Anyone using a overdrive auto?

[69 GTX]

I'm looking for advice on a OD unit/tranny. My car is an auto with 3.73 & 28" tires so I'm guesstimating about 2800@ 60 mph. I'm hoping that with the OD maybe .7-.75 reduction I should be able to cruise @ 75-80 @ maybe 2500. Any insight by someone using one would be helpful. right now I'm leaning towards a Gear Vender. Must be able to handle 650 crank HP. It will see some track action so I want it to be a strong piece. I know I will need a special converter to keep from building to much heat in OD. Thanks guys.

 

[Greg Ducato]

At 650HP I'm guessing you will need a stall speed of at least 2800-3000 to support the cam specs, that leaves out the 727 and Gear vendors as your cruise rpm will be less than stall speed. The 518 uses a locking converter but it will be a feat to get the 11 inch converter to that stall level and still be efficient. That leaves only the GM 4L80E as a choice for strength and locking converter. Ratio in overdrive is .75-one, prepare for some floor and crossmember modification on any overdrive auto you are looking into.

 

[5.7 hemi]

Greg, I don't understand why he couldn't use a 727 with a gear vendor! What ya said doesn't make any sense to me. Here is my reasoning for saying that.....545rfe trans with overdrive, 3.91 gears, 28 inch tires, cruising at 70 was 22-2300rpm and the factory stall is around 24-2600.

So what does the stall have to do with od? I ask cause I don't know....not knocking ya Greg, just not educated enough on the subject.

 

[69 GTX]

My understanding is that the advertised stall is for a flash at max horsepower. And if I understand correctly I can have a converter built for a stall of 3000 at say 400 hp but a cruising stall at 2000. My cam will idle at 850-900 with very little lope. My engine should make 580hp 580 torque according to the builder. I told him I wanted a high torque motor that'd run 11's in the 1/4.

 

[Greg Ducato]

Greg, I don't understand why he couldn't use a 727 with a gear vendor! What ya said doesn't make any sense to me. Here is my reasoning for saying that.....545rfe trans with overdrive, 3.91 gears, 28 inch tires, cruising at 70 was 22-2300rpm and the factory stall is around 24-2600.

So what does the stall have to do with od? I ask cause I don't know....not knocking ya Greg, just not educated enough on the subject.

At best any non lockup converter has 15 percent slippage even when it reaches an rpm beyond its maximum stall speed. A locking torque converter has zero slippage when locked up, thus eliminating this heat source. You cant build a 3000 stall converter that cruises at 2000 rpm, the converter will always retain it's stall speed. You can build a small diameter converter that flashes to a high stall but remains "tight" at lower rpm but even that will be a real heat pump running down the road.

 

[natas33]

You want to run a computer controlled 4l80e with stand alone controller. because there are bulletproof lockup converters available for them.. what you lose in performance from the extra weight and rotating mass versus a 727, you will gain if you lockup the converter at the track in top gear... becomes like a manual gearbox, direct drive

do it once so your not redoing it over. a standard new 4l80e from GM will hold 650hp all day long

 

[69 GTX]

Does anyone sell these as a kit? Do they make one with out a Electric controller

 

[69RRGTX]

If you want to spend money converting to a GM style transmission, I would go for this:

http://www.tciauto.com/tc/6x-six-speed-gm-automatic-transmission-850hphtml/

Like the 4L80E and similar trans it requires the stand alone trans controller, as for bolting it up an adaptor plate / flywheel is available or you could run a JW ultra bell.

http://www.tciauto.com/tc/383-440-chrysler-to-chevy-transmission-adapter-kit-6-holehtml/

With a good converter you are going to be out around 8000.00 for any of these options.

Kind of make me like this:

http://smrtrans.tripod.com/smrtransmissionsintro/id32.html

Good luck either way,

Mark

 

[69 GTX]

Yep that's just about what I've decided on. Tranny/OD & converter about 5500