starting line gear ratio?

rod · 08-12-2021, 07:08 PM

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

Adger Smith · 08-12-2021, 07:49 PM

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...

Jim Caughlin · 08-12-2021, 08:33 PM

How about 21.39?

Jim Caughlin
SS/ES 6019

6130 · 08-12-2021, 09:06 PM

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

6130 · 08-12-2021, 09:14 PM

Quote:

Originally Posted by rod

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]

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.

older racer · 08-12-2021, 11:23 PM

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

Rory McNeil · 08-13-2021, 08:00 AM

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.

Stan Weiss · 08-13-2021, 09:24 AM

This is what my software suggests.

Stan

Mike Pearson · 08-13-2021, 10:31 AM

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.

Bench Racer · 08-15-2021, 10:06 AM

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

08-12-2021, 07:08 PM	#1
rod Member Join Date: Dec 2009 Location: Kingman, NW AZ. in the middle of the longest stretch of Route 66 Posts: 314 Likes: 0 Liked 20 Times in 15 Posts	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

08-12-2021, 07:49 PM	#2
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	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... __________________ Adger Smith (Former SS) Last edited by Adger Smith; 08-12-2021 at 08:01 PM. Reason: add

08-12-2021, 08:33 PM	#3
Jim Caughlin Senior Member Join Date: Mar 2002 Location: Woodburn, Or Posts: 685 Likes: 82 Liked 805 Times in 245 Posts	Re: starting line gear ratio? How about 21.39? Jim Caughlin SS/ES 6019

08-12-2021, 09:06 PM	#4
6130 Member Join Date: Jul 2012 Location: Texas Posts: 409 Likes: 295 Liked 117 Times in 50 Posts	Re: starting line gear ratio? Tire height, flywheel weight, clutch, torque curve, and so many other things would factor into this. Last edited by 6130; 08-12-2021 at 09:14 PM.

08-12-2021, 11:23 PM	#6
older racer Member Join Date: Aug 2010 Posts: 212 Likes: 13 Liked 68 Times in 26 Posts	Re: starting line gear ratio? watched vid on 289 mustang, ss/L 20.398 start ratio

08-13-2021, 08:00 AM	#7
Rory McNeil VIP Member Join Date: Jun 2007 Location: from Vancouver BC Canada, now in Nova Scotia Posts: 1,311 Likes: 317 Liked 1,103 Times in 301 Posts	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. __________________ NHRA 6390 STK M/S 85 Mustang

08-13-2021, 09:24 AM	#8
Stan Weiss Senior Member Join Date: Apr 2020 Location: Phila, PA Posts: 794 Likes: 0 Liked 733 Times in 384 Posts	Re: starting line gear ratio? This is what my software suggests. Stan Attached Thumbnails

08-13-2021, 10:31 AM	#9
Mike Pearson VIP Member Join Date: Mar 2007 Posts: 2,446 Likes: 614 Liked 1,919 Times in 576 Posts	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. __________________ Mike Pearson 2485 SS

08-15-2021, 10:06 AM	#10
Bench Racer Member Join Date: May 2002 Location: Green Creek (Tryon) North Carolina Posts: 331 Likes: 69 Liked 99 Times in 21 Posts	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