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Registered
Join Date: Jun 2009
Posts: 1,241
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header size
For a track car, 3.0 engine, 11.8 to 1.0, D60 cams, MFI, twin plug. What size header do want for that set up, OD/ID. Thanks, Bob
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Puny Bird
Join Date: Nov 2002
Location: Port Hope (near Toronto) On, Canada
Posts: 4,566
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I'd go with the 1-3/4" primary pipes or at least 1-5/8".
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'74 Porsche 914, 3.0/6 '72 Porsche 914, 1.7, wife's summer DD '67 Bug, 2600cc T4,'67 Bus, 2.0 T1 Not putting miles on your car is like not having sex with your girlfriend, so she'll be more desirable to her next boyfriend. |
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Registered
Join Date: Jul 2013
Location: Brisbane, Australia.
Posts: 2,607
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My thoughts; 1&5/8. I'd think 1.75 might be a tad large for a 3.0?
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Always learning. www.aircooledporsches.com.au See me bumble my way through my first EFI and TURBO conversion! https://youtu.be/bpPWLH1hhgo?si=GufVhpk_80N4K4RP |
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Racer
Join Date: Oct 2010
Location: Franklin, TN
Posts: 5,885
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1 5/8" for sure. 1 3/4" is too big for a normally aspirated 3.0L.
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Scott Winders PCA GT3 #3 2021 & 2022 PCA GT3 National Champion 2021 & 2022 PCA West Coast Series GT3 Champion |
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Puny Bird
Join Date: Nov 2002
Location: Port Hope (near Toronto) On, Canada
Posts: 4,566
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Quote:
I have a 914 with a similar spec 3.0, except webers with big ports and 1-1/2" headers. It's a street car so I haven't been chasing HP, but I picked up a soup to nuts twin plug EFI system so I'm going to 1-5/8" headers.
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'74 Porsche 914, 3.0/6 '72 Porsche 914, 1.7, wife's summer DD '67 Bug, 2600cc T4,'67 Bus, 2.0 T1 Not putting miles on your car is like not having sex with your girlfriend, so she'll be more desirable to her next boyfriend. |
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Moderator
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Quote:
![]() but most likely 1 5/8" ID which is ~1.75" OD
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Bill Verburg '76 Carrera 3.6RS(nee C3/hotrod), '95 993RS/CS(clone) | Pelican Home |Rennlist Wheels |Rennlist Brakes | Last edited by Bill Verburg; 05-06-2022 at 03:34 PM.. |
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Racer
Join Date: Oct 2010
Location: Franklin, TN
Posts: 5,885
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No. 1 5/8" O.D. is the way to go here. Theory versus reality here.....
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Scott Winders PCA GT3 #3 2021 & 2022 PCA GT3 National Champion 2021 & 2022 PCA West Coast Series GT3 Champion |
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Racer
Join Date: Oct 2010
Location: Franklin, TN
Posts: 5,885
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Let me give more perspective:
I had a 3.6L race engine with stock 1995 993 EFI intake system and 1 5/8" O.D. headers (not with overly thin wall tubing) make over 320 HP. Testing indicated that the intake was the limiting factor as more power could be made with a larger throttle body. I now have a 3.6L race engine with 45mm AT Power ITBs and 1 3/4" O.D. headers (again, not with overly thin wall tubing) make over 430 HP. There is no way the 3.0L engine described needs more exhaust flow than what 1 5/8" O.D. headers would provide. In fact, the 1 3/4" O.D. headers would hurt power output especially under 6000 RPM.
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Scott Winders PCA GT3 #3 2021 & 2022 PCA GT3 National Champion 2021 & 2022 PCA West Coast Series GT3 Champion |
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Registered
Join Date: Jun 2009
Posts: 1,241
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header size
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Under the radar
Join Date: May 2007
Location: Fortuna, CA. On the Lost Coast near the Emerald Triangle
Posts: 7,129
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Bill. How does this flow graph relate to pipe size? What am I missing?
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Gordon ___________________________________ '71 911 Coupe 3,0L outlawed #56 PCA Redwood Region, GGR, NASA, Speed SF Trackrash's Garage :: My Garage |
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Registered
Join Date: Jan 2003
Location: Langley,B.C.
Posts: 12,000
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diameter is only part of the equation. That said, a 3.0 NA motor should not need more than 1 5/8....
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Turn3 Autosport- Full Service and Race Prep www.turn3autosport.com 997 S 4.0, Cayman S 3.8, Cayenne Turbo, Macan Turbo, 69 911, Mini R53 JCW , RADICAL SR3 |
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Registered
Join Date: Jul 2021
Posts: 689
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Pipe diameter goes up with the square root of flow, so the graph shows you how you need bigger pipes if your redline and desired power band are higher than if they are lower.
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Under the radar
Join Date: May 2007
Location: Fortuna, CA. On the Lost Coast near the Emerald Triangle
Posts: 7,129
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Right, but I don't see any relationship to pipe diameter in the graphs.
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Gordon ___________________________________ '71 911 Coupe 3,0L outlawed #56 PCA Redwood Region, GGR, NASA, Speed SF Trackrash's Garage :: My Garage Last edited by Trackrash; 05-09-2022 at 12:11 PM.. |
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Registered
Join Date: Jul 2021
Posts: 689
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Moderator
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Quote:
the 2.7 operating up to 8k may want the same exhaust as a 3.8 operating to 6.5k general rule of thumb for the eigen values of stockish street motors all ~31" primaries +/- to 3.0 1 3/8" ID to 3.4 1 1/2" ID to 4.0 1 5/8" ID
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Bill Verburg '76 Carrera 3.6RS(nee C3/hotrod), '95 993RS/CS(clone) | Pelican Home |Rennlist Wheels |Rennlist Brakes | |
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Racer
Join Date: Oct 2010
Location: Franklin, TN
Posts: 5,885
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Maybe on the back of a napkin….but never in real life.
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Scott Winders PCA GT3 #3 2021 & 2022 PCA GT3 National Champion 2021 & 2022 PCA West Coast Series GT3 Champion |
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Under the radar
Join Date: May 2007
Location: Fortuna, CA. On the Lost Coast near the Emerald Triangle
Posts: 7,129
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Quote:
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Gordon ___________________________________ '71 911 Coupe 3,0L outlawed #56 PCA Redwood Region, GGR, NASA, Speed SF Trackrash's Garage :: My Garage |
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