According to one of my "automotive math" books, the ET, HP and WEIGHT are
related by the formula:
1/4 Mile ET = (Cube root of (weight / hp)) * 5.825
1/4 MPH = (Cube root of (hp / weight)) * 234
optimum gear ratio (Manual):
ratio = (tire diameter/340 mph) * (rpm/mph)
optimum gear ration (Automatic):
ratio = (tire diameter/335 mph) * (rpm/mph)
So, how does this work in practice?? My QC 5.9L has a curb weight of 4573
lbs. and 245 HP so the 1/4 ET would be, according to the formula above,
15.45 sec. The 1/4 MPH would be 88.4 mph. Since I have an automatic trans
the optimum ratio would be for what, say, 88 MPH at oh, let's just say 5500
RPM on my 28" tires. This gives 5.25:1 as the optimum ratio! Assuming that
I'll be in 4th gear as I get to the 1/4 mark the transmission ration is
0.69:1 so 5.25 * 0.69 = 3.62 as a rear axle ratio. Since I have a 3.92 axle
ratio so my RPMs are going to be higher or maybe I need a slightly larger
tire.
Are these realistic figures? Since I'm not a racer I don't have a feel and
some of the racers will have to let you know how close these numbers might
be.
Regards, Mike Klinke
-----Original Message-----
From: Stlaurent Mr Steven <STLAURENTS@mctssa.usmc.mil>
To: 'dakota-truck@buffnet.net' <dakota-truck@buffnet.net>
Date: Tuesday, August 01, 2000 4:07 PM
Subject: DML: BERND - REAR GEARS FORMULA
>Bernd
>
>How can you determined with given HP at the rear, body weight, and wanted
>1/4 mile speed time, how can I determined what gearing should I apply for
>the rear?
>
>-------------------------------------------
>Steven St.Laurent
>Test Engineer
>Test Branch, GSD, MCTSSA
>MARCORSYSCOM, USMC
>760-725-2506 (DSN 365-2506)
>Work:mailto:stlaurents@mctssa.usmc.mil
>Home:mailto:saint1958@home.com
>
>
>
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