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Old 05-07-2006, 03:46 PM
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trans and rear end ratio choice?

I have a modified,rebuilt Chevy 350 in my 1971' Chevy C30 longbed.I have the stock turbo 400 in it.With the stock 4.10 posi rear end in it.Ive upgraded the engine with a comp cam 256h extreme energy cam,Magnum roller rockers 1.52 ratio,Gear drive,Ported stock heads,9.25:1CR,Edelbrock performer rpm intake,Thunder avs series 650cfm auto choke carb.Deep sump 7Qt oil pan.
It accelerates very well.But highway speed is horrible.It's uncomfortable because the rpms are way up there.I have a TCI streetfighter 700-R4 trans with a Breakaway Converter lockup.Im installing it in a month from now because im waiting on the shifter to be shipped.But I wanted to know what kind of gear ratio I should change to?I drive this truck every day to work,And once a month to L.A from Bakersfield.I see highway use a couple of days a week.But I'd like to fun and burn out once in a while.Any advice would be appreciated.Thanks.
Bonzipenguins

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Old 05-07-2006, 04:38 PM
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Cam

You can't have stump pulling power & high speed. that stock cam looks better all the time. my .02
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Old 05-07-2006, 04:49 PM
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350, or 373, gears, you should still be able to burn out
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Old 05-07-2006, 05:44 PM
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Gotta know tire size.

The 700r4 is a very wide ratio transmission. First gear is 3.06 compared to the 2.48 in the 400. So your current first gear final ratio is 10.17:1. In order to maintain the same first gear final ratio with the 700r4, you only would require 3.32 gears. (I know they don't exist, but mathematically speaking) But, depending on your tire sizes a 3.32 rear with the .70:1 overdrive might make your cruise RPMs way too low. That's always the trouble with 700r4s. Huge gear splits and wide ratios make honing in on the right gears tough.

Why not just keep the 4.10s? They'll be multiplied with the OD so it would act the same as your 400 with 2.87 gears after the 700r4 swap. Tire-roasting burnouts, low stump pulling tow power, and low highway RPMs.
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Old 05-07-2006, 08:04 PM
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Quote:
Originally Posted by curtis73
Why not just keep the 4.10s? They'll be multiplied with the OD so it would act the same as your 400 with 2.87 gears after the 700r4 swap. Tire-roasting burnouts, low stump pulling tow power, and low highway RPMs.
Try the above first and see how you like it.

I have a TH400, 4.11 gears and a Gear Vendors overdrive (.78 OD) so my effective final drive is 3.20. If I were doing long 65 to 75 MPH drives I would change my gears to 3.73's for an effective 2.90 final drive and a more comfortable cruise.
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Old 05-07-2006, 11:39 PM
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Im not sure how to calculate tire height.But the size is a 275/60R15 in the rear though.It does'nt have to much trouble getting to highway speeds.It's just loud up there.These ideas sound very good.4.10 sounds like it will run pretty good with overdrive.I will post when I install the trans.To let you know how it runs.Thanks,for your advice.
Bonzipenguins
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Old 05-08-2006, 12:40 AM
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By the way: Your tire is 28" in diameter. Do a search for "tire size calculator" or "gear mph calculator" and you'll come up with tons of 'em. You can input your ratios, tire sizes, redlines, everything, and it will plot your RPMs/MPH for you.

With a non-lockup converter you might want to add 200 or so RPM to the final numbers they calculate
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Old 05-08-2006, 07:35 AM
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Here are some handy tools for you: http://www.tciauto.com/tech_info/calculators.htm
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