I need some help! I have a '72 Mach-1 351c stroked to 408cid and C-6 trans. I'm trying to figure out what size pipes to use for this combo. I want good deep throaty sound but not extremely loud. Thinking about 3" pipes from the hedders back and turbo mufflers, but will 3" pipes hurt the performance? Maybe 2 1/2" to keep the exhaust gasses moving faster? Also, does it matter where the H-pipe is located in the system?
Thanks.
I wouldn't run anything larger than 2.5" on it and would try to keep the crossover as close to the headers as possible. In most configurations, the closest place is right behind the tailshaft of the transmission.
The June issue of Mustang & Fords has a copy of Flowmaster's suggested pipe-sizing table. It says 2.5" for dual exhaust for your size engine. 3" for single.
Any idea on the power level of your 408? for up tp 400hp dual 2.5" is good for a 400 cid engine. If your up around 450hp then you should probably give
3" a closer look.As for the cross over pipes location there is the old racers trick of painting a stripe on your pipes and running the car hard for a while. where the paint stops burning off is the spot where you put you cross over. Of course most of the time you have to place it based on making it fit on the car.
MadDAWG
Well, according to the Dyno simulation software, this engine will be about
500hp @ 5700rpm and 512fp torque @ 3800rpm. 10.78-1 comp. ratio with 4v close chamber heads and 0.536 lift 288 duration cam. I guess I will have to put the cross-over behind the trans. to keep the heat away from it and for clearance concerns. With the large exhaust ports of the 4v heads, maybe I should go with the 3" pipes?
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