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The gear that all the Calculators give me seems too high! I don't know why but it just seems that way! I have tried over a half dozen different Drag Race rear gear Calculators and I usually agree with them, but why does this Gear seem too high numerically?

Here is my Cars basic combination, It has not been run yet/new car:

1964 Chevelle Race only.
Approx. 3450 with driver.
496 N/A BBC approx 750-780 Horsepower MAX RPM 7200!
Camshaft 775/723 284/292 4800/8200 rpm.
Dart 325 Pro 1's w/ Nextex Triple springs, setup for approx. 75-7600 rpm max.
Glide 1.76 w/Brake.
8 inch 5500 Convertor.
Tubbed 4-link back half car.
13x31x15 M/T Slicks.
12 Bolt Chevy with Strange Spool and 33 spline axles w/Strange GM small ends.

Calculators say 4.88's which are already in the car. Most combinations like mine run a 4.56. I am not a follower, but 4.88's seem steep to me. What do you think? Oh yeh QUARTER MILE RACING ONLY!
 

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My quick #'s show you should run 140MPH with a 31 tall tire thats like 7400 rpm. if you want to run 140mph the 4.56's show 6900rpm. Don't think calc takes into account converter slip which can vary greatly. But avg. 500 RPM added to your 7400 4.88 gears is 7900 and 500 added to your 6900 4.56 gear is 7400 which is pretty close.
 

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I would take the car out and see what it does and adjust from thier.... speculation is fun but the converter is a huge variable..:)
 

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I'm not going to say our cars exact but they're close in specs and performance.

All the calculators said I should be running 4.56. I've had my best runs with 4.86. I tried some 4.57 gears for a couple of races and didn't like them. The car just felt sluggish. Put the 4.86 back in and it was much better.

I think with the 4.57 gears, I would have needed to do a converter swap. My converter stalls at 6200 on the transbrake and the 4.86 gears love it. I've been tempted to put in some 5.00 gears but think it may be a little too much. Perhaps with the cam swap I just did, 5.00 may work even better.
 

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Sometimes a car will run quicker even when it's well past peak hp through the traps. This occurs because time lost at the first part of the track is very hard to make up at the top end. I agree with trying what you have unless it's obviously WAY off.
 

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steve, i run 4.88s in my car 540 31x10.5w tire shift 7500 trap 7800



same car with my 468 shift at 7000 went thru the traps 7200, i guess it all in motor because both used same converter
 

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4.88 sounds perfect to me but i like a lower gear than most, here is where a lot of guys get messed up, to run MPH you need RPM , i have a friend that went from 4.56 to 4.11 he kept telling me he was going to gain big MPH , when it was said and done he slowed down 2 tenths and if i remember right about 4 MPH, but if you are wanting to drop RPM at the finish line then go with a higher gear
 

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A 4.88 will tighten the converter up early, so it will MPH

General rule is finish 500 RPM over peak HP, for a starter gear. If you cant lock the converter up then the gear really does not seem to matter much we have found it just rides in the converter.
 

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REBUILDING
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Discussion Starter #13
The gear that all the Calculators give me seems too high! I don't know why but it just seems that way! I have tried over a half dozen different Drag Race rear gear Calculators and I usually agree with them, but why does this Gear seem too high numerically?

Here is my Cars basic combination, It has not been run yet/new car:

1964 Chevelle Race only.
Approx. 3450 with driver.
496 N/A BBC approx 750-780 Horsepower MAX RPM 7200!
Camshaft 775/723 284/292 4800/8200 rpm.
Dart 325 Pro 1's w/ Nextex Triple springs, setup for approx. 75-7600 rpm max.
Glide 1.76 w/Brake.
8 inch 5500 Convertor.
Tubbed 4-link back half car.
13x31x15 M/T Slicks.
12 Bolt Chevy with Strange Spool and 33 spline axles w/Strange GM small ends.

Calculators say 4.88's which are already in the car. Most combinations like mine run a 4.56. I am not a follower, but 4.88's seem steep to me. What do you think? Oh yeh QUARTER MILE RACING ONLY!

Typo..... PAC Springs Coated..... not Nextex.
 

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A 4.88 will tighten the converter up early, so it will MPH

General rule is finish 500 RPM over peak HP, for a starter gear. If you cant lock the converter up then the gear really does not seem to matter much we have found it just rides in the converter.
Do you use a calculator to figure out the gear ratio to be 500 rpm's over peak power? for instance my motor makes 550hp at 6500 rpms. Do I go to say Randysringandpinion.com and use his gear ratio calculator to find a gear that will be 500 rpms higher then peak power when I cross the traps?
 

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Do you use a calculator to figure out the gear ratio to be 500 rpm's over peak power? for instance my motor makes 550hp at 6500 rpms. Do I go to say Randysringandpinion.com and use his gear ratio calculator to find a gear that will be 500 rpms higher then peak power when I cross the traps?
*most* cars like crossing 500rpms over peak power. However to the OP I still recomend getting a baseline with what you have to see where the converter is etc... :cool:
 
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