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914World.com _ The Paddock _ Header sizes for /4

Posted by: stownsen914 Feb 19 2020, 04:55 PM

I'd like to confirm the proper header primary size for a high performance, small bore 914/4 engine. I recall that 1 5/8" OD is what was recommended back in the day. Is that correct?

Posted by: yeahmag Feb 19 2020, 06:31 PM

That's a good universal size.

Posted by: wndsrfr Feb 19 2020, 07:55 PM

QUOTE(stownsen914 @ Feb 19 2020, 02:55 PM)

I'd like to confirm the proper header primary size for a high performance, small bore 914/4 engine. I recall that 1 5/8" OD is what was recommended back in the day. Is that correct?

PM Len Hoffman on that with info on bore & stroke & what you're doing with valve springs for redline limit...he'll know.

Posted by: HAM Inc Feb 20 2020, 05:19 PM

5/8's is a good all around size on a 4-1 header. The collector size and shape is waaaaay more important than primary size, though.

CR and revs and cam impact size selections greatly.

How much power do you expect to make?

Posted by: stownsen914 Feb 20 2020, 10:01 PM

Thanks guys for the input.

Len - I hope to get 150-160 hp. If you have any wisdom to share about the collector, I'd love to hear about it. Thank you.

Scott

Posted by: HAM Inc Feb 21 2020, 08:16 PM

I'd run a 2-1/4 collector with a nice taper and experiment with tail pipe lengths and shapes.

I was able beat sound readings without a muffler by running a tail pipe that ran from left to right under the trunk tucked up tight with a downturn that pointed at the track. The outlet was out of the line of sight of the DB gun so they never got a good sound reading. The car was louder than they thought.

The tail pipe length was ~ 3' long with 2 ~ 90* bends.

Not saying that's optimal for your car (or even ours) but some variation of that is what we ran.

Posted by: Charles Freeborn Feb 22 2020, 12:43 AM

http://www.gt-racing.com/porsche-914-european-racing-headers-headers-for-914-4-motors-part-914-4-158h/