Need advice on rear end gears (4:11-5:38) Drag only
03-03-2003, 08:32 PM
#16
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Join Date: Mar 2000
Location: 51°N 114°W, 3500' elevation
Posts: 2,037
Originally posted by Joe Brodman
At 6200 RPM, stock tires (about 25.66"), 3.73 gears, in 4th (6-speed) or 3rd (4L60E) aka your 1:1 tranny ratio, your speed would be: 126.94
What formula did I use. The following:
MPH = (RPM x Tire diameter (in inches)) / (tranny ratio x rear end ratio x 336)
Now remember, that formula does NOT take into account a couple factors, such as any driveline slippage, which you should hope you don't have), and tire growth.
At 6200 RPM, stock tires (about 25.66"), 3.73 gears, in 4th (6-speed) or 3rd (4L60E) aka your 1:1 tranny ratio, your speed would be: 126.94
What formula did I use. The following:
MPH = (RPM x Tire diameter (in inches)) / (tranny ratio x rear end ratio x 336)
Now remember, that formula does NOT take into account a couple factors, such as any driveline slippage, which you should hope you don't have), and tire growth.
Assuming you're crossing the finish line at 6200 rpm with those above tires and gears, a tight converter with 7.8% slippage will mean you're doing 117 mph at the finish instead of 127. A loose converter with 11.8% slippage drops your mph down to 112. Simply by using a tighter converter, you can increase your mph with no changes to the engine.
03-03-2003, 09:12 PM
#17
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Join Date: Nov 1999
Location: Columbus, Ohio
Posts: 645
Originally posted by Stephen 87 IROC
Typically you can estimate anywhere from 8-12% slippage through the converter. All converters slip. It depends on the size and the stall speed so no 2 are the same.
Assuming you're crossing the finish line at 6200 rpm with those above tires and gears, a tight converter with 7.8% slippage will mean you're doing 117 mph at the finish instead of 127. A loose converter with 11.8% slippage drops your mph down to 112. Simply by using a tighter converter, you can increase your mph with no changes to the engine.
Typically you can estimate anywhere from 8-12% slippage through the converter. All converters slip. It depends on the size and the stall speed so no 2 are the same.
Assuming you're crossing the finish line at 6200 rpm with those above tires and gears, a tight converter with 7.8% slippage will mean you're doing 117 mph at the finish instead of 127. A loose converter with 11.8% slippage drops your mph down to 112. Simply by using a tighter converter, you can increase your mph with no changes to the engine.
Not everyone runs an auto
12-14-2003, 01:00 AM
#18
Registered User
Thread Starter
Join Date: Dec 1998
Location: Cleveland, Ohio
Posts: 455
Hi guys, it's time to put this topic to rest. It's been a long summer of fun with the car and I am here to post the results of my progress.
First I went with 4:56 gears over my 3:73's. for the first 3/4 of the summer. I tested them at a private track rental, and with a 150 shot, stock shocks, springs, front tires, I went 11.41@ 119 mph shifting into 5th spinning off the line (no 60' # I can't find that time slip but I have it on video). I broke the trans at the end of that day so the car was out for about a month and a half while the trans got a real nice rebuild w/ a viper out put shaft. Next went on the QA/1's front & rear, upgraded sway bars, and skinnies. It went 11.213 @ 121.83 60' 1.507 (that pulled both front wheels about 6+" 2x, 1 at launch and 1 into 2nd. shifting into 5th at about 990-1000'. That was the quickest E.T. of the summer, hell it was the best ever. Later on the track went away and I ran higher in the 11's. I was upset about not duplicating my time, but it was alot of fun. It was so much fun I kept the car in full drag gear for about 2 months and drove it on the street. It was fun as hell under 100 MPH then it feels like it falls on it's face. It felt slower but N/A it would et a little quicker and run the trap about the same (-.5 MPH.). Just a quick side note here, a really cool trick with a set up like mine is hopping the front wheels about 12" up at a 20 MPH roll. Now understand when I say this, it's a cool "TRICK" I am not claiming that the car has the HP to just yank the front off the ground at will. I am stating it's a trick, so here it its... simply put the car in 1st gear go about 15-20 MPH mash the gas 2x in order to get the momentum working for you. after you let off the gass for the 2nd time the K-member should scrape the ground, then mash the gas agin and hit the N2O. The SOTP feel is wild. the hedders & k-member get scrapped up a bit, but that's what it's for. Any way back to the gear comparo. At the end of the year I went to smack down @ Norwalk. I really wanted my 10 sec pass, so I jetted up to a 200 shot. But, after listening to count less people tell me that shifting into 5th is bad I caved in and put the 3:73's back in. I am sure most of you know what smack down is, but for those that don't, smack down is an open event, but 99% of the cars there are fords. So I made a few passes N/A on street tires just to lay low. Need less to say most of the 03 cobra guys, and GT power adder guys thought they would dog the only 4th gen f-body there (an SS to boot), after bosting 4 runs ranging from 13.1-13.5 @ 109-110 MPH. Then I took the gloves off threw on the wheels and tires, and turned on the nitrous. I went a best of 11.43 @ 122.5, again I don't have the slip, but I have the video, and it launched verry well, but at the launch the car bogged down every time, and I launched at 5900-6000 RPM. Then I jetted up to the 200 shot I went 11.415 @126.02 (5500k launch speed) 60'1.880, and that was it. The bottle went dry and the track closed.
So 4:56's cut .22 off my ET and where .7 faster than 3:73 gears with the same shot (150). The 4:56's where not tested with the 200 shot. I dynoed 475 HP 510 TQ on a 150 shot. No Dyno time w/200 shot. 3:73's are much better for street/HWY than the 4:56's, but that's not saying 4:56's are bad, 3:73's just feel better. If you don't care about the "feel" of the car on top and mostly street drive the car 4:56's are verry verry fun, also the top speed w/4:56's was GPS'd @169, on nitrous in 6th, I was not watching the tach so I don't know where the RPM was. Which brings me to another point... Gears are cheap, cheap enough to have a couple of sets. I can change my gear ratio in under 30 min. so I will add a set of 4:10's to the collection by spring, and go with a 28" tire, and start again.
First I went with 4:56 gears over my 3:73's. for the first 3/4 of the summer. I tested them at a private track rental, and with a 150 shot, stock shocks, springs, front tires, I went 11.41@ 119 mph shifting into 5th spinning off the line (no 60' # I can't find that time slip but I have it on video). I broke the trans at the end of that day so the car was out for about a month and a half while the trans got a real nice rebuild w/ a viper out put shaft. Next went on the QA/1's front & rear, upgraded sway bars, and skinnies. It went 11.213 @ 121.83 60' 1.507 (that pulled both front wheels about 6+" 2x, 1 at launch and 1 into 2nd. shifting into 5th at about 990-1000'. That was the quickest E.T. of the summer, hell it was the best ever. Later on the track went away and I ran higher in the 11's. I was upset about not duplicating my time, but it was alot of fun. It was so much fun I kept the car in full drag gear for about 2 months and drove it on the street. It was fun as hell under 100 MPH then it feels like it falls on it's face. It felt slower but N/A it would et a little quicker and run the trap about the same (-.5 MPH.). Just a quick side note here, a really cool trick with a set up like mine is hopping the front wheels about 12" up at a 20 MPH roll. Now understand when I say this, it's a cool "TRICK" I am not claiming that the car has the HP to just yank the front off the ground at will. I am stating it's a trick, so here it its... simply put the car in 1st gear go about 15-20 MPH mash the gas 2x in order to get the momentum working for you. after you let off the gass for the 2nd time the K-member should scrape the ground, then mash the gas agin and hit the N2O. The SOTP feel is wild. the hedders & k-member get scrapped up a bit, but that's what it's for. Any way back to the gear comparo. At the end of the year I went to smack down @ Norwalk. I really wanted my 10 sec pass, so I jetted up to a 200 shot. But, after listening to count less people tell me that shifting into 5th is bad I caved in and put the 3:73's back in. I am sure most of you know what smack down is, but for those that don't, smack down is an open event, but 99% of the cars there are fords. So I made a few passes N/A on street tires just to lay low. Need less to say most of the 03 cobra guys, and GT power adder guys thought they would dog the only 4th gen f-body there (an SS to boot), after bosting 4 runs ranging from 13.1-13.5 @ 109-110 MPH. Then I took the gloves off threw on the wheels and tires, and turned on the nitrous. I went a best of 11.43 @ 122.5, again I don't have the slip, but I have the video, and it launched verry well, but at the launch the car bogged down every time, and I launched at 5900-6000 RPM. Then I jetted up to the 200 shot I went 11.415 @126.02 (5500k launch speed) 60'1.880, and that was it. The bottle went dry and the track closed.
So 4:56's cut .22 off my ET and where .7 faster than 3:73 gears with the same shot (150). The 4:56's where not tested with the 200 shot. I dynoed 475 HP 510 TQ on a 150 shot. No Dyno time w/200 shot. 3:73's are much better for street/HWY than the 4:56's, but that's not saying 4:56's are bad, 3:73's just feel better. If you don't care about the "feel" of the car on top and mostly street drive the car 4:56's are verry verry fun, also the top speed w/4:56's was GPS'd @169, on nitrous in 6th, I was not watching the tach so I don't know where the RPM was. Which brings me to another point... Gears are cheap, cheap enough to have a couple of sets. I can change my gear ratio in under 30 min. so I will add a set of 4:10's to the collection by spring, and go with a 28" tire, and start again.
Last edited by 526 SS 96; 12-14-2003 at 01:07 AM.
12-14-2003, 01:20 AM
#19
Registered User
Join Date: Mar 2000
Location: 51°N 114°W, 3500' elevation
Posts: 2,037
You only need deep gears to multiply torque to get a heavy car moving with a low output engine but it also depends on the tire height and your shift point.
After having a difficult season chasing ghosts I finally got some good mid 10 second passes during the last day (at altitude). It also gave me some good data numbers to do some number crunching. My car currently uses 4.56 gears and 29" tall tires. Because of the amount of torque the alcohol BBC produces, I don't need such a deep gear even with the powerglide tranny. This winter I'm swapping in a set of 4.30 gears. ET should pick up because I won't be overpowering the tires so much on the line.
After having a difficult season chasing ghosts I finally got some good mid 10 second passes during the last day (at altitude). It also gave me some good data numbers to do some number crunching. My car currently uses 4.56 gears and 29" tall tires. Because of the amount of torque the alcohol BBC produces, I don't need such a deep gear even with the powerglide tranny. This winter I'm swapping in a set of 4.30 gears. ET should pick up because I won't be overpowering the tires so much on the line.
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