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Tranny mods for efficiency? (MPG)

JoeMama

JoeMama

New member
Most people talk about modding transmissions for handling more power. But are there any mods to help with efficiency? I mean, my car is stock and probably won't put any power mods into it, but I sure can use extra savings for MPG.

While i've got the transmisison out, I figure if there are any efficiency mods, I may want to look into it.
 


I dont think you will find many at all because it is the nature of an automatic transmission. Quicker shifts help, but not so much with mileage as with keeping wear down on the tranny. Ideally you'd want to reduce friction, but since the clutches rely on it for engagement thats not so practicle.

I just dont know that there are any 'bolt in/on' type mods that can be done to help with efficiency. It is a fluid coupling so that kinda limits what can be done. About the only thing that could be done I am aware of is using synthetic fluid. But with an automatic transmission, in my experience, that may get you one to two miles per gallon maybe. I usually do not treat synthetics in a transmission as a fuel economy improver, nor do I present it that way to anyone. Now in the engine or manual transmission, thats a different story, but what frictional losses there are in a automatic transmission are generally needed for operation.
 
but can you change the lockup? Mine doesn't lock up until I hit about 47 mph, below that and I run the same rpm as I do at 72
 
You can turn on and off lockup whenever you want, just keep in mind the engine lugging at a low rpm doesnt mean better mileage since the engine is under more load but every car/combo wants something different. There is more room in the tune for mpg increase. As Scotty mentioned above there isnt really anything internal to the trans that is going to help with efficiency. From the factory clearances are set pretty loose on all clutch packs which will help prevent centrifugal drag but other than the input/forward clutch its not going to make much difference going down the highway in 4th gear. GM added what is called "Turbulator" holes to the Low/Reverse and Reverse Input clutch pack steel plates in the 4L60E transmission to help reduce drag as it allows oil to stay in the clutch pack better and has been said to give minor gains in economy and quarter mile times. For the 4T65E however there really isnt anywhere to gain anything. Synthetic fluid may gain you a small amount but without lots of back to back mileage tests in the same exact conditions such as wind, temp, humidity, it is hard to say its wortheness and many people that switch to synthetic in an aging trans find it causes more problems than good. Dex 6 may help out a very minor amount, it surely isnt going to hurt any as far as mileage goes.
 
JoeMama,

What year / make / model have you got?

Assuming you have a GPGT, you almost certainly have 3.29 gearing, and probably have a 245mm TC with a fairly high stall speed (as stock TC's go). You could easily gain a few mpg's with a lower gear ratio (3.05 or even 2.86) and a 258mm lower stall stock TC (and flexplate) out of certain later model H-body's (for example).

You'd have to program / tune for these, of course.
 


agrazela,

Yes it's a GPGT and a '99. Completely stock. Would lowering my gear ratio jack up my speedometer?
 
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