3.23 gears question

[dogma]

I have a 1996 Buick Roadmaster wagon.
Weight: 4400 lbs
Engine: 5.7L LT1
Cam: Comp Cam 07-304-8
Torque Converter: Transmission Specialties 12LS
Tranny: 4L60E
Gears: 3.73
Tires: 255/50/17.

I don't race, just want a good daily driver with the best MPG.

I don't like 3.73 gears due to higher RPMs and the 3 MPG hit I take on the highway versus higher gears. Is it possible to swap in 3.23 gears for slightly lower RPMs on the highway? Question, would 3.23 gears work well with my setup, this cam and the TC?
I don't want the engine to lug and the TC should lock-up. I realize the cam needs somewhat higher RPMs than stock to be in the efficient range.

One auto tech I talked to thinks I would be going in the wrong direction with the swap to higher gears like 3.23, that it won't get me what I want. And that it's better to swap in a tigher, more efficient 9" Torque Converter instead of changing gears.

So what should I do, swap in 3.23 gears, go to a more efficient Torque Converter or both?
I am worried that if I go with a TC with a higher stall speed, it won't work on the street so well.


Competition Cams Comp Cam LT-1 LT-4 Chevy 93-96 part # 07-304-8

· Application 1993-1996 Chevy 350 LT-1 and LT-4 engines
· Power Range 1000-5000 RPM
· Idle Quality/special requirements-Best for original LT1 with stock computers
· Valve Lift 500/510
· Adv Duration 266/276
· Duration @.050 210/220
· Lobe Centerline 114



Torque Converter: Transmission Specialties BigShot 12LS

GM Big Shot 12LS
Primarily used in cars that are slightly modified, and mostly street driven. An excellent converter for the GM Target Master crate motor. Rear ratios should be in the range of 3.23 to 4.10. Hydraulic and flat tappet cams with good low-end and mid-range torque work well with this converter.
Stall speed range: 2000-2400 rpms.
New pump hub
New bearing between stator and pump
Computer balanced and pressure leak tested
Rebuilt sprag assembly
Pump and turbine fins tig spot welded for extra strength
Competitively priced

The 12" Street Converter is available in Chevy, 700R4, 2004R, 4L60E and AOD in both high stall and low stall.

[iwannagofaster]

In all honesty, the stock converter would have worked just fine with that cam. The only reason you would need a stall would be for take off if you were bracket racing or something like that. When the tech you spoke with said "tighter", that actually refers to a lower stall speed, but a 9" convrter would not be the way to go for that. The smaller the diameter of the converter, the higher the stall speed and most 9" converters aren't available with a lock-up and are oriented toward a racing application. Now, back to your question, the 3.23 gears will be fine with your setup and the converter will help to keep some torque around when you change to the higher gear ratio. In other words, yes, change the gears to a 3.23 and you will pick up some mileage and it iwll work just fine.

[dogma]

That's what I needed to know, thanks for the feedback.

Re: Torque converter, you are right, I don't really need it with this setup but I inherited it like that. My main concern would be that the 3.23 gears are low enough to make the TC lockup in city driving. It's rated from 2000-2400 but I am not really sure at what speed it will lockup. Looking at the TC specs, they say any gear from 3.23 to 3.73 should work with it. Is the lockup speed controlled by the PCM or is more complicated by that and is determined by weight and engine torque? e.g. different weight cars with different engines but the same TC will lockup at different speeds?

Re: gears, I realize 3.23 will be a little slower at 0-50 speeds but I should gain some top end speed. Now with 3.73 my cruising RPMs are 2300 at 70 and should come down to 2000.

In my experience with 3.73 gears, the MPG drops like a rock between 70 and 80 as it's turning between 2300-2650 RPMs. For best mileage, have to keep it at around 55-60, which is usually impossible on the highway.

Once upon a time I had a Caprice wagon with a stock L05 5.7L and 3.23 gears and it had respectable power for a daily driver, I never felt it lacked power. The engine didn't have that much HP (only 195HP) but it had good torque. It was a good compromise gear between mild performance enhancement and highway MPG. 3.73 is not the best highway gear, it would drive me nuts if I had to drive for 10 hours interstate. In some states with high speed limits and long straight highways, its not uncommon to drive for hours and hours close to 80 mph.

I hear that those who swap gears from 3.08 to 3.73 usually lose about 3MPG, which is huge for these cars that don't get all that great MPG to begin with. So my thinking is by going from 3.73 to 3.23 I should gain almost 3MPG on the highway only, now with the city driving, it's more complicated.

[amick]

Sounds like you got a plan there. Let us know how it works out for you.

[dogma]

The 3.23 gear install is done and it's nice. I reached my target RPM range of 2000 at 70mph. The gears are dead quiet and the engine is much quieter on the highway, it used to turn 2300 before.

Now I will have my PCM reflashed, the shifts are all wrong, as expected. It's shifting too late or too high. What was right for the 3.73 gears is no longer right for 3.23.

Great highway gear, though definitely slower in town than 3.73. But I wanted to build a nice highway cruiser instead of a 0-60 speed demon.

[amick]

Sounds like things are coming along nicely for you. Keep us informed.

[dogma]

3.23 is not the best for all city driving, although it's not that bad either. But it's a delight on the highway, and the faster you go, the nicer it is than 3.73. At 80, the RPMs delta is something like 350-400 RPMs. The decibels get to you after a while. I drove non-stop from Missouri to the East coast, 900 miles and was turning 2300-2600 with 3.73s the whole time, not fun.

So with 3.23 gears, does this mean I will be hitting peak torque at speeds above 70? I think peak torque doesn't mean best efficiency?
With 3.23, it's nice to have the capability of going faster than 70 without being overly penalized for it, sure you can do same with 3.73 but the rpms get insane even with overdrive.

[amick]

You will reach peak torque in a higher RPM range than the 2000RPM's you are turning at 70mph. Of course if you floor it from take off you will reach that RPM sooner than 70mph.