Gears & Axles - What will happen to 1/4 mph after gear swap?
06-09-2012, 11:29 PM
This is a non F-body question:offtopic::angel:
Hoping you guy's can help me figure out what will happen to my finishing 1/4 mph.
I swapped the gear ratio in my GXP, and went from a 2.93 to a 3.69
Last year I crossed the line doing 12.7's@110ish toping 2nd gear (6500-6800)
I shift at 6500rpm, and my car really comes on hard after 5000rpm, so I am a little worried about 3rd gear.
Trans ratios are:
3.69 finial drive w/26" tire
Will I trap 110mph at 5200-5300rpm? Or will I trap less now, since 3rd will have to recover from 4500-4600 rpm after the shift? My 1/8th mile mph was 87mph last year and this is where the trans shifts into 3rd now. I can't see a 22mph gain in 600-700rpm.
Yes it's a FWD... I already know:violin:
06-10-2012, 12:01 AM
I can't really help bc I'm not a calculator kinda guy but I can't see I hurting the ET or the MPH, but in the end does it matter if you ET quicker what the MPH is? By the way, where do you race at? I lived up there about 10 years ago.
06-10-2012, 12:25 AM
By the way, where do you race at? I lived up there about 10 years ago.
Pacific Race Ways or SIR
06-10-2012, 04:00 AM
You will be close to 5k in 3rd with that gearing change. That wouldn't be a bad setup. Is the car a street driven car?
06-10-2012, 09:59 AM
Yes, its street driven.
The gears have made a huge difference when accelerating. 3rd gear feels a little weak until 5000rpm.
5.3 with pat g cam, ls6 p&p heads, ls6 intake, headers, and 3" exhaust.
I haven't made any new passes with the upgraded heads and gears yet though. Hopefully in a week or two.
Best et was email@example.com
1.9 60ft last may
06-10-2012, 01:16 PM
I would work on the 60' time. Get some good tires on there and you will definitely pick up some time.
06-10-2012, 03:09 PM
With the 3.69 @ 110 you'll be doing 52-5300 rpm through the lights in 3rd. That's below your power peak, I think you may slow down.
06-10-2012, 03:41 PM
you have to account for RPM lost with shifting. You won't drop to the exact RPM through gear changes because you lose speed when you shift. The RPM will be lower than 5200 because of this.
Ideally you want to set up your gearing so that you are crossing the line just after power peaks. This can make the car a little less than fun to drive if it's a daily driver though.
06-18-2012, 12:47 AM
Went racing last Friday, and trapped 110.58 and 110.2's all night long. So I am happy to report that I didn't loose any speed. My 1/8th mile mph is now 88.8 so I picked up a full mph.
Traction was horrible, so I was only getting 2.2-21 60 ft. I was still running low 12.9's though...
06-18-2012, 12:51 AM
;16404008'] Ideally you want to set up your gearing so that you are crossing the line just after power peaks. This can make the car a little less than fun to drive if it's a daily driver though.
This is true, and it's what I was afraid of. I am crossing at 5200-5400
I was dyno'd last week and put down 349@6000 hp and 334@4900 tq
06-18-2012, 07:21 PM
Right on, it's a little less than ideal for the track, but it's a street car. You don't want to ruin it lol