Bill Verburg

993 picked up 22 hp and 14lb-ft from combination of exhaust head/valve and air flow measurement changes

w/o valve overlap tuned headers only provide better mass flow

a 964 oe exhaust has 3.75mm primary tubes flowing into 64.9x33.5mm x over, flowing into 2 mufflers and a cat

the most restrictive part is the primary muffler(396cfm@6500)followed by the cat(442cfm@6500) and then secondary muffler(462cfm@6500)

at 100% VE a 964 flows 413cfm@6500

surprize, surprize the factory put an adequate flowing exhaust on the cars

now if you change the cams to something w/ a little bite, say SS cams then the headers can add something to the party.

escar0le

bill-

I know we haven’t Met but you’re a true knowledge master on this forum and appreciate the follow up. You don’t happen to know what the 3.8 L RS 993 flow looks like as it pertains to exhaust size?

badbiturbo

Currently running a cat delete with secondary bypass, it's definitley the most rewarding sound on a 964 IMHO. Im sure there's small gains to be had but as Bill mentioned, not much without head/cam work.

Bill Verburg

3.8 flows 436cfm @6500 100%VE
993 street exhaust is 39mm(1.53") ID primary tubes, Cup and RSR ran 42mm(1.625") ID primaries but also ran to 7400 rpm, where low is 503cfm

escar0le

you rock

Peteinjp

So for a mild 7000 redline 3.8 a cat and primary delete from the stock 964 should flow plenty- unless I'm over simplifying.

Pete

m_a_saunders

On this side of the pond in Switzerland two specialists with rolling roads recommended independently of each other the standard headers, sport cats and a primary cup by pass.
(Mecacomponents & Sportec)

Peteinjp

Colin of 9m also recommends the same based on comparisons with his dyno as well.

spartansix

This doesn't shock me. It's called the Cup pipe... because that's how Porsche set up the Cup cars!