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I recently learned that my 93 Ranger needs a certain amount of backpressure to run properly. Is the same thing true for a 65 289 engine that is in my 67 Mustang? I now have factory HP manifolds connecting to 2 1/2 pipes to the turbo mufflers and 2 1/4 pipes over the axle and out the back. This is something that I would have never cared about before, but now that I have access to the VMF and "experts" from all over the country well why now ask. fd

1967 GT coupe been in my garage since 1974
1993 Ranger ExtCab 4.0L daily driver
1996 Aerostar wifes ride
 
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no. i have the same setup u have except with headers. i luv it. but if u dont have anyback pressure then u actually loose a bit of torque. or so ive heard.

Corpus Christi TX
 
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First off, backpressure itself is not necessarily a good thing. Backpressure is a biproduct of an exhaust system that will scavenge exhaust gases at low rpms.

Torque is only lost when you loose exhaust velocity. When you are open header, you have no low end because there is no scavenging in the exhaust to help draw in the intake charge. In a muffled system, exhaust velocity is kept up to a speed where the enertia of the hot exhaust moving out will draw in the intake charge during the period of valve overlap.

The trick is to build a system that will keep up the speed of the exhaust gasses (ie. keep them hot and keep the transitions smooth) to maintain low end torque, while keeping the backpressure to a minimum for higher rpm power. Mufflers, crossovers, primary diameter, pipe diameter, and basic design all influece these aspects.

John

[color:blue]'68 Coupe
250/C4, 221 Argentine Head
Breakaway Converter, 9", 3.50's/T-lock</font color=blue>
 

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Discussion Starter #4
fd

1967 GT coupe been in my garage since 1974
1993 Ranger ExtCab 4.0L daily driver
1996 Aerostar wifes ride
 

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Yes, what John says.

However, I thought the modern computer controled cars need a little back pressure inorder for the oxy sensor to get a stable reading and the cats create it just because they need a bit o' time to convert HC, NOx and CO.

Or I may be wayyyy out there.

Dean T

Shikatta Ga Nai - "It cannot be helped"
 
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Dean,

You may very well be right. I don't know how well a some EFI motors would run open header (granted the O2 bung was in the collector). As long as there is no fresh air contaminant I can't see why it couldn't do it's job.

John

[color:blue]'68 Coupe
250/C4, 221 Argentine Head
Breakaway Converter, 9", 3.50's/T-lock</font color=blue>
 
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