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Gearing... Acceleration?

117329

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117329 Enthusiast

117329

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I have an 84 sierra I am restoring. The motor is out of a sprint car, a 350 with a 400 turbo trans. I don't know much about cars yet, but I know it has a lot of power. It is tough to start from a stop without chirping the tires, but it seems to be a dog compared to what it should be through 1st.

 

When going 50 and shifting down to 2nd it is stupid fast. But would changing the gears in the pumpkin improve 0-60? If so, is this something easy to do or is it extensive?

Chanks7 Enthusiast

Chanks7

Posted
Posted

Yes, changing to a higher gear ratio (going from 3.42:1 to 4.10:1) will increase acceleration but you will compromise on highway driving, your RPM's will be higher when cruising down the highway.

117329 Enthusiast

117329

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Yes, changing to a higher gear ratio (going from 3.42:1 to 4.10:1) will increase acceleration but you will compromise on highway driving, your RPM's will be higher when cruising down the highway.

 

 

 

How hard is it to install this? Is it something the average Joe could figure out? How much top speed is sacrificed? I think this truck already hits 130 as is.
Chanks7 Enthusiast

Chanks7

Posted
Posted

If you havent done it before it can be time consuming, also if you dont have the tools I wouldnt recommend it. You'll need a tool for setting pinion depth, a press for installing bearings, a dial indicator gauge for setting backlash and an assortment of shims for changin backlash (most gear install kits will come with an assortment of shims). If you want to do it yourself you can probably pick up a pinion depth kit and a dial indicator for a reasonable price at a auto parts store, then I would get a service manuals' procedure for replacing the gears.

mmmikkke Senior Enthusiast

mmmikkke

Posted
Posted

The THM400 became the 4L80E and the 4L80E is known for having a tall first gear.

 

1. What's the torque converter stall speed? Maybe raise the stall speed.

 

2. How big are the tires? Maybe just put 10% smaller diameter tires on. It would be like changing the axle ratio by 10%.

TieRod Enthusiast

TieRod

Posted
Posted

Sound like you a smaller toque converter aka more stall speed.

I have a 3000rpm stall and 3.08 gears in my Chevelle and it will blast the tires from a dead stop.

117329 Enthusiast

117329

Posted
  • Author
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The THM400 became the 4L80E and the 4L80E is known for having a tall first gear.

 

1. What's the torque converter stall speed?  Maybe raise the stall speed.

 

2. How big are the tires?  Maybe just put 10% smaller diameter tires on.  It would be like changing the axle ratio by 10%.

 

 

 

I really have no clue at all. I am green in the high perfomance area. An alternator goes, I know it and fix it, a carb gets gummed, I rebuild it, I can doo all that stuff but I don;t understand the high tech stuff. I know a torque converter is in the trans, the round thing, but I don't know what it is other than the trans has to be dropped to change it. Whats this mean if you don't mind me asking and whats the benefit and cost? I am trying to learn.

 

The tires, I would have to check, not huge, but I guess I could pop low profiles on it?

mmmikkke Senior Enthusiast

mmmikkke

Posted
Posted
...What's the torque converter stall speed?

 

 

I really have no clue at all.

 

 

 

Do a (1-second) brake torque at maybe half throttle but with brakes on. Check your rpm. That's your stall speed. If it's stock it is probably around 2200 rpm. If it's below your peak torque rpm, installing a higher stall speed torque converter will improve your 0-60 time because it lets your engine run closer to max torque "off the line."

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