I have a 79 Mustang with a C4 and I have 3.55s to put in the rear end. So what would be my RPMs at 60 mph? Right now I have 2.73s (7.5inch rearend) and I am running about 2250 RPM going 60 mph. Gas milage isnt really an issue, but I still want it to be streetable. Any help would be appreciated. Thanks.
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1979 Mustang Ghia-302 HO @ 300hp, holley 600 carb, edlebrock intake, under drive pulleys, Bullet proof C4, 8.8 inch rear end with 3.55, Flowmasters Delta 40s American Thunder 2, pioneer head unit with sony speakers.
2004 Mustang Mach 1-281 DOHC @ 305HP, Shaker, 5 speed, 8.8 rear end with 3.55, Mach 460, Sat radio, Flowmaster Delta 50s, Clear Bright Fog lights, alum items for interior dress up, and an eject button.
The set up in my '70 is: stock C4, 9" Chevy rear end(I KNOW, I KNOW. I BOUGHT IT THIS WAY) with 4.11s, and 275/60 rear tires and at 60mph I'm at 3,000rpm. So you should be somewhere just above midpoint between your rpm range and mine. Roughly, maybe 2700rpm..
I run close to 3K RPM with 3.55's gears and 16" wheels.
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Thanks guys and by the way I am runing 15in wheels.
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1979 Mustang Ghia-302 HO @ 300hp, holley 600 carb, edlebrock intake, under drive pulleys, Bullet proof C4, 8.8 inch rear end with 3.55, Flowmasters Delta 40s American Thunder 2, pioneer head unit with sony speakers.
2004 Mustang Mach 1-281 DOHC @ 305HP, Shaker, 5 speed, 8.8 rear end with 3.55, Mach 460, Sat radio, Flowmaster Delta 50s, Clear Bright Fog lights, alum items for interior dress up, and an eject button.
Use 1.0 in the transmission gear box (3rd gear on a C4). Its the circumference of the tire that matters and not the wheel size. The program uses the tire info to calculate this figure.
RPM at highway Speeds with a C4 
