Header size recommendation 2.7L almost RS Spec motor
 

Thinking about installing headers/sport muffler on my car. The engine is now a 2.7L displacement with RS Spec Mahle P/C 8.5:1 compression I believe, 40mm Webbers, ported intakes and Webcam 104/102 cams (similar to S-cam profile I believe). I did not build the motor originally, but has been rebuilt with similar specs.

What would be the recommended header size? 1 5/8" seems to be what is in most of the catalogs suggest. Just wondering if anyone has any input on being the right route to go? Also any recommended brands?

Did a search but didn't find similar set up, maybe using wrong key words.

Thx
Erik

Smaller is more

SSI's are a great choice and you get heat. 1 1/2" OD=38mm. ID = 35mm.

Also you could get old used factory heat exchangers to save some sheckels. Look in the used parts classifieds.

Headers, I would recommend the same size. George Narbel (European Racing Headers), and others.

1 5/8" is too big, in any case.

Best of luck,

Living in AZ I can skip the heat, have the old H/E's, but want something a little sportier.

Will try calling George and look for 1 1/2" set of headers.

Thanks for the tip.

+1

i've seen several sets of factory heat exchangers in the pelican classifieds. they're great...just remember they're 30+ years old

Erik, my .02 cents : go 1.625" (1 5/8") Header sizes are in OD, when you minus the 16 gauge* wall thickness, you are at 1.5" ID.
Do the math , the 1 1/2" headers (anyones brand) will be 1 3/8" ID...way small for the engine you are running. You will have great exhaust velocity/ response at low end, for the trade off of not enough scavenging up in the top rpms. If you have nothing else to do but try out headers...buy both sizes and compare , trust me you will want the 1.625" OD style.
* with the exception of the cheaper priced off shore knockoffs, which have a wall thickness of 18 gauge...and an operating life of about 1/2 of our U.S. made originals. How do I know? I see all that goes on from my little bunker at the SEMA show :D
Martyhttp://forums.pelicanparts.com/uploa...1172811648.jpg

It depends on the usage, for mostly street or DE, the SSI 1 1/2" OD are fine.

If it's a pure race car the SSI still work well, but you may be able to profit from 1 5/8" OD.

The dyno doesn't lie.

On the dyno, the 1 5/8ths headers made no more peak power than SSI's. It was only above 7000rpm that the 1 5/8ths headers were an improvement, as the power did not drop off as steeply, and made about 10 more horsepower at 7300 rpm. They both made the same peak power at 6500. But the mid-range favored the SSI's. (The muffler was a factory sport muffler.)

So you should ask yourself how much time you spend above 7000 rpm, and if that's worth the poorer throttle response, mid-range power, and not having heat.

Tyson-

Its been many years, don't even know if you would remember, but we used to Auto-X up in Seattle together on occasion, I had a Red RS America and was usually competing with Chris Ruggles C4S and Jeff Spaulding in his '91 Turbo in P2/P3. You were running Scruffy back then and working up on Phinney Ridge I believe. (Took all my stuff to John Walker down the street back then). Living in the Desert nowadays, quite a climate change.

Anyway, appreciate the input. The car will be mainly street and autocross (I know I have the wrong cams for autox in this car) and some DE stuff. Not a lot of time going to be spent above 7 grand in the Revs. I really want to go with headers vs. SSIs, but if I can find a pair of SSI's cheap enough, may go with the heat. Then again, might as well run the factory H/E's and save some money if that is the case.

Good luck in the bay area.

Erik

More about the car project in this thread.

http://forums.pelicanparts.com/porsche-911-technical-forum/333040-1971-911-project-w-pics.html



http://forums.pelicanparts.com/uploa...1172938888.jpg