Acceptable torque converter slippage?

[Shorthorse]

Did the Wallace calculator using a recent time slip. What is the acceptable torque convertor slippage? 60 foot times seem to be going away. Wallace calculator said 13+%
10:80 car, @3400 lbs, 5200 stall converter, @6300 trap rpm.
Thanks,
Terry

 

[LemonWedge]

What size converter? In general for most 8” - 9-1/2” performance converters that stall in the 4000 to 5500 range, I’d think that anything under 10% is decent, with under 8% being golden. At 13%, you may have an issue, especially if you’re seeing performance go away. This can be a really tough issue to define, though. I’d tend to lean on your converter company for real advice, as it can be a sliding scale. Any advice you get here is just a guess.

 

[Frank Mopar]

Time for tires?

 

[Shorthorse]

Time for tires?

New this year and not a lot of passes.

 

[Shorthorse]

What size converter? In general for most 8” - 9-1/2” performance converters that stall in the 4000 to 5500 range, I’d think that anything under 10% is decent, with under 8% being golden. At 13%, you may have an issue, especially if you’re seeing performance go away. This can be a really tough issue to define, though. I’d tend to lean on your converter company for real advice, as it can be a sliding scale. Any advice you get here is just a guess.

Thanks LemonWedge. I looked online and converter companies have tons of info on stall speed and selection. They mention slippage and TCI also has a calculator but I missed or can't find any defined parameters. Some forums will mention between 6-10 so I'm guessing south of 10% is at least a benchmark.

 

[dvw]

Finish line slip doesn't always mean anything. If your trap rpm is below your shift rpm at the finish line, slip will be higher. Excessive slip can slow you from a poorly built converter. But in most cases 13% isn't all that bad. Heck when we ran my sons turbo car with a 2.76 gear is was up around 30%. Even now with the 3.55 it still shows high. The best indicator I've found for converters is to watch how far back the rpm falls on the shift. It's a truer indicator of flash stall. With my stuff 700-1000 rpm has been the best. Loose is quick. Loose is more consistent. This assuming a well built converter that is sized to the combo. To much power and you'll drive right thru it. Very little rpm drop on the shift. To tight it'll pull down way to much. Three examples; My blown small block 3900 street car. 3000 rpm street converter 11.65@122. PTC 5300 2 weeks later 11.03@123. My old racecar ran fine with a turbo Action 3800. 426 Max wedge 11.20@117. Then we built a 498 with -1 heads, stock cross ram. 10.60's@125. Car was driving thru the converter. Replaced it with a "J" converter, 10.40's@127. My current racecar. 572 -1, .800" roller, 15-1 compression, Indy cross ram. Engine combo has had the same heads, carbs, cam, intake, headers, etc. Converter #1 9" 5600 flash. Car would run 9.30's. Converter #2 a very loose 9" (6400), 9.10's. Now has a slightly tighter 9 1/2" (6000), 9.0's. I would have never thought a high torque engine like this would need a converter this loose.
Doug

 

[Frank Mopar]

Good stuff Doug. Great info. The OP is relating it to his drop in 60 ft time though.

 

[dvw]

i guess I should add. If the sprag in the converter is slipping the stator won't hold. 60 ft will drop do to loss of torque multiplication. However a slipping sprag will not show up as converter slip. A seized sprag will kill top end but 60ft will be Ok. A million reasons for 60ft loss. One of the biggest that's over looked is engine power. Weather gets lousy, power goes down , 60 ft suffers. When I pull the power out of mine to slow it to 9.25 from 9.00 the 60 goes from 1.25-1.26 to 1.29-1.30.
Doug

 

[gtxracer]

Great info and food for thought, Thanks too all!
Bob

 

[383man]

What are your et's and 60 ft times ? You may be able to get a comparison to my car as its run 10.70's. This is a time slip from my 3725 lb 63. Its a street/strip car and I use a Dynamic 9.5 converter that flashes about 4200 rpm. I shift around 6200 and trap about 6400 rpm . Ron

 

[Shorthorse]

What are your et's and 60 ft times ? You may be able to get a comparison to my car as its run 10.70's. This is a time slip from my 3725 lb 63. Its a street/strip car and I use a Dynamic 9.5 converter that flashes about 4200 rpm. I shift around 6200 and trap about 6400 rpm . Ron


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Thanks Ron. The car belongs to a friend of mine. Your time slip is very, very close. The car used to 60 almost the same with some dips into the mid-high 1.40's. It has a worked J converter that is due to be looked over. We did the Wallace calculator to see just how "due" it is. The next time we will do the calculator when the converter is fresh so we will have a good comparison. It's now doing mid to high 1.50's consistently (different tracks, different conditions). There have been some changes made prior to the season, a little weigh added, Dana 60 (still 4:30 gears), Caltrac's and double adjustable shocks. Tried several setups and had lots of help from trusted people that know suspensions. We can easily see slight changes but the 60's still hover in the mid 1.50's. It appears from all the helpful feedback that "acceptable" slippage is variable. At this point, a freshened converter will probably tell the tale.

 

[dvw]

1.50 on a 10.80 bracket car is pretty close. Now if the car should be a 10.65 car and the converter is holding back that's another story. You'll see Stock eliminator cars cut some pretty good 60ft. But look at the gear ratio and rpm they run. Not that bracket friendly
Doug