rskrause

I am thinking about a TH400. Two questions.

1. I know nothing about automatics, so forgive me if this seems ignorant. If you get the transmission with a "manual valve body" can it be downshifted while driving?

2. The second question is more involved. It's about gearing. I don't like the idea of spending >$2K on the GV overdrive. What about running the TH400 with 2.73's? My car now runs ~135mph in the quarter. Next year it will have enough power to run >140mph. First gear will go to 55mph and second to 104 with a 26" tire and my 6,000rpm redline. Do you think I will be able to pull that much gear? The shift from first to second will drop me to ~3,200rpm. The traps would come up at a bit less than 5,000rpm in third. The advantage is that with 2.73's, 70mph will be a bearable 2,500rpm in third. If I go with a TH400 I am tempted to try this. Any thoughts? What stall should I run with this setup if I try it?

Rich Krause

Brady

1- Manual valve bodies vary in operation (by manufacturer), but most if not all have no engine braking in 1st and 2nd gear. This means you can downshift with no problems.. Say you're going through the traps @ 140+ mph. You have a reverse pattern valve body in the tranny, the only way to get to neutral is through 2nd, then 1st gear. Follow me? Having no engine braking in 1st and 2nd gear is WAY fun on the street. You can be driving along at say 40mph, drop the tranny into second gear (with out raising the rpms (& attention)) and then when you nail it, it's very suprising to whoever is beside you.. I love my TH400. I got it through MadMan. $1250 w/ J&W ultrabell, reverse pattern manual valve body w/brake and a dipstick.

2- I run 3:50 gears w/a 28" tire. It's very livable. I'm running approximately 3300rpm @ 70mph. Generally, I just drive in the slow lane at 65mph and keep the r's around 3k.

I had originally envisioned using a Gear Vendors OD, but after driving the car I decided I don't want one, and I sure don't want the extra parasitic drivetrain loss and added weight.

Hell, we spend cubic dollars on Nascar quality engine parts, it better be able to live at 3,000 rpm on the highway

Did I mention I love my TH400?

Good luck!

(edited for coherency)

rskrause

Thanks, that's a big help.

Rich Krause

Fast Caddie

Brady.....a little advise please. Did you see the thread about the 4L80 swap? We were discussing this and one guy on there said he did it without too much trouble. When you put the TH-400 in your car, could you "see" a 4L80 in there? Would you attempt it? I want to put one in my Z when I get to building it. This may be something you want to look into Rich.

rumair

rich- i'm running a reverse valve body TH400 in my 74 firebird. the valve body is a very nice Turbo Action unit that behaves exactly as Brady described, no engine braking at all when downshifting. with a 3:55 gear and 28" tall tire i'm seeing ~3400~ rpm at 70 mph. i am running an 8" steel stator converter with a stall speed of ~4800~ rpm on my current engine setup. i run strictly race gas and don't drive my car on the street very often, so gas mileage isn't a concern.

i don't think 2:73 gears would be a good idea on your setup for a couple of reasons. you will need to make tons of torque at <3000 rpm to get the car going with that gear ratio. you will have to get a converter with a relatively low stall speed, which probably won't allow the car to get into it's powerband as soon as you would like. the cam you choose will have to make power from ~2500~ rpm all the way to whatever your redline is.

IMO it would be easier to go with a relatively steep (3:55 or 3:73) gear and a mild stall (3000-3400). going this route would give you more options when choosing a cam (assuming you haven't already done so). if you already have a cam picked out, you could post that info. and probably get some more helpful responses.

the only reason to go with the setup you are contemplating would be if you are driving the car on the highway alot and gas mileage is a concern. speaking from more than a year of experience, 3500 rpm on the highway isn't that bad. knowing the quality of engine and drivetrain parts you are likely to be running, i wouldn't be too concerned.

rskrause

Thanks for the info. Experience is a good teacher! I am still deciding what to do about a transmission, but the information is very helpful!

Thanks again.

Rich Krause

Mezmorized

Ok, a little off topic here... what's your e.t. on the quarter?

89ProchargedROC

Just something that was mentioned on LS1tech that sounds interested is using a TH400 like a powerglide by using 2.73 gears and having third gear (1:1) like an o/d

follow me down the math river....

Gear ratio for a standard TH400:
2.48
1.48
1:1

Gear ratio for a standard Powerglide:
1.76
1:1

now lets do a little math:

2.48 x 2.73 = 6.77
1.48 x 2.73 = 4.04
1 x 2.73 = 2.73 final

1.76 x 3.50 = 6.16
1 x 3.50 = 3.50 final

Difference of 1-2 in the TH400 is 2.73 and the 1-2 in the PG is 2.66
very very similar. Plus the pinion is so damn big on a set of 2.7X gears if would be pretty damn hard to break

I'll link you to the other thread when i find it

edit:
http://www.ls1tech.com/ubb/ultimateb...=003423#000021

We'll see how well this works....i'm running a TH400 with 3.08 gears with a TT 355

rskrause

That's exactly what I am contemplating. What I wonder is if having only 2 gears for the 1/4 will really hamper my times. I am hoping to hear from someone who has tried it, so I will definitely check out that thread. Thanks!

Rich Krause

rskrause

10.77 @ 134mph, which is not so great as my mods suggest. There are two reasons. First is weight - my car is a street car and a 'vert at that with no weight reduction mods (~4,100lbs with driver). And I launch it a little soft and don't power shift for fear of breaking the T56. I think there is a good 0.5sec to be gained with a harder launch and power shifting (or with an automatic). Next year there will be another 100+rwhp and more weight (full cage), so the tranny issue will be even more acute.

I am really in a quandry between trying T56 upgrades, TH400 +/- Gear Vendors or an exotic manual tranny (G-Force, Lenco). I want to "have it all": a 9sec, fully equipped street car that is enjoyable on the street and has full emissions equipment. Just my own particular "dream car".

Rich Krause

Shon Herron

I did the TH350 swap and thought the MPG would suck and was contemplating the GVOD unit or dropping the $2400 on an FLP A4 but after driving my TH350/3.73/26" car I like it alot!! It is alot of fun!! Going up an 1" in tire size drops the RPMs like 100RPMs per inch...this is for street use, i use 26" tires on the strip and need more gear, but that is another issue. I also thought about going to a 3.23 gear to pull the revs down but after driving 80MPH and still getting 14ishMPG I think I will keep it. NOW the revs are 3500-4000 and that sucks with the exhaust I run but the car is fun to drive!
With the A4 1st would be loose-ie break the tires loose, but with the A3, 1st and 2nd are FUN! punch in 1st or 2nd and the light up, and shifting the thing manually is a thrill again!!

Good luck and have fun!!!!

89ProchargedROC

Well rich, your car makes a boatload of power so i wouldn't be worried about setting up the TH400 like the way you are thinking....it will pull it through the traps

Plus if you really do this and it doesn't turn out well you only have to change GEARS, nothing else.



You might wanna talk to GeorgeC over @ ls1tech.com as he has run all three popular autos: PG, TH350, TH400

he could give you some good insight. I would say that the only reason setting up a 400 like a 2speed might hinder you is the weight BUT you could use the aftermarket 2.75 first gear ratio to help you get out of the hole

97SS ragtop #077

i weighed my 97 convertible, with a vortech supercharger, no roll bar,otherwise as delivered,,,weighed in at 3540....you sure your at 4100 with you in it?


Jeff

rskrause

The last time I weighed it I got 3,810lbs. I am ~235lbs and since then I put in the nitrous system. The scales are at the local track, and I have no idea if they are accurate. The 12-bolt is heavy as is the roll bar. This probably accounts for ~150lbs. There are ~120lbs unaccounted for. Most likely the scales are not consistent.

pink68

It may not be exactly like your setup Krause (can I call you that?) but I have a Hughes reverse valve body 400 with brake, 9" convertor that stalls at under 4000 somewhere (long story) and its all backed up by a Gear Vendor I bought off ebay. With a 28" tall tire, 4.56 rear (dana 60) I turn 2600rpm at 60mph on the freeway. It was important to me to have the GV as I drive over 50 miles one way to one track and almost 30 to the other. I have never used the GV at the track other than to drop rpm after the finish line and rolling up to the 2nd return road.

jim