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post #1 of 10 (permalink) Old 11-01-2012, 08:43 AM Thread Starter
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best gear ratio

Just wondering what gear ratio any of you performance guys are runninf.my 78 is auto and when we finish the motor in a month we will be at about 375hp. I dont race the car and use it as a cruiser part idling around town and then on to the backroads to cruise at highway speeds,but I do want a hole shot and not get beat by a grocery getter.. We had already decided on 370 but I am second guessing myself now.
your experience and advise please
Ron
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post #2 of 10 (permalink) Old 11-01-2012, 10:18 AM
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if you still have the old TH350 in it, 3.70 might be a bit much on the hiway..... 3.55 s are a good all around choice.. I run 3.73 s behind my stroker ,but I converted to a TH700r4 w/overdrive
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post #3 of 10 (permalink) Old 11-01-2012, 04:10 PM
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Originally Posted by randers View Post
Just wondering what gear ratio any of you performance guys are runninf.my 78 is auto and when we finish the motor in a month we will be at about 375hp. I dont race the car and use it as a cruiser part idling around town and then on to the backroads to cruise at highway speeds,but I do want a hole shot and not get beat by a grocery getter.. We had already decided on 370 but I am second guessing myself now.
your experience and advise please
Ron
What gear are you running now?
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post #4 of 10 (permalink) Old 11-02-2012, 12:03 AM
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Rough numbers here, but a 3.70 gear, you can figure on 3500 RPM being right about 70 MPH. That's with a 1:1 final trans gear (TH350 in 3rd) There are a bunch of calculators out there to help figure speed/RPM/gear ratio.

Like fishslayer pointed out- 3.55's are a pretty good all around gear.

I'm running 4:11's, crap on the highway, but a blast around town. I'd like to have 3.08's but I'm making the HP/TQ to pull them with a BB. Won't help much with mileage in my case either. Ol' Red drinks gas nearly as fast as I do Jack Daniels'.
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post #5 of 10 (permalink) Old 11-02-2012, 05:56 AM Thread Starter
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I have the stock 305 now
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post #6 of 10 (permalink) Old 11-02-2012, 06:56 AM
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The 3.55's will work well for you. IT's really a good all around gear. The 3.70 will be a tiny amount better around town, but noticeably worse on the highway.

You said you've got a stock 305? Have you checked the numbers on the block to verify? THe L-82 and the L-48 were the factory offering in 78.
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post #7 of 10 (permalink) Old 11-02-2012, 07:20 AM Thread Starter
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Sorry! gears are 3.05 (stock) It is a 350 l48 built to about 375 hp and a stock torque converter and stock th350 trans
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post #8 of 10 (permalink) Old 11-02-2012, 10:50 AM
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Sorry! gears are 3.05 (stock) It is a 350 l48 built to about 375 hp and a stock torque converter and stock th350 trans
The stock 3.05 gear will make it a better highway cruiser that a 3.55 gear. Even with the stock setup, it should still spin the tires. I would get it back on the road first and see how I liked it before just switching out gears.
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post #9 of 10 (permalink) Old 11-30-2012, 08:48 AM Thread Starter
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Smile gears done

Thanks for the advise on gears as I didnt want to do it twice .I went with the 373 even though a 355 might be a better overall but for what I wanted they are great and really put some pep in a realitvly mild motored car. At 70mph I am at 3500 rpm but at the low end where i wanted it WOW what a difference. The shift kit is a must for all you auto trans guys.
Thanks again for the advise
Ron
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post #10 of 10 (permalink) Old 12-01-2012, 05:56 AM
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For a good power gear and run around gear the 3.55 should do it for teh 700R4 , but for the 350 or 400 units with a taller first gear 3.73 would give best low end take off and not much worse MPG ,, Usually for good street driving multiply the trans first gear by the rear end gears and try to maintain a 10 multiplier . 3.55 x 3.06 10.8 (700R4)
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