From 4.11's to 2.80 gears...track results
09-17-2009, 02:57 AM
#1
From 4.11's to 2.80 gears...track results In my rx7 I hurt the 3rd member so I took out the 4.11's and put in some 2.80 gears as a quick fix for now until I can get 3.55's in it. I also should mention I'm running a 315/60/15 mt drag radial, so a 30" tire, an a th400 with a 8" coan nitrous converter(about 3600rpm in my light car, was a 4000 in my firebird). These gears make the car drive nice, 2300rpms at 75mph. Also on the street the car LOVES these gears, leave on motor and spray 30ft out no spinning!
Before/after results...
Motor passes...
60ft.. before 1.480....after 1.589
1/8th before 6.843....after 7.028
mph.. before 100.22....after 98.38
1/4... before 10.765....after 11.021
mph.. before 125.45....after 123.03
Before:
http://www.youtube.com/watch?v=NAh6asKK4hE
After:
http://www.youtube.com/watch?v=SVSiqtkN-ZI
Only difference is the gear and in 1st I'm spinning it only to 6000 or so vs before 6500. With the new gear it goes through traps around 6500rpm in 2nd, before around 6400rpm in 3rd.
100 shot passes...
60ft.. before 1.470....after 1.606
1/8th before 6.544....after 6.665
mph.. before 105.43....after 106.39
1/4... before 10.287....after 10.366
mph.. before 129.34....after 131.86
Before:
http://www.youtube.com/watch?v=kn8gLXw7ahQ
After:
http://www.youtube.com/watch?v=0z8BGbNWYs4
I was spraying around 60ft out on both these passes. Before with the 4.11's I was running out of gear, I'd quit spraying it around 6200rpm and run it out the back down on motor up to 6700-6800rpm. With the new gear I shift to 3rd so I don't run out of gear, although that 3rd gear change not far from the traps probably isn't helping me. Also the new passes with the nitrous I wasn't spraying through the shifts like I did before. The car has done 131.98 with the 4.11's on another pass when I spun and quit spraying at 6200rpm and went through traps at 6900-7000.
I'll try to hit the track again Friday to see if spraying out the gate will get me a 1.4x 60ft again. Just thought it was interesting, took out A LOT of gear and lost a tenth in the 60ft on motor and 2.5 tenths on the back end and 2.5mph(didn't expect to lose the mph)
Before/after results...
Motor passes...
60ft.. before 1.480....after 1.589
1/8th before 6.843....after 7.028
mph.. before 100.22....after 98.38
1/4... before 10.765....after 11.021
mph.. before 125.45....after 123.03
Before:
http://www.youtube.com/watch?v=NAh6asKK4hE
After:
http://www.youtube.com/watch?v=SVSiqtkN-ZI
Only difference is the gear and in 1st I'm spinning it only to 6000 or so vs before 6500. With the new gear it goes through traps around 6500rpm in 2nd, before around 6400rpm in 3rd.
100 shot passes...
60ft.. before 1.470....after 1.606
1/8th before 6.544....after 6.665
mph.. before 105.43....after 106.39
1/4... before 10.287....after 10.366
mph.. before 129.34....after 131.86
Before:
http://www.youtube.com/watch?v=kn8gLXw7ahQ
After:
http://www.youtube.com/watch?v=0z8BGbNWYs4
I was spraying around 60ft out on both these passes. Before with the 4.11's I was running out of gear, I'd quit spraying it around 6200rpm and run it out the back down on motor up to 6700-6800rpm. With the new gear I shift to 3rd so I don't run out of gear, although that 3rd gear change not far from the traps probably isn't helping me. Also the new passes with the nitrous I wasn't spraying through the shifts like I did before. The car has done 131.98 with the 4.11's on another pass when I spun and quit spraying at 6200rpm and went through traps at 6900-7000.
I'll try to hit the track again Friday to see if spraying out the gate will get me a 1.4x 60ft again. Just thought it was interesting, took out A LOT of gear and lost a tenth in the 60ft on motor and 2.5 tenths on the back end and 2.5mph(didn't expect to lose the mph)
Last edited by skinnies; 09-17-2009 at 05:42 AM.
09-17-2009, 07:59 AM
#5
On The Tree
Join Date: Apr 2009
Location: canton MI
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you must have a m6 i took the 2.73 stock posi out on my a4 car and put a ten bolt with a 3.42 gear posi out of a m6 car into mine and im at around 2500 at 75
09-17-2009, 08:58 AM
#6
nice, it's the torque these Lt1's make then on n2o it's that much better. I just put some 29.5x10.5" slicks on my T/A and it really likes the taller tire. I can't wait to spray it and see how it works. You need to have the n2o coming on much sooner and you could be running 9's. Good luck and glad to see your out racing again. Later Clint
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09-17-2009, 03:05 PM
#10
nice, it's the torque these Lt1's make then on n2o it's that much better. I just put some 29.5x10.5" slicks on my T/A and it really likes the taller tire. I can't wait to spray it and see how it works. You need to have the n2o coming on much sooner and you could be running 9's. Good luck and glad to see your out racing again. Later Clint
I will next time, it's a stock shortblock with 90k mile on it and was heads/cam before I got the shortblock so it's had a hard life. I'm going back Friday to try to make some more passes, might be all bottle passes though seeing as I couldn't get in many passes Wednesday night.
09-18-2009, 08:58 AM
#14
The difference in you MPH on motor with the two gears is probably directly related to changing you shift points. I would bet the MPH would be very close if you shifted at 6500 like you did before.
I leave in second gear every once in a while, and when I do I always go 2 tenths slower with the same MPH. I have a TH350 with a 4.11 gear. From my calculation leaving in second gear would give me a similar gear ratio off the line to having a 2.50 gear.
I leave in second gear every once in a while, and when I do I always go 2 tenths slower with the same MPH. I have a TH350 with a 4.11 gear. From my calculation leaving in second gear would give me a similar gear ratio off the line to having a 2.50 gear.
