How to chose rear end gearing?
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larrywalk
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The 3.08 case (3-series) will also work with 3.36, 3.55, and 3.70 gears!
cocobolo
Member
About the 10:1 ratio being golden...I'm an old guy, and back in the day it was considered that 12:1 was the preferred ratio to leave the line with.
With an automatic and a higher stall converter, this may not necessarily be the case. But with the higher gearing - say 3.08 vs 3.55 - it's all too easy to fry the tires with the 3.08's. While that may sound contradictory, from experience it's true. Once your tire let's loose with the 3.08's it is difficult to get it to grab again.
You could actually go as high as 4.11's with your first gear being as high as it is, and that multiplies out to the low 11's off the line. With your O.D. ratio you are back down into the low RPM's for the highway.
You can always play with rear tire sizes after that for your finer tuning for the RPM's you want. I don't know if you can fit a 29" tire in your wheel well, but compared to a 27" tire that will drop your RPM by about 7%.
Lots of things to play with.
With an automatic and a higher stall converter, this may not necessarily be the case. But with the higher gearing - say 3.08 vs 3.55 - it's all too easy to fry the tires with the 3.08's. While that may sound contradictory, from experience it's true. Once your tire let's loose with the 3.08's it is difficult to get it to grab again.
You could actually go as high as 4.11's with your first gear being as high as it is, and that multiplies out to the low 11's off the line. With your O.D. ratio you are back down into the low RPM's for the highway.
You can always play with rear tire sizes after that for your finer tuning for the RPM's you want. I don't know if you can fit a 29" tire in your wheel well, but compared to a 27" tire that will drop your RPM by about 7%.
Lots of things to play with.
84rzv500r
Knows just enough to be dangerous!
DeeVeeEight
Fast Pedalphile
The ROD 6 final gear is almost identical to the TKO II's, .80 and .85 respectively. What is the advantage to the extra spread in the lower gears?
84rzv500r
Knows just enough to be dangerous!
Im not gonna get this exactly right but here goes...
2,3,4, and 5 are essentially the same as a Close ratio 4 speed, which is what I had originally (Super T 10)... now I have a very streetable low gear and a OD for Highway.
The thing I liked about the ROD is that it is hell for strong and the ratio selection is very broad for each gear also the 0.8 OD is rated for continuous use at max torque.
Really a BBC with such a broad Flat torque curve as the ramjet does not need so many gears... I almost went with a wide ratio muncie with an OD 4th gear set.
The ratio selection and spread should be made to keep the engine in the fat part of the torque curve so that when you shift the engine rpm dont fall below the power...
as you increase the speed the drag goes up by the cube of the speed and the power requirements to over come the drag are greater hence the gear spacing narrows to keep the rpms closer to the peak torque for max acceleration.
and don't think just because it has 200 mph gearing it will pull it... a C3 needs something like 700 flywheel HP to tag 200... by comparison my E55 AMG needs only 550 or so... can you say coefficient of drag
with all that said... the fun part is never running out of gears... or bullets...:mobeer:
2,3,4, and 5 are essentially the same as a Close ratio 4 speed, which is what I had originally (Super T 10)... now I have a very streetable low gear and a OD for Highway.
The thing I liked about the ROD is that it is hell for strong and the ratio selection is very broad for each gear also the 0.8 OD is rated for continuous use at max torque.
Really a BBC with such a broad Flat torque curve as the ramjet does not need so many gears... I almost went with a wide ratio muncie with an OD 4th gear set.
The ratio selection and spread should be made to keep the engine in the fat part of the torque curve so that when you shift the engine rpm dont fall below the power...
as you increase the speed the drag goes up by the cube of the speed and the power requirements to over come the drag are greater hence the gear spacing narrows to keep the rpms closer to the peak torque for max acceleration.
and don't think just because it has 200 mph gearing it will pull it... a C3 needs something like 700 flywheel HP to tag 200... by comparison my E55 AMG needs only 550 or so... can you say coefficient of drag
with all that said... the fun part is never running out of gears... or bullets...:mobeer:
68/70Vette
Well-known member
Enjoyed reading everyone's comments. The ROD(Richmond OverDrive) 5 speed is rated at 450 foot-lbs torque...is the 6 speed rated at more than 450?
a C3 needs something like 700 flywheel HP to tag 200. I wonder about this. In the early 1980's Glen Banks (now specializing in turbo setups for trucks) set the worlds land speed record for a stock bodied car. The stock bodied car was a 68 Corvette Convertible with a hardtop option. I saw the car and talked to Glen about it. He (his driver) drove the stock bodied 68 Corvette hardtop vert at 230 mph at Bonneville. IT WAS A TRiCK CAR. It was stock bodied..yes.. but.. the front end of the car air dam was about 1 1/2 inch above the road surface......the front engine coolant radiator had been removed and in it's place was a 50 gallon water tank, 400 lbs,..the 400 pound weight was to prevent the nose of the car from becoming airborne. The car was powered by a twin turbo 427 developing 1200 hp. Glenn told me he could get more hp out of the engine but he said he only wanted to run it at the boost level to set the worlds record and wanted to minimize the possibility of blowing up the engine/loosing the car, etc. If you want to run 230 mph with a stock bodied 68, loaded down with 400 pounds in the nose, you need 1200 hp. I'd guess that 700 flywheel hp will not get a C3 to 200 mph, and in any event if it did start to approach 200, the nose would lift off the ground a lot lower speeds.
I vaguely remember that the stock C2's will start to have nose liftup at about 120-130 mph. Can't cite this absolutely.
84rzv500r
Knows just enough to be dangerous!
the Richmond 5 speed is 1:1 in 5th... the ROD has a bunch of OD ratios available for 6th from .91 to .52 and .when ordered my transmission from Richmond... talking to their tech support they wouldn't warranty the ROD behind the 502 Ramjet with out using the special 9 DP road race ratios K=.80 or L=.84.
never seen torque ratings on ROD6 I'm sure they exist. I know the Street 5 speed is rated at 450 in the lower gears but it drops off in the higher gears... I haven't been able to break it... my ROD6 and 3.08 Rear has held up well with annual fluid replacements...
I did snap my front differential mount off... built a new stronger one, more pinion down angle, urethane mounts instead of the stock rubber and added traction bars to take some of the load off.... didn't break at the drag strip... didn't break auto crossing... broke on an interstate in OD rolling on the throttle up a hill... BANG...
dunno about Gale Banks' vette... Id bet while the body was "stock" the body itself was tilted nose down about 2-3 degrees on the body mounts...
Chassis was lowered and there was prolly 2 rolls of duct tape sealing the thing up....
lotsa 700 HP c3's in the 200 zone... agreed not stock body'd.. If you look at the math the Coefficient of Drag is really important... IIRC a stock C3 is around 0.44, a C4 is around 0.33 and my ancient E55 AMG SEDAN (takes less than 30 seconds to bang into the Speed limiter at 168MPH from a dead stop) is around 0.28...
a good article...
http://www.hotrod.com/techarticles/body/hdrp_0609_aero_tricks_tips/
Anywho... depends on what you wanna do with the car.... 10 or 11 to 1 overall makes a great street-able 1st... space the rest of the gears to match the power charterisitcs of the motor.. my advice is do the math... simulation is much less costly than experimentation In this case...
:thumbs::thumbs:
never seen torque ratings on ROD6 I'm sure they exist. I know the Street 5 speed is rated at 450 in the lower gears but it drops off in the higher gears... I haven't been able to break it... my ROD6 and 3.08 Rear has held up well with annual fluid replacements...
I did snap my front differential mount off... built a new stronger one, more pinion down angle, urethane mounts instead of the stock rubber and added traction bars to take some of the load off.... didn't break at the drag strip... didn't break auto crossing... broke on an interstate in OD rolling on the throttle up a hill... BANG...
dunno about Gale Banks' vette... Id bet while the body was "stock" the body itself was tilted nose down about 2-3 degrees on the body mounts...
Chassis was lowered and there was prolly 2 rolls of duct tape sealing the thing up....
lotsa 700 HP c3's in the 200 zone... agreed not stock body'd.. If you look at the math the Coefficient of Drag is really important... IIRC a stock C3 is around 0.44, a C4 is around 0.33 and my ancient E55 AMG SEDAN (takes less than 30 seconds to bang into the Speed limiter at 168MPH from a dead stop) is around 0.28...
a good article...
http://www.hotrod.com/techarticles/body/hdrp_0609_aero_tricks_tips/
Anywho... depends on what you wanna do with the car.... 10 or 11 to 1 overall makes a great street-able 1st... space the rest of the gears to match the power charterisitcs of the motor.. my advice is do the math... simulation is much less costly than experimentation In this case...
:thumbs::thumbs:
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