[BlackoutSteve]

If you have any decent converter in the car, forget about fitting an overdrive.
The overdrive will lower the engine rpm, yet the converter will simply slip and allow it to speed up again.

Originally Posted by RichSchmidt

I put it in with a 3200 stall convertor,th 350 and 3.90 gears and 26 inch tall tires.I attempeted to drive it to work once and got towed home.The engine was screaming like the rods were going to come out of it and it was running 4000 rpm at 75 mph

75mph with 26" and 3.9s is 3800.. You must have one seriously slipping converter if it's stall is only 3200, yet your engine is doing 4000 at that speed. Is this why you're suggesting numerically high gears and high stall converters overheat at cruising speeds? I'd say if your speed and rpm are what you say it is, you'd be overheating for sure.
My 4.11s with 3500 run coolest on the highway and I had a trans temp gauge, so it's not a guess.. About 160F.

[RichSchmidt]

Yes,I am recommending numerically higher gears to match his convertor.With a 3000 stall,he doesnt want to have to run continous on the highway at under about 2400 rpm or so.He would have no problem with 3.55's if his cruise speed were 60 mph or better.If he went with 3.08's,the cruise speed would be too low and the convertor would slip and cook the trans.My real recommendation centered around how high he wanted the engine to rev.Anything over 2500 rpm for me is extremly annoying to listen to for hours on end.Even with stock rubber body mounts,a 2.5" full exhaust and quiet mufflers you cant hear a radio unless it is cranked and it isnt a relaxing experiance.My 74 camaro came from the factory with 3.42's and somebody put 3.90's in it,and I drove it for a short while and it was revving way higher then I was comfortable with.When I first put the rear in the car it had a stick in it,and it was reving too hihg.I knew I was going to have to swap the gears,but I have a bunch of money into this rear with a new posi unit and all,so I wasnt about to sell it for peanuts just to get a rear with highway gears.I was just giving him some advice about how high his car might be revving with a gear change.That stuff was cool when I was 18,the novelty has worn off over the last few decades.

[BlackoutSteve]

If cruising rpm is lower than converter stall speed, the slipping converter will not cook because it's not under load.. It's just cruising (..and with loads of aiflow through the cooler).
However, you mentioned that your rpm at 75mph was 4000 with a stall speed of only 3200. Your rpm should be been 3800 and with 200rpm above stall speed, that's a concern for heat for sure. -if what you say about your specs is correct.

[RichSchmidt]

Well to be truthfull,my speedometer doesnt work since the trans has a 2.73 speedo gear and the rear is 3.90's.I am not 100% on the tire size since they are just some 235/70/14's that I threw on the car,and the engine speed I mention was measured on the factory in the dash tach.I also drive up and down a lot of low grade hills during my commute,so I was on the throttle a good bit just to keep the car moving at 70+ mph.I know that merging on the highway the first day I was just a tick under 5 grand before I lifted off the gas to start cruising,and I really needed to be going faster.

[98blackburb]

I am running a 12 bolt 3.07 factory gear,turbo 350,2000Holeshot drive on highways 70-75 have'nt had no troubles.

[nev68]

Originally Posted by BlackoutSteve

If you have any decent converter in the car, forget about fitting an overdrive.
The overdrive will lower the engine rpm, yet the converter will simply slip and allow it to speed up again.

So Steve, would a "lockable" converter be required to get the benefit of an overdrive trans?

[BlackoutSteve]

Yes but I don't like your chances of getting one in the stall speed that would suit what you need. I'd imagine they are all 11" diameter (maybe 10") and for electronic transmissions like 4L80E for example.
Don't know enough about them.. I'm sure someone will enlighten us..

[nev68]

According to the Gear Vendors web site.......

"Can I run a high stall converter in overdrive with a 3.42 axle?

Yes, this is one of the most often confused questions (even when you ask people you would think would be knowledgeable). Here is the detail. Our example could be this 3.42 Chevy guy. In overdrive he is going to be a 2.67 final drive ratio. He is a Cutlass body with 27 inch tire and so at 75mph in overdrive the motor will be turning 2484 rpm and he has a 3500 stall speed on the back of a pretty nicely built 350ci motor making close to 400hp. 95% of the people you would ask (even tranny guys) would say no-way and yet we know this is an awesome package (drives wonderful, no high temps in the trans etc) why does it work? When his converter was made it was set up to stall at 3500 with 400hp. However if you put 600hp to it it would stall at something like 4500. Conversely if you only put 125hp to it (as when you are just crusing at 75mph not accelerating) then the stall is way down at 2,000 rpm. So his stall with a 3500 converter is not 3500 at cruise because he is not making 400hp. Car drives wonderful. If he romps on it while cruising then the trans is going to downshift to a lower gear and get him into the powerband. (note: read gear vendors passing gear in this section) So, this is why you never lie to you converter builder (because if you overstate your hp you will not get the stall you wanted)."

[BlackoutSteve]

Although that is true, a portion of the expense of a 0.75% overdrive unit will still go to waste because the converter will still slip and "soak up" some of the overdrive. That's what I think anyway.

I'd like to see actual results as to the amount of slip, not theoretical.

[nev68]

Originally Posted by BlackoutSteve

Although that is true, a portion of the expense of a 0.75% overdrive unit will still go to waste because the converter will still slip and "soak up" some of the overdrive. That's what I think anyway.

I'd like to see actual results as to the amount of slip, not theoretical.

I tend to agree Steve.
It does sound good in theory but it would be good to hear some feedback from some one who actually has fitted a GV o/drive.

Anyone had any experience?

[madcarson]

I'm running 3500 stall w/GV od and trans temp never exceeds 160F on freeway,usually about 145-150F !

[BlackoutSteve]

Originally Posted by madcarson

I'm running 3500 stall w/GV od and trans temp never exceeds 160F on freeway,usually about 145-150F !

What is your ratio, tire height and rpm at 60mph when in OD?