Header Flow Test

[So Cal Mark]

Here's a simple test you can do at home to see if your header/exhaust system is effective. Using an air compressor and nozzle, blow air down a tube simulating exhaust flow and see if you have suction or pressure on the other tubes. This is not a very scientific test, but I watched a Holley test on a new header they released and I thought it was interesting. I've performed this on the headers that I offer for Spiders and X1/9s and I've also tried it on some of the other Spider headers on the market as well as all of the variations of stock cast iron manifolds with startling results. Here's a video of my test;
https://youtu.be/jhrO3aQiKmQ

[fiatfactory]

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[So Cal Mark]

well actually I did the same test on an FI manifold and also a 79 manifold which is also 4-2 and got the same results. You'll find pressure on 2 cylinders. If I have to do a video to show the results I will but if you have one of those manifolds I suggest you try it yourself. If you look at layout of a stock manifold you'll see that flow wants to travel back up opposite runners rather than try to bend to escape through the outlet.
At the moment I don't have a competitors header to video, but I've tried it with a few other headers and have gotten similar results to that of a stock manifold

[RRoller123]

That's a really interesting result! Wouldn't the inertia of a complete running system, with mufflers, pipe, Cat etc, cause a negative at the start and pull exhaust gases along through all the ports, albeit at different rates?

[So Cal Mark]

I've tried this on several different headers, stock exhaust manifolds and complete systems on cars. On the complete header systems I had cars with the head off and the exhaust intact. I was curious to see the results of a complete system compared to a header or manifold that wasn't attached to anything.
The whole idea of a header is to help scavange the other cylinders. if you have pressure from a cylinder pushing back into other cylinders you will have reversion and that's a power killer.

Here's the Holley video that gave me the idea;
https://www.youtube.com/watch?v=zTheO-8n8AI

[RRoller123]

Were the results similar when the entire system was tested? I.E. still a scavenge draw on only 2 of the 4 ports on the 4-1 factory header? and reverse flow on the other 2 ports? I would expect there would be slightly better results from the 4-1 manifold if the whole system was installed, but one would need to get the air flowing out the end to create some realistic momentum. I expect that it would still show far better results with your header system! With the 4-1 manifold by itself, the momentum of the air from the compressor gun clearly just draws it across the outlet zone.

One question that lingers for me is the benefit of a custom header system versus the 4-2-1 factory manifold. The general feeling seems to be that the 4-2-1 is pretty good on its own.

Pete

[So Cal Mark]

the results were identical when testing a complete system. Pressure on 2 cylinders. I suggest you try it and draw your own conclusions. On the stock manifold I believe the results are influenced by the routing of the runners. That design forces the air flow to turn to exit the manifold so a certain amount of air goes straight into the other runners. What is interesting to me is some of the competing headers that I tested. They showed the same results as a stock manifold. I would expect the collector design on those headers isn't correct but I didn't spend a lot of time analyzing a competitors' product, especially when it didn't perform any differently than the oem cast iron manifold

[RRoller123]

That is amazing. Good work, very interesting!

[fiatfactory]

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[JohnMc]

https://www.youtube.com/watch?v=jhrO3aQiKmQ

The link was not working - here it is. Really interesting. Using a smoke tube or cigarette is more visual - but I really like the test. Of course no cigarettes around flammable vapors.

[So Cal Mark]

that's odd, it works for me. I'll post another video, perhaps this weekend. I tested 2 styles of 4-2 exhaust manifolds since fiatfactory seems to disagree with my results. On the 4-2 manifolds, the opposite cylinder of the runner with flow shows pressure.

[So Cal Mark]

here is part 2 of the flow test;
https://youtu.be/l25Dt1smFhk

[So Cal Mark]

and part 3;
https://youtu.be/Y3czPaA853o

[MrToon]

Hi Mark,

I'm just studying for my vehicle propulsion exam in automotive engineering, what a coincidence! I just want to note that the dynamics part of your airflow matters a lot for the performance. Like you said, sucking the exhaust gasses out of a cylinder can result in a power loss. It is however possible that the stock header was engineered to get a resonance in the header and following exhaust system to do this more effectively than just a static suction. Not that I think that 4-1 header will be better than those performance headers

Kind regards,
Toon