Hi, does anyone know how much torque I can send through the stock Doug Nash 4+3 (I never use the overdrive) without destroying it? I've done a few basic mods to the engine, including intake, injectors, throttle body, and ignition. Once I get it all back together, I'm planning on having it tuned. I'm not certain but I'm hoping for between 400 and 500 ft lbs of torque. I know that the Doug Nash transmissions were timebombs from the factory, and I was wondering if anyone knows what they can handle torque wise. As far as I know the transmission is stock, but I'm not sure what year it was from. Any advice is welcomed and appreciated!

 

The 4+3 was used behind the B2K Callaway twin turbo motors in 87 and 88. These motors generated about 465 ft-lbs of torque @ 2800 RPM. HP was 345 @ 4000 RPM.

Given the mods you have listed, you will probably not get too close to that figure. If you add head work, a big cam and headers, you should get up around 400 ft-lbs.

These guys: http://www.skspeed.com/ have lots of knowledge and experience with the Dough Nash unit. The 4-speed portion was simply a Borg-Warner Super T-10 and they are a very stout unit that saw duty behind many of the muscle cars from the 60's and 70's.

If you start to go beyond that level of power, you may want to look at the Kiesler 5-speed or Richmond Gear 6-speed. There are versions of these trannies that are bolt-in swaps to the C4. Figure on about $3000 but they are supposed to be strong units.

 

Currently, I am lamenting the lack of a smiley face with a big 'ole 'Thank you' sign! The fact that the 4-speed is in fact a Borg Warner gives me more confidence. As far as the cam, heads, and headers, they'll have to wait, I'm a college student and I bought the car in high school with my dad, and we don't have too much time as I'm living about four hours from home, but I love these cars, and I am proud to be a member of the community that drives them!

 

Lots of people seem to put the 4+3 down but I really like mine in my 87. The car is mostly for autocross and track days and as long as you perform regular maintenance on the OD unit which basically consists of fresh fluid and a filter every 12-15K miles, it should work fine.

I don't engage the OD unit for track days so I'm pretty much limited to speeds around 125-128 in 4th gear but that's good enough at the track I run at. For autocross, I usually don't get beyond 2nd gear as the L98 has so much low-end torque, I havent had a need to go beyond that.

Sometimes I like to play with the OD unit in traffic. I can use OD in 1st and can effectively use 7 forward speeds. The "sports compact" guys really look confused when I shift a bunch of times between lights! The auto kickdown feature out on the freeway is fun too

This page has some interesting info on the operational differences between the units installed between 84 and 88: http://www.5speeds.com/43table.htm

 

That's interesting. I've gotten deep into the 120's with plenty of room in fourth gear and the overdrive off.

I definately need to go through and pull the pan off of my overdrive, and swap the filter and fluid. I'm not actually sure what year transmission is in my car. The car is a 1985, but the engine is updated. The engine has the aluminium heads, but does not have roller-rockers. I don't know if the engine is the same year as the engine or if it was the original from the car.

The switch for the overdrive is rather worn, and I don't know what it says. It appears to be a three position switch, how does one operate the overdrive from the switch?

The gentleman who owned the car before they guy who sold it to me was big into clubs in the East San Francisco Bay Area. Just in case, I'll throw his name out there; Jim Neylan. The car was black when he had it, and it was painted blue right before he sold it.

Thanks!

 

I've run a 150 shot on a full-bolt on/headers/dual exhaust TPI 350 for a year and a half, went through at least one 15lb bottle per week. Began doing this with ~100k miles on the original engine/trans. After a few months, my clutch was failing, so I switched to a McLeod twin-disc clutch and sent the 4-spd out locally to get rebuilt and then sent the overdrive to S-K Speed to be beefed up. All told I ran this combo for about 20k miles.

Ran a carbureted 421 monster for a summer, spun tires at the top of 3rd with 3.07 gears. Maybe 2-3k miles.

Ran a carbureted 355 with 150 shot for a year, a bottle every other week (it was not a daily driver at this point) Probably about 10k miles.

Running a carbureted 360 now, haven't put the NX kit onto it yet. Need to change gears, so I don't drive it much.

All combos using a twin-disc McLeod clutch, running BFG drag radials.

The key is to use the clutch when engaging/disengaging the OD. If you don't use the clutch and you are sending alot of torque through the unit when you trigger the OD, it's going to rapidly accelerate wear on the unit and it will go real soon. Going out of OD under load doesn't seem to hurt it as much as going to OD under load.

And don't abuse the car with holeshots all the time, especially if you have elevated power levels and hook the car up. Too much stress, imho for this particular trans... I seem to recall some threads years back on this subject and the max rated torque value for the Super T-10 was 360ft/lbs, I think? But there are plenty of people going above that with just bolt ons on an L98. the B2K Callaway bested that by almost 150 ft/lbs in 1988... Maybe the ratings are conservative, I think even the mighty ZF-6 is rated at 400ft/lbs, black tags maybe 450?

In any event, when shifting from 4th gear to 3rd/Overdrive (like shifting from 4th to 5th on a standard 6spd) clutch-in, hit OD button, wait until it clunks and then go up into 3rd and release the clutch. Yes, it takes a bit of time to pull off. It would hurt you in the standing mile or when racing at 130mph plus. Other than that, it will save you clutch packs and $$$ and time...

I love the 4+3, running at 100mph while loafing along at 2500rpm. The L98 has the grunt to get away with it.

 

Hi. I have an 85 4+3 z-51.
I had a breake down on my gearbox which was a bearing that went west. I changed it to the much stronger later edition without the TV cable and it has worked well now for 8 years. As I have modified the engine and did not know so much about american cars and gearboxes I phoned those guys that repair the 4+3 boxes and asked how much they manage. They said 450 ftlbs. Then I phoned Callaway and they were very, very nice and discussed the topic very much in detail. They said when accelerating hard never use the overdrive. The overdrive will kick in anyhow over a certain speed( as far as I can remember). I was a bit comforted by these infos and as I do not drive on the track (I will try though )normally I guess the gearbox will last some more years.

 

That's half the problem there, the "logic" of the computer...

When full into the throttle at 120 in 4th gear and the OD automatically "decides" it's a good idea to kick in, the sound of a 1 second sloppy rubbing clunk in your transmission is not comforting.

Make the O/D totally manual, on/off switch in the passenger compartment, solves the problem of the bad logic in the computer.

And just remember to "clutch-in, activate OD button, let OD engage, shift to 3rd, then let clutch back out" when going from 4th UP to 3rd/OD.

Don't let the bad logic of the driver burn out an OD either...