Auto+twinscrew = Traction Problems?

Discussion in '1996 - 2004 SN95 Mustang -General/Talk-' started by yelowjaket, Mar 12, 2014.

  1. I am wondering if those of you in the 400-500rwhp range, utilizing a twin-screw are having traction problems with an auto trans and drag radials? I’m considering this setup:

    1. Twin-screw (400-500rwhp)

    2. Auto w/ 2000 rpm stall

    3. 26” tall drag radial tires

    4. Stock 3.31 final drive (Possibly 3.73’s?)

    Thoughts on this?

  2. Stock 3.31? What year is your car? I like your plan but need more info.
  3. 99' mustang GT. I'm pretty sure the 3.31's come in the 4R70W's? I need to update my sig, I no longer own the '90 gt, sorry if that was causing confusion.
  4. Hmm. Maybe they do. Mines a stick and came with 3.27 gears.
  5. That's probably stalling too low to kill the tires. But 26" DRs are not ideal. 28" Radial PROs are the best. Also, suspension upgrades are important.
  6. You'll probably have traction problems in 1st only. The gears are what is going to determine traction. I would go 3.55 MAX wit a PD blower. Stock ratio is 3.27.
  7. As well as the rear-end setup as mentioned above.
  8. Rear suspension will definitely help traction, but not as much as you may think and not at those power levels.....and especially not with a PD blower. His best course of action is a conservative gear ratio (staying with the 3.27's may not be a bad idea) and getting a nice sticky tire.

    Also, a 2000-stall converter is a waste. For the amount of money you're spending, it is a pretty irrelevant mod.
  9. The stock gears are 3.27s (36 tooth ring + 11 tooth pinion = 3.27272727272727272727272727272727272727272727272727272727....well, you get the idea). Unless you are making BIG power (i.e. rolling faster than 130 in the 1/4), I'd put 3.73s in it. 3.73s on a 26" tire are good to 130 mph at 6000 rpm. I switched from 3.27s to 3.73s, and there's no way I'd go back down any unless I had to for trap speed purposes at the track.

    The stock converter stalls around 2400 rpm. So a 2000 rpm converter would actually be less, which is a terrible idea. The stock converter stall speed is definitely not enough, even with a PD blower, and especially not if you're going to spend money to put a new one in anyway. With a ported roots blower, 3.73 gears, stock converter, and around 400 rwhp (with LOTS of low rpm torque), my car would rarely cut a sub-1.80 60', which is pretty bad for a 400 rwhp auto car. These times were power limited, NOT traction limited. If you put a converter in it, I'd say it needs to stall to 3000 RPM on the foot brake at a MINIMUM. Which means you're looking for around 3500-3600 RPM actual converter stall. Depending on the rest of your trans build and what you want to do with the car, it certainly wouldn't hurt to go a few hundred RPM higher. Contrary to popular belief (that the ideal stall speed is 600 rpm less than peak torque), the higher the stall speed, the better times you'll turn (assuming that speed isn't above where the RPM drops to on gear changes). But for a street car, that may make it a little tough to drive a lot.

    Speaking of traction, you won't have too many issues at the 400 rwhp area on a stock converter. I can't speak so much for the 500 rwhp range. My car has very few suspension mods, and the ones it does have are for corner handling (Bullitt springs, shocks/struts, and sway bars). At around 400 rwhp, 3.73s, and stock converter, I have relatively no issues hooking my car up in 1st gear as long as it's warmer outside (65+ degrees) on regular NT555 street tires (275/40-17). If it's cooler outside, they start having a hard time hooking up in 1st. But I feel that'll be the case with any tire that you haven't put any heat in (i.e. burnout). My Nitto 555R drag radials won't hook in the cold like that on the street, but will hook just fine at the track after I've done a burnout. I've only ever had traction problems in 2nd gear when it's really cold out (sub-freezing temps). Now with a higher converter, you may have additional traction problems, but only if you aren't careful with the way you drive it. Remember, above the stall speed, the aftermarket converter will act just like the stock converter; you only get your big torque multiplication just before and at the stall speed. So as long as you are easy with the throttle until that RPM, everything after will be just fine.
  10. Thanks for the good info guys, I'm looking forward to getting this build under way.
  11. I hear that. My car's been down for 3 months now. About ready to get it back together and running.
  12. I used to have a Tork Tech MP112 kit on my factory 4.6L 2V making roughly 400 rwhp, and traction was difficult to come by in 1st gear, but second was fine as long as it wasn't cold / rainy / snowy. This was with a factory longblock, factory 4R70W, and 3.73s.

    With my new setup (at ~10 psi on the street), first and second gear are useless on the street, and it'll also spin in 3rd if the converter isn't locked or if I mash the throttle instead of rolling onto it. Unfortunately, I have no idea how much power it's putting down as I haven't had a chance to dyno it since my valve float issue a year ago.
  13. 1. Twin-screw (400-500rwhp) nice!

    2. Auto w/ 2000 rpm stall install the blower then see if you even need this

    3. 26” tall drag radial tires hell ****ing no those will get you killed! some loose sand, water, ice, or snow and yer dead!

    4. Stock 3.31 final drive (Possibly 3.73’s?) install the blower then see if you even need this

    You might find that the blower and the supporting mods are a lot of money and will do for the time being.
  14. Excellent info, thanks for sharing. Just to clarify one thing, were you on street tires or drag radials?
  15. You may be right about the money thing, I'll start with the blower and see what's going on with the car after that.
  16. I was on 275/35R18 Sumitomo HTRZ-II tires at the time. Now I have Dunlop Direzza SP1 Star Specs in the same size.

    EDIT: I agree with Kilgore. Install the blower and supporting mods first, then see what else you need. There's a big difference between 400 rwhp and 500 rwhp in terms of traction (and really, what we're talking about here is torque, not rwhp). I think 3.73's are perfect for a 400 rwhp 4R70W car, but if you're making more than that, it may be too much gear depending on other variables (tire diameter, redline, etc.).

    One other point: A 2000 stall converter would be a pointless waste of money, and in my opinion there's no need to touch the factory 4R70W at all at those power levels (if it has been well cared-for). I rebuilt / upgraded mine at 93k miles, 35k of which were supercharged, and based on the condition of the bands, clutches, steels, and "hard parts", it could have easily gone another 30k-50k miles without issue.
    #16 Flghtmstr1, Apr 3, 2014
    Last edited: Apr 3, 2014
  17. Alright I will definately consider your advice for the drivetrain. I'll simply go with the blower kit (and supporting mods) and see where the car is at as killgore also suggested. If something breaks, no biggie as I am anticipating to upgrade it anyway.
  18. That's a lot of your problem right there. My granddad has a STOCK '01 GT with Dunlops on it, and it has a harder time hooking up than my 400+ rwhp car does on Nittos. OP, be sure to get a decent set of tires. I'm a huge fan of Nittos (NT555s), but I've heard good things about BFGs KDWs also.

    Mostly agreed. However, EVERY 4R70W that has any power at all to it should have an oil cooler at a minimum, and pre '01s should do the J-mod (at least the drilling out of the valve body part). I wouldn't bother building it until you put a higher stall in it or are running north of 400 rwhp. Mine was good for years at the 350-375 range, but in the last few months at 400-425, I started to notice it not always holding on long WOT pulls.
  19. Sneaky, I'm not sure if you're familiar with the Star Specs or not, but they're not your average, run-of-the-mill Dunlop. They are basically a "street legal r-comp" autocross tire and are way stickier than NT555s in acceleration, cornering, and braking (I've used both). The Sumitomos weren't terrible (I cut a 1.8 60' on them), but they almost killed me when the tread delaminated at speed.

    You're right about the oil cooler; I forgot to mention in my previous post that I installed a large B&M on mine within the first week of ownership (42,000 miles). As for the J-mod, I highly recommend it, but my factory trans held up fine without it. As always with this sort of thing, YMMV.
  20. Ah, I am not familiar with those. The ones my granddad has might as well be tossed in the garbage. Haha. Along with the Falkens on another one of his cars, and the Goodyears on another. I'm surprised you still had traction problems with them if they're stickier than a 555. My 555s hold up pretty darn well as long as it's 60+ outside, and as long as I don't just stab the throttle. I don't know exact power levels I was at, but I was trapping just a tick under 120 in the 1/4 last time I was at the track, which would indicate in the 400-425 area.

    Your car is an '01, right? I wouldn't bother with a J-mod on those cars either (they pretty much come with it already done from the factory), but it's worthwhile on the 99-00s, and downright required on 98-downs. It made the shifts on my car MUCH better, but didn't add any harshness at all.