Exhaust balancing

I have 2 sets of dual out headers with different pipe layouts. The one on my car now has 1,2,3 going to one split and 4,5,6 going to the other. A separate header has the evens going to one pipe and the odds going to another. Since the firing order is odds then evens, you basically have one out doing all the work while the other does nothing, then vice versus. Is there a performance reason for this on the second header? I figure the concept is either performance gain on the second 2 cylinders riding close to the previous firings vacuum wave, or maybe it works better on a certain RPM scale.

Anyone know for certain?

I don't know the answer here but am very interested to find out. I am curious, though, what brand of headers do you have and which one is which? Thanks.

I think it's more sound, look at the fireing order, the 123-456 exhaust... 15,36,24, it's front the back x3, I don't like the odds then evens idea... back and forth will get you 'even' amount of balancing. I don't know about the sounds though... I think the sound could be cool?? but I know my front and back collectors sound really close to a v8

Invectivus":35wdlq7l said:

I have 2 sets of dual out headers with different pipe layouts. The one on my car now has 1,2,3 going to one split and 4,5,6 going to the other. A separate header has the evens going to one pipe and the odds going to another. Since the firing order is odds then evens, you basically have one out doing all the work while the other does nothing, then vice versus. Is there a performance reason for this on the second header? I figure the concept is either performance gain on the second 2 cylinders riding close to the previous firings vacuum wave, or maybe it works better on a certain RPM scale.

Anyone know for certain?

Click to expand...

Yes, the second header makes more torque, and as much power without compromise.


For the benefit of others here, the first header is the Jag XK/Aston Martin/Jeep XJ Cherokee style, which gives low backpressure, but a loss of low end torque with good top end power. Like this
http://imgc.classistatic.com/cps/kjc/12 ... nh_20.jpeg


The second system was used on some aftermarket kits, never a standard I6 set-up that I'm aware of. A system similar, but not the same was the tri y Australian XT6 Holden Commodore Ei 6, used for a . It was a punny 142 hp, 198 lb-ft 3.3 liter engine which was stuck with the GM Strasborg 3 stage auto and 3.36:1 diff. It gave a 16.7 to 17.2 sec 1/4 mile depending on appiontments, and was faster than the 135 hp 4.2 liter V8 by 1.3 seconds because of the header, cam and EFI package. It gave stunning performance, a great engine not and was, in my opinion, the very best exhast ever used by GM on its 12 port engines. The exhast system looked like this.



When the odds and evens cylinders are matched, the engine note changes. A further split, and it flows even better, with a BMW M3 I-6 style engine note. The difference between the 85 3.3 Ei Holden and the 85 4.1 EFI Falcon X-flow was that the Holden engine had more urgency, a better rev range, and a crisp, Germanic, almost Cologne V6 style note which was alwas inspirational. The non tubing header single out Ford was latent and unresponsive, even with 20 more hp and 48 more lb-ft of torque.


http://oldholden.com/ohfiles/images/130 ... review.JPG

I figure the concept is either performance gain on the second 2 cylinders riding close to the previous firings vacuum wave, or maybe it works better on a certain RPM scale.

Anyone know for certain?

Click to expand...

You do get some help scavenging of the combustion chambers for each cylinder from (exhaust pressure, flow pulling) depending on the header design. Together with the carb and intake, port's flow (CFM), plus the cam. This stronger signal helps pull more fuel into combustion chamber as well as pull exhaust out raising the engines Volumetric Eff. Cylinders pipes paired together in right order will also help pull some flow with the next cylinder to open it's exhaust valve. Yes it can also be designed and tuned for a certain RPM too, equal length primary pipes of the right size plus length and size of the collector. It gets involved to figure it all out on a race system, and if you next add in the exhaust system after the collectors. You might also look at Falcon Fanatic post on the zero loss exhaust system he was building.

Thank you for the pic, just love it when clickin any open.
I can't tell much from them, but am short on auto-engineering knowledge anyway.
All ways heard "long tubes 4 for tq & shorties R 4 hp" or may B the other way round...

The order in which they're grouped is a new one for me. And how to "tune" for 'note', now as minor an issue or arbitrary/personal taste oriented that is - sorta interests me.(C my longish thread on tryin 2 sort that out).

Long article (may B cited here) convinced me nothing real for us in "back pressure" the scavenging properties are the real deal tho...

Invectivus,
I,too, am intriged by thought of different header designs. So much that I'm partly through the making of one that pairs cyls 1&6,2&5,3&4; just don't know when it'll be finished,just like my 2 deuce log head.

I know for a fact that 360* system helps torque on 4 cyl,will see what it does for 6cyl. Jack Clifford said any pairing or arrangement other than 123,456 wouldn't make much difference,andI want to believe him. However I get to thinking and have to experiment.

Probably pairing, stepping,playing with length etc. is rewarding but splitting so that the collector is effectively dead part of the time is hard for me to comprehend. I did read about it once in some print decades ago (said it was for special apps,didn't say what). I did witness a C**** II at the strip early 70's with that arrangement---ran like on 2 cyls until he turned it loose then sounded like a V8. Sorry, meant to say it was a 4cyl duke.

You have to hand it to those BMW guys their little bear is tremendous---and silky!!!

Good to know you or anyone else notices, persues variances like these.

Truck on.

Gary

Is either one of your headers a Hooker 6602?

The second header is probably one of the old "Cyclone" headers, I've never seen any other brand with that kind of collector grouping. The first is better for power because it has balanced exhaust flow. The second one sounds better at idle but I don't know about performance gains, it overloads the collector for a better rumble like a crossplane V8. You'll notice a flatplane V8 or one with GT40 "bundle of snakes"/crossover headers sounds different than a standard Ford or Chevy because they have balanced exhaust pulses. Either of the two headers would be much better than the stock manifold, of course.

The BMW M3 I owned had 340 horsepower, naturally aspirated, out of a 3.2L I6. It used the first header style: 123 456, and each bank got its own outlet. There was an X-pipe crossover about 4 feet down. The Pacesetters, the Classic Inlines, the Hooker 6601/6602 were all the same way, and it's the best for power in my opinion. I feel that something else would have worked better, BMW would have used that. Though their goal was all-out high RPM performance, not torque production.