rear end ratio selecting
Thread Starter
Instructor
Joined: Feb 2005
Posts: 188
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From: Kearney Nebraska
rear end ratio selecting
I want to go with a lower gear in the rear. It has a 3.08 in it now and I'm thinking about either a 3.55 or 3.73. The motor is a 427bb, afr heads, crane cam hyd roller, lift 587/610, duration 226/234, adv 288/296, rpm range 2500-6000, Keisler TKO-600(2.87 1st gear, .64 OD). Car is for street driving and a few times a year the drags.
I want a good burnout first gear, but will 3.73 be too low?
PS.. Happy New Year
I want a good burnout first gear, but will 3.73 be too low?
PS.. Happy New Year
Race Director
Joined: Dec 1999
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From: Forked River NJ
I don't think so. I am running the TKO 500 with a 3.27 1st gear and a 3.73 rear. 1st gear is a little short but it gets moving in a hurry. With the 1st gear you have in the 600 it should be just right. I would prefer the 1st gear you have but the 600 was not available the time I got my trans.
Drifting
Joined: Jun 2005
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From: Chino Hills CA
Assuming you have a 255/60R15 tire which about 27" tall, your current 3.08's turn about 2875 rpm at 70 mph in top gear. If you switch to a 3.55, the rpm goes up to 3300, with the 3.73's, you'll be turning almost 3500. Man, that's gonna get old real fast, Unless all you do is drag race, that's a high price to pay in driveability. Right now, take your vette for a nice drive and never go past 3rd gear, can you live with that? I ran 4.11's in my '55, and even with a 5 speed overdrive, I couldn't take it, settled on a 3.36. ( was nice to be able to chirp'em in 4th though).
Race Director
Joined: Jan 2003
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From: State of Confusion
2.87 Low Gear, with 3.55s, is the equivalent of 4.56 gears with a standard M21/M22, while 3.73s would be like having 4.88s with a close-ratio 4-speed:
with a torquey BBC, would you need all that gear to get off the line?
with a torquey BBC, would you need all that gear to get off the line?
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
With a 427ci BB you don't need any help with gears, unless you plan on slicks for the drag strip. I have 3.08 in mine and can't get any traction until 4th gear if I am on it hard, a gear change would just make it worse. If you did change I would not go any higher than 3.36 
Thread Starter
Instructor
Joined: Feb 2005
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From: Kearney Nebraska
Originally Posted by lowbuck72
Assuming you have a 255/60R15 tire which about 27" tall, your current 3.08's turn about 2875 rpm at 70 mph in top gear. If you switch to a 3.55, the rpm goes up to 3300, with the 3.73's, you'll be turning almost 3500. Man, that's gonna get old real fast, Unless all you do is drag race, that's a high price to pay in driveability. Right now, take your vette for a nice drive and never go past 3rd gear, can you live with that? I ran 4.11's in my '55, and even with a 5 speed overdrive, I couldn't take it, settled on a 3.36. ( was nice to be able to chirp'em in 4th though).
... oh you must be thinking I still have the muncie turning 1:1 in top gear...
Last edited by big69; Jan 1, 2006 at 12:40 PM.
Race Director
Joined: Dec 1999
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From: Forked River NJ
Originally Posted by big69
Thanks for the help. I'm looking at the keisler speed analyzer I have 285/40/17 tires on the rear.. 25.6" tall. It says with a 3.73 rear in 5th at 2300 rpm I'll be going 72mph.
... oh you must be thinking I still have the muncie turning 1:1 in top gear...
... oh you must be thinking I still have the muncie turning 1:1 in top gear...
Melting Slicks
Joined: Jul 2005
Posts: 2,545
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From: 406ci SB, AFR 180 Heads - 490 HP @5,600 RPM 529 lb-ft @ 4,100 RPM
Just remember with a higher gear your fuel mileage will be hurt. I just removed 4.56's from mine and installed 3.55's. My 4.56's were a fun gear, but fuel mileage sucked. I only have a 3 speed auto so you can imagine the RPM I was pushing at 70mph.
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Thread Starter
Instructor
Joined: Feb 2005
Posts: 188
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From: Kearney Nebraska
Originally Posted by MotorHead
With a 427ci BB you don't need any help with gears, unless you plan on slicks for the drag strip. I have 3.08 in mine and can't get any traction until 4th gear if I am on it hard, a gear change would just make it worse. If you did change I would not go any higher than 3.36
Last edited by big69; Jan 1, 2006 at 12:53 PM.
Thread Starter
Instructor
Joined: Feb 2005
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From: Kearney Nebraska
Pulled the plugs and they are black with soot. Before it got cold I installed a Innovate LC-1 wideband standalone gauge and changed jets until I was around 11 to 12 and assumed all was well. I guess not. These plugs are way rich. I was trusting the meter and should have looked at the plugs. Guess I'll go back to playing with jets.
When the thing warms up it was staining the driveway with black when the condensation runs through the sidepipes. Probably another sign it is rich...
When the thing warms up it was staining the driveway with black when the condensation runs through the sidepipes. Probably another sign it is rich...
Last edited by big69; Jan 1, 2006 at 02:15 PM.
Safety Car
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From: Pettis Performance 565 with two stages of Nitrous Supply nitrous 1.082, 4.61 at 155, 7.17 at 192
Some of you are missing the fact his 5th gear is an over drive. The 2.87 first with a 3.73 rear will be fine. I ran a 2.77 first with a 3.70 rear with a 620 hp 454 and I liked it a lot.
Melting Slicks
Joined: Sep 2003
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From: Orange Ct
Former Vendor
Joined: Apr 2002
Posts: 534
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From: Cookeville TN
Rear gear choice with the Keisler TKO600 kit
Big69 -
The TKO600 with a 3.73 is the most popular combination with our customers. My personal favorite is the 3.55.
All that being said, our company Vette has 3.73 's and the 600. It has logged thousands of miles and offers an excellent balance of low end grunt and top end cruising. We're getting about 25 MPG with an injected ZZ4.
Robert
The TKO600 with a 3.73 is the most popular combination with our customers. My personal favorite is the 3.55.
All that being said, our company Vette has 3.73 's and the 600. It has logged thousands of miles and offers an excellent balance of low end grunt and top end cruising. We're getting about 25 MPG with an injected ZZ4.
Robert
Race Director
Joined: May 2005
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From: Millington Illinois
St. Jude Donor '08-'09
Hi. Got a 3:55 with less than 1500 miles on complete rebuild. Changing to 4:11 which will work better with my heavy cammed 327. Will sell the 3:55 for 750 plus shipping. This is a 78 rear with the bigger front yoke, pinion shaft and bearing. Heard these are more durable for High HP applications than the smaller pinion rear ends.
Safety Car
Joined: May 2005
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From: Jennings LA
[QUOTE=big69]Thanks MotorHead.. After hearing this, I think I must have a tune-up problem. Without cheating and using the clutch it only almost looses tracking in first gear. I'm 98% sure my air-fuel mixture and carb is now tuned good, but I've had this vibration deal going on when placing a slight load on it going down the highway. I wonder if I'm only running on 7 cylinders or something.. What is the best way to figure out if I have good spark in all cylinders? I'm going out there and pulling the plugs to see what color they are.[/QUOTE
you also have some very wide tires in the back. it has to hook up good with that much rubber on the ground
you also have some very wide tires in the back. it has to hook up good with that much rubber on the ground
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Gears are just torque multipliers, good for mild powered cars but a Vette with good torque like big69 should have should be fine with 3.08.
If you are already spinning the tires with a 3.08 ( and I don't mean dumping the clutch, I could spin the tires on a 6 cylinder Rambler stationwagan that was only running on 5 cylinders
) then adding gear is just going to make it worse.
Now if you are running slicks at a race track and you are hooking with the 3.08's then a gear change might help, but maybe not even in this case.
BTW what carb and jet sizes are you using ?
If you are already spinning the tires with a 3.08 ( and I don't mean dumping the clutch, I could spin the tires on a 6 cylinder Rambler stationwagan that was only running on 5 cylinders
) then adding gear is just going to make it worse. Now if you are running slicks at a race track and you are hooking with the 3.08's then a gear change might help, but maybe not even in this case.
BTW what carb and jet sizes are you using ?
Thread Starter
Instructor
Joined: Feb 2005
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From: Kearney Nebraska
Originally Posted by MotorHead
BTW what carb and jet sizes are you using ?
Primary jet 82, Secondary jet 90
Power valve 4.5 (primary only)
Squirter size: primary .035, secondary .037
I had a barry grant 750 on it before this...and couldn't get rid of the lean off idle. Out of the box the Aed is holding the airfuel throughout rpms and loads.. around 11 to 13. Although like I mentioned above, I pulled the plugs this morning and they are very rich.
With the 3.08 rear and the keisler tko-600 overdrive I have to get up to 60 or 65 mph before putting it in 5th to keep from lugging. Last time I drove it when it was still warm it was highway driving at 60mpg in 5th and almost lugging... Maybe that is why the plugs are black...
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Why don't you back off on the jets a few sizes, I have 825 Race Demon setup at 76/84 and the plugs are fine.
OD is usually just for the highway. Mine will pull fine at 1600-1700 RPM which is somewhere around 60-65MPH. THat sounds about right for yours also any lower and you are idling
What is the average speed on the highway around there ? If it is, say, 65 - 70 miles an hour then you are OK and you will also save alot on gas
OD is usually just for the highway. Mine will pull fine at 1600-1700 RPM which is somewhere around 60-65MPH. THat sounds about right for yours also any lower and you are idling
What is the average speed on the highway around there ? If it is, say, 65 - 70 miles an hour then you are OK and you will also save alot on gas
Thread Starter
Instructor
Joined: Feb 2005
Posts: 188
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From: Kearney Nebraska
Originally Posted by MotorHead
Why don't you back off on the jets a few sizes, I have 825 Race Demon setup at 76/84 and the plugs are fine.
OD is usually just for the highway. Mine will pull fine at 1600-1700 RPM which is somewhere around 60-65MPH. THat sounds about right for yours also any lower and you are idling
What is the average speed on the highway around there ? If it is, say, 65 - 70 miles an hour then you are OK and you will also save alot on gas
OD is usually just for the highway. Mine will pull fine at 1600-1700 RPM which is somewhere around 60-65MPH. THat sounds about right for yours also any lower and you are idling
What is the average speed on the highway around there ? If it is, say, 65 - 70 miles an hour then you are OK and you will also save alot on gas
Thanks everyone for the help...
I'll keep you posted after the ride.
Last edited by big69; Jan 1, 2006 at 10:43 PM.