What rear gear are you using? - Ford Mustang Forums : Corral.net Mustang Forum
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Old 07-18-2017, 11:18 PM Thread Starter
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What rear gear are you using?

I have a 408w with aprox 500hp and backed with a C4, 4000 rpm stall. Whats a good starting point for 1/8th mile racing? How about 1/4 mile? I dont know what rpm I will be crossing the line at but red line is 6500. Thanks.


1983 GT sold. Old school. 302, gt40p heads,
B cam. Shorty headers. H pipe. Flowmaster 40's and Ford Motorsports mudflaps.

1988 coupe. Build in progress. 408w . Cams to big, Heads are to big, Intake to tall, Compression to high, Carb is oversized. Everything is alll righttt.
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Old 07-19-2017, 08:11 AM
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Depends on how tall the tire is.


1989 Saleen 414 358cid SBF 2.8L Kenne Bell S/C
26 X 8.5 Hoosier
Best 1/4 mile time 8.623 @ 159.82 mph with a 1.34 60' (5.57 1/8th at 128)
Best 1/8 mile time 5.339 @ 133.46 mph with a 1.29 60'
08' Bullitt #4097 N/A 340ish RWHP <<<<<FOR SALE!
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Old 07-19-2017, 12:06 PM
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What rear gear does it have now?
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Old 07-19-2017, 05:30 PM
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If you plan on running 8th and quarter I would stick with what the quarter is going to give you. Its either gonna be a 4.10 or 4.30 with a 28'' if your figuring between 127 to 130 mph and a lot of other things included. And knock it down a notch for every inch less in tire diameter. But I am just taking a wild ass guess using my experience's in that HP level.
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Old 07-19-2017, 08:36 PM
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4.10 would be my suggestion from my experience. My converter is looser out of the gate, but only shows 4.5% slip through the traps. I make a little more hp but my numbers should give you an idea. 28" tire here, 4.10 gear, trap 135 @ 6930 rpm. combo is in my signature. I'm getting ready to swap in 4.56's for 1/8 mile. I run a 9" rear, so gear swaps don't take very long.

..5.95 @ 115, 1.30 60', naturally aspirated.

1991 notch, dart block 427W, , AFR225's, super vic intake, solid roller, UCC 8" converter, glide, Carbureted E85, 28" radial.
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Old 07-20-2017, 04:07 PM
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Quote:
Originally Posted by 2 step View Post
If you plan on running 8th and quarter I would stick with what the quarter is going to give you.
This ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^


Changing the rear gear for the 1/8th will net you zero. If the car is optimized for the 1/4, changing the rear gear will do nothing but add rpm to your 1/8 mile finish rpm. I run 5.3's in the 1/8th with my car. It had 3.73:1 gears. I switched to 4.10:1 gears and saw zero improvement in ET. The only improvement was in my reaction time. Because of the gear, the car responded faster and my reaction times went from high .180-.200 down to .060-.080. My finish line rpm went from 7,400 rpm to 7,800 rpm on the switch as well. This on a 26" tall tire. Otherwise same exact ET. Same mph as well.

1989 Saleen 414 358cid SBF 2.8L Kenne Bell S/C
26 X 8.5 Hoosier
Best 1/4 mile time 8.623 @ 159.82 mph with a 1.34 60' (5.57 1/8th at 128)
Best 1/8 mile time 5.339 @ 133.46 mph with a 1.29 60'
08' Bullitt #4097 N/A 340ish RWHP <<<<<FOR SALE!
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Old 07-20-2017, 10:12 PM Thread Starter
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Thanks for the responses. To be honest this is my first time building a car for mostly drag racing. Ive only just for fun and around town raced with a mild 302. I havent bought tires yet but Im getting close. The rear end I have laying around has 31 spline and a 3.73. I didnt think it would be enough but just needed to know a good starting point. I have a set of 4.10 laying around and I also have a rear end with 33 spline, clip elemenator 4.30 gear but it is a spool. Dont know if I want to do any street driving with a soild rear.

1983 GT sold. Old school. 302, gt40p heads,
B cam. Shorty headers. H pipe. Flowmaster 40's and Ford Motorsports mudflaps.

1988 coupe. Build in progress. 408w . Cams to big, Heads are to big, Intake to tall, Compression to high, Carb is oversized. Everything is alll righttt.

Last edited by Mustang 2422; 07-20-2017 at 10:19 PM.
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Old 07-20-2017, 10:54 PM
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My starting point would be to run with whatever gear is on the car, then assess where to go from there
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Old 07-20-2017, 10:54 PM
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Use the 33 spline c-clip eliminated rear and put the 3.73's in with the trac-loc diff and you should be good to go.
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1989 Saleen 414 358cid SBF 2.8L Kenne Bell S/C
26 X 8.5 Hoosier
Best 1/4 mile time 8.623 @ 159.82 mph with a 1.34 60' (5.57 1/8th at 128)
Best 1/8 mile time 5.339 @ 133.46 mph with a 1.29 60'
08' Bullitt #4097 N/A 340ish RWHP <<<<<FOR SALE!
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Old 07-21-2017, 11:56 AM
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To figure out your gears for 1/8 or 1/4.... go to wallace racing calculators and Calc what your best ET should be by entering the Weight and HP. 1/8th Mile ET-MPH-HP Calculator

Then with that MPH ... go to the gear calculator and enter your data to play with gear ratios so you cross the line at max rpm. Calculate GEAR, RPM, MPH, TIRE DIAMETER


69.5 Maverick, 480 RWHP 363 NA, Faceplated TKO 600, 4.30 gears, 9", E70-14 Whitewalls. "Stock Appearing" Sleeper. 1.72, 11.49 @ 124.87
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