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BlueOvalRacing

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Discussion starter · #1 ·
What's the best method to figure out what your SLR should be?

Also, how does it tie into your over all gearing for going through the traps?

Let's say the car is 2,800lbs with 900-950FWHP

Does it change with a radial vs a slick? If so how much?

3 speed automatic
Shift point of 8-8,500rpm
Full 1/4 mile
 
#2 ·
BlueOvalRacing said:
What's the best method to figure out what your SLR should be?

Also, how does it tie into your over all gearing for going through the traps?

Let's say the car is 2,800lbs with 900-950FWHP

Does it change with a radial vs a slick? If so how much?

3 speed automatic
Shift point of 8-8,500rpm
Full 1/4 mile
Click to expand...
If you go to less or more rollout on the rear tires it changes the 'effective' rear gearing. The rear gear times your low gear is your "SLR". 3.14 × tire diameter=rollout.

Yes SLR changes with tire diameter effectively.
 
#9 · (Edited)
I don't know the exact numbers but obviously the lighter the car with lots of power is going to need less SLR than a heavy car with less power. At 2800 race weight and 950 hp I wouldn't think you would need a crazy SLR... with your weight hp rpm combo I'd gear it to cross the strip at peak rpm.
 
#10 ·
Outlaw Bill said:
Gear the car to cross the traps at what ever rpm and adjust the transmission gearing to get your SLR in a workable range.
Click to expand...


Trap is more important then starting line when I pick the gear.
Unless you can spend the dough on a fancy trans, most of us run 1-1 high gear.
I did this test, with a 4.88 I had an awesome launch, but it was spinning too high at the end.
So I had to compromise so I didn't beat up the engine.


.
 
#11 ·
mrdragster1970 said:
Trap is more important then starting line when I pick the gear.
Unless you can spend the dough on a fancy trans, most of us run 1-1 high gear.
I did this test, with a 4.88 I had an awesome launch, but it was spinning too high at the end.
So I had to compromise so I didn't beat up the engine.


.
Click to expand...

bills referring to adjusting your first gear ratio as there are so many to chose from now a days in the turbo 400/proflite/powerglide transmissions so gear for the trap and then make a wise choice of first gear if youre going to spend the money on the trans.
 
#12 ·
BlueOvalRacing said:
How do you know what your ratio should be? How do you know what's optimum for your combo?
Click to expand...
Way too many factors to give an accurate answer. Is it a 3 speed automatic or a 5 speed manual? Big tire with great track prep or a smaller tire with so so prep? Radial or a slick?

How wide is the engines power band? Its one of those things when you need to balance everything. In a 3 speed automatic you can usually only choose 1st and 2nd gear ratio, often they are locked together (cant mix and match) so you need to balance starting line ratio with shift drop rpm. In my experience engines with larger power curves are less sensitive to the 1-2 drop then narrow power band pieces. We still want as much SLR as we can get so we can get the car moving, but if we dont pay attention to what happens when we pull 2nd we can knock the wind out of the engine 2 seconds into the run.

This is one of the reasons a proflite is such a popular transmission for high end/high rpm combos, there are so many ratio options available compared to other lightweight low drag 3 speeds
 
#13 ·
Shawn Finn said:
Way too many factors to give an accurate answer. Is it a 3 speed automatic or a 5 speed manual? Big tire with great track prep or a smaller tire with so so prep? Radial or a slick?

How wide is the engines power band? Its one of those things when you need to balance everything. In a 3 speed automatic you can usually only choose 1st and 2nd gear ratio, often they are locked together (cant mix and match) so you need to balance starting line ratio with shift drop rpm. In my experience engines with larger power curves are less sensitive to the 1-2 drop then narrow power band pieces. We still want as much SLR as we can get so we can get the car moving, but if we dont pay attention to what happens when we pull 2nd we can knock the wind out of the engine 2 seconds into the run.

This is one of the reasons a proflite is such a popular transmission for high end/high rpm combos, there are so many ratio options available compared to other lightweight low drag 3 speeds
Click to expand...
And this is why as bad as I want to get my transmission ordered, I am determined to wait until the engine is dyno'd.
 
#15 · (Edited)
Shawn Finn said:
Way too many factors to give an accurate answer. Is it a 3 speed automatic or a 5 speed manual? Big tire with great track prep or a smaller tire with so so prep? Radial or a slick?

How wide is the engines power band? Its one of those things when you need to balance everything. In a 3 speed automatic you can usually only choose 1st and 2nd gear ratio, often they are locked together (cant mix and match) so you need to balance starting line ratio with shift drop rpm. In my experience engines with larger power curves are less sensitive to the 1-2 drop then narrow power band pieces. We still want as much SLR as we can get so we can get the car moving, but if we dont pay attention to what happens when we pull 2nd we can knock the wind out of the engine 2 seconds into the run.

This is one of the reasons a proflite is such a popular transmission for high end/high rpm combos, there are so many ratio options available compared to other lightweight low drag 3 speeds
Click to expand...


ive changed my first and second gear in my 400 4 times now, whats interesting is the 2nd gear in 2 of the combos was the same but the drop from first to second reacted completely different, you would imagine when you have the same gear ratio for 2nd that it would act the same but that's not the case 2 different animals once it was locked up.

Heres in car video where i had the different first gears but had the same 2nd and 3rd, you can hear the difference.:-Daw

 
#16 ·
calypso50kid said:
ive changed my first and second gear in my 400 4 times now, whats interesting is the 2nd gear in 2 of the combos was the same but the drop from first to second reacted completely different, you would imagine when you have the same gear ratio for 2nd that it would act the same but that's not the case 2 different animals once it was locked up.

Heres in car video where i had the different first gears but had the same 2nd and 3rd, you can hear the difference.:-Daw
https://youtu.be/5RYBKV5bKRg

https://youtu.be/jz8YJJJptVQ
Click to expand...
Can definitely hear the difference, thanks for sharing the vid

Which gear set hit the sprag harder? I know a 2.10/1.40 will hit it much harder then the 2.08/1.56

I have learned the higher rpm/narrow power band combos definitely are faster, but need every part of the rest of the car to be right in order to really shine.
 
#17 ·
Shawn Finn said:
Can definitely hear the difference, thanks for sharing the vid

Which gear set hit the sprag harder? I know a 2.10/1.40 will hit it much harder then the 2.08/1.56

I have learned the higher rpm/narrow power band combos definitely are faster, but need every part of the rest of the car to be right in order to really shine.
Click to expand...
I dont want to give away ratios as ive spent considerable amounts of money testing, but the bottom video where it tugs the motor down harder was the least "efficient" of the 4 gear sets. I believe it was the hardest on the sprag from talking with coan
 
#18 ·
calypso50kid said:
I dont want to give away ratios as ive spent considerable amounts of money testing, but the bottom video where it tugs the motor down harder was the least "efficient" of the 4 gear sets. I believe it was the hardest on the sprag from talking with coan
Click to expand...
Thats cool info. Thanks for sharing. Pm sent
 
#19 ·
calypso50kid said:
I dont want to give away ratios as ive spent considerable amounts of money testing, but the bottom video where it tugs the motor down harder was the least "efficient" of the 4 gear sets. I believe it was the hardest on the sprag from talking with coan
Click to expand...

Shit I don't care which of the two gear sets was quicker, the second video was WAY more FUN to watch.

I love big wheelies!!!!!!!!!
 
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