Best Diff Ratio with Keisler 5sp?
Former Vendor
Joined: Apr 2002
Posts: 534
Likes: 2
From: Cookeville TN
I would go with the TKO600 due to better overall gear spacing. Both trannies (500 and 600) have good overdrives. The difference is in 1st gear.
I agree with Travis. A 3.54 / 3.55 rear would be my first choice. That also falls in line with the "10" formula
2.87 1st gear x 3.54 = 10.16
I agree with Travis. A 3.54 / 3.55 rear would be my first choice. That also falls in line with the "10" formula
2.87 1st gear x 3.54 = 10.16
Burning Brakes
Joined: Mar 2002
Posts: 839
Likes: 0
From: Lewiston, Maine
Check this math out. This is on my, shall we say, "torque challenged" daily driver with 14" wheels (roughly a 23.25" tall tire). She's got 3.94:1 differential gears X 3.45:1 first gear = 13.593 overall.
With the small tires and only 5500 RPM to play with (early Rabbit GTI), I'm shifting out of first before 30 MPH, but that hasn't bothered me in the 3 years of driving the car.
When I swap a T-56 transmission into my Corvette, my goal is to install the 2.66:1 first gear T-56, with 4.56:1 rear gears. Sure, my overall ratio in first gear will equal 12.1296, but to counter that, I will have 315/35/17 (roughly 25.68" tall) rear tires. This would give me until nearly 35 MPH (at 5500 RPM) before first gear becomes useless; stretching the engine's legs to 6000 RPM means I can drive to a shade under 38 MPH in first gear. That would be acceptable to me, but it may not be for others.
For now, since I only have an M-21 and 3.70:1 rear gears, I'm going to build my 383 stroker, swap in some 3.08:1 gears and let the 430 lb./ft. of torque pull like a freight train.
The T-56 I want has a 0.50:1 6th gear, which would turn 4.56:1 differential gears into 2.28:1. My current M-21 plus 3.08:1 diff. gears won't be down as low as 2.28, but it'll be closer than my 3.70s are now.
With the small tires and only 5500 RPM to play with (early Rabbit GTI), I'm shifting out of first before 30 MPH, but that hasn't bothered me in the 3 years of driving the car.
When I swap a T-56 transmission into my Corvette, my goal is to install the 2.66:1 first gear T-56, with 4.56:1 rear gears. Sure, my overall ratio in first gear will equal 12.1296, but to counter that, I will have 315/35/17 (roughly 25.68" tall) rear tires. This would give me until nearly 35 MPH (at 5500 RPM) before first gear becomes useless; stretching the engine's legs to 6000 RPM means I can drive to a shade under 38 MPH in first gear. That would be acceptable to me, but it may not be for others.
For now, since I only have an M-21 and 3.70:1 rear gears, I'm going to build my 383 stroker, swap in some 3.08:1 gears and let the 430 lb./ft. of torque pull like a freight train.
The T-56 I want has a 0.50:1 6th gear, which would turn 4.56:1 differential gears into 2.28:1. My current M-21 plus 3.08:1 diff. gears won't be down as low as 2.28, but it'll be closer than my 3.70s are now.
Team Owner
Joined: Jun 2004
Posts: 20,216
Likes: 4
From: Smile, it's just the internet.
I'm very pleased with my combination...
27" tire, 3.36 gears, TKO-600-.64. Makes for a very lively launch and lazy cruise. I'm getting approx 20 mpg on the highway and this in on a 427 +.060 and a Holley 850 DP.
27" tire, 3.36 gears, TKO-600-.64. Makes for a very lively launch and lazy cruise. I'm getting approx 20 mpg on the highway and this in on a 427 +.060 and a Holley 850 DP.
Melting Slicks
Joined: Oct 2004
Posts: 2,662
Likes: 8
From: Knoxville Tennessee
With my 1 to 1 3rd gear ratio in my TH350 auto and 3:55 rear gears I was running 3400 RPM at 70 MPH, now with my .68 to 1 5th gear and 3:55 rear diff gears I am turning 2,100 RPM. Do the math.
Bernie
Bernie
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Michael S. Palmer
Team Owner
Joined: Jun 2004
Posts: 20,216
Likes: 4
From: Smile, it's just the internet.
Originally Posted by Bismarck
Has anybody done any top speed testing with the Keisler 5 speed to see if it actually extends the top speed?
Too individual to answer. That's a function of drag, power, and gearing (and lift
). Only you know the combination for your car. The L88 cars were clocked over 200 mph with a Muncie...
Instructor
Joined: Aug 2005
Posts: 138
Likes: 0
From: Virginia
Originally Posted by Bismarck
Has anybody done any top speed testing with the Keisler 5 speed to see if it actually extends the top speed?
Seriously, I can clearly see that when I reach 85 there's still a lot of pedal distance to the floor.
80 Black Vette/Travis
Racer
Joined: Apr 2006
Posts: 312
Likes: 0
Well, one of us is going to have to speed test it out. Actually, two of us; one with a brutal big block and the other with a healthy small block. I think it is quite relevant to the value of the 5 speed swap whether or not it extends the top speed of our vettes.
Burning Brakes
Joined: Jan 2006
Posts: 761
Likes: 0
From: san jose California
Originally Posted by Bismarck
Has anybody done any top speed testing with the Keisler 5 speed to see if it actually extends the top speed?
i think after i finish my 383 this summer itle be capable of 160+...
(200???) but due to my tires, suspention and aero...(which i have already designed and have yet to build) i dont think ill try to top her out just yet...
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Originally Posted by Bismarck
Well, one of us is going to have to speed test it out. Actually, two of us; one with a brutal big block and the other with a healthy small block. I think it is quite relevant to the value of the 5 speed swap whether or not it extends the top speed of our vettes.
If you had perfect gearing for the availiable HP. You will go the fastest speed in a given vehicle.
I figure that a TKO 600 might give me 25 more RWHP over my racing 700R4. If you have more HP than you need for your gearing and RPM limited high speed. You will just get there in less time.
Max speed with a C-3 body aerodynamics without lots of earo modifications is gearing in the 2.50 – 2.80 overall gearing in overdrive with 28 inch diameter high speed tires. So you’re talking 3.90 or 4.11 rear ends.
I figured out 4.11 with my .70 OD would make my 79 go as fast as it could with 28 inch tires. Out at the open road races mild modded C-5’s can actually go faster in 5th gear than 6th because the gearing is wrong with .50 ZF-6 trannys.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Originally Posted by Bismarck
You two should be politicians. Just answer the question, Clinton! 
Has anybody with a 5 speed run their car to see if it improved top speed?
Has anybody with a 5 speed run their car to see if it improved top speed?
Simple math will tell you that a manual tranny has less HP loss than an auto tranny. If I gain 25 HP at the rear wheels it should be enough that you can feel the change.
I wish now that I would have kept accurate logs of before and after when I was doing acceleration runs in lockup OD from 60 mph to 160 mph and now try it with a TKO 600 in 5th gear
I just plugged my numbers in the Richmaond gear sight and going from my old .70 OD to a TKO .64 goes from an little over 200 @7000 rpm to a little over 220 mph @7000. 220 mph would be tough without some Earo thoughts and 1000 lbs in the passenger seat.
Last edited by gkull; May 5, 2006 at 04:21 PM.
Melting Slicks
Joined: Dec 2005
Posts: 2,441
Likes: 0
If you've got a 3.08 rear ratio, 26" tires and 1:1 top gear at 5500 rpm you'll be doing 138 mph if you don't run out of HP. Mine will do that without running out of HP, and shifting to 5th would obviously extend that top speed figure. I haven't had a suitable place to see what my max speed is, and wouldn't want to for the above stated reasons.
The fastest I've ever had the opportunity to drive is 185MPH on the back stretch of Talladega in a Dale Jarret racing adventure car, it was fast.
The fastest I've ever had the opportunity to drive is 185MPH on the back stretch of Talladega in a Dale Jarret racing adventure car, it was fast.
Last edited by shafrs3; May 5, 2006 at 08:51 PM.
