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Old 11-27-2010, 06:17 PM
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Th350 very low geared?

I am running a 350 trans and 3000 stall torque converter with a 327 mildly modified and it seems this combination is very low geared, more then I thought it would be. Is this normal? It shifts fine and runs good but seems low, could just be me. Rear end is stock non posi 10 bolt gm 1968 chevelle. I replaced this tranny from it's original power gilde stock.

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Old 11-27-2010, 06:53 PM
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Is this your first drive with a stall converter ? What rear gears do you have ?


Cole
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Old 11-27-2010, 07:39 PM
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th350 low gear?

hi rally68,the stall is giving the feel of a verry low gear in my opinion.good stall speed for the race track.not for the street with mild mods.for my customers buying a performance trans i do my best to steer them toward 2300 with a mild small block.a 3.73 will feel like 4.88 with 3000 stall.is this driven mostly on the street?
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Old 11-27-2010, 07:51 PM
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trans

Well it could be. A lot of things everything adds up, let's start what's your rear end gear, and tires size ,pwr glide 1st gear is 1.76 and 2nd gear 1.00 and th350 is 1st 2.52, 2nd 1.52, 3rd 1.00 , so there is a formula that figures your rpms in gears and rule is that at cruising speeds you need to to be 500-600 rpm above your cam power curve (example your cam is 1500-5800 rpm range you need to cruising speed 55mph you need to be at or around 2000rpm to be in the power band) so you can figure it out by mph x. Rearend gear ratio x 1st gear ratio x 336 then divide that number by tire diameter will give you your rpm in that gear. Compare your old trans to your new and see the differ between the two, you will be surprise hope this helps
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Old 11-27-2010, 08:28 PM
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low geared

oh,i didnt realize he had lockup converter.i thought he might be adding a couple thousand rpm from slip in high gear.sorry
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Old 11-27-2010, 10:11 PM
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th350 low geared?

I drive this mostly on the street and not on the track, I will try to do the math on what you guys proposed, but at 65mph tach reads 3000rpm with a stock 10 bolt non posi. It does shift great, nice and smooth, so no complaints just low. I will try your formula, I have to look up what gear my stock rear end is, I am not sure off the top of my head. But I know it is stock 1968 gm 10 bolt non posi. Thank Again Fellas!
Michael
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Old 11-27-2010, 10:16 PM
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I still say you are just feeling the effects of the stall converter exspecially if it still has the stock gears.JMO



Cole
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Old 11-27-2010, 10:35 PM
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350 Low Geared

i agree cole,a non lockup 3000 stall will do it every time unless the trans has a lockup clutch.
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Old 11-28-2010, 08:54 AM
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You need to know what the rear end ratio is, "stock" means nothing as there were several "stock" factory ratios. You also need to know how tall the tire is.
My T-Bucket with 2.79 gears and a 27.5 inch tire turns about 2500 RPM at 60MPH on the highway just as a reference point.
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Old 11-28-2010, 09:31 AM
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68 chevelle rear end

This is a street driven car and I believe it is a 8.2 gm 10bolt with 3.36 gears, it is the weaker of the gm rear ends. But I think I made a mistake the stall on the torque is 2800
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Old 11-28-2010, 09:32 AM
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I am running 275 R15 on the rear with 15inch rims with rally caps
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Old 11-28-2010, 02:29 PM
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There are several RPM calculators available on the net. Measure how tall your tire is and plug in the info.
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Old 11-30-2010, 05:52 PM
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rpm

well lets guess,, your tire 275/??/15 need to know the middle number but , i can do the math a get it if your car is at 65mph at 3000rpm,,

EXAMPLE
you mph x gear ratio x 336 then divdied by tire diameter to get your rpm

so figure your tire size ... 2 x section width x aspect ratio + rim diameter then divdied that number by 2540 to give you tire diameter

so if your tire 275/60/15? 2 x 275 x 60 + 15inch 2 x 275 x 60 = 33000/2540= 12.99 inches + 15 rim size = 27.99 diameter of tire(?if thats you tire size)
so with that 65mph x (rearend gear)3.36 x(trans gear)1.00 x 336= 7338.24 then divdie by rim diameter 27.99 you results is 2621.73rpm in third gear with a th350 trans at 65mph
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Old 12-01-2010, 12:30 AM
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rpm

Nice calculations, you rock! I run 275/60/r15 and 245/60/r15 on the front so does that mess up the numbers you calculated? And if it doesn't and the rpm is around 2600-2700rpm and mine is around 3000rpm at 65mph. What does that mean? Should I do something to try to correct it?
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Old 12-01-2010, 12:41 AM
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Stall converter slippage is typically between 5-15%, your rpm of 3000 at 65mph shows about 10%. Sounds about normal, only a manual trans will have no slippage so the math actually matches.

Your 275/60-15 tire might be less then 28" tall also, as many brands are less than sidewall listing(normal for tire companies, IDK why they can't just make the sidewall and actual running size match but they never do), measure it to be sure.
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