I currently have 2.5 intercooler piping on my car. Does anyone know what hp level I should switch over to 3"? Car is a 274. I know it has @700hp on pump gas. I am trying to decide if I should go to a bigger piping/FM. I know at some point is going to restrict flow. Any advice or suggestions? Thanks
2.5" or 3 intercooler piping?
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Way back when on the gnttype mailing list there was a "discussion" between Tony DeQuick of CAS and Harry Hruska of PTE about this. Paraphrasing from memory, Tony felt (and said he had numerical flow calculations to back it up) that 2.5" pipes were fine down into the mid-11's, maybe to 11.0. One of his concerns is that with a 3" pipe the bend radius is smaller so you have a sharper bend in a bigger pipe and that isn't necessarily a net win. Harry just said that the 3" pipes were better. What I took from that was that in the 12's 2.5" is good enough, in the 11's start looking for a good deal on 3" pipes, and by the low 11's make sure to have them. Neither really commented on where to go up to 3.5 or 4" pipes 
. At your cubic inches and hp I think you need 3" pipes at least, and the popular front mount choices would be the PTE or Cotton units which both come with 3" pipes.
. At your cubic inches and hp I think you need 3" pipes at least, and the popular front mount choices would be the PTE or Cotton units which both come with 3" pipes.MIB said:
What I can tell you is the smaller piping is noticeably more responsive at the lower RPM levels (3.8L) then the 3" (this was during the I/C'less experiments). With a 4.2L (bored 4.1L stocker), the sluggishness (around town driving) of the 3 that I had with the 3.8L with the 3" was about gone. With a healthy 274, I'd not worry about having too much with the 3". IMO, the 3" will slightly drop the *port velocities*, and that makes for less inertia in the air column, and better cylinder filling. Not to mention if you look at any of the last pics of the Lingenfelter Cavalier, it seems they were using the intercooler plumbing as part of the plenum, which, again, IMO, on higher rpm engine is important.
What I've wound up doing, was going to the 3" (now with a Cotton's F/M) but reducing the TB size. It seems that for the small motor, that's the best of all words.
I have a PTE on my other car. Maybe I'll sell this FM and move to something larger. I was just curious as to what the cut-off hp level would be. I believe this one is a kennebell maybe old PTE? It has gone 10.40's@136 on pump gas. I just don't like the fact that the pipes are so small compared to everything else. I know the car would probably benifit from larger pipes/intercooler. It sure would be nice to run 10.0's@19psi. I'll look into changing to cottons. Any other suggestions? Thanks fellas
Mike Licht
I was here first
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I saw about a 3 HP difference on a mid 10 car on the dyno. the margin of error was bigger. Lots of low 10 high 9 import cars with 2.5" pipes.
Mike
Mike
Mike I know that it can be done :biggrin: A car with a 76, 4-bolt and 2.5 intercooler piping just doesn't seem right. The only reason I haven't made the switch is because the pipes/FM are powdercoated. I will be going faster. I just am trying to figure out the @limits of 2.5 piping to justify buying another FM. Thanks
steve hughes
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I don't know how much difference it makes but i went 9.41 at 141 at Morocco last weekend with a 240" stage II with an old V2 with 2.5" pipes and a 62mm TB in a 3500# GN. If i was starting from scratch i'd go 3". I also am running a 76 GTQ.
Pronto
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You mention powercoated FM. Maybe the coating is making the FM less efficeint. Stripping it might be worth testing before spending money on a new FM.
Pronto said:
I don't know if the FM is ineffecient because of powerdercoating. I know it's not supposed to be coated. My FM has a thin gloss-black powdercoating. The pipes are powercoated. You won't even notice the FM unless you know what you are looking for. I will probably just pull my P/FM off the other car and test it to see if there is a difference. Thanks
steve hughes said:
I am still in the tuning phase. I would love to run those times. What was your final rpm? I still have my rev-limiter @6500
I hoping to get some race gas/slicks on the car for the next track session. Car is not tuned yet 
Car managed a 10.40 @136 1.4 on 275/60 ET-Street radials, pump gas. Thanks
steve hughes
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It was going thru the traps at 6900 rpms. Ted i checked intake air temps after our talk at Salem. I never saw over 140 at the end of the runs in Salem. At Morocco most were about 130 - 135 at the end.
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