Exhaust header design
 

I am removing the head on my Formula ford race car and notice that the exhaust header pipes must be at least 1/4" larger diameter than the ports coming out of the head. I tried to read a bit about it and it seems that bigger tubes will raise the rpm level at which torque peaks and longer pipes do the same.

I am thinking of making some pipes which are smaller diameter and lots shorter, like the 37 Auto union racers with the shorty pipes exiting straight out and no collection at all. Lower torque delivery and lighter weight.

Anybody with expertise on these here?

Have you seen this?
Header Design Calculator | HorsepowerCalculators.net

I remember back in the mid 50's when Chrysler really went into sonic tuning. There is one version that has a four bbl carb sitting over the coil spring and feed the opposite side of the engine. Really long intake length yields low RPM boost. Mid to late '50s, Hot Rod magazine ran a tech article. It had the formula for calculating header length for any RPM range you desired.

Thanks MS! I'll delve into that soon.

The slant six mopar intake was based on ram air logic. Two long, two medium and two short runners to help widen its power curve.

I'm interested in the exhaust manifold....the intake is restricted to a very basic design.

You need to check out what some of these scandanavians have whipped up over on super turbo diesel. Amazing freeform header fabrications

Larger pipes than the port supposedly helps prevent some of the exhaust flowing back into the head when the valve is closed. Supposedly....

My understanding is that with exhaust, there are 2 benefits to work for
1) lack of backpressure - a larger diameter helps with this.
2) tuning/extraction - where the exhaust pulses resonate in such a way that it helps the exhaust gasses travel out quicker...and reduces backpressure. A larger diameter *sometimes* helps with this.

Since 2) is a function of 'tuning' the resonance of something, things like manifold material, number and size of welds, tube lengths, tube curve diameters, placement of mounting bolt holes all affect how the exhaust systems resonantes.

its likely that the aforementioned items make little difference, and in this case the calculator listed above would suffice for TW racing (...but maybe not for F1 or MotoGP).

I must defer to BC here. A lot of things make a difference on paper but dont affect anything when bolted to an engine. I'm losing my touch of these things.

-John

Also, on my NA 4cyl when I ditched the stock cast manifold(small diameter runners) and replaced it with a wrapped tubular manifold I lost some torque under 1,500 rpm and gained noticeable power above 2,500 rpm. No other changes

Low end torque is always a plus in autocross. High end power too though....but i would give up some high end for added grunt off the corners.

On the first SL's Mercedes had some very long intake runners. They said it was because there was no other way to package the engine under the hood.

But that was just to keep the other carmakers in the dark about how the longer runners reduced the HP needed to suck in and transport air from the outside world to the interior of the combustion chamber. The increase in pressure generated by the actions of the intake valves was almost negated. Another way to say this would be: Less back pressure is a good thing.

Exhaust headers do the same thing: Reduce the HP necessary to push exhaust out. The shorty tube you are speaking of should work great since that exhaust is not leaving the engine by itself and the longer the exhaust system the more friction the gasses have to overcome to exit the system.

If anyone is unclear on the concept of friction losses in gas pipelines then all they need to do is visit a NG compressor station and notice the 1,000 HP motors that are used to push NG through the line.

What pressure is the NG at when it leaves the pump station?

Depends on the operating pressure of the system. The system I worked on was 1000 PSI.