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Discussion Starter #1
Hello guys , i will be making a custom exhaust for my car (BPU++) ,This is from the turbo to the back ,there will be no cat and muffler installed. Should i go 4 inch or 3,5 inch ?Thanks
 

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no muffler? shit i hope thats a drag only car :-/

3.5" is completely unrestrictive untill around 8-900 hp i think, 4" is overkill unless you're up around that mark
 

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3,5inch is more than enough for a BPU++!
 

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bigger is better for turbo'd cars... go 4". I've still got a stock DP and turbos, but am going with a 4". Not only will it perform better than a smaller diameter, but when I eventually go single I won't have wasted money on a 3" exhaust that I want to replace with a 4".
 

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Discussion Starter #5
Yeah but 4inch post abig ground clearance problem, i did some measurement already and the safe way is to run 3,25 front and downpipe and go3,5 inch to the back.In my country there is no rules about exhaust regulation, and turbo car dont make as much noise as NA car, thanks guys.
 

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supralover93 said:
damn with a 4" you will have no backpressure and no low end. i would go with a 3-3.5".
This is completely false. You will NOT lose low end power. The turbo itself creates backpressure. Bigger is better when it comes to piping size.
 

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cwtt said:
This is completely false. You will NOT lose low end power. The turbo itself creates backpressure. Bigger is better when it comes to piping size.
:dunno: when i took my cat-back off and ran w/open dp my car felt like shit in the lower rpm's and didn't pick up until about 3-3500.
 

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exactly, then why not just dissconnect everything off from the downpipe and create the least restrictive exaust system possible?
 

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idrewfelix said:
exactly, then why not just dissconnect everything off from the downpipe and create the least restrictive exaust system possible?
Well, if it was a track only car that would work. It would create massive noise (not a good sounding exhaust - noise), it would vibrate your teeth, it would cook the paint under the car and make a funny smell, and you'd get stopped by the police every three blocks. Same reasons Mustang, Vette guys don't run open headers on the street.
 

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well my car wasn't very loud unless i was at WOT and full boost. at idle it was a little quieter than a z28 with flowmasters.
carboy: if you want the least restrictive exhaust then you should just get a cheap cat back and then put a cut out on your DP.
 

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Discussion Starter #12
I think i will go for 3,5inch, the most balance set up i think for a supra.Running a 3 inch on a Supra is definetely too small. I have tried the Fujitsubo legalis R cat back (3,1inch) which i found out to too restrictive (During dyno tuning) then i bought a SARD cat back (3,5inch) this perform much better and sounds really nice but its getting rusty and had many holes so i must change it....
 
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