What Rear End and Gears is Everyone Using?
07-27-2015, 09:27 PM
#1
Staging Lane
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What Rear End and Gears is Everyone Using? Hey guys,
Well just got back from the track this past weekend, everything went great and I didn't break anything... Or so I thought... Long story short, went to a car show a few days later and leaving the car show as soon as I pulled out of my spot I was surprised with 3 loud clunks.. moved forward a little bit more and same thing.. Thankfully I was only 2 miles away from home and was able to get my car back.
Figuring I must have sheered some teeth off of a gear, I'll be putting it up in the air and pulling it apart tomorrow but until then I got to wondering what everyone else is using with their road race machines?
Well just got back from the track this past weekend, everything went great and I didn't break anything... Or so I thought... Long story short, went to a car show a few days later and leaving the car show as soon as I pulled out of my spot I was surprised with 3 loud clunks.. moved forward a little bit more and same thing.. Thankfully I was only 2 miles away from home and was able to get my car back.
Figuring I must have sheered some teeth off of a gear, I'll be putting it up in the air and pulling it apart tomorrow but until then I got to wondering what everyone else is using with their road race machines?
07-28-2015, 12:10 PM
#2
Great question. First, I'm sorry to hear about the carnage.
So much depends on your setup and the tracks you like to run. I've run both 3.90 and 4.10 on track and can attest that they are not ideal for the tracks I enjoy the most. No shocker here -- they're great on the street, however the extra shifting on track isn't desireable.
I've spent a good time playing around on the rear gear calculators to try to determine the optimal setup for my car at Road Atlanta and I'm thinking a 3.73 would be the best.
I'm inclined to give it a go with the stock 3.42's next time I shred a ring/pinion --- it would certainly eliminate a bunch of shifts and would expand the top end range of 4th gear considerably, however I wonder how much the car would suffer in powering through the gap speeds where you're too fast to go down a gear.
Now, your setup is a completely different animal. You have plenty of torque to power through down low, so in the absence of having a very aggressive cam profile, I would be inclined to run a taller rear gear in favor of traction and top end.
So much depends on your setup and the tracks you like to run. I've run both 3.90 and 4.10 on track and can attest that they are not ideal for the tracks I enjoy the most. No shocker here -- they're great on the street, however the extra shifting on track isn't desireable.
I've spent a good time playing around on the rear gear calculators to try to determine the optimal setup for my car at Road Atlanta and I'm thinking a 3.73 would be the best.
I'm inclined to give it a go with the stock 3.42's next time I shred a ring/pinion --- it would certainly eliminate a bunch of shifts and would expand the top end range of 4th gear considerably, however I wonder how much the car would suffer in powering through the gap speeds where you're too fast to go down a gear.
Now, your setup is a completely different animal. You have plenty of torque to power through down low, so in the absence of having a very aggressive cam profile, I would be inclined to run a taller rear gear in favor of traction and top end.
07-28-2015, 02:09 PM
#3
Staging Lane
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Great question. First, I'm sorry to hear about the carnage.
So much depends on your setup and the tracks you like to run. I've run both 3.90 and 4.10 on track and can attest that they are not ideal for the tracks I enjoy the most. No shocker here -- they're great on the street, however the extra shifting on track isn't desireable.
I've spent a good time playing around on the rear gear calculators to try to determine the optimal setup for my car at Road Atlanta and I'm thinking a 3.73 would be the best.
I'm inclined to give it a go with the stock 3.42's next time I shred a ring/pinion --- it would certainly eliminate a bunch of shifts and would expand the top end range of 4th gear considerably, however I wonder how much the car would suffer in powering through the gap speeds where you're too fast to go down a gear.
Now, your setup is a completely different animal. You have plenty of torque to power through down low, so in the absence of having a very aggressive cam profile, I would be inclined to run a taller rear gear in favor of traction and top end.
So much depends on your setup and the tracks you like to run. I've run both 3.90 and 4.10 on track and can attest that they are not ideal for the tracks I enjoy the most. No shocker here -- they're great on the street, however the extra shifting on track isn't desireable.
I've spent a good time playing around on the rear gear calculators to try to determine the optimal setup for my car at Road Atlanta and I'm thinking a 3.73 would be the best.
I'm inclined to give it a go with the stock 3.42's next time I shred a ring/pinion --- it would certainly eliminate a bunch of shifts and would expand the top end range of 4th gear considerably, however I wonder how much the car would suffer in powering through the gap speeds where you're too fast to go down a gear.
Now, your setup is a completely different animal. You have plenty of torque to power through down low, so in the absence of having a very aggressive cam profile, I would be inclined to run a taller rear gear in favor of traction and top end.
Are you still running with the stock 10-bolt? The next gear set I wanted to try out would be 3.73s as well.
The track I was at was Autobahn Country Club (south course 2.1 miles), and I do/had planned on running similar type courses (Grattan, Gingerman, Mid Ohio, etc.).
Braking was already (and still is) my major point of focus, so I was already saving up for larger wheels to accommodate a big brake kit until this happened. I'd love to not have to dump $3k+ for a new rear end but thinking about it, I'm not sure what is ideal for 4th gens on a road course anymore. So now I'm kind of questioning what direction to go all together.
When I was around the racing scene at my prior job, the (few) SCCA 4th gens I saw were still running 10-bolts. With that in mind when I built my car, it was the major reason I kept my 10-bolt.
Either way, I'm a little frustrated in determining what to do moving forward, any other input is much appreciated!
07-28-2015, 02:37 PM
#4
TECH Addict
You can build a 10-bolt to be plenty strong. A lot of the more dedicated road course vehicles over on lat-g are using 3.55-3.73 gears out back, even with T56 trannies.
But each situation is different. If you know the rpm range you want to be in, with your motor, in your car, on your track... Then look at your transmission gearing, and pick a rear gear that puts you in the transmission gear you want, at the rpms you want.
It's not rocket surgery, and quite frankly, it doesn't matter what everyone else is using unless everyone else is driving your car on your track.
But each situation is different. If you know the rpm range you want to be in, with your motor, in your car, on your track... Then look at your transmission gearing, and pick a rear gear that puts you in the transmission gear you want, at the rpms you want.
It's not rocket surgery, and quite frankly, it doesn't matter what everyone else is using unless everyone else is driving your car on your track.
07-28-2015, 08:16 PM
#5
3.42 gears, 8.5" 10-bolt, with TrueTrac diff. The diff unit *just* got replaced because of excessive slop/noise after roughly 3000 miles of road race use. I do wonder if the fact that it was made in Taiwan had anything to do with its short life. We'll see how the the new one holds up.
FWIW, the symptom I was getting was a clunking when I got off the gas. Going under the car for inspection, turning the drive shaft with the car in neutral, I would get about 15 degrees of play in the diff (not gears, those were still lashed within spec) before the wheels moved. New diff has almost zero play.
FWIW, the symptom I was getting was a clunking when I got off the gas. Going under the car for inspection, turning the drive shaft with the car in neutral, I would get about 15 degrees of play in the diff (not gears, those were still lashed within spec) before the wheels moved. New diff has almost zero play.
07-29-2015, 10:39 AM
#6
I don't road race and only autocross but I put in a Eaton TruTrac. A lot better than the stock unit, but I can still get the passenger rear tire to spin under RH turns occasionally. This is also on toasted 275/40/17 Khumo V710's.
07-29-2015, 03:59 PM
#7
99% of people stick with 3:42. You need to gear the car to top out in 4th, 5th is too steep for these cars to pull effectively on a road course. Also, you want to minimize shifting.
Good luck with the 10 bolt. If you have higher than stock power levels, be prepared to chew through diffs like candy. Also if you run sticky tires, you will obliterate axle bearings. Yes, lots of A-sedan and CMC cars still use a 10 bolt, but they replace axle bearings after every event. I get one track day out of a set on sticky rubber. Granted, I push the car pretty hard. I'm at bolt on power levels, and I've gone through 2 rears in 3 years. I tried like hell to make the 10 bolt work, but in the end it was just a waste of money because it prevents me from truly enjoying the car.
Good luck with the 10 bolt. If you have higher than stock power levels, be prepared to chew through diffs like candy. Also if you run sticky tires, you will obliterate axle bearings. Yes, lots of A-sedan and CMC cars still use a 10 bolt, but they replace axle bearings after every event. I get one track day out of a set on sticky rubber. Granted, I push the car pretty hard. I'm at bolt on power levels, and I've gone through 2 rears in 3 years. I tried like hell to make the 10 bolt work, but in the end it was just a waste of money because it prevents me from truly enjoying the car.
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07-29-2015, 05:36 PM
#8
99% of people stick with 3:42. You need to gear the car to top out in 4th, 5th is too steep for these cars to pull effectively on a road course. Also, you want to minimize shifting.
Good luck with the 10 bolt. If you have higher than stock power levels, be prepared to chew through diffs like candy. Also if you run sticky tires, you will obliterate axle bearings. Yes, lots of A-sedan and CMC cars still use a 10 bolt, but they replace axle bearings after every event. I get one track day out of a set on sticky rubber. Granted, I push the car pretty hard. I'm at bolt on power levels, and I've gone through 2 rears in 3 years. I tried like hell to make the 10 bolt work, but in the end it was just a waste of money because it prevents me from truly enjoying the car.
Good luck with the 10 bolt. If you have higher than stock power levels, be prepared to chew through diffs like candy. Also if you run sticky tires, you will obliterate axle bearings. Yes, lots of A-sedan and CMC cars still use a 10 bolt, but they replace axle bearings after every event. I get one track day out of a set on sticky rubber. Granted, I push the car pretty hard. I'm at bolt on power levels, and I've gone through 2 rears in 3 years. I tried like hell to make the 10 bolt work, but in the end it was just a waste of money because it prevents me from truly enjoying the car.
07-30-2015, 01:39 PM
#10
Staging Lane
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Well got everything torn apart and yes I toasted the posi and pinion. For now I decided to go with the truetrac and try out 3.73 gears to see how I like them on the track (also because I am able to get a very sizable discount on these parts). At least this will give me a good point to start at so I can start planning on what I want to use when I build a different rear end and go from there.
Thanks for the feedback everyone, its always nice to get everyone else's opinions and experiences to take into consideration!
Thanks for the feedback everyone, its always nice to get everyone else's opinions and experiences to take into consideration!
07-30-2015, 03:18 PM
#11
I have 4th gen brakes on mine, but deleted the e-brake due to the bearing clearance issue.
07-30-2015, 04:02 PM
#12
Good to know they offer that product now, solves some issues. No need for a parking brake on a track car, I removed mine also.
The other big issue is the 7.5 diff. They are simply too small to handle LS1 power levels. The trutrac is ok, but could use more bias ratio (can get inside wheel spin) and the auburn racers diff lasted 1.5 seasons for me. The larger 8.5 ten bolt does not have these same issues due to the added beef.
The other big issue is the 7.5 diff. They are simply too small to handle LS1 power levels. The trutrac is ok, but could use more bias ratio (can get inside wheel spin) and the auburn racers diff lasted 1.5 seasons for me. The larger 8.5 ten bolt does not have these same issues due to the added beef.