4L80E + 9" = What gear ratio?

Well I swapped out my 4L60e for a full manual 4L80 and now I'm going to a 9" I am putting together in place of my 3.73 geared 10 bolt. Knowing the 4L80 has different gearing [2.48/1.48/1.0/.75] I've notice that my seat of the pants torque feeling is lacking a bit and with the added 9" strength I want to go bigger.

I used some basic calculations to determine 1st gear torque multiplication, for instance:

My old setup with a 4L60E and 3.73 geared 10 bolt: 3.06 x 3.73 = 11.41
My new setup with a 4L80 and 3.73 geared 10 bolt: 2.48 x 3.73 = 9.25
My 4L80 with 4.11 gear option: 2.48 x 4.11 = 10.19
My 4L80 with 4.56 gear option: 2.48 x 4.56 = 11.31

As you can see it would take 4.56's to get me where I was with a 4L60E and 3.73's. What do you guys think? I have a set of 4.56's laying under my bed, so it seems logical. But I'd have to move to a taller 28" tire since my M/T's are 26" currently and I'd be running out of RPM's in the 1/4. Although its easy to change gears in a 9" carrier so I could easier to 4.11's down the road. Just wanted to see if anyone has done this. I figured the TH400/TH350 crowd might have some input too.

I know your not supposed to over gear too much with juice, but how would you gear if spray were to be factored in?

-Dustin-

well when you do 28's the gearings goes all the way back down and makes the 4.56 pointless...youll never get the first gear you want...80-e can use a trans brake though...looked into that? think they are pretty reliable with them also

You need to look into high gear(1.00:1) what RPM you want to cross the traps in max?

I would say a 4.10 will do fine with a 28"....wouldn't go anymore than that, 3.73 would work o.k. too.......it all depends on the combo. I don't think your going to really notice loss with the 9" so don't worry about that too much.....

If you really want the low first you could go 4.56 or 4.88 and just use overdrive in the 1/4.

If you really want the low first you could go 4.56 or 4.88 and just use overdrive in the 1/4.

terible idea...
OD is not made to handle full power at WOT.....no need to add a shift etc. etc. etc.


not bashing you but itsa bad idea.


don't worry about first gear.......2.50 vs. 3.06 is not big enough for you to notice on a street car....trust me

terible idea...
OD is not made to handle full power at WOT.....no need to add a shift etc. etc. etc.


not bashing you but itsa bad idea.


don't worry about first gear.......2.50 vs. 3.06 is not big enough for you to notice on a street car....trust me

frank tells his customers its fine...ive sprayed overdrive before....80-e i would think would be even better off

I ended up getting some 4.11's, I feel like its a perfect compromise. I have 4.56's here that I wont be using though if you need some. Now its time to buy a spool and assemble this thing.

-Dustin-

terible idea...
OD is not made to handle full power at WOT.....no need to add a shift etc. etc. etc.

I quess that all depends on who built your tranny.
My tranny loves overdive on the bottle.;)


don't worry about first gear.......2.50 vs. 3.06 is not big enough for you to notice on a street car....trust me

I disagree, have you ever swaped out a TH350 for a 700R4 in a car with tall gears. The low first gear seems to make a big difference to me.

But I do agree not to worry about it in a low geared race car. First gear seems almost too low in my car.

I would dyno the car and get some ideal of what type of performance you can expect.

Then start playing with the gear calcs.

What did the 4l80e setup end up costing you? What tq did you go with? How long of a driveshaft did you end up getting? Crossmember woes? Transmission tunnel mangled?

I would dyno the car and get some ideal of what type of performance you can expect.

Right now the car is a full bolt on + CC306 cam. I may have some things in store for it this winter, probably a nice N/A setup. But I want to get a 9" in there before winter hits.

Then start playing with the gear calcs.

What did the 4l80e setup end up costing you? What tq did you go with? How long of a driveshaft did you end up getting? Crossmember woes? Transmission tunnel mangled?

The basic 4L80e setup ended up costing me around $1075. I went with a Vigilante converter which was the bulk of the investment [$625]. I spent $100 on the stock 4L80e from a 1 ton Chevy, $250 for the Transgo Full Manual Stage 3 kit, $100 to shorten the driveshaft about an inch with brand new spicer U-joints. A few optional things I added was a Derale Deep Pan $80, B&M Mega Shifter [traded two 1/2 tread tires for]. I also picked up the BMR Trak Pack and boxed subframe connectors for $300, since you cant mount the stock TQ arm to the tailshaft of a 4L80e. I am assuming most people who would need a 4L80e would probably already have a chasis mount TQ arm.

The crossmember I just fabricated from a stock T56 trans brace. I welded on some steel plates to extend it further to the rear and torched out and ground some mounting holes. The 4L80e mounting point sits 3-4 inches further back than a stock T56 would. You could buy the BMR or Yank ones, they they start at $180. I went with the budget method, and really there arent as many external forces working on that mount after you take the TQ arm off the tailshaft.

I didnt have to mangle the tunnel at all. Since I have the pre-1997 4L80e I have the forward style trans cooler fittings, so I just used a pry bar to bend the tunnel out so the fittings wouldnt be too close. Although I later found that if you use some NPT fittings in place of the typical trans connection the prying would not be necessary. If I would have had the later model 4L80, I would have had plenty of room since they are closer to the tailshaft of the trans.



I had ALOT of people being skeptical about even attempting this swap, but it's very hard to beat a trans similar to a TH400 with overdrive that can hold 600hp+ in stock form, and 1200+ built. You can keep lockup, even with the full manual valve body like I have. I'll be adding the lockup switch to a panel I am making for my console. I'll be writing a full thread on it soon, its just a matter or getting all the pictures organized.

-Dustin-

I want to do this swap next winter, but I want to be able to control it with the stock PCM, I know the LS1 guys can do it and I've looked at alot of the schematics and it seems very similar. Any reason you didn't stay with computer controlled?

Because I wanted to be able to shift to whatever RPM I wanted to on each pass. If I ran N20, shift to XXXXRPM, N/A to XXXXRPM without retuning. It also costs about a thousand less to do a full manual. I got the ratchet shifter for next to nothing, so it only made sense.

-Dustin-