It's Finally Available! The 981 GT4/Spyder Shorter Final Drive Ratio
10-30-2017, 10:39 AM
#76
Originally Posted by Mech33
Ideally youÂ’d optimize all gearing for your particular use. But itÂ’s not as simple as just increasing the final drive to drop your top speed to the highest youÂ’ll see on track. YouÂ’d want to analyze exactly what speed ranges you see on track most and optimize for those ranges in particular. Otherwise you may switch final drives and accidentally end up with less thrust on the key speed ranges of acceleration for your particular track config.
Really depends on the specific power curve, gear ratios, and application. Not as simple as a general rule, in my opinion...
Really depends on the specific power curve, gear ratios, and application. Not as simple as a general rule, in my opinion...
10-30-2017, 12:06 PM
#77
No. The thrust of the GT4 with the lower diff is higher if you compare each gear on their own (ie..1st gear vs 1st gear, 2nd gear vs 2nd gear...) between the two.
If you use speed to compare thrust then of course it might be different. You neglected the time factor if you only measure thrust at a specific speed. That is the reduction in time to get to a particular speed with the lower diff.
I am trying to simplify the acceleration matter because not everyone here is a mechanical engineer.
The end result is with 2 identical cars, the one with the lower diff will get to any particular speed faster as long as gearing permits. Period.
If you use speed to compare thrust then of course it might be different. You neglected the time factor if you only measure thrust at a specific speed. That is the reduction in time to get to a particular speed with the lower diff.
I am trying to simplify the acceleration matter because not everyone here is a mechanical engineer.
The end result is with 2 identical cars, the one with the lower diff will get to any particular speed faster as long as gearing permits. Period.
The 4.62 car has a big advantage in 1st gear, so in a “drag race” starting from a stand still the 4.62 car will get the jump.
But start that “race” while rolling at higher speeds side by side and stop when you run out of road, and it’s no longer clear which car will out accelerate the other.
You never use 1st gear on a track, so which car is faster on a given track layout where they are accelerating over different speed ranges between every turn becomes a lot harder to determine.
10-31-2017, 09:24 AM
#78
Which car will get from speed 1 to speed 2 the fastest depends on speed 1 and speed 2.
The 4.62 car has a big advantage in 1st gear, so in a “drag race” starting from a stand still the 4.62 car will get the jump.
But start that “race” while rolling at higher speeds side by side and stop when you run out of road, and it’s no longer clear which car will out accelerate the other.
You never use 1st gear on a track, so which car is faster on a given track layout where they are accelerating over different speed ranges between every turn becomes a lot harder to determine.
The 4.62 car has a big advantage in 1st gear, so in a “drag race” starting from a stand still the 4.62 car will get the jump.
But start that “race” while rolling at higher speeds side by side and stop when you run out of road, and it’s no longer clear which car will out accelerate the other.
You never use 1st gear on a track, so which car is faster on a given track layout where they are accelerating over different speed ranges between every turn becomes a lot harder to determine.
I have driven countless cars with modified diff and they always accelerate faster up to top speed after the diff modification.
The 4.62 car will have an acceleration advantage in every single gear while scarifies in fuel economy and top speed.
The 4.62 car's advantage will be most obvious on a twisty mountain road or in a car racing environment.
10-31-2017, 05:33 PM
#79
I have driven countless cars with modified diff and they always accelerate faster up to top speed after the diff modification.
The 4.62 car will have an acceleration advantage in every single gear while scarifies in fuel economy and top speed.
The 4.62 car's advantage will be most obvious on a twisty mountain road or in a car racing environment.
The 4.62 car will have an acceleration advantage in every single gear while scarifies in fuel economy and top speed.
The 4.62 car's advantage will be most obvious on a twisty mountain road or in a car racing environment.
10-31-2017, 07:52 PM
#80
Back in the day, I raced an MGB. There was only one set of optional close ratio gearbox gears we all ran. I had 6 different rear axle ratios (3.90, 4.11, 4.30, 4.55, 4.88, and 5.12). I could change them at the track as I had carriers with the pinion gear already set up and just swapped out my one Detroit Locker LSD and ring gear. I choose the ratio needed to hit redline just before the brake zone of the longest straight. On track, just changing out the final drive on a GT4 will gain little. I am rarely using 2nd gear and when I do, it goes to 82 mph. On most tracks I run, you need 5th gear on the longest straight. A shorter rear axle ratio will just allow you to shift earlier. A close ratio gear box would be an improvement.
11-02-2017, 11:32 PM
#81
Advanced
What will happen is there will be speeds where the lower diff car will have to be in 3rd, but the stock car could be in 2nd and accelerate better. Much better (higher revs so more power and better gear ratio, double bonus)
The graphs above show that, advantage at some times, but have to change gear and you lose the advantage. It’s more often in a gain, but it’s “small gain often, big loss occasionally”
The problem with the gearbox is not so much the final ratio, it’s the split between the lower gears is too big, you change from 2nd and the revs drop too much. Changing final diff doesn’t fix that, only changing individual ratios to make it a close ratio gearbox does. That helps and give overall gains because it can actually increase average power - it keeps revs up and power up.
Changing final diff ratio doesn’t change the average power across the rev range for each gear, so doesn’t really gain much (if anything) across any typical range of speeds.
11-27-2017, 01:29 PM
#83
Three Wheelin'
12-01-2017, 04:29 PM
#84
Former Vendor
Thread Starter
Getting that is one of my top priorities. We would have had some from the amazing weekend at Sebring two weekends ago but we had some issues with our GoPro equipment, and the streets around the shop are very heavily populated this time of year. We'll make it happen though one way or another 
Last edited by AutoQuest Motorsports; 12-01-2017 at 04:46 PM.
12-16-2017, 11:43 AM
#86
Rennlist Member
+1
12-19-2017, 07:53 PM
#88
Rennlist Member
Interested in the side by side as well.
Thanks.
Thanks.
12-20-2017, 09:07 PM
#89
Former Vendor
Thread Starter
Thanks for all the interest! I reached out to a few guys to chime in as they get some more seat time with it, and I have some video recording equipment ordered to do some comparison videos : )
01-15-2018, 11:42 AM
#90
What do you mean by "reinforced"? Is the weld on both 3rd and 6th just stronger, or are the synchros splined?
Also are there any feedback reports on those first installations?