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View Full Version : RPM calculator - what percent slip from lock-up converter?

Derek69SS
11-30-2005, 10:55 PM
I've been playing with the RPM calculator on TCI's website to see if I think I'll be able to live with my 4.10 geared 12-bolt posi rear I just bought.

The trans is a '95 4L60E with lock-up converter, with (I believe) 0.7:1 ratio 4th gear.

How much do these slip on the highway at cruising speed? I would assume they don't actually "lock" like the name suggests, or do they?

I may just stick the old 3.08 10-bolt rear back in for the long trips, which will be easy since it has disc brakes (don't have to disconnect anything, and bleed them :) ), the speedo is programable, and I'll have an "extra" computer programmed for the similarly set-up LT1 in my wagon, which will be programmed for 3.08s also.
sinned
11-30-2005, 11:12 PM
If it is a true lock-up converter slippage is less than 2%. On cars utilizing a CEL and computer transmission intergation anyhting more than that will trigger a CEL fault. Keep in mind that full lock-up only occurs in very rare cases during 3rd gear operation and steady-state cruise 4th gear operation.
Derek69SS
11-30-2005, 11:17 PM
Cool, that puts me in the "tolerable" range. :)

Note to self: quieter exhaust is a must this time :yes:
mattsv8_03
12-01-2005, 04:10 PM
to find rpm at certain mph

mph*gr*336/td.

just be glad your not me. v8 s10 5.14 gr. th 400 trans no overdrive and 5500stall converter. and i drive it to the track runs 10s and drive it back. rpm at 65 3750.
sinned
12-01-2005, 06:24 PM
to find rpm at certain mph

mph*gr*336/td.

just be glad your not me. v8 s10 5.14 gr. th 400 trans no overdrive and 5500stall converter. and i drive it to the track runs 10s and drive it back. rpm at 65 3750.
You are failing to calculate for torque converter slippage which is what Derek is asking. His combo has very little slippage at cruise while your combo has a greast deal of slippage
mattsv8_03
12-02-2005, 12:35 AM
just multiply the final answer by the pecentage of slip. would that work.
sinned
12-02-2005, 08:06 AM
Yeah, if you knew how much converter slippage was present. Converter slippage could be determined by checking your actual speed (using a 100% accurate speedometer) against the math at 0% slippage and figuring out how much spped is lost.