Exhaust systems
 

Kinda dead around here lately. Thought I would bring up the "exhaust" topic.

As we know, today, many guys are building more and more powerful engines. The days of a 500HP engine being a hot item, have transformed into a 600HP engine, being a "mild" engine.

Sooo.....the guy who's building the N/A 502, 540, 572+ with "custom" cam, high flowing heads, and rarely is the exhaust system discussed. Exhaust header primary diameter, length, collector diameter, collector length, all play a big part of the build, esp on N/A engines. With cars, its easy to get deeply involved with various header designs, and one surely would want to if he was building a 600,700+ hp engine for his Chevelle. But then on the boat stuff, a guy will argue over the proper CFM carb, the ideal textbook intake runner volume, which aftermarket head has the best flow number, order a custom cam with the ideal duration, lift, degree it in, port match things, and then slap on some general marine aftermarket manifold like a Gil, Stainless marine, imco, emi, etc.

At what point does a custom big block pumping out 1.3+ HP per ci, start seeing the effects of a poorly designed for the engine exhaust?

Another question I have.

Back in the day, alot of the old crane, comp, and other BBC cams, were designed for the GM iron castings. It was no secret, those heads left alot on the table as far as flow, esp on the exhaust side. Big split duration cams worked with them, to help out the poor flowing exhaust ports.

Now, lets say you have some good flowing modern heads. Your ordering a custom cam. You cam guy wants the flow numbers. You provide him with the flow numbers , which say were flowed with a 2 1/8 pipe on the port. BUT, you don't have a 2 1/8 pipe/header, you have a 1 7/8 header, or even a manifold with a small ID, and very short exhaust tube before it dumps into a common pipe. Now, that head that flowed 300CFM with the 2 1/8 pipe, maybe only flows 280CFM with a 1 7/8 pipe. Does you cam guy take that into consideration when designing your cam, maybe adding some exhaust duration, or lift? Or is this irrelevant?

And if you're running a 1 7/8 ID header, should your head be bench flowed, with a 1 7/8 pipe?

Good question, what is the tube diameter of your standard Gil, S. Marine or IMCO manifold?

Your cam grinder will ask what exhaust you're using before he specs the cam so as to account for the limitations or lack thereof of the exhaust. In the planning stages of an engine build the exhaust is determined before the cam is specified.


In a car, there is much more liberty and availability of header primary diameter/ length, collector diameter and length and there is no consideration of the issues of water intrusion. Even a true custom race car header will cost a fraction of what a "shelf" marine header will. in a boat, we see "manifold" style exhaust systems because of the fear of leaking headers, fitment and budget. Ever see a manifold type exhaust on anything but a nearly stock automotive application or because of class rules as seen in "pure stock" or FAST racing?

I'm sure if one had an unlimited budget, access to a wet dyno for back to back testing and the tooling to produce jacketed headers in multiple sizes and configurations the optimal header for a specific engine could be built. That said, in the 650 HP BBC marine world, it would be much more cost effective to find that 40HP gain in another way.

I would think an exhaust system that is not matched to the rest of the build would effect any engine wether it's a 350HP smallblock, a 700HP big block or a maximum effort build. In my mind it comes down to reliability (leaky headers) fitment and cost when talking marine exhaust.

These are just some random thoughts off the top of my melon.

For what it's worth, the shop rebuilding my engines is pretty confident he'll be able to run my big tubes on the dyno. Hopefully it works out and shows the difference between them and the automotive dyno headers.

I do hear you on the cost, and choices being an issue. I do think the leaky header thing is a bit over rated. My stellings are now 20 years old, and still working just fine. I had a small leak at the collector, but nothing horrible. Another friend of mine, had lightning headers for 10 plus years or so with no issues. I certainly wouldnt be spending thousands on cnc ported heads, only to run an exhaust system that is a poor choice for the power level I am shooting for . I would like to think the power loss from a Gil manifold vs a teue header, is not nearly as great at 400hp, as it is at 700hp. How often do you see a "gil" manifold on a skater, mti, apache, nortech, etc. Heck, even mercury went from manifolds to headers on 500efi, 525efi, and about everything above that power wise.

Plus , there is the option of a cast header manifold, like the PF marine /eickert/ lightning manifold.

I'm going to run lighting headers on my engine with dry tails. Freshwater use.

I decided that early on and bought the system and went from there.
I hope you're right about the leaking header woes being exaggerated.

It seemed counter intuitive to build up a cool mill and then cap it with manifolds (although lots of guys submit that there is little to no loss with a good manifold system, IE. Stainless marine)

Time will tell, I suppose.

Gotcha beat by a few years in the long lasting header dept. I called CMI to decipher the numbers/ letters stamped on the flange and found out they were made in 92.

I vaguely recall recommending my buddy joe to check his port match of his imco manifolds which had a square port flange, to the afr's large round exhaust port . If i recall, the manifolds opening was slightly smaller than the heads port, in the corners. Hows the exhaust port flow when theres that going on ? Lol

Anyone ever check their exhaust port match ?

I think alot of header failures are due to lack of cooling, as well as lack of tailpipe support. I cant tell you how many guys ive seen running -12 an lines to feed their headers. I personally would never run anything less than a -16 line to feed headers, and always make sure the sea pumps are in good shape. Cmi had a youtube video on this topic.

Nothings harder on double walled stainless headers with lots of welds than drastic temp changes . Now, salt corrosion, thats another story.

I have seen some exhaust comparisons at 450hp levels for marine engines, and there wasnt a huge difference in power. Id like to see some of those same manifolds at the 700+hp NA level. Forced induction is a different animal.

I know cam guys want to know what exhaust will be ran on a boat engine for a reversion standpoint, but i dont know of any that have the tuning parameters of a Gil, imco, stainless marine , Eddie marine, etc, when it comes to primary ID, runner lengths, and so on.

Maybe if full force tim dynos his afr headed 540s, he can try it with his stainless marine manifolds, and then a set of CMIs.

Another thing most dont mention. Your typical manifold has a 3.5 inch gas pipe, with water being injected early on. At high rpm , being fed by a sea pump (not garden hose on dyno), there is an enormous amount of water being introduced into the exhaust stream. Which, consumes much of the gas pipes volume. The water itself, can be like putting a muffler, or smaller ID pipe in the exhaust stream, hindering flow.

Maybe not in the same comparison but with cars headers primary tube diameter and length is pretty easy. What about the bends in the rest of the exhaust and the mufflers? I remember years ago on cars the hot ticket was to put a H pip connecting both banks then that evolved into a X pipe. Has anybody hone a H or X pipe exhaust on a boat? Would the benefits of it be negated because the exhaust is so much shorter on a boat compared to a car?

exhaust port match. The big tubes are larger than the AFR exhaust port all the way around.

you are correct on the imco manifold not being right out of the box,i spent several hours with the die grinder to get it gasket matched.i had the imco power flo,s on my cat.they were 950 on the dyno with dyno headers so in sure their was a little power loss with the imco,s but they ran very good.the engines were 548s with dart 320s.

that is why i,and you run dry to the tail exhaust,loud but effective.

I had an engine masters magazine where they did a header shootout on a bbc . I think it was a 572 ci making 700 plus. I recall them trying several different headers with various ID's. I recall there being a pretty good difference from a 1 3/4 to 2 1/8. I dont recall the exact power numbers, but it was pretty significant. Ill look and see if i have it still.

i think a not so good exhaust manifold will hurt a 650 hp n/a engine more than a 950 blown engine.the blown engine does not rely on the scavenging like the n/a engine.

Can't agree with this more, I can't tell you how many times I've seen someone fry an impeller or clog up a sea strainer get the exhaust scalding hot, fix the blockage or put a new pump in and shock the burning hot headers with ice cold water. Recipe for cracks.

My CMIs are atleast 10 years old always in brackish water and I sent them back to cmi this year to have them tested and 2 small dings fixed and they complimented me on the condition on them. They were good to
Go. But I religiously flush for extended amount of times every single outing period. No exceptions.

I would think that, along with water reversion, the cam grinder would want to/need to know if you were running a short primary ( 10 to 12 inche's like in a manifold system) or a longer primary (20" long as in a long tube header style exhaust) to be able to get his best shot at the cam. Not so much which manufacturer of the manifolds or headers, but wether or not the primary's are long or short.

Funny you bring up tailpipe support. I was brainstorming the other day about how to rig a support clamp on the inner transom to help hold the dry tails as they pass freely through the transom and I plan on hanging a pair of clamp on mufflers to exacerbate the issue. We need to modify my tailpipes to provide a downward kick to clear the rubrail and I'm going to talk to the tig welder to work up some kind of support as well.

Maybe we just hear about every failure with headers but those who have no issues have no reason to post as they have experienced good results.

I agree that spending a ton of time porting a pair of cylinder heads and paying no attention to the exhaust match is shortsighted.

A support is a good thing, especially if the tails are long, like a TRS, SSM, setup. I'd want the support brackets attached to the rear engine plate, or something affixed to the engine/transmission itself, so that if there was any movement, the tails move with the engine. Prob not a big deal for the guys running in small lakes and rivers, but on the great lakes, ocean, etc, that stuff can move around in big water! Main thing though is I think making sure your tails when going thru the transom, have a decent amount of room around them, so they dont bind against the transom. You don't want the tails wedged in place, then stressing the header when things move around/flex. Just my thoughts on that, could be wrong.

If your cam guy doesn't consider the exhaust system, you need another cam guy. ;)
Seems this is always the compromise with off-shore style marine engines, is their exhaust system both with all the different styles of manifolds, cast headers, and tubular, plus the water issue. Water in the exhaust system kills ex flow and power...another factor that needs to be taken into consideration.

While a blower engine may not benefit from a tuned exhaust, it's processing a lot more air and fuel and still needs a good exhaust system and will benefit just like any other engine. The manifold, while not tuned, may not be as much of a restriction on the smaller engine as it would on the larger blower engine and that restriction will kill power on the blower engine.

I've done many header comparisons on the dyno. Lot of our customers order custom headers with their engine combinations. We do initial testing with the dyno headers but will always do the final pull and tune with customers headers. One thing I can say about headers, especially with NA engines; bigger is not always better. ;)

The IMCO's I've worked with seem to be good up to about 850-900hp. After that, they're going to start hurting power over something tubular and more tuned. I did a blown pump gas 540 that made 1020 hp with dyno headers, but when in the boat with the IMCO's the engines performed to right about 900 hp, given rpm, prop and pitch. This kind of goes to the above post where there's no way the IMCO's would kill 100hp on a NA 540 even over a set of tuned headers, but they kicked the blower motor in the nuts.

I can believe that entirely!

Good example is stainless marine gen 3 exhaust. Not to be confused with their standard manifold. The gen 3 is huge. Makes the imco,gil, emi stuff look tiny.. Giant elbow, 5 inch tailpipe, etc. That exhaust worked very well on big power blower engines, as thats what it was designed for, and has outperformed even some big headers on those engines. Now, i would not chooose that for a N/A exhaust .

My stellings "green" headers were designed for the merc 575. Which was a 540ci making 575hp in late 80s. 1 7/8 primary. In a recent conversation with a well versed offshore builder who is familiar with those headers, said they certainly can be hindering power a bit, even on my 800hp blower engines.

For support I have another set of trim rings on the inside of the transom with a thick non stretching rubber/ canvas type material. It is flexible to allow movement but not stretchable so it supports the pipes at the transom.

Another thing I was wondering about.....
My "dry" tails have six 3/8" water outlets right at the tip. I was considering welding those shut and welding in bungs near the ends of the tails and dumping the water that way.

Is there any advantage to either way of expelling the water? Can the water migrate back up the tailpipes even when it's introduced at the very tips of the pipes?

Furthermore:
When exhaust hit's the atmosphere, an energy wave is sent backwards towards the exhaust valves. This is why collector length is very important, yet no one seems to give a schit about it.

If you are going to weld the tailpipe shut 100 percent what you need to do is cut the outer sleeve off of the tailpipe first, then cut 1" out of the outer tailpipe and then slide a 6" piece of 4.5" wet exhaust hose up over the existing outer tailpipe then slide the outer piece you cut off back on and weld it up. This allows expansion of the inner pipe because it's much hotter then the outer and if it's butt welded at the end it'll always be prone to crack. Atleast I have experienced this. All this is inside the bilge obviously. Use the wet exhaust hose as a "coupler" if you will except the inner pipe will be continuous you're simply holding water from spraying out. Then add your dumps in the tailpipes. You should also consider drilling a 1/4" hole in the bottom of the outer pipe outside the boat so that way the bottom of the tailpipe can drain when you shut the engine down. I've had great success with this tailpipe setup for a long while.

And as far as your question about can your engine pull water back up from the very end of the tailpipe? Absolutely. I know of a SVL team that had issues with water reversion on their sealed 525 with 100 percent dry tailpipes. They caught on their camera systems at idle the dumps were too close to the tailpipe and water was getting sucked over and back up the dry tail at idle. Wouldn't have believed it if they didn't show me the video. They moved the water dump and the problem went away.

JMO . . . Loud pipes save lives:daz: and engines:eek:

Anyone ever test say a stainless marine, emi, imco, style manifold against a header at the 650-800hp N/A range ?

There fixed it for you

Not really answering your question, but worth mentioning

KE's beat them all at 500hp - many tested on a stock HP500. As they should.
2" x 34" primaries. 4" collector.

I'm confident they'd kick ass against the others up thru N/A 650hp anyways.

I'm sorry. They are now Diamond Marine's Thunder N Lightning Exhaust
http://www.diamondperformanceparts.c...cat=282&page=1

Manifolds/back pressure also increase engine heat, no?

Exhaust tips can be an overlooked item. The stock Corsa mufflers on my 272 were killing my 502.

Yup, GGB custom inserts killed a mild small block almost 2mph !

edit in: their old spiral style they haven't made for years.

SB, which GGB inserts (dia and length)? I've found them to be non-restrictive. Others not so much.

The old spiral one's they made when GGB first came onto the scene. A few years later they came out with their open style.

Got it. I'm using the 4" diameter 'performance' 4 or 5 ring open style. They knock about 6dB off the sound, make a better sound, and have not been restrictive in the least bit. The CP inserts on the other hand squashed about 500 rpm off the big end.

I`ve found it depends on how long the tail is .. My STEROID headers the collector was so far back there was a short tail and it reverted. The collector would be soaking wet... worse with mufflers closed. Had to buy a bunch new valves this year due to pitting from reversion. The current SM Gen 3 have a long tail and no issues whatsoever.

I do dump overboard from inside the boat but have a hole inside the tail at the end to keep the mufflers from burning up.


http://33outlaw.zenfolio.com/img/s6/...84605872-3.jpg

I'm gonna change my screenname to ICNIPPLE, is that okay ?

LOL. And thanks.:lolhit: