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View Full Version : Header type pros &con?



MOP
03-09-2003, 11:04 PM
I think it would be a great topic to get into the plus's and minus's of different header types and the real gains and loses. I feel either lightly or not modified stuff runs just as good off nice center riser setups. My favorite is the Volvo long lay down that Osco makes for small block Chevy's. Its inexpensive, its water injection point is well away from the manifolds exit, it does'nt usualy affect tuning much like going lean. Where as the types that really breathe seem to hurt them go lean,lose torque in varying degrees and should be only used on the stuff that gets enough air in that it needs a way out. I was an old drag racer not big time for sure, but did do alot of exhaust plumbing as I called it. Pipe length and diameter when matched to the engine really works, I saw signifigant gains fooling with my junk. My feeling is especialy in fresh water many guys are far better off with a well designed stock item running out the back. What do you guys think?? In SALT S/S becomes interesting, but still costly.

BigGrizzly
03-10-2003, 12:19 AM
I don't agree with that at all. I have done dyno and real world testing from small sixes to big blown V-8's. With out getting into much detail some gains are bigger than others. The Osco stuff has too smal an exit to work as well as a set of Stainles Marine or tube hedders like CMI- both the forementions I have found to be superior. Most Marine cams are pretty good stock and are far superior to stock auto cams. Most times jetting need not be chaigned, because stock marine engines run rich to begin with. This is done because of the usage and the poor flow of the exhaust, yet the exhaust is fairly non restrictive compaired to autos. Marine engines have a much richer mid-range than other applications such as autos. We did discuss this topic two or three years ago thoe.

I can say that I don't know anyone that didn't get gains from a good ehaust such as Stainless Marine or CMI, with no other changes. I did know someone who did change exhaust and jetted up too far (to be safe) and actually lost rpms! We did rectify the problem when he said "I even jetted up and it still slower".

One reason a good exhaust helps and usually doesn't need jetting is volumetric-efficiency. The biggest mistake people make is jetting too rich. On a marine application the exhaust plays the smallest part in jetting. A prime exhample is a boat with silent choice. From prop ehaust(very restrictive) to transom streight through-no jetting here! As marine is evolving they wil be O2 sensor controled and (to a point) fuel metering will be a thing of the past.

The exhaust does help. There have been many articles in boating mags over the past 20 years and all have shown an increase. One I remember was on a 22 Donzi classic and it gained 300 or 500 Rpms(can't remember which) with a set of Stainles Marine manifolds with no changes. The test was performed on the same day on the same boat. I can also remember CDMA doing a swap back and forth on his boat with great gains. At this point in the pros and cons, the only con is cost.

Greg Maier
03-10-2003, 05:36 AM
Griz,

I have a copy of that article here at my house. I will scan it and post it if I can find it. A 22 classic with a 454 gained 6 mph (if I remember correctly) just by swapping stock to SM exhaust. The testers were very surprised, but it was verified by radar.

I have a question that I wanted to ask you. I watch Horsepower TV on occasion. When they show some of the aftermarket exhaust systems on these cars, there usually is a crossover pipe between the two large pipes coming off of the headers. Why do they do this? Why don't boats do this? Does this equalize the presure on both sides of the engine?

MOP
03-10-2003, 07:16 AM
Excellent and I do agree with Griz a 100% my point are real world gains in the normal operating ranges especially low end when skiing really worth the cost. There is absolute proof that any engine will gain in the mid upper RPM ranges. Everyone I have ever seen got some top end, some mild some alot. Griz do you see actual gains down low also. My point from the start of this is it enough to really warrent the cost to the average guy with a basicly stock mill and average depth pockets. I am tickled I got one of the best Top Guns to come out on this thanks Griz. I would like to hear from the little guy that did it for more input. Also to a man all will agree they sound so sweet coming out the back.

BigGrizzly
03-11-2003, 02:39 PM
That pipe in autos is called an H-pipe. It evens out the exhaust paulses and takes the raspy noise away. It is suppose to give some driviblity,midrange and less ehaust restriction. It is like the balance tube used on multi cylinder motorcycles years ago. This system is used on boat exhausts. CMI offers it as do Stellings the problem is that in a boat it takes up room and you run it accros the top pf the engine.

Greg Maier
03-11-2003, 02:55 PM
Griz,

Thanks for the info. Does the H-Pipe need to be the same diameter as the exhaust pipe (4 inches) or can it be a smaller pipe? Do you think it would help top-end or is it more for sound and driveability?

Formula Jr
03-11-2003, 04:09 PM
Has anyone ever developed a scavaging type of header for marine use? I mean here, something that will suck out, with mechanical assistance, and help the volumnmetric effect on the exhaust side? or am I just too platz to think about this stuff? wink

<small>[ March 11, 2003, 04:14 PM: Message edited by: Formula Jr ]</small>

BillG
03-11-2003, 05:11 PM
The H-pipe is there to help midrange torque. The proper place to locate it on an auto engine is just behind the point on the exhaust that the paint burns off,if you were to paint the pipes.
Bill G

knots2u
03-14-2003, 12:34 AM
For fresh water, stock/mild mod applications I would recommend aluminum center rise manifolds. Use the old iron log manifold for an anchor!

MOP
03-14-2003, 04:46 PM
I was hoping to get a little more input from the light to non modified guys that did the swap from log to center riser. Volvo I believe was one of the first to go the the High center riser, I remember in school thay said it was a decent improvement over the logs. I've been trying to find out from some of the old techs how much diffence. I am running that type which leaves me 1/2 inch from the hatch. Even in salt the aluminum style do pretty well, better than iron especialy on flushed rigs.

BigGrizzly
03-15-2003, 08:14 AM
JR, CMI, Stellings hqve true scavaging exhausts also soon to be released Harding hedders willbe out in about 90 days, these are water jacketed. there are seveal real hedders on the market for above the deck instalations.

MOP Volvo wasn't the first they all entered the market at the same tine. To get a feel from the old techs is a wast of time because it was seat of the pants. 20 years ago the center risers were not much better than the logs, in fact some tapered loges were better. To day exhausts are a new ball game. My old Osco manifold only had 2 inch id on them. Funny my intake valves on that old H&M 351 Ford Clevland are 2.15. So on that point alone new style exhaust do help!

MOP
03-16-2003, 08:05 AM
Point well made on true headers can't beat good breathing. I guess having raised 5 Rug Rats I always tried to get the most from the least $$'s. When I got the 302 done I did poking around for a deal on decent exhaust, little Ford stuff is like Hens Teeth and spending more on exhaust than the engine did nothing for me. I did settle on the Osco's they are had the biggest holes. I figured good enough for the mild cam, maybe I'll get talked into chopping holes in the back Yet!