Exhaust diameter requirements for 400 HP
02-16-2006, 06:24 PM
#1
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Exhaust diameter requirements for 400 HP I have been looking around, and have confused the crap out of my self with flow formulas, pounded my head against the keyboard once, and fell out of my chair twice trying to figure out "sufficent" exhaust flow for the LS2 I am stuffing in a '73 240Z. My delemma is using 2.25" or 2.5" headpipes off of the header flange. The will both dump almost immediately into a Y to 3" all the way back to the stock location on a 240 with a stock motor.
My question is, will 2.25" make any difference to 6500rpm (LS2 redline) as compared to the 2.5"? The 2.5"s are going to be much harder to tuck under the car, and I do not want exhaust hanging down...
Also, If I go 2.5", will I need to make the 3" tailpipe 3.5"? That will really cramp and muffler choices...
Let me know
Mike
My question is, will 2.25" make any difference to 6500rpm (LS2 redline) as compared to the 2.5"? The 2.5"s are going to be much harder to tuck under the car, and I do not want exhaust hanging down...
Also, If I go 2.5", will I need to make the 3" tailpipe 3.5"? That will really cramp and muffler choices...
Let me know
Mike
02-16-2006, 08:41 PM
#2
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Sticking with 1 3/4 - 1 7/8 primaries would be enough to support 600hp easy, let alone 400hp. If you want to run full exhaust, run true dual 3" all the way back.
2.5" primaries would look silly.
2.5" primaries would look silly.
02-16-2006, 08:51 PM
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Noted Tech writer David Vizard says each square inch of (muffler length) pipe will flow ~115 CFM and that from a pure flow standpoint (i.e., behind any tuned header system and muffler) an engine requires at leat 2.2" per HP in order to lose no power vs. an open header. This would suggest that you need more than a 3" single behind the muffler. Ahead of it, we are talking exhaust tuning, not flow, and a 400 HP V-8 needs at least 2 -1/2" pipes per side (Millions of GM pickups use 3")
02-17-2006, 10:16 AM
#4
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Headers with 2.5" primaries.... 
Reading is fundamental.. 
Madbill,
Thanks for the input, I was afraid of that. The 2.25" pipes tuck fairly well, but the 2.5" will be more of a challenge. I am going to use a Y-pipe from Dr. Gas, so that part is accounted for. Not many choices for 3.5" mufflers, that do not sound like a NASCAR...
Continuing to search....
Reading is fundamental.. Madbill,
Thanks for the input, I was afraid of that. The 2.25" pipes tuck fairly well, but the 2.5" will be more of a challenge. I am going to use a Y-pipe from Dr. Gas, so that part is accounted for. Not many choices for 3.5" mufflers, that do not sound like a NASCAR...
Continuing to search....
Last edited by Desert Dog; 02-17-2006 at 10:25 AM.
02-17-2006, 10:32 AM
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02-17-2006, 04:02 PM
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I'd go 2.5" or bigger. The .25" difference in clearance would not be worth the restriction it would cause...especially in the future if you do motor mods in the future. I had a friend with a 383 in a 280 and it was out of control...I'm not sure I'd recommend it.
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02-18-2006, 09:57 AM
#8
Use the 2.5" headpipes. If you are merging into a Y-Pipe be sure to use a true merge. I'd suggest going into 3.5" I-Pipe with an electric cut-out. After that neck down to 3" and get a quiet exhaust. That will give the best of both worlds. Max power when needed and solid non-NASCAR loud performance the other 95% of the time.
