Gears & setup

[buick83-T]

Thinking of getting a posi unit and want to go with a better gear. Is the 3.73(or 3.90) a good streetable gear as far as gas mileage goes;I have a 2800 stall torque convertor. Anyone tried using 2800 stall and 3.73 or taller gear?

(Can someone give me an idea on what this setup would put me in the 1/4 mile:2800 stall,3.73 gear, accel super coil, heads mildly ported and 15 psi boost, single 3 inch eghaust/w dynomax bullet muffler(gutted cat) and larger downpipe)

 

[jdub]

Well, I don't have a turbo at the moment, carbed 231, but I do have 3.73s and about a 2400-2800 converter. I can't speak for 1/4 times, I wouldn't go much higher than this (even with overdrive), unless you're also running 28" tires.... I've only got a 3 speed, and it really starts to sing up around 70

 

[brewmeister7]

Gears

I wouldn't go any higher than 3.73.Actually I think you'd be better off with something like a 3.08 or 3.23...You're gonna be hurtin on the freeway.Gas mileage will suffer.Present setup looks like it's good for high 15's.

 

[b4black]

The '83 TR has the 200-4R overdrive trans with a 3.42 stock. (Olds HO & 442 and the Chevy MCSS had 200-4R with 3.73 gears.)

3.73's are a bad idea on a 86/87 TR. But, I think our '83 TR's can benefit from a 3.73 gear since we are slower than the 86/87 cars. (I have already gone to a 26" tire.) By the time the 3.73 is a problem, so is the weaker 7.5" rear.

On a non-OD car, I would go with a 3.23.

I keeping an eye open for a 85/88 MCSS rear. A nice 3.73 with limited slip. It's a 7.5" ring gear, but I think it will hold up for what I want out of my '83.

 

[buick83-T]

Oh, so the 3.73 would benefit our 83 TR's. How much of a difference do you think it should make swapping from the 3.42 to the 3.73 and going to a 26 inch tire also. (I thought i had saw somewhere where someone had used a 3.73 gear a larger cam and 15 psi of boost to get mid to high 14's on a 83 TR so shouldnt my setup even with stock cam but the other additions I listed get me into about the mid 14 sec range?)

 

[brewmeister7]

Gears

Your quarter mile time improvement will be negligible.But on the other side of the equation,you will have diminished your streetability alot.Your gas mileage will suffer as will your freeway RPM.It's going to be a tradeoff.But with 3.73's that pups gonna be whinin when you get up around 75.I'd stick with the 3.42 and build the engine.

 

[b4black]

A 3.42 with OD has a final drive ratio of 2.29 (0.67 factor).
A 3.73 with OD has a final drive ratio of 2.49.

The 3.73 is less than a 10% increase over the stock 3.42. By going up to a 26" tire, the effective difference is even less.

Either combo is turning far less RPM's on the highway than my '82 TR. It has a 3.08 (stock) without OD. Buick even put 3.23's behind some 4.1 V6's without OD.

I wouldn't recommend swapping gears just to go from 3.42 to 3.73. But since I'm looking for a limited slip rear, I willing to try the taller gears.


I haven't been able to get a clean pass at the strip yet, but I'm guessing your combo is somewhere in the 15's. Get rid of the air cleaner box and use a K&N cone. 15psi would be nice if it doesn't knock. Box the lower control arms. Maybe a shift kit? Do you have a scan tool? You'll need to do some good tuning for the 14's.

Mid 14's is my goal as well for my '83.

 

[brewmeister7]

Gears

My My Rich,
You are good with the numbers.Makes good sense as long as you're running a 200-R4.But,why don't you just tub that baby and get into the 12's ?

 

[buick83-T]

Rich, I have the K&N filter with heat shield on it connected to canister with 4 inch aluminum hose running behind headlights. No scan tool just a boost/vacum gauge,oil psi,water temp,and volts gauge.Motor just rebuilt-mildly ported heads,stock cam,double roller timing chain, high volume oil pump,three angle valve job.160 thermostat. I added a accel super coil.And i got poston enterprises 2800 stall street/strip torque convertor.Cat gutted with single 3 inch pipe(dynomax race muffler). Soon to have a lager down pipe made. Also i do have a shift kit.Reason for wanting to change the gear to a 3.73 was because I was going to add a posi unit anyway.

 

[buick83-T]

Rich,
How much does one of those otc scan tools like the one you use run for? Also what all can it read?

 

[BuickTV6]

Well it really depends on what you want to do. If you want a highway car, a 3.73 will not be that bad. They put them in 305 monte carlo's with a 200R4 and they were okay. But a 3.42 is a decent setup. I have that stock in my 85. I know a guy who put 4.11's in his 84 and it goes good, just don't take it on the highway without having a gas station on every block
But if you're looking for both street and good hwy mileage, go with the 3.23's

 

[b4black]

Originally posted by buick83-T
Rich,
How much does one of those otc scan tools like the one you use run for? Also what all can it read?

I think you can get a OTC 2000 for about $75-100 on ebay. They sell similar tools at auto parts stores, but I don't know brand or prices.


They read whatever goes into or out of the ECM. Tach, knock, O2, coolant, TPS, TCC, open/closed loop, MAP, BARO, and more.

 

[b4black]

OK, maybe this will help:

http://www.richmondgear.com/streetcalculators.html

Try some different ratios. The stock P205/70R14 is a 25.5" tire. OD ratio is 0.67.

At 75 mph, With OD, the rpms are:
2139 for a 3.23
2264 for a 3.42 (stock '83 TR)
2470 for a 3.73
2721 for a 4.11

At 75 mph, Without OD, the rpms are:
3044 for a 3.08 (stock '82 TR)
3192 for a 3.23 (stock '82 GN 4.1)

As you can see, a 3.73 (or even 4.11) with OD is better on the highway than a 3.08 without OD. And my '82 TR is just fine cruising at 75 mph.

Going from a 3.42 to a 3.73 will lower MPG by about 10% or 2 MPG, if all driving is highway. For mixed city/highway driving, the difference will be even less. Going to a 3.23 will increase MPG by only 6% or ~1 mpg highway.

Gearing does not have that huge of an impact on fuel economy. Not when making only one step or two either way. These MPG changes are small when compared to loss in MPG when hammering the gas pedal. Many other mods will impact MPG much more than gears. I am willing to sacrifice a MPG or two for a quicker car. Otherwise, I would have a Geo Metro.

 

[be_regal]

What is the best or easiest way to find out what my gears are? The reason I ask is because on my 82 4.1 Regal it boggs down when I let off the gas while driving down the expressway. I can be doing 80-85 let off the gas and be back down 55 in now time. This is cool when I see a copper in the distance but is terrible on the gas milage. Also did they have limited slip, I ask because when the ground has snow or is wet my passenger side spins but the driver side spins every once in a great while. Could my bogging have anything to do with my transmision (I don't know what it is either) it sounds like it could shift again. I know its a 3 speed and it shift all 3 times. Oh yeah I have the stock wheels back on the car.

I won't try to even act like I know anything about tranys or rear ends so any help would be nice.

Thanks.....

 

[b4black]

A three-speed at 80-85 will be turning a lot of rpm's, so the engine breaking is probably normal.

To figure out the ratio, put the trans in neutral and jack up one rear tire. Spin it TWICE and count the number of times the driveshaft turns. The number equals the ratio. (You also jack up both rear wheels and turn them together ONCE.)

Limited Slip is possible, but not likely. The most common way to tell is to jak up both wheels. Spin one, and watch the other. If it rotates in the opposite direction, it's an open rear. If you had LSlip, then neither wheel would spin freely on ice. Both would try to move the car together.