Starting line ratio for manual transmission application

[tavbfl]

This may be common knowledge for those in the stock/super stock community, but searching the internet only comes up with automatic info.
My slr is 14.19 with a 5.14 and I cross the finish line 500 rpm below peak hp. Changing to a 5.57 would change it to 15.6 and I'm concerned as to whether it would be a gain or a loss for et as well as consistency. Thanks in advance for any insight, Tony Aiello.

[Dave Noll]

The SLR in my automatic Cougar is 18.1 & my EF/S Stick Escort is 12.1. I may be changing the Cougar to 19.6 & the Escort to 13.5. The Cougar I'm trying to get to the "Airing Out" point. The Escort I'm just trying to get more.

[Rory McNeil]

My starting line ratio is 16.39, and I drop the clutch at 6000-6600 RPM, and run similar 1/8th mile numbers to you, although I run on 1/4 tracks.It looks like you have plenty of tire,so I see no reason why your consistency should suffer at all, provided you are somewhere close on your clutch setup. I always like to be crossing the finish line a little higher than my shift RPM. Are you 60 foot and 330 numbers pretty consistent now?

[Nmbr1GMfan]

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[Jim Caughlin]

Originally Posted by Nmbr1GMfan

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Oh man, I'm completely off the chart 21.4 with a 28" tall tire...

[Mike Pearson]

When I ran a stick in my super stock car the SLR was about 19 to 1 3.11 low gear and 6.17 in the rear. Had to yank the handle real quick low to second.

[Rory McNeil]

I am assuming the original poster must have a low gear ratio of 2.76, which is quite tall for a drag car, especially as it looks like he has a fairly big tire on there. Going to 5.57s should increase his trap RPM around 600 RPM, but I would also be looking for a lower first gear in the transmission. What the current 60 foot and 330 numbers, and what size tires on the car would be helpful.

[tavbfl]

Thank you all for your comments! The chart from Black Magic was exactly what I was looking for. To answer some of your questions, my 60 ft has been between 1.38 and 1.46, 330 ft between 4.10 and 4.15, and my first gear is 2.80. Finding gears for the Doug Nash is a challenge so this can be my callout to any racers that have them in a box on the shelf somewhere. I am looking to change to 5.57 gears as I am crossing at 6300 with the 5.14's and motor makes power to 7000. I am also dialing in a slipper clutch for the first time so it's a matter of optimizing my combo and then focusing on consistency.

[bykr]

Originally Posted by Mike Pearson

When I ran a stick in my super stock car the SLR was about 19 to 1 3.11 low gear and 6.17 in the rear. Had to yank the handle real quick low to second.

Real close to my #'s 3.28 and 6.20's. 2nd gear has to be in about 1 second.

[Jim Caughlin]

Originally Posted by bykr

Real close to my #'s 3.28 and 6.20's. 2nd gear has to be in about 1 second.

The shift light is on in my car about as fast as I dump the clutch, I'm in 2nd well before the 60' timer. Looking at the data logger, the engine never drops below 6,000 and is at 8400 within 1 second. That's with a 3.29 1st gear, 6.50 rearend and 28" tall tire. I would guess that your car would be about the same. The ratio is so low that I usually drive around the pits in 2nd gear, I can outwalk the car in 1st!