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View Full Version : Gearing question for a TKO'd BBF


My427stang
06-01-2007, 10:10 AM
I have a 70 Mustang, 489 cid FE, TKO-600 and currently a 3.70 nine inch. The motor is built for a very flat torque curve and peaks under 6000 rpm at approx 575 hp. Mild by stroker standards but not a truck motor

I run a 3.70 gear with a .64 OD to make a 2.36 final drive. The motor doesnt mind at all and will pull 5th gear happily down to about 1500 rpm, however, with a 242/248 duration solid lifter cam, its really not in its most efficient range

I am considering a 4.11 or 4.30 gear to get the final drive to a more usable 2.63 - 2.75 when in 5th

Any of you guys running that steep of gear? Seems like 1st gear will be a little short, but it should get it closer to about 2200 rpm on the highway when cruising, right now at 65 I am closer to 1800 rpm

Opinions? Just tossing ideas around right now, not really a "problem" but wodnering if anyone else has run that much gear with a TKO

Thanks in advance
chicane67
06-01-2007, 10:47 AM
The only issue is going to be... the first gear final ratio being somewhat short.

Anything outside of 10.5 - 11.0:1... first becomes almost useless.
parsonsj
06-01-2007, 11:29 AM
Boy, it seems the .82 TKO 5th would have been a better option for you. Is it possible to swap 5th gear? Any TKO experts know?

jp
My427stang
06-01-2007, 12:06 PM
In hindsight it may have been, but the car runs great, just trying to sneak a few more mpg out and slow down a bit. Right now comfortable cruising is closer to 80 mph
chicane67
06-01-2007, 12:15 PM
Boy, it seems the .82 TKO 5th would have been a better option for you. Is it possible to swap 5th gear? Any TKO experts know?

jp

Its the cluster shaft that makes this a question. If it were a splined unit... Id say sure. But its limited to what's already produced.
My427stang
06-01-2007, 04:14 PM
No doubt I'd have to change the assembly, I cant imagine the gear is replaceable nowadays, but honestly the issue isnt evena second thought when driving, just playing with options.

I have a set of 215/60's I am going to throw on for a quick test drive in place of the 275/60's and see if I like it better, then make a decision on gearing.

Thanks for the inputs