another exhaust question
06-09-2010, 04:30 PM
#1
Rennlist Member
Thread Starter
another exhaust question
I have an 85 euro 4 speed 928, i am wondering which would be better 2.5 inch or 3 inch exhaust? Part of the reason is i have 3 inch ss tubing 45's 90's etc but only very little 2.5 inch. I just wonder if 3 inch would offer to little back pressure and thus loose power . No super charger. thanks Ray
06-09-2010, 05:18 PM
#5
Inventor
Rennlist Member
Rennlist Member
3" is hard to make un-noisy, and it's heavy.
On my '85 US 5-speed I've got a no-cat Y-pipe made from old 32V cat down pipes, and a cat-back from an '84 16V with a debaffled stock pumkin. (16V singles are 65mm OD, which is slightly larger than 2.5" = 63.5.)
I made 314 rw tq/hp with it, and it is only a bit louder than stock at part throttle. This makes driving with 'SWMBO' less noisy, as well.
On my '85 US 5-speed I've got a no-cat Y-pipe made from old 32V cat down pipes, and a cat-back from an '84 16V with a debaffled stock pumkin. (16V singles are 65mm OD, which is slightly larger than 2.5" = 63.5.)
I made 314 rw tq/hp with it, and it is only a bit louder than stock at part throttle. This makes driving with 'SWMBO' less noisy, as well.
06-09-2010, 05:30 PM
#6
Addict
Rennlist Member
Rennlist Member
3" is hard to make un-noisy, and it's heavy.
On my '85 US 5-speed I've got a no-cat Y-pipe made from old 32V cat down pipes, and a cat-back from an '84 16V with a debaffled stock pumkin. (16V singles are 65mm OD, which is slightly larger than 2.5" = 63.5.)
I made 314 rw tq/hp with it, and it is only a bit louder than stock at part throttle. This makes driving with 'SWMBO' less noisy, as well.
On my '85 US 5-speed I've got a no-cat Y-pipe made from old 32V cat down pipes, and a cat-back from an '84 16V with a debaffled stock pumkin. (16V singles are 65mm OD, which is slightly larger than 2.5" = 63.5.)
I made 314 rw tq/hp with it, and it is only a bit louder than stock at part throttle. This makes driving with 'SWMBO' less noisy, as well.
And my 3" single is much lighter that what it replaced, the factory duals all the way back with multiple mufflers and mongo cat.
06-09-2010, 05:46 PM
#7
Inventor
Rennlist Member
Rennlist Member
There was the little matter of higher fuel pressure, and a chip or two, but what I'm sayin' is that a 2.5" single exhaust is not a restriction.
Joe's exhaust sounds pretty good... what's that... oh... JOE'S EXHAUST SOUNDS PRETTY GOOD.
Joe's exhaust sounds pretty good... what's that... oh... JOE'S EXHAUST SOUNDS PRETTY GOOD.
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06-09-2010, 05:46 PM
#8
Rennlist Member
Thread Starter
3 inch exhaust
yes sorry, i was thinking of dual exhausts , if people are making 30hp more with dual 2.5 inchs a single 3 inch would not be as good? and making over 300 rwhp? what do you have on it? wow
06-09-2010, 09:36 PM
#9
Captain Obvious
Super User
Super User
A 3" single is more than what you need and you already have the pipes, so go with that. A dual 3" is too much. Bigger is not always better. When it comes to flow, a singel 3" is pretty much there with a dual 2.5" system. BUT it's a lot lighter and simpler to build.