SuperL98

See if I can get this all right
Thought I would post some results from my torque converter swap.
I think it's interesting because I always viewed higher stall converters effecting the cars drag strip launch more than anything else.
Looking at my data, it actually hurt my 60ft but helped a bunch everywhere else.
The 60ft loss was all traction related, to much stall and power to get a good launch with street tires.

The Car:
1988 automatic, 2.59 rears (highway car not a drag racer), ZZ4 crate engine, roller rockers, ProBuilt transmission, high flow manifold and runners, supercharger around 7psi boost, high flow cat and turbo mufflers, no headers.
Trans governor set up to shift @ 5200 rpm (should be higher but...someday)
Stock converter stalls around 2000rpm.
Precision Industries "Vigilante" stalls around 2900 rpm (ordered a 2600 rpm)

Tests:
All data taken with my Vericom meter.
No rollout on 60 ft and 1/4 times with this meter so about .40 sec slow.
Averaged data for about 10 full runs with both converters, 0 to 150 mph.
Runs were over a period of different days/months (early mornings).
Same engine tune and chip with both converters.

Results:
Stock Converter (average 10 runs)
60ft = 2.41 sec
0 to 60 = 4.92 sec
1/4 = 13.42 sec
1/4 speed = 106.6 mph
0 to 150 mph = 30.4 sec

Vigilante Converter (average 10 runs)
60ft = 2.51 sec (traction problems)
0 to 60 = 4.89 sec
1/4 = 13.16 sec
1/4 speed = 113 mph
0 to 150 mph = 26.5 sec

In the chart the purple line is the Vigilante, red line is the stock, and the black lines are the "theoretical" rpm with no slip in each gear.
You can see that the high stall converter keeps the engine in a much smaller rpm window and because of the added slip shifts sooner mph wise.
It obviously helps as much on the shifts and it does at launch.
Almost 4 full seconds off the 0 to 150 mph time, I was amazed.
Would have been even more if I could get it to launch.
Graph is averaged from my scanner data taken on the same runs.

On the down side, almost twice the slip as the stock converter makes for crappy driving around town below 40mph (before the clutch locks up), and from a standing start, highway is fine (with converter locked up).
I've actually pulled the converter and asked them to drop the stall to around 2500.
When it goes back in, I'll test and post the results.

Hope this was interesting to someone

:)


[Modified by SuperL98, 12:47 PM 8/22/2003]

azzkikr

While I have a G-tech pro - I could record my data as well, but I haven't yet. I have an '87 L98. With the motor freshly rebuilt (at 170,000 miles) the tranny also had 170,000 to 180,000 when I raced it. My best 1/4 mile time was 13.03 (this is from memory- so I don't remember 60' or any other stats)
It was also running street tires with a stock rear end gear ratio - which I don't know what it is either. (13.03 was with a slipping automatic tranny!)

O.K. so now I (overpaid) to have my tranny rebuilt and added a Transgo shift kit with a 2200 stall speed converter added.

Same problem you had... I can't get off the line with street tires! I spin them at the line and again when it hits second!

I think I really suck at drag racing... the faster my reaction times - the slower my elapsed times! I guess I can't launch at a high RPM. My best time with the same tires with the new tranny was 13.36 not the 13.03 with the slipping tranny. I even dropped my tire pressure to around 20psi - that didn't help either.

So now I'm going to replace or rebuild the differential and add some 3:73's and 6 solid U-joints. Add some drag radials and I better be in the high 11's
My differential is the only link in my drive train that is still original (196,000 miles) (Fluid changed only twice in the last 105,000 miles)

Anyway, I found you post interesting!

Chefskeez6

I don't know how much faith you can put into those. A 2.41 60ft time is horrible, i know you can do better than that on street tires. Even with a higher stall converter and traction problems 2.51 60ft i don't know maybe it is better at figuring other data 1/4 etc.

The part i am having a hard time understanding and if this is true then i guess i really don't understand stall and torque converters but at 4000rpm in second with the vigilante you are going 50mph at the same rpm with the stock converter you are going 68 i am confused.

JUAN J SANCHEZ

Very interesting topic! Something I've tried to figure out for a while. After talking to several converter manufacturers, some testing myself and now your tests, the easiest way to look at a converter( non-lock ups and for the most part lock-up units) is to figure them as added gear multiplication to the whole trans and final drive. This is also a good way to see how efficient a convertor is. For the most part a good tight stall converter will add .20:1 of gear multiplication and lock-up units will add this effective ratio but when in lock-up mode it's not effective. This .20:1 is worth about 300rpm more slippage or example: If you have 3.45:1 gears and you add a higher than stock stall speed your final drive will now be more like 3.45:1 + .20:1= 3.65:1 with a lock-up unit you will get this multiplication till you lock-it up so it's like going from 3.65:1 in non lock-up mode and then once your out the hole, passed your 60' mark, or in the power band (now much sooner than with the stock converter) the converter locks up giving you a taller gear multiplication ( back to 3.45:1) giving enough power you will now see a ET and MPH improvement but it is important to add this converter multiplication factor to you overall final drive when figuring out what gears to use when optimizing 1/4 mile or 1-mile accelerations. This is just my rule of thumb or $.02. I'm not a drivetrain specialist of any sort but I've been around enough good and bad eng/drivetrain combos to get a good idea on what goes on when swapping converters and gears. Excellent testing and observation on SUPERL98'S part. That 26 sec mile or 0-150mph time is very impressive! How much power do you have? This might answer (Chefskeez6) question. :thumbs: P.S. I have a old style vericom meter and although they may not be 100% accurate the can be used to determine gains and losses when variables are kept to a minimum and accurate data is kept. Be safe!


[Modified by JUAN J SANCHEZ, 3:13 PM 8/23/2003]

SuperL98

Yes the 60ft times look bad, but keep two things in mind.
These accelerometer gauges start reading when the car first moves.
At the drag strip, you have about 12 to 14 inches of rollout before the timer starts.
I've been told this is about .3 to .4 seconds on a 12 to 13 second car, bringing these times around 2.0 second 60 ft times.
Second, I am after consistency not "big" numbers, so I leave at idle, no foot braking.
With the stock converter no bog or spin, with the Vig the tires just cooked.

The rpm comes down to "no free lunch".
With the converter unlocked (full throttle) torque multiplication in the converter comes from slip, stall (whatever you would like to call it) between the stators and the turbine.
At the rpm point you called out (4000 in 2nd) the stock converter is only slipping about 6% from ideal, the Vigilante is slipping almost 31%.
I hear the stock converter has a torque multiplication of about 1.6 to 1.8 and the Vigilante is about 2.4 to 2.5, at full stall.
The good thing is torque multiplication, the bad thing is the heat generated by this slipping.

Juan, I agree with your comparison to a gear change, and I am starting to think that a gear change is preferable because you don't have to live with the excessive slip during normal driving.

Also I have an odd combination, a low rear gear (2.59) and a supercharged engine. The ZZ4 is actually slower than my L98 was at low rpms.
With the centrifugal blower the power bellow 3000rpm is almost stock, and really takes of when the boost starts in.
Probably why the higher rpm's helped me so much.

mackeyred96

INTERESTING

dbwade36

I have a new tranny and 3.54 rear-end, engine mostly stock for now.. On Monday, I am having a full Transgo kit installed and the shop owner suggested the possibility of disconnecting, disabling whatever, the lock-up. My problem is that the car (auto) tries to shift into OD from 2nd gear under normal street driving, too quickly, thus dropping RPM's to around 1k and the car feels like it is bogging down. I want to solve this problem, one way or another. Will the kit do it? Is eliminating the lock up advisable. Do I need to swap out torque converter (new, but stock)?

Aggravated4life

dbwade,
While Im not a Pro at this,I dont think you need a new converter unless they installed one with a low low lock up speed.That being said,eliminating lock up completely is not good for the transmission.You can however,get the lock up delayed so it only locks up in 4th gear only.Either a chip change or custom prom can do that,or some companies sell a wire harness device that plugs into the trans harness to delay lock up until 4th.Your trans has a "lock up" style torque converter and to eliminate lock up completely will cause alot of heat and wear and tear.

I would rather see it lock up in 4th only,so at least around town and lower rpms,it wont feel like its bogging down.Having torque converter Lock up in 4th would retain fuel economy on the highway and keep the heat down in there some.

Also be sure your TV cable is properly adjusted too.If its out of whack some,it can make the shifts feel out of sync.

:)

SuperL98

I agree, I think you are feeling the converter lockup also, not a shift to overdrive (4th gear?) from 2nd.
Most aftermarket chips move the lockup to 40mph and unlock to 38mph (hypertech chip does).
On the transmission valve body there usually is a one therminal pressure switch that works with the ECM to control the lockup. Changing this with a two terminal switch and doing some rewiring eliminates the ECM control and uses only pressure to lock the converter in fourth gear only. Any transmission guy that understands 700r4's should be able to do that for you.