TC78 Downpipe size??
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09-10-2008, 09:52 PM
#8
3" is fine, downpipe size required should be whatever the turbine housing is and nothing less than that. 3" is what it is, so 3" is what you should use, anythig bigger will be wayyy more expensive and be a pain in the butt for clearnance. Guys with a T6 turbo will obviously need bigger downpipe options, but most T4's are simply 3.0"
09-10-2008, 10:27 PM
#9
3" is fine, downpipe size required should be whatever the turbine housing is and nothing less than that. 3" is what it is, so 3" is what you should use, anythig bigger will be wayyy more expensive and be a pain in the butt for clearnance. Guys with a T6 turbo will obviously need bigger downpipe options, but most T4's are simply 3.0"
09-11-2008, 01:40 AM
#11
I've heard a general rule that you want the downpipe to be 1.25-1.5x the turbine exducer. That would mean a minimum of 3.5" for the TC78. However, as long as the pipe is at least as big as the exducer, you're not giving up a lot of power.
I'm running a 3" downpipe on my T76GTS (2.96" exducer) and it works reasonably well, though I do think I could gain some power if I upgraded. I do know that a 3" downpipe is good for 140++ mph in the quarter, maybe even 150.
I'm running a 3" downpipe on my T76GTS (2.96" exducer) and it works reasonably well, though I do think I could gain some power if I upgraded. I do know that a 3" downpipe is good for 140++ mph in the quarter, maybe even 150.
09-11-2008, 07:24 AM
#12
I'm not sure if its anything to do with my exhaust change, but when I first got my car together back in mid July, I ran around with a 3" open downpipe that stopped at the firewall. I drove the car a few days like this and it was bogging alot, loading up, etc.
I wanted a reasonably quiet exhaust but didn't want to restrict it. I ended up using a couple of reducer cones backwards that I had sitting around from a previous build, and went from the 3" outlet of the downpipe up to a 4". I had the exhaust shop weld in an old 4" dynomax 12" bullet where the stock cat goes (another old piece I had lyin around) and bought 2 - 4" mandrel 'S' bends and had them cut and welded up to tuck the 4" pipe up tighter into the tunnel. I'd bought a 6" round 4"in/out magnaflow muffler and had that welded up just under the backseat area with a turndown.
I swear the car ran 10x better with the exhaust on it. That may have been largely due to the car 'learning' the tune that had been loaded into the PCM prior to startup (mainly for the 60lb injectors I'd swapped to), but the car seemed to spool faster and build boost quicker with the exhaust on. The car sounds great, very deep and throaty, really alot like an LT1 actually. Its not too droney for a dumped exhaust, you can carry on a conversation in the car and not have to raise your voice any.
Heres the best pic I have of it...
I wanted a reasonably quiet exhaust but didn't want to restrict it. I ended up using a couple of reducer cones backwards that I had sitting around from a previous build, and went from the 3" outlet of the downpipe up to a 4". I had the exhaust shop weld in an old 4" dynomax 12" bullet where the stock cat goes (another old piece I had lyin around) and bought 2 - 4" mandrel 'S' bends and had them cut and welded up to tuck the 4" pipe up tighter into the tunnel. I'd bought a 6" round 4"in/out magnaflow muffler and had that welded up just under the backseat area with a turndown.
I swear the car ran 10x better with the exhaust on it. That may have been largely due to the car 'learning' the tune that had been loaded into the PCM prior to startup (mainly for the 60lb injectors I'd swapped to), but the car seemed to spool faster and build boost quicker with the exhaust on. The car sounds great, very deep and throaty, really alot like an LT1 actually. Its not too droney for a dumped exhaust, you can carry on a conversation in the car and not have to raise your voice any.
Heres the best pic I have of it...
06-19-2009, 07:47 AM
#14
this post is from last year...lol. But depends on how many bends. If you calculate how a straight peice of pipe flows, each bend will add so many feet of pipe to the flow characteristics. Example. A peice of 3" pipe (straight) might flow the close to a 4" pipe with 4 bends in it. Im not sure the exact formula, every pipe and bend would be different.
