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Old 05-29-2011, 10:53 AM
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Proper Converter and Rear end gearing question

Hello,

I have an engine with a cam powerband of 2500 to 6400. The THM-375 tranny currently has a 1500 stall in it and I know it should have a 2500 so I'm looking into getting that done.

However, question I have is. The rear setup is stock so when I'm driving down the road at 60mph it runs at about 2200 rpm; does that mean with the current setup a 2500 stall will never lock up causing excessive heat?

So, I should then do the rear end first? (I will have to work out what rear end gearing to go with)

Thank You
Gary
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Old 05-29-2011, 11:05 AM
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The only time the torque converter will achieve its 2500 stall rating is when full power is applied, at lower throttle amounts it will couple up pretty much like a stock converter. You have nothing to worry about, the slipping and heat concerns are just erroneous info the car mags have been mistakenly publishing for years. Might be a problem with 5000 rpm stall and your 2200 rpm cruise, but not with a 2500 rpm converter.

I wish car mags would quite printing that baloney.
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Old 05-29-2011, 11:18 AM
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An auxiliary transmission cooler is always a good idea for a performance street car even w/o a higher stall TC.
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Old 05-29-2011, 11:28 AM
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How to change low RPM shifts

Excellent, thank You ericnova72 (and cobalt327). Aux cooler is already on the list to do.

So, next question then. The tranny shifts early so that the engine never really gets into it's power band. for example, WOT 2-3 shift is at around 3500 rpm.

Hence my thought to go to the proper 2500 stall to hope it balances it all back out. The tranny was originally built for a 2500 stall. (long story on why a 2500 was not put in when the engine/tranny went into the vehicle).

I like the idea of leaving the 1500 in so what are other options to bring the shift points up - governor weight changes?

Thank You
Gary
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Old 05-29-2011, 11:50 AM
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Quote:
Originally Posted by ggevaert
Excellent, thank You ericnova72 (and cobalt327). Aux cooler is already on the list to do.

So, next question then. The tranny shifts early so that the engine never really gets into it's power band. for example, WOT 2-3 shift is at around 3500 rpm.

Hence my thought to go to the proper 2500 stall to hope it balances it all back out. The tranny was originally built for a 2500 stall. (long story on why a 2500 was not put in when the engine/tranny went into the vehicle).

I like the idea of leaving the 1500 in so what are other options to bring the shift points up - governor weight changes?

Thank You
Gary
If the tranny is already kitted, I would suggest you manually shift it. Otherwise you can alter the governor weights/springs to get higher WOT shift points.

The 1500 RPM stall TC will not be the best for acceleration but if the engine doesn't try to pull through the brakes excessively when stopped at a light for example, then it will suffice. Personally I would go w/the higher stall TC.

Last edited by cobalt327; 05-29-2011 at 11:56 AM.
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Old 05-29-2011, 11:55 AM
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kitted and shift points

Yes, the tranny came with a stage 2 shift kit and I manually shifting it works awesome, I was just trying to clean it up by making it work the same in full auto. I will add researching/changing governor weights to my todo list.

Gary
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Old 05-29-2011, 02:56 PM
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What cam ? what vehicle? what engine? How will you be using the vehicle?

What rear tire diameter?
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Old 05-30-2011, 08:45 PM
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Truck Specs

1984 GMC Pickup; was a straight 6 but engine replaced with a rebuilt V8-350 4 bolt main.
Stock bottom end but rebalanced and new seals/bearings.
Heads: high output 416 heads unshrouded with large valves
Cam: 450 lift, 224 duration, 206 lobe centre.
Ignition - standard HEI
Intake - edelbrock performance intake
Holley 600 street carburator - pn 0-80457S
Tires: 31x10.5R15
rear axle: currently stock from when truck was a 6 cylinder; have not yet spun wheels to figure out what ratio is - think stock was 3.08. it is 10 bolt unit.
Tranny; THM-375 rebuilt with stage 2 shift kit; 16 spline yoke
Drive Shaft was balanced

Driving: Not a daily driver, sometimes off road (but nothing serious, just in behind the farm), some towing in its future to tow the car trailer. Maybe the track once or twice just for fun. As it is my learning platform it is down more often than running these days.

Gary

Last edited by ggevaert; 05-30-2011 at 08:51 PM.
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Old 05-31-2011, 05:24 PM
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4.33 to 4.56 gears. 10" 3000 stall converter.

Recurve the distributor for 20-24deg at idle and 34-36 at max advance.
Shorten the mech advance curve limit.

Then dial in the vacuum advance for cruising efficiently using a fully adjustable and limitable vac advance. (crane)
(approx 10-12 deg added at high vacuum low load part throttle driving)
adjust as required.

Champion RV8C @.035" or equal spark plugs

Last edited by F-BIRD'88; 05-31-2011 at 05:30 PM.
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