Trying to educate myself on starting line ratio
1st gear x rear axle ratios==slr
What about tire size
And how do I decide which ratio I want ?

Slr is really power and weight dependent. A big motor in a a light car needs less than a high rpm small block in a heavy car.

how do I decide which ratio I want

1. what top speed do you expect?
2. with what tire diameter?
3. transmission O/D: Y/N?
4. now you know your axle ratio
5. what 1st gears are possible with your transmission?
6. lower than optimum number (PG): looser converter

Power, weight, stroke, chassis/suspension type, rear gear, what kind of racing (you want to go fast, consistent, hit the pro tree, etc) quality of track prep you usually see,...

Transmission choice will determine your options and the costs. You can get a variety of gear sets for 3 speeds, even use 2nd gear to start. Glides have fewer choices but they are usually right for many applications. They top out at 1.96 for a decent gear set with 1.80 being popular unless you're making a ton of power and/or real light. Tire size matters but usually just knowing big tire ~32" or small tire ~ 28" will get you close.

Back in the day the desired ratio was 10:1. I'm now at 8.04:1 and could probably go higher. The choices are much greater today in all areas. Sometime it's just trial and error after you listen to all the knowing people and get a starting setup.

8.67:1 with sticky tires and good prep = 1.54 60 ft.

5.13:1 for no prep street/true street tire action = 1.72 60 ft.

Ok this is easy. You decide by what they tell you hear on Moparts !! Sorry guys but I could not resist. Ron

9.66 using that formula (rear gear x low gear)

No 383man, I didn't say all of the people on Moparts were knowing people!!!

Don't forget about the torque multiplication of the torque converter in each gear, especially on the starting line in low gear.
I can remember many stick shift modified production cars with very small C.I. motor running 2.98 first gear ratio and 6.17 to 7.17 rear gear ratio for the 1/4 mile a long, long time ago
I shoot for the lowest starting line ratio I can run that won't spin the tires on the line You may need to experiment some on your car to find what works best for you at your track
Good luck

And don't leave out the fact that many of them had 40 pound or heavier flywheels along with all that gear.

Can you say 10 or 11 thousand rpm's in the traps? Can you?

I run a fair amount of SLR with my 572. 10.535 SLR with 10.5Wx31 (w/tubes). Car weighs 3340 when not weighed down for index. 60ft with no weight 1.25-1.26, with weight and throttle pulled back 1.29-1.30. Consistent with-in .01 through out the day on foot brake and no rev chip.
Doug

Pro tree chassis car, light (2350# loaded), 525 HP, 5.29 with a 3.31 stroke - 4.86 with a 3.60 stroke, 32" tire. I had everything in this car from 1.76 to 2.74. A 2.45 3 speed was quick, but would turn the tire and kill 03-04 reaction time and 60' often enough that I always had to have some in my pocket and then race the finishline based on how it left. 1.76 was a turd. 1.96 with a 4.86 = 9.52 worked nice on most tracks with an aggressive 4 link set up. As quick as the 2.45 but more consistent. 1.87 may have been a good choice but we never tried that.

They'll have to pry my low gear set 904 from my cold dead fingers!!
428 small block, small shot of nitrous, 3.89 geared 9", 8" 4800 stall convertor, 29 tall tire, 3100lb street car. I may go up to a 3.73 gear, but not giving up my 2.77 first gear!

Ok
2.45 first and a 4.56 rear axle
Comes out to a 11.17
Plans are to run a 7.0 index which won’t be a issue with the combo
But I also want to maximize the package
Looking to run in the bottom of the 6.60’s and maybe a 50
Kinda looks like will be hitting the tire pretty hard when
Trying run max effort Learning the Caltrac’s don’t like being hit hard


Looks guys I know I’ve been beating this forum to death
Silly questions and want to make sure I say thank you
For taking the time and helping
Especially the guys that have a been there done that
Or are doing it as we speak
Max ET is very important to me as I don’t wanna embarrass myself or my dart

Billy has a very good point about SLR, I switch low gear ratio in my old M.W. stocker in 1988 for the NHRA World finals at Pomona in 1988, took out the stock 2.45 low gear ratio and put in the Mopar brand 2.77 low gear (2.45X4.89=11.98) and swapped the third member from the 4.89 ratio to 4.56 which = 12.63 SLR
That made the car quicker and faster than it had ran that year
If you don't test you don't learn

60' is where the ET is. Stacking gear will make it 60', if it doesn't spin the tire excessively. It's a balancing act. Again, do you want to get up on the tire and go fast, or stick it and do the same thing every time. If you use radials, that's a different situation.

Cab, how fast did the car run in 1988?

What cam did you use back then ?

Trying run max effort Learning the Caltrac’s don’t like being hit hard
[/quote] well I'm not exactly sure what you mean by that. but I hit mine pretty hard.. as a matter of fact the racepack will see close to 3 G's for the first few feet of the track.. which I think is relatively hard for a stock suspension door car..

From what I’m seeing the most guys using a 3 speed
With a aggressive rear axle ratio and a trans brake have trouble
With the 60’s Or from what I can tell anyways
You use a 904/727 or a glide whitedart