starting line gear ratio?
 

passing the hot AZ Summer afternoon reading...
in Dick Millers book, the starting line ratio chart is interesting, but...
[target ratio is 11.25]

with my 2.64 low 4 speed, I would need a 4.56 gear. I cant believe that a 350 hp/3550 lb car would ever leave hard enuf to go 12.20 [unless a 9,000 launch-and I aint gonna do that]. even a 2.20 low with a 5.13 [11.29] seems way to old school.
so is this just theory or is this chart for real?

where does finish line RPM come into the equation?
educate me.
thanks Rod in AZ

Re: starting line gear ratio?
 

Is that is like saying 12-1 AF ratio is perfect..
Test it.
Keep going up on SLR and find what your combo likes.
Rear gear selection and tire size for finish line RPM and MPH
BTW back in the old school days It seemed that the sticks we played with liked about 20% more SLR than the automatics. That may not be the case these days with modern converters and clutches...

Re: starting line gear ratio?
 

How about 21.39?

Jim Caughlin
SS/ES 6019

Re: starting line gear ratio?
 

Tire height, flywheel weight, clutch, torque curve, and so many other things would factor into this.

Re: starting line gear ratio?
 

I'm sure my car was all wrong, but I used what I had available at the time- 25.5" slicks, 6.17 rear end gear, and 3.64 first gear.

As far as your horsepower, weight, and potential ET, your numbers sound about right. My car was about 250 horsepower, about 2,300 pounds, and launching at 9,000 rpm resulted in high 11s at about 110 mph. With a modern clutch, a lighter flywheel, and a closer-ratio transmission with a taller first gear, I'm sure it would have gone faster.

Re: starting line gear ratio?
 

watched vid on 289 mustang, ss/L 20.398 start ratio

Re: starting line gear ratio?
 

What is the intended combination, and combination? With my old M/S 85 5.0 Mustang, I ran a 3.19 low gear in the Jerico, and with 4.88 gears, that made for a 15.56 SLR, and with 5.13, a 16.36 SLR. That was with 29-29 1/2" tall tires. I would have liked to have tried a bit lower rear axle ratio, but for the Ford 8.8, there was nothing between 5.13 and 5.7. Unless it is a really lightweight car with lots of power, and borderline ability to hook up, I can`t imagine a 11.25 SLR would be anywhere close to ideal. My SB Ford 4 speed G Force bracket car also has a 16.36 SLR,albeit with 31" tall tires, plus an additional 25 MPH, but looking to add a bit more rear gear ratio, or shorter tires to give another 1 or 2 hundred RPM at the 1/4 mile finish line. Same with my old hot rod type cruiser, currently has a 2.78 low Toploader with 3.50 rear and 28" tall tires, a 9.73 SLR, and I am barely hitting 4th gear at the finish line. Plus at over 4000 pounds, the organic street style clutch isn`t very happy. Hopefully the 4.33 gears (12.03 SLR) will help performance, and clutch life, at the track. And if I was to decide to switch to a modern overdrive 5 speed, I would be looking for a low gear in the 2.8 to 3.1 range.

Re: starting line gear ratio?
 

This is what my software suggests.


Stan

Re: starting line gear ratio?
 

Back when I ran a stick in my car the SLR was about 19 to 1. With the same engine combo and a glide the SLR is 12 to 1. The engine is much better now and the car is about a second faster than it was with the stick.

Re: starting line gear ratio?
 

For what it’s worth, my brother ran a 58 Chevy wagon back in the 80’s in IHRA Super Stock (basically a econo modified engine). It was a 283 that weighed 3839 and ran a turbo 350 with a 6:83 Dana and 29 and 30 inch tires for the 1/8 and 1/4. The torque converter was pretty a good piece back then but could likely have been ran on the street now. The car held the IHRA class record before he bought it and did until he sold it. I don’t remember any 60’ numbers but the car got quicker after putting In a 2:75 low gear. Don Jackson

Re: starting line gear ratio?
 

How does engine cubic inch and an engine's ability to RPM factor into the SLR?

Re: starting line gear ratio?
 

I caught a little NHRA Stock qualifying highlights today from Topeka. I don't know much about this class really as far how elaborate the engines are allowed to be, or how much they have to weigh, but this car runs about like my n/a 23 degree sbc on 10" tire 69Nova.

What SLR do these class cars typically run? What transmission and how many rpm's do they typically cross? It was a current model Camaro, is it limited to an LS? I think the announcer said 409cid. Just curious, run pretty good seemed like.


https://i.imgur.com/LUQbPl3.png

Re: starting line gear ratio?
 

An FS/C car is not a traditional Stock Eliminator race car, it's a factory race car with no VIN. The factory race cars come with Ford 9" rear ends and engine combinations that may not be available in regular production-based cars.

A better comparison with a traditional production-based Stock Eliminator race car, might be a '99-'02 LS 346 V8 Camaro A/SA car. The current national record in A/SA is 9.65 at 136.3 mph.

A car like that would have a stock throttle body, stock intake manifold, stock heads with an NHRA-legal valve job, stock bore (plus up to .040"), stock stroke, stock compression ratio pistons, stock valve lift, stock rocker arm ratio, and so on, with a "metric" TH200 3-speed automatic transmission with no trans brake, an 8" converter, and 9x30" tubeless radial slicks.

Re: starting line gear ratio?
 

here's a more detailed chart borrowed from Cale Aransons Black Magic clutch website ..........lots of useful information there.

http://www.blackmagicclutches.com/index.html

Re: starting line gear ratio?
 

Very cool, thanks

I gotta find a way to watch/follow these cars more

Re: starting line gear ratio?
 

Rod: 350HP and 3600LB = 12.20 should be attainable.

Our Aspen Wagon NOP Stocker with 318 that put out actual
340 HP and weighed 3600 plus held the record @ 12.0 over
ten years ago.and ran 11.70 to 11.80 when needed.

It is an Auto so not comparable on ratios but shows what can be done on that HP/Weight.2.75 Low and 5:13 gear at Sea Level. 14.11 ratio and I think that stick would need a bunch more without a torque converter. 9.0x30 Radials (92.5 Cir.)

Re: starting line gear ratio?
 

While HP and weight are very important you cannot leave out tire size when talking about SLR.


Stan

Re: starting line gear ratio?
 

Stan,
I think I said" If traction is unlimited" or did I say available... ??

Re: starting line gear ratio?
 

Adger,
Size was to general a word to have used, I should have said Diameter.


Stan

Re: starting line gear ratio?
 

You get my vote for "Clueless Post Of The Year".....

Re: starting line gear ratio?
 

guys, thanks for the input. the charts are very neat. very possibly the Dick Miller 11.25 # was with a torque converter [didnt say in the book] and when you ad in torque multiplication, it changes everything.
with mine,as is, at 13.69, its high from Miller and low for both the 2 charts. however, I will rather be under geared than over reved at the stripe. plus I could just gain more MPH if the engine will continue to pull.

have to wait till Thanksgiving to run at Vegas [that just sucks-every track in the country is runnin' except Vegas]
Thanks again, all.
Rod in AZ

Re: starting line gear ratio?
 

It was a copo with a 409cid LS. The explanation may not be up to your standards, but at least I understand the announcer when he says "this is a copo.

Re: starting line gear ratio?
 

Need Help,2350# 15x33 tire,6.20 rear gear. going stick racing with G-Force 2000,Ram billet Clutch as reccomended by Mike @ Ram. tranmission is coming from G-Force with 3.167 1st,2.148 2nd,1.576 3rd1.250 4th 1.000 5th according to my calculation SLR of 19.63 ,engine makes 850@8750 and peak torque 595@6500 is this too much SLR ?

Re: starting line gear ratio?
 

That sounds like a lot to me in that light a
racecar and that HP!

Re: starting line gear ratio?
 

I’m thinking 4.56

Re: starting line gear ratio?
 

Yes that seems very high.


Without changing anything, I would think it would like launching in 2nd much better than 1st gear.


Stan

Re: starting line gear ratio?
 

Hey guys do the math for me and tell what you think.
987 Hp
5.83 rear gear
2.81 1st gear G force 2400
3200 lbs
33 x14.5 Goodyears
Really don’t want to go over 9500 but I can in 4th if I have to

Re: starting line gear ratio?
 

► 5.83 * 2.81 = 16.3823


Looks good to me. That is just about 1% different than I calculate as a good starting place.


Stan