View Poll Results: What size exhaust?
2.75"
1
6.67%
3"
14
93.33%
Other: Please post say why
0
0%
Voters: 15. You may not vote on this poll
Exhaust pipe sizing
12-27-2006, 11:24 PM
#1
Three Wheelin'
Thread Starter
Exhaust pipe sizing
The Callaway is becoming my DD here in about a week or two so I need to get a new exhaust for it since the 20+ year old one is full of holes. Right now it's straight 2.5" pipe from the turbo out to the muffler. Since I'm changing it out I figured I'd go up in size, add a resonator, and of course replace the muffler. I'm thinking 2.75" pipe or should I just go for 3"? According to the Callaway specs I'm making ~280HP on 10 PSI of boost so would I be better off running 2.75" or 3"? I'm not really looking for any major power gains and I definitely don't want it to be really loud.
12-27-2006, 11:33 PM
#2
Addict
Rennlist Member
Rennlist Member
I'd go for 3" for that HP and also, 2.75" will be harder to find than 3". It would also help if you aren't going with mandrel bends or need to ding the pipes for clearance. I laid a 3" for the 954, it all worked out with decent clearance. 3" would leave room for more power later on as well.
12-28-2006, 12:06 AM
#3
Three Wheelin'
Thread Starter
Originally Posted by nine-44
I'd go for 3" for that HP and also, 2.75" will be harder to find than 3". It would also help if you aren't going with mandrel bends or need to ding the pipes for clearance. I laid a 3" for the 954, it all worked out with decent clearance. 3" would leave room for more power later on as well.
Andy, my gut tells me to go with 3" too but right at this point I am trying to figure out what direction to go in with the car. Obviously stuff that needs to be replaced will be replaced with equivalent or better parts, but past that I haven't determined if I want to preserve the originality of the Callaway or make some insane HP.
12-28-2006, 04:26 AM
#4
Three Wheelin'
3". Depending on the size of the turbo, though, you might not see a very significant gain in horsepower since you already have a cat-less exhaust. On stock turbo 951's, the cat accounts for probably 80-90% of the power gain (keeping the stock 2.5"), and people have seen minimal gains going from a straight 2.5" to a straight 3". Not too much larger of a turbo and 3" should be worthwhile, plus it will be less restrictive if you do decided to do very many upgrades in the future.
12-28-2006, 09:43 AM
#6
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3" will work fine. Trust me. 
Sounds good too.
FWIW the original piping provided by Callaway was only 2.5" (I have the original pipes and can measure them to verify) but a 3" will absolutely help. You'll need to either be a good welder or have access to a decent exhaust shop to custom-fabricate a pipe to come off the back of the turbo - plus the flange is a little different than most, but it's not a big deal really.
My setup plan is a 3" all the way straight back with a Borla muffler in the stock mounting location. That's it. Pretty simple and easy, very little restriction.
Oh, and insist on a shop that has a mandrel bender too.
Sounds good too.
FWIW the original piping provided by Callaway was only 2.5" (I have the original pipes and can measure them to verify) but a 3" will absolutely help. You'll need to either be a good welder or have access to a decent exhaust shop to custom-fabricate a pipe to come off the back of the turbo - plus the flange is a little different than most, but it's not a big deal really.
My setup plan is a 3" all the way straight back with a Borla muffler in the stock mounting location. That's it. Pretty simple and easy, very little restriction.
Oh, and insist on a shop that has a mandrel bender too.
12-28-2006, 06:57 PM
#7
Three Wheelin'
Thread Starter
Originally Posted by theedge
Well since most of us have never seen a Calloway setup.... Is a larger pipe going to fit in the first place?
Callaway just has the turbo mounted on the passenger side slightly behind the engine mount, I'll try and snap some pictures when I get it down here with me. There should be plenty of room for the 3" to fit in there but it might just be an almost instant drop from the turbo outlet rather than out a little then drop.
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12-28-2006, 08:48 PM
#9
Three Wheelin'
Thread Starter
Originally Posted by Porsche-O-Phile
Do you run the original Callaway MicroFueler controller on yours or something else?
I've still got the 5th injector and wiring to it but I have yet to find the micro fueler itself and I have suspicions that it isn't working or the injector is bad. I took it for a run last week and it pulls really hard up to about 5k rpms and then seems to fall off. I need to get some A/F data to verify this but I think once it hits 5k it leans out which makes the power fall off.
