[jboxcar818]

i have a 72' mustang with a 351c 4v and i have 2.75 gears in the back and i want to get up to 100mph faster than i am now but i still want to go real fast could you help figure out what gear ratio i should put in the back i'm thinking a 3:83 or 4:10 my mach 1 is an automatic.

[ December 08, 2002: Message edited by: jboxcar818

[ December 08, 2002: Message edited by: jboxcar818 ]</p>

[DoubleVision]

the 3.83 ratio would get you up to 100 mph, maybe, before the engine ran out of breath and the tranny ran out of gear. if your running a 3 speed automatic, the final ratio is 1:1, if you want to go a ways over 100 mph with a low gear in the rear, your gonna have to get a overdrive tranny. you can`t have low gears and high speeds without a engine that will rev to hell or more gear in the tranny. depending on your tire size, you could likely run some 3.55`s or 3.42`s and get up fast and go over 100 mph. not preaching here, but I hope your intending on doing 100 mph someplace other than the street. high speeds will get you and others killed, and you can`t enjoy your Mustang dead or in prison.

[ December 08, 2002: Message edited by: DoubleVision ]</p>

[Frisco]

[quote]Originally posted by jboxcar818:
<strong>i have a 72' mustang with a 351c 4v and i have 2.75 gears in the back and i want to get up to 100mph faster than i am now but i still want to go real fast could you help figure out what gear ratio i should put in the back i'm thinking a 3:83 or 4:10 my mach 1 is an automatic.

[ December 08, 2002: Message edited by: jboxcar818

[ December 08, 2002: Message edited by: jboxcar818 ]</strong><hr></blockquote>

With 27" diameter rear tires and 3.83 rear you need to get to 4894 RPM with a three speed automatic to reach 100 MPH. With the same tire size and trans and 4.1 rear gears you will need to get to 5239 RPM to get to 100 MPH. Larger diameter rear tire will lower the RPM some. Overdrive will lower the RPM even more.

[steppenwolf]

so 100 mph isn't 'real fast' enough for ya? to fit your criteria, as frisco said, you'll need either an od trans, or an overdrive... a Gear Vendors (don't mean to advertise, but have heard good things about it) separate overdrive unit would definitely help, i think the ratio is .67, or maybe it's .75. i don't remember what the overdrive auto trannys are, maybe a 700r4? those take a pretty serious build to work well with lots of power, so it depends what you're pushing it with.
basically, 4.10 is a lot of gear for most anything street-driven. depends on your engine setup, and stall converter, too (see other posts for more knowledgeable people than i commenting about that). good luck, keep researching!
-z-

[2quik]

Try these guys, they can help...

www.pchotrod.com

[ December 09, 2002: Message edited by: 2quik ]</p>