean burn situation on my motor.... but I don't understand why the timing would be affected?

I put Imco Powerflows on my t/330's and picked up about 2 MPH and a few hundred rpm ...can't remember exactly after all I've slept since then:rolleyes:

gains
 

Most of our customers have seen a 2 to 5mph gain depending on the package.

Don B.

[QUOTE]most of these aftermarket companies do little or no actual testing on a boat, be careful.


IMCO does extensive testing on thier equipment, both on dynos and in boats. they are also very helpful when in the middle of a project and you get stuck.

Tyler Crocket has a lot of info on dyno tests on most aftermarket exhaust Chuck. Give him a call.

And you don't have an efi motor, so why do you care???

Saber28, well said.

I have the Powerflow Plus headers on one of my 41's. The engines are tall deck,600inch, 685hp naturals. big,dumb,5100 rpm engines. 685hp with car headers on the Chief Engines dyno,680hp with the Powerflows on the same dyno. I had Stellings that were not repairable and spent $7500. between the headers and Stainless Marine-installed tailpipes for the short stagger. I feel like there is no difference between the two. the PP Plus headers have much longer primary and secondary runners. They are also around 3 7/8 exhaust diameter compared to the 4" exhaust size of the Stellings.

We run a P boat " Wazzup" 556cu.in. 730 hp. at 7200 rpm no power loss on Power flow and no dam leaks

Dennis Moore has address this a little in his book. Some of these manifolds have better primary designs than others and some have only a 2.5 inch collector even though they a 4" hose going out through the transom. Its weakest link of restricted flow is still the 2.5 inch collector.

Anyone ever here using/testing the new Stellings manifold design? I think it's a couple of years old...you can even get them with 5" tailpipes. I know Doctor Dave is running them on his Cig with blower engines. I wonder how they stack up to the tubular headers?

The KE's sound interesting as well.

KE's all the way, they are just LOUD and $$, But have run mine 4+ yrs. in the salt water and they are still doing great. I put shotguns mufflers and that seem to help quiet them down a bit!
BTW, they are on an KE tuned HP500
Hope this helps,
MD

So far, it sounds like questionable results for an EFI motor. This is a couple nickels, especially if you have twins, for what may be nothing more than a weight savings. Hopefully, some others will reply with more info, good or bad.

We have installed Imco, Eddie Marine, and Stellings headers, and cast alminum on 502 EFI motors. We have not had any negative feed back from any of our customers. On the Stelling headers, we did install a different fuel pressure regulator to compensate for lean conditions.