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i have a 95 gsr and i just got a high flow catalytic converter and 2.5 " mandrel piping installed with my hks super drager, and everytime i release the gas or when the rpm is declining, its makes a plumping noise, like its back firing.on the side, my car is stock besides exhaust and intake. Is it because i need more air? any suggestions or comments are welcome.
 

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i dont think 2.5 is too big..i have 3 inch piping on my car..mine also sometimes make a backfire noise when the rpm is declining also..
 

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3" is too big unless you are boosting some nice numbers...for N/A, 3" is way too big and you are most likely hurting performance...
 

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His profile says stock...2.5" would probably be ideal.
 

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"2-1/4" up to 210HP @ the flywheel (about 180-185 whp)

2-3/8" (60mm) up to 235HP @ the flywheel (about 200-207 whp)

2-1/2" up to 265HP @ the flywheel (about 225-235 whp)

2-3/4" up to 325HP @ the flywheel (about 275-285 whp)

3" big for big HP (Forced Induction: > 275 whp) "

Is he really going to be makig more than 275 whp MD on a supercharger?

I've seen the 8 psi pulley pull around 220 to 230 whp...The problem is, it's hard to find a 2.75" exhaust...so 3 would work I guess...
 

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the Kakimoto is a 2.75 in. od (2.6 in ID) but you need to replace their resonators which neck down quite a bit with Magnaflow straight thru resonators.

JK : you're right for the most part. However, those are just guidelines by SMSP to prevent people from going TOO SMALL and believing in the "need backpressure" ignorance that's still so prevalent despite the education put out by Dave (SMSP) many years ago (4 to be exact). If you run FI, I suggest people go a little more than those guidelines and use 3 in.

The backpressure relief is even more important when you stuff in more air rather than passively fill or use ram air-scavenging with passive filling (N/A) because you have more residual in cylinder gases to remove after combustion.

The main power robber of FI is the exhaust side and contamination of the next incoming intake charge with residual gases. Remember exhaust gases don't make power...EGR's are great for fuel economy and emissions but not power.
 

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Yeah, the extra air stuffed into the combustion chamber would need more space to exit. I understand now. =)
 

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sorry guys..but yea i really do have a 3" pipe on for my supercharger...i was gonna go with 2.5" but then figured might as well chip in another 20 bucks for the 3"...
 
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