Aftermarket Exhaust

[Ric 232]

Does anyone have experience with IMCO exhaust manifolds? As many of you have read here, I installed Gil on my 454 Mag MPI (385hp) along with the usual other mods (flame arrestor, adj. fuel pressure reg., reprogrammed ECU) and got ZERO performance increase at WOT.
I just talked to a guy at Teague. When I was telling him about my current mods, he stopped me as I said "Gil" and he said " . . . and you got 0 - 2 mph, right?". He said, "put your Gils on E-bay and put on Imco Powerflows." He claims that IMCO Powerflow manifolds will get me 4-6 mph easily. He claims they have many customers who have had the same experience I've had. He even says they sell Gil but don't recommend them (although, from what I'm hearing, nobody can get Gil's right now).
Am I being fed another line to convince me to throw yet another $2,000 away ???
Ric

[Whatboat]

My 2 cents. You need to get over 450 HP for after market exhaust to do any good. Stock BB mercruiser manifolds are better than most people think. Keep the Gils and invest in more horsepower

[Ric 232]

Well, I have been trying to invest in more HP, but everyone says there isn't anything short of a blower for an MPI motor.
Teague also said they don't recommend any cam upgrades for the MPI motors as they have seen no cam/ECU packages that work well.

[Ric 232]

Dennis, do you have an opinion on this Gil versus IMCO thing?
Ric

[Dennis Moore]

This is a very touchy subject because of the many manifolds on the market. I was actually threatened with a lawsuit about what I printed about exhaust systems in my book.
I think they are both excellent. I know Fred Inman at IMCO very well and he makes an excellent product as well as being a really nice guy. I have also installed Gils and talked to the guys at Gil and they also really know there stuff.
What I said in my book stills goes.
I honestly wouldn't think that there would be much of an increase or decrease switching from one to the other! Both exhaust manifolds increase performance by lowering backpressure and neither have long enough runners to create a scavenging effect.
Dennis
PS It wasn't either IMCO or Gil that threatened me with a lawsuit. They are way too cool for that!

[Craig]

I put a set of IMCO's on the boat when it had a stock 454 Mag. Didn't really see any big speed increase, but the low end was more noticable. It also seemed like it was easier to hit top speed in more varied conditions. They must be pretty well built as well. Charlie and I were out tear assing around at the last years Parade of Lights and I blew the outlet hose off the seawater pump at 100 mph eek! When I slowed down enough to hear the alarm, it was steamin'!! I thought sure I'd blown the whole mess up. Even bubbled that thick black powdercoat that came on them in a bunch of places. Pumped out the center pod, hooked the hose back up and she's still running good. Just had to have the manifolds recoated!
Craig
[ September 19, 2002, 06:37 PM: Message edited by: Craig ]

[Ric 232]

It's funny, but the largest performance increase I've experienced in my boat was after I scraped the corrosion off the contacts inside the distributor cap. The corrosion was not bad enough for the motor to miss, but I gained 75rpm after cleaning the contacts. I just looked at them again tonight, and even with a new distributor cap about 6 mos ago (25hrs), they have some corrosion again. Oh, well.
Ric

[SPECTRABRENT]

I ran IMCO's on my 509 in my jet boat and did see an increase over the stock log exhaust. I am going with a bigger 540 inch motor for my v-drive and will run the same exhaust.
When I bought my IMCO's, I thought the Gils were better. I think they were more $$$ too.
If I were to buy new exhaust, I would go with CMI's or Lighting's.
Brent

[Charley]

Craig:
I put a set of IMCO's on the boat when it had a stock 454 Mag. Didn't really see any big speed increase, but the low end was more noticable. It also seemed like it was easier to hit top speed in more varied conditions. They must be pretty well built as well. Charlie and I were out tear assing around at the last years Parade of Lights and I blew the outlet hose off the seawater pump at 100 mph eek! When I slowed down enough to hear the alarm, it was steamin'!! I thought sure I'd blown the whole mess up. Even bubbled that thick black powdercoat that came on them in a bunch of places. Pumped out the center pod, hooked the hose back up and she's still running good. Just had to have the manifolds recoated!
Craigoh I remember it well!! It looked like you caught fire!!! steam and smoke billowing out the engine hatch.... I'm was happy as hell that it was a field fix............................................... . I didn't wanna tow ya all the way back hehehe
wink

[HighRoller]

I've always wondered,why go with elbow top headers when you could get long tubes like Lightning or CMI sweepers?It seems like merging the cylinders so soon after the exhaust port makes elbow tops kinda like an exhaust manifold.Just out of curiousity Charley,what did you have on your quad Rotor?

[Rexone]

The CMI Elbow Tops were designed as a cheaper alternative to the pricy sport tube full headers and are primarily targeted at Bravo applications although they can be adapted to anything with the proper tailpipes. They are still the finest constructed header of their design class given the quality of the welding and the materials used.

[HighRoller]

I can understand that Rex,but now the CMI's are about the most expensive header out there.So much for saving money eh?What's your opinion of the Lightning header?

[Rexone]

Yes, I think is kind of one of those "you get what you pay for things though". Most of the cast systems are cheaper, some substantially. Most the stainless headers are not much cheaper however, if any. CMI also has the Unitop which is a little less money that the Elbow Top. Comes with a integrated tailpipe...the disadvantage is it only comes in one configuration for stock bravo apps. in terms of the tailpipes. There are no variations available. The CMI Elbow top though is still about half the cost of the full header Sport Tubes which are still the ultimate way to go if you have the bucks to spend.
As far as Lightning, we haven't sold them. I've seen the stainless version and they seem ok but I still don't feel the workmanship is at the CMI level in terms of clean welding and am not sure of their material quality...CMI uses all 317L stainless which is very non-corrosive. CMI welding for the most part is done robotacally, which produces a very consistant and high quality part. I would stay away from the Lightning steel version though as the life expectency of them would be limited. I really have little knowledge on the Lightning so I hesitate to recommend or bag on them. There's a lot of them out there in use, as well as there are CMI's.
I think also its important for one to consider what type of motor, how big, and what his future plans for upgrade are before choosing any exhaust system. Many of the cast systems will perform just as well on the smaller motors. I could go on for days on exhaust systems pros and cons but just try to make a wise and informed choice. The cheapest route is not always the wisest route with this type of purchase.

[HighRoller]

I gotta give mike a big thumbs up for those comments.I think most importantly about not knowing enough about Lightnings to bag on them.Very respectable.FYI mike the Lightning Magnums(stainless)go for 1800-2000 bucks so they are competitive with the CMI's.I've seen the CMI platinums for as much as 3500!!!I do really like the appearance and workmanship of the CMI's,and of course I would NEVER buy a mild steel exhaust header for a marine application.I'm gonna go to the Rex website and order a catalog....Thanks dude