BB Exhaust manifold testing revisted

I agree with you Rob, lessening the overlap should help, that was my thinking 10 years ago when we did that first testing.

But I think what we found was that backpressure is backpressure and we could not effect enough change with 4* to make any difference.

I might go wider this time, if we do a new cam for it.

Thanks

JW

 

Jim
On Sandys X we had the best luck with the venerable kb118 plus was more street friendly
Gary

 

Gary, is a version of this cam available from any of the cam vendors today? Back in the 80's, I wanted to put a KB118 in my 71 Stage 1.

 

Steve Long can grind them, he used to grind for KB and Poston at one time. However, any cam grinder can do it, it just won't be the "KB" lobe.

 

2.5" no more than 18" long into 3" at least to the muffler inlet. X pipe is the only way to go.

 

2.5" no more than 18" long into 3" at least to the muffler inlet. X pipe is the only way to go.

Unfortunately 3" pipe wont bolt directly to the manifold, so a reducer is necessary.

 

Let the exhaust valve hang open a while too.

 

Ya, I was wondering about that.. thanks.. 2.5 it is

JW

 

Agreed!

 

TA still grinds them, got one from them for a customers motor this past spring.
gary

 

Hi Rob,

Was this the comparison?

http://www.buickperformanceclub.com/Exhcompare.htm

 

First of all, thank you Jim for taking the time to do all this.

Second, the results are a bit misleading for real-world usage, and I'll explain why:

Headers have a scavenging feature built into them by their very nature, while the manifolds (ported or no) do not. This comparison would be valid if one were to simply use separate dual exhaust pipe. Add in an "X" pipe after the manifolds, and the story changes.

If there was any way you could do a comparison using an "X" pipe on manifolds vs straight headers, this would show a more accurate depiction of how much difference scavenging makes (as is evident by using headers).

To add to the 'devil's advocate' even further, no one would run straight headers on the street for long, without attracting the attention of local law enforcement. They will be using an exhaust system, which typically has restrictive reducers and smaller pipes, then their choice of mufflers. All this will tone down the perceived benefits of those headers considerably.

So while this dyno demonstration bolsters headers, it hinders the manifolds.

The power differences, when all things being equal, will be less than what is presented. I think we'll see that ported manifolds with a properly set up "X" pipe will be closer to headers than these graphs indicate here.

Not cheering for one or the other, just the real-world facts.

Now I'm going to duck out before the rotten tomatoes start being slung my way. lol

P.S.-this is in addition to the 'small into large' pipe as was suggested earlier.


Gary

 

Gary,

No open exhaust in this testing. All headers/manifolds were hooked to a full, separated dual exhaust system. On headers, the system hooks right onto the collectors, on the manifolds, aprox 18" of pipe comes off the manifolds and hooks to the system.

Here is the same facility, different motor obviously, but it shows the exhaust system.




I agree that if you put your headers into a 2" exhaust system, with restrictive mufflers, the gains would be muted.. but who does that?

I would be interested in seeing documentation that demonstrates an X pipe helps manifolds more than headers.

I have no concern as to who puts what on their cars, and don't sell headers or ported manifolds... just doing the testing.

JW

 

Marco, that's it, thanks for posting the link!