Tuesday, March 17, 2009

Who Dat Ya Gonna Call?

Knowing that we were going to be using longer primary headers than usual in order to clear the zero roll bars, I started wondering what effect that was going to have on performance. Who do you call when the ghost busters can’t help? Jim Shring at SR Racing and Fred Clark at Caracal cars.

To each of them I posed the following question:

Let me pick your brain a bit.
What effect does the length of the primary headers have on the performance of an engine? I am assuming they are of equal length of course.
Thanks for your input.

The same day I got back a response for Jim.


Lengthening the primaries moves the peak HP and Torque points lower on the RPM curve. Inversely, shortening the primaries moves the peak torque and HP up on the RPM curve. This does not necessarily increase or reduce peak HP, it will simply move that point to occur at a higher RPM. That is the simplest way of explaining it. It gets a bit more complex, but that is it in principle.

Typically you want the Peak HP to occur somewhere around the point where you need it most. Most Vee's peak in the 5100 to 5400 range.


The same day I also got a response from Caracal.

“Mr. Lamb,
Fred went to the hospital early this am. He is doing ok now but will be there for some testing. He will write you back as soon as he can.
Mrs. C.”

The next day I heard from Fred.

Hi Frank,

OK, here goes, Using the same collector like the flat four, the shorter the primaries, to the point of 38“, which is the shortest we have ever fit on a current vee, the higher the useable power curve, with 40 to 38 in. pipes the engine works in the 4500 to 6500 to 6800 rpm range, that said the 4000 to 5500 range suffers.

Now along comes the 4 into 2 into 1 collector, when you use this collector you regain the use of the bottom end of the power band with out losing the top end.

There is still the requirement that you have the intake and heads to get this into this power band, but most of today's engine builders are there.
My best combination is 40 in primaries and the flat 4 into 2 into 1 collector, there are non flat ( firing order or square type) collectors that work as well as the flat ones.
When I built my first vintage car a few years ago I had only an old set of pipes from an original Lynx Vee, they were 47 in long primaries, the car was a real stump puller out of the corners but 5600 was it on top end, with a current engine.

Hope this helps.


It’s amazing what you can learn if you ask.


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