#1  
Old 09-07-2022, 08:58 AM
adamo adamo is offline
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Join Date: Feb 2005
Posts: 45
Default 3.5” or 3” collector

Hello everybody I have a question if anyone wants to answer. I have a 69 gto. It has a 428 with 270+cfm 722 heads. It has a old faithful cam with Crower solid rollers. Has a sd performance real ram air IV cnc style ported intake. Max a lite connecting rods with je pistons. 10.5 compression. 4 speed M22w with 3.73 gears. The headers are 1 7/8” Indian adventures headers with 3.5” slip on collectors and a 3” exhaust with x pipe and dynomax ultra flow mufflers. Just wondering if changing to a 3” slip on collector would pick me up some torque? My thinking is first of all the exhaust slows down a bit in the large 3” collector them reduces abruptly to the 3” exhaust. Wouldn’t the stranger flow from the 3” collector to 3” pipes work better? Idk. The car works great but you know how it goes. Can never leave these cars alone.

  #2  
Old 11-19-2022, 01:37 AM
cjs64goat cjs64goat is offline
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I can only speak from experience. When I went from 1 /34" w 3" collector to 2" w 3 1/2" collector my car went faster in the 1/8th. I want to connect my 3" exhaust but a tapered 3.5-3 reducer and the X pipe I have and reusing my Walker dynomax mufflers doesn't appear to fit. Engines no way as much as you have. Been 12.0 @ 110 in 1/4 with old headers.

  #3  
Old 11-19-2022, 10:01 AM
Skip Fix's Avatar
Skip Fix Skip Fix is offline
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Location: Katy,TX USA
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I ran 3.5 to 3 with reducers Dr Gas X into 3" system. Flanged the reducers at both ends.

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Skip Fix
1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever!
1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand
1965 GTO 4 barrel 3 speed project
2004 GTO Pulse Red stock motor computer tune 13.43@103.4
1964 Impala SS 409/470ci 600 HP stroker project
1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs
  #4  
Old 11-19-2022, 01:41 PM
cjs64goat cjs64goat is offline
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How long are the reducers? Mine are about 12". Was trying to not have an abrupt reduction. I have the Pypes X pipe. The Dyno max mufflers are pretty long, may have to get shorter. Also my headers are longer than most off the shelf ones.

  #5  
Old 11-23-2022, 10:51 AM
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Skip Fix Skip Fix is offline
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Mine were about that long also. I think flowmasters and pretty thick tubing also. Also made it easy to go open headers. had front brackets to hold the rest of the exhaust up

__________________
Skip Fix
1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever!
1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand
1965 GTO 4 barrel 3 speed project
2004 GTO Pulse Red stock motor computer tune 13.43@103.4
1964 Impala SS 409/470ci 600 HP stroker project
1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs
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