Truck currently has stock gears (idk if they're 3.08s or what) but they suck driving on the street especially with the 4.8/S480. I plan on swapping in a FTI stage 4 TH400 next year since it currently has a built 60e. I already know everyone is going to say to go with a 80e but unless it's bone stock, I'd rather spend less money to build a stronger trans with a transbrake. But I am open to a stock 4l80e and leaving off a footbrake/2step since it looks like some people here have gone 9s doing that, I just planned on making at least 800rwhp once I have it turned up so I don't think that will hold.

My question is what rear gear should I go with so it's not screaming on the highway but still get this heavy bitch moving? I've had TH400 cars in the past and I can tolerate cruising around 3k rpms but a few hundred less, would be nice. Has a 30" tall tire and will stay that way indefinitely. 295/65/15. I'm leaning hard towards 3.90s or 3.73s.

 

What size tires? And what truck? I think either should be fine. I guess converter stall speed also comes into play here if you have one in mind.

My nephew has a nitrous forged LQ4/TH400 in a ECSB 1990 OBS with 4.10s. He got the engine and transmission built, so I don't really know the details. He's got 15" wheels, not sure the OD. Maybe 27"? I honestly can't remember. I think he said he cruises at 3,000 rpm on the highway.

What rear axle are you running BTW? 🤔

 

It's in the post but 295/65/15 so 30" tall. My old Fbody with a th400, 28" tall tire, 4.30s, would cruise 60-65mph @3000 and it was just tolerable enough for me. Current stall is Yank 3400 but I'll be switching to PTC with whichever trans I decide to go with and assume stall speed will be very similar.

 

Your glove box will tell you what gear ratio you currently have, if the sticker is still there. Takes the guess work out of things...

I'd go with a 4L80e over the Th400 but that's just me. They can handle a lot of power. They just can't handle the power if you forget to pull shifter down into 3, leaving it in drive will slowly hurt it or just straight grenade it with enough power. 3.73's or 3.90's with a 4L80e will do great.

The weak link from there is the rear end. A 10 bolt can take some abuse but a upgrade won't hurt.

 

Thanks, I'll check the glove box. This is my first truck as of last Friday. I'll be content with 800rwhp which should be a walk in the park for this Billet S480. I'm really leaning towards a stock 4l80e and running it until it goes. This wont be getting raced every weekend, my schedule and other hobby won't allow for it. I'm glad I'm in the right ball park with 3.73-3.90s though.

The 10 bolt has an Eaton Truetrac and I plan on doing a girdle cover as well. I figured the 8.5 should hold with that especially leaving on very low boost/foot brake (if I go stock 4l80e route).

 

I Agree with FFDP. No way I'd use a Th400 in a truck unless it was trailered. And it had 1st 2nd and 3rd gear transbrake options.

I use 4L80Es in all the turbo trucks and so far have never hurt or broke one and several of the trucks are making well over 800 to the tire and running low 9s and High 8s with simple rebuilt trans and 3.42s in 10bolt or 3.50s in 9".
They all have pressure sensors in the line port to make sure the pressures are in spec tho.

 

I will be releasing a new valve body to the public at the end of this month that is totally safe to race in "OD" shifter position.
No need to pull shifter into D3

Transbrake will also be able to be 1st gear apply only, or apply in 1/2/3 if desired.

 

How can I get ahold to you about the new fancy valvebody?

 

So you’re recommending 3.42s even with a 30” tall tire? Seems like most people on here are using 3.90-4.10s to get these heavy things moving, but real world experience of running a good time is what I’m looking for.

 

The turbo drag cars running 1/8th mile we run a 28" with 4.10s and most them are running 8000-8500rpms at the trap.

The last turbo truck left the shop had 4.10s and kept breaking them in the 10 bolt. Went to a 3.50 in a 9" and it ran the same 60' and picked up a couple mph and ran the same times in the 1/8 but dropped 2 tenths in the 1/4 with same tune and boost.