Starting line ratio ???

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

12.49 in my truck with 28" tires and its totally uncontrollable on the street

Shouldn't SLR be somehow equatable to power to weight ratio?
Seems like you should be able to get something that would compute to an approximate 60 ft time

I have both a 904 and a Powerglide.. I think the issue is shocks. And Springs.. I believe it was Al that said by the best shock you can afford and I agree 100%.. also have worked with John Calvert with getting the correct leaf spring for my car..

Except that doesn't take into account
A; Tire type/size
B; Suspension type
C; Shocks
D; Weight distribution
E; Trans type stick/auto
F; Converter/clutch
G; Starting line RPM
H; trans brake/foot brake

It's no secret that just like anything else in racing there are different levels of tuning. The fast guys put as much power to the starting line as possible. That is power x SLR x torque stall ratio. Others run huge tires and less gear for consistency. That being said as power goes up you will reach a limit of how much SLR the track can take. Some guys can go both quick and consistent with SLR that others say won't work. Depends on how hard you want to work at it.
Doug

That car ran a best of 11.23 at 119.+ MPH at that race, it had a bunch of string sucked up into the fuel pickup that I was not aware of until after I sold it right after that race. All the other M.W. Mopars running in B/SA at that race where running 122.+ MPH but I contributed that to them having the bigger 1964 carbs, intake and camshaft
I had all of them cover by .17 ET, but I was my car was down 3.0 MPH I ran the Firestone 30x9x15 slicks tubeless that where around 96.3 inches in circumference with 16 to 18 lbs. in them on a ten inch rim.
The cam was a Lunati legal cheater cam with the lash set at .012 and .014 hot, that car was completely legal
I loved that car, I won a bunch of races with it and made a lot of money racing it
The good old days

Thanks for the reply.
Sounds like it was a 63 car.

03heavy,
For the type of racing you want to do, don't get hung up on killing the 60ft. clocks. I've done a ton of index racing over the years, and getting the car to react the same every time in the first 10 feet is more critical to good reaction times than an impressive 60ft.
My car is ladder bar/coil over, so I realize you have more challenges to make it work, and the .4 pro tree is a pain for these types of classes. In addition to driving my car on Drag Week, and spraying it on occasion, I knew I would end up index racing as well, and I love the D Gas 10.60 index .4 tree racing at NHRA Nostalgia races, and I've also done some of the 10.0 stuff at Street Car Takeover.

My 428 small block made 615Hp at 6700, and is over 500 ft.lbs of torque from 4400 to 6200 on the dyno. The top picture on my previous post was the car leaving on the trans brake, with the two step at 4200, NA. My sixties are typically 1.40-1.43 in this configuration, but my best light is .042 in a .4 tree without rolling in a little. The car just has too much front travel right now, and perhaps a little more tire pressure in the rear would help. For reference my best NA ET is 10.39-128. I think the converter is 300rpm too tight, and the 3.89 gear is too tall for max effort. Best on nitrous is 9.43-139. The 8" converter can't really hold the torque, and the 3.89 gear is too short to pull all the way to the stripe! Such is the the plight of a multi-use street car!!

Shocks and springs and tuning are critical to getting the best from your combination. But if the combination (i.e. low gear ratio) is out of whack, one way or the other, it becomes difficult or impossible to get the car to run as quick as it's capable of or even control the tire. The suspension and transmission parts - including available gear ratios, tuning, converters and tech, coming out of the very high horsepower Pro Mod and drag radial world, is crazy. All about tire management.

Thanks guys for the insight
And whitedart you have a nasty machine ( Been checking it out on YouTube )
Mines gonna go together as planned
But now I have a little more direction
Will call Calvert and talk about the springs suggestions and probably get a good DA shock
on it before I even put it on the ground

Whitedart I found some of your videos from under the car while launching
Not sure if they were the glide or the 904 they were about a year old
The videos are helpful
Gonna set mine be up like yours
Nice to know the lower blocks aren’t a issue
Who’s shock are you using
Any-who thanks

At the time those videos were taken I believe I was on a 28.10.5 Tire.. with viking da shocks. Set up with drag radial valving the lowering blocks are made by Calvert they are half inch thick made of steel and designed to be stacked.. if you're going to stack blocks make sure you get the steel ones. When you speak to Calvert you will want to talk about the type of racing you are planning on doing. As well as the weight of the vehicle and right height lower the better
..

What's wrong with the aluminum lowering blocks? I only need 1/2 to maybe 3/4 inch drop so I won't need to stack them. Is aluminum ok if I don't stack them?

I have alum 1 inch on mine and no issue so far

I have been told it's not the best of ideas

I've heard the same thing on race cars

Ok thanks. Glad I heard this because I'm just getting ready to order them. I'm buying steel.

Thank you

Aluminum captured between 2 exactly flat, very rigid parallel structures is safe.
Otherwise not.

SLR = 14
but then....someone left the torque converter out