Excessive torque converter slippage?????????

I have a Coan 10" Maximum Performance Converter w/anti balloon plates behind a 502 BB and C-6 in my (street mostly/strip occasionally) 1992 Mustang GT. It's supposed to be around 3,700-3,800 stall behind my engine on motor alone. The converter seems close enough on the stall but seems to be very inefficient since it has at least 10% slippage on motor alone. I would assume that if I sprayed the motor the slippage would be even higher? I'm almost redlined now in the 1/4, so I'd have to change the rear end gears to a lower numerical gear in order to spray it with NOS, or only run the 1/8th on spray.
Why would my converter be so inefficient and have so much slippage? How much effect would that much slippage have on ET and MPH? Will it slip even more if I spray it? I'm baffled, anyone have any input?
Gary

did they custom build it for you or is it a off the self part?

how much rpm? may not be turning it hard enough to get it into lockup.

After I had the engine dynoed I gave them all the engine and vehicle info and this is what they sent me! I'm not sure if it was truly custom built for me, but they said this was the converter for my combination.
Gary

richter69 wrote:how much rpm? may not be turning it hard enough to get it into lockup.

6200-6300 at the end of the 1/4.
Gary

Seems a 10" would have less slip at that rpm, goes to show there is more to a converter than stall speed.

I'd give them a shout and see if they can improve on it, if not sell it and find another converter company.

Sometimes it takes more than one shot to get it right, its all part of the tuning process.

10% is acceptable on most racing converters. In fact it was the standard 10 years ago and is a lot higher in the 1/8 mile unless you have one built for 1/8 mile only. Today it can get a lot closer. It was built to handle N2O, how do you know its wrong if you're not spraying it?

You are dealing with one of the very best converter companies out there . Bad data in = bad data out. They need to know what you're doing with it. I know that they will work with you to get it right.

Curt wrote:10% is acceptable on most racing converters. In fact it was the standard 10 years ago and is a lot higher in the 1/8 mile unless you have one built for 1/8 mile only. Today it can get a lot closer. It was built to handle N2O, how do you know its wrong if you're not spraying it?

You are dealing with one of the very best converter companies out there . Bad data in = bad data out. They need to know what you're doing with it. I know that they will work with you to get it right.

I was planning to sort out my chassis,suspension, and traction issues first before attempting to spray it. Other than the slippage issue, the converter seems to do what it was supposed to do. My only worry was that the seemingly excessive slippage was a sign that something was wrong with the converter. Coan had said that it would probably be 6-8% slip. I was worried that if it slipped 10%+ now, it would slip even more when I sprayed it with a 100-150 shot. I guess I'm going to have to do a rear gear change to run the 1/4 on NOS.
Gary

what the complete motor combo? 6400ish rpm could be a little low if its a race engine.....

dfree383 wrote:what the complete motor combo? 6400ish rpm could be a little low if its a race engine.....

Street-strip, pump gas motor. 594 ft/lbs at 4800 and 631 hp at 6000 (10.2:1, A-429 heads, FRPP Victor, 950 QFT 4150, solid lifter flat tappet cam 261-268 .660 lift) C-6, 8.8 w/ 3.73 gear,, 325x50x15 Hoosier DOT drag radial slick. Primarilly street use, occasional dragstrip use.
Gary

Honestly 7000+ rpm in a drag situation is pretty common with a BBF. I'm assuming you have a good Oiling system and rods in the motor?

dfree383 wrote:Honestly 7000+ rpm in a drag situation is pretty common with a BBF. I'm assuming you have a good Oiling system and rods in the motor?

Randy Malik built the motor with a forged Scat stroker crank, Scat H-beam rods, SRP forged pistons, a Kaase oil pump along with the required mods to the oiling system.
If the motor makes peak power at 6000 rpm, how high should I be turning at the end of the 1/4?
I figured on keeping it below 6500, to avoid it "falling on it's face" at the end of the 1/4 as power
falls off on motor. I'm sure that "on the spray" the power curve may move higher in the rpm band.
Gary

jst because it peaks at 6000 doen;t mean you can't run it out the back and still turn some good ETs, might want to talk with Randy.

u want the converter to drop about 1500 rpm on your shifts if making power to 6000 shift at 6000 but that cam will run out the back door 7000 + if your running 6400 now on spray it will be 7400 i dont see a problem with that what does randy say call mike riding vortec converter 586-255-3426 he'll take care of u but i think your ok
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