After much deliberation, I'm going to be mimicing a friend's setup in his old Grand Prix. He's got a built 355, TH350, 12 bolt rear, and between two stages is running a 450 shot.

This leaves me with a limited choice of transmissions. My first thought was TH400, it'd be bullet proof and take whatever I'll throw at it. Plus the taller 1st gear would let me put down more power out of the hole.

I'd like to have to have it be a lockup TH400, which will increase the cost of the unit and of the converter. Which lead me to maybe putting a 4L80E in? I thought I heard that they can be put in an F-Body, plus they've got a OD and lockup. Could I build one as strong as a old TH400?

Another guy I know in a simmilar car runs a TH350 and he says it works great. Do TH350's come with lockup, or could it be cheaper to put a lockup kit into a TH350?

I've got a reputible tranny builder located, and I'd like to get something in my car in the winter months because as soon as I hit the 1.6x 60's, I started running into the OBD1 doesn't like big stall problem.

Any advice would be appreciated.

 

If you dont really plan on driving it on the street and have to have a 3 spd then TH400..That kind of power the 4L80E will work if you put money into it..You can get a Freddy Brown TH400 with a brake and a matched converter..

Th350 is lighter and takes less power to turn but the internals limited size will require more frequent teardowns..

Forget the lockup tranmissions as the converters are not strong and very few have any high stall small dia units..Then there is the glide...SEtup right you can get a glide to rival and manual tranny or autosetup sans a liberty or g force..

If you tell me your cams specs,car weight, tire size, rear gear and rear suspension setup i could direct you towards the proper converter..

 

Thanks for the help!

I was thinking also about a built 700R4, and then put both stages of spray on window switches to keep from spraying through the shifts? Do you think that would help? Or should I stick with a non-lockup TH400 and keep spraying through the shifts? Plus I don't plan on using both stages but maybe a hand full of times each year.

Cam Specs: Something CC306 sized, maybe a hair smaller. I only want to spin around 6500-6800. No need to spin to the sky. Maybe 230/240, near 600 lift, and I don't know what lobe seperation, what would be good for a big hit? My friend with the GP runs a 112 lobe, but wouldn't wider be better for nitrous?

Weight: 3400-3500 pounds, its going to be a full weight car.

Tire size: 28x11.5x15 ET Streets

Rear Gear: 3.08, 3.27, or maybe a 3.55? I hope to hit at least 140's in the quarter, so I'll need quite a bit of gear, maybe upwards of 150, but I doubt it.

Suspension: QA1 "R"s when they come out, and Eibach drag springs are my tentitive setup. I'll have a Madman torque arm, and I've got a BMR cro-mo PHR, BMR adj cro-mo LCA's & relocation brackets, and I'll throw on a BMR Extreme rear roll bar. Plus I'll have air bags for both rear springs.

I was thinking of a converter around 3000-3500 so I can spray out of the hole on a 150 shot, then save the 2nd stage of 300 for late in 1st if I can hook it, or 2nd gear. I heard Yank has a converter that will automatically lock up at 475 ft-lbs of torque.

Thanks for bearing with me, I'm still learning about trannies and engine internals.

 

AFAIK there is no lockup converter that will hold up to the kind of hp you are talking about. Especially with a high stall converter, nobody has figured out a way to get enough friction area in there to handle the hp. So, forget a lockup converter, unless there is something new out there that will work.

What you need to decide is do you need an OD transmission? If you do not, then just go with a TH400. The kind of hp you will need to run 140+mph in a 3,500lb car will need a sturdy transmission, unless you want to be rebuilding it on a regular basis. I'm told a 4L80 can be installed in a 4th gen. It may be a viable option if you need an OD transmission. It is heavy and expensive though. Then there is the option of the TH400 plus Gear Vendors OD. Even more costly and also quite heavy.

If you can run through even a 3.55 with a 28" tire and a 6,800rpm redline, you will be going hella fast. Allowing 1" for tire growth and a couple hundred rpm converter slip, a 3.55 gear and a 28" tire puts you well over 150mph. If you plan on street use and don't go for an OD tranny I'd suggest a little shorter tire and a taller gear combo. I am running a 27" tire at the track with 3.42's, and the 3.42's are tolerable on the street.

You will not find a hi-po steel stator converter that will stall as low as 3-3,500. They don't make them any bigger than 10", AFAIK. And with over 800rwhp, the stall will be 4,000rpm at least.

Rich Krause

 

Hey Rich, thanks for the input!

Well knowing that I can't go to a lockup tranny will save me some serious money.

Sticking with OD and lockup were just creature comforts I were trying to stick with, but I've driven around with a non-lockup converter before and its no biggie. I was originally planning a lockup TH400 w/ 3.27 rear gears and a 28" tire, that'd let me cruise at 60 at 2400 rpm.

Could you explain converter slippage to me, I just saw the term not too long ago and I had no clue what it is. Is it that the converter is less efficent and doesn't deliver all the mph that the gear can?

I have no problems getting a 9.5" converter again, if they make one like that. What would be the difference in driveability between a 9.5" and an 8" converter? Would it take more throttle to get away from stop lights like the way a 11" is different from a 9.5"? I've got a friend who's a Precisions Industries dealer, so I can get another converter from them. That and the converter I've got right now is real loose, it flashes 3800-4000, and flashed 5500 on a 100 shot before the cam.

Also, what should I look for in a converter that's being built for some serious spray?

Thanks again!

 

A non-lockup converter always "slips", it is never 1:1, like a lockup converter. How much slip will vary with the "efficiency" of the converter. Mine, for example, crosses the line at ~6,300rpm when the gear and tire size predict ~5,700rpm. So, there is ~10% "slippage". A 3.27 gear would be street friendly, but will slow you up at the track because it's too tall. Like all this performance stuff, you need to decide what's most important to you.

You need a strong converter to handle that much hp in a heavy car. Look for components like nickel furnace brazing, billet turbine hubs, tool steel sprags, and anti-ballooning plates along with a HD steel stator assembly. I think you have your converter sizes backwards. In general, bigger converters have lower stall speeds. AFAIK, the largest HD steel stator converters are 10". That's why I said I doubt you can get one as tight as a 3-3,500 stall. I am making hp in the same range you are talking about and wanted the tightest converter I could get. Mine is a 10" Coan and it transbrake stalls at 4,200 without the nitrous. With the nitrous, it stalls around 4,600. No problems driving it on the street though, except I wouldn't want to drive it all day in heavy traffic.

Rich Krause

 

Very cool, thanks for clearing that up for me.

I may go along the same route and call up Coan and see what they can offer me, and try to get a tight as possible converter as well.

Thanks for the help!