Tall Rear End Gears
 

After searching for years I found out that Salt Flat Racers are the ones with Tall Rear End Gears sets.

There are a couple of face book pages that cater to these racers etc. But it is a bit hard to get on there and they may want to keep them for fellow racers…so I am putting this on all the car sites I belong to.

I am looking for tall gear sets for my 8.8 Ford in a 03 Crown Vic and for my 10 Bolt 5 lug G20 93 Chevy Custom Van.

For the Ford I found that they made these gears sets: 2.26, 2.47, and I think something around 2.56.

And I am looking for the closes to those numbers for the Chevy.

I am hoping someone here can help me.

Rich

WHY?? I plan on running 6R80 in the Crown Vic and a 8L90E in the van and with the super low lower gears will have the same power at take off as the stock transmission and rear end.

3.08 final ratio is the modern one it will put you at 1600rpm @ 85mph 0.65 8th) gear

2.41 is the lowest you can go but you risk stalling the engine
you can lower the ratio further by putting taller tires...

All possible differential ratios above 2.73 can be swapped without having to change carriers (except for the truck differentials with 30-spline axles).]


your acceleration will stink with anything below 3.08... you will probably end up wasting more gas. in the long run

So unless you got a diesel engine or electrical motors to back up that ratio lower then 3.08 final (low end torque and electrical or diesel motors have a ton a of torque )


so i suggest the 3.08 with the "taller tires"

For the Ford that would work, got any or know where I can get a 2.41 set??

The Chevy Van is getting low RPM torque monster 383 with its torque peek at 2000 RPMs...running a 85/90 Camaro TPI with matching PCU with Highway mode able to lean to 16.4 on light throttle and load.

It too could be golden at that ratio, same question where to get a set?

Thanks.

Rich

PS I have a 2.73 already.

1971 Firebird has a 2.41 ratio might be able to salvage one from that

should look into a second overdrive gear? 0.5 gear?

I'm skeptical. In my experience, there's always a lower gear, unless you're already in first. If you can still accelerate in top gear, there's still room for improvement. A large change in rear end is basically like trading your bottom gear for an extra one at the top.

I have considered that very idea, I have two 50s/60s Borg Warner 3 Speeds with over drives.

And I was very close to putting one behind a TH400, using 2nd gear as a under drive with very tall rear end gears, so that when in a city drive I would have a low geared rear end, giving 4 speeds in low, the stock 3 in the auto and the B&W over drive, and then by shifting into third gear (1:1) switch to high and again have four speeds in high. A 8 gears...

BUT it would be a little complicated....I would need a floor shifter between the seats. And complex set up to INSURE I never back up in overdrive, that will rip the overdrive's gears out. And shifting the OD in and out of OD.

The new 6 and 8 speeds give all of that, super low first and second gears at 4.03 and 2.36 for the 6 speeds 6R80, and 4.56 & 2.97 for the 8L90s Both lower gears are BELOW the stock Fords first gear ratio of 2.48 and GMs 4l60E's 2.48 as well. The 6 speed second gear is near the 4's first gear, but the 8 speed both first and second are lower that the 4 speed's first gear.

So there is no need for an under drive...

PLUS these are fully controlled automatics, insuring smooth up shifting and down shifting.

And as I am NOT building a high HP over revving hot rod but a stock motor in the Crown Vic and a Chevy 383 built for LOW RPMs for the Van, totally built to operate around the 2000 RPM range both the motor and drive train will be a match. i figure the 383 should be pulling around 250/300FP of toque at that speed which should be great for cruising.

I have read everywhere that you want your engine to be running near its torque peek for best power and MPG.

So I plan on using a used trans mission, which for the 6R80 can be had now for around $500.00 and the 8L90s running from $700.00 to $1200.00.

Which leaves the problem of controlling them.

One idea is to run dual PCMs, the factory PCM to operate the motor and a Factory PCM for the 6R80, and the same for the 8L90.

OR an aftermarket controller which adds about $1000.00 to the costs.

So for the Crown Vic $500.00 for the 6R80 plus say $100.00 for a factory PCM, or $1000.00 for AM Controller so $600.00 to $1500.00 for the Vic.

And the Van, $800.00 for 8L90, and $100.00 for GM PCM, or $1000.00 so from $900.00 to $1800.00.

I feel and think these will work very well, and not only majorly improve each vehicle's drive-ability with all the extra gears during acceleration plus being to down shift a closer lower gear in traffic a function limited with only four gears.

AND with the tall rear end gears using the top overdrive gears be running both engines below 2000RPMs and at 80MPH..with I think will give me great MPG, even before I do some tweaking to improve MPG.

Like Highway modes, running 16.4 lean at cruse.

Rich

IF I could post a picture here with out a damn URL I could show you the charts of the transmissions RPMs in each gear from 500 to 5000 with the gear sets I want.

IN each case the first gears of the 6 & 8 speeds are running higher RPMs at 10MPH that the stock transmissions with the stock rear end gears. So the lower first gears are making MORE Power even with a 2.26 or a 2.47 than with the stock 3.27 gears.

So the numbers show a slightly higher performance off the line than with the stock transmissions with stock rear ends.

And at this time I am very happy with each vehicle's power off line and driving. This will just improve it.

I end up with more gears up to cruse and a very high final gearing.

From 1600RPMs to 2000 RPMs with both vehicle's.

Rich

I think you'll be fine. The c7 base model cruises 70 at 1260 rpm.

Can you give more details, as in what is a C7 Base model??

And what are we talking about, make model and year, and if possible transmission and rear end gearing, please.

Rich

Corvette 7th gen. There are 8 generations, typically referred to as C1-C8. The C7 has incredible gearing. I believe the rear end for the auto is a 2.56 with a 0.67 6th gear, while the manual has a 3.42 rear end with a 0.42 7th gear. Tires are P285/35R19.

EDIT: I believe I recall seeing the C7 as being able to break 40mpg from the factory (at the right speed) with a 6.2L pushrod V8.