1/4 mile converter slip??

One of the most critical areas of a automatic race car

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bracketracer
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1/4 mile converter slip??

#1 Post by bracketracer » Wed Nov 20, 2013 6:16 pm

Just what are we looking for as far as % of slip in the quarter???

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Marty Chance
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Re: 1/4 mile converter slip??

#2 Post by Marty Chance » Thu Nov 21, 2013 8:36 am

slippage is a necessary thing and the amount you need is dependent on many variables like ratio split in the transmission and the torque curve of the motor. The best way to accelerate is to keep the motor "happy". If you lock up the converter too fast you will labor the motor (lug) and the acceleration will suffer, or if you lock up the converter too slow you will make hp that never reaches the rear tires. So the best way to see if the slippage is the correct amount for your combination is to look at an rpm graph of your vehicle going down the track , the engine rpm drop at the shift will tell you most of this. High torque motors will want 800-1200 rpm drop at the shift and low torque motors will want 500-900 rpm drop at the shift.
Hope this helps. Marty Chance
Neal Chance Racing Converters
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wheels
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Re: 1/4 mile converter slip??

#3 Post by wheels » Thu Nov 21, 2013 11:13 am

On this topic (hopefully) with my combination, the rpm's fall to about 58-5900 no matter if I shift at 65, 7, 72, 74, (depending on class and weather). Marty you stated an generic rpm range per combination. I would say mine is the low torque combo but my question is does my situation seem right or should the recovery rpm move up with the shift point? I have a video playback if interested.

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Marty Chance
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Re: 1/4 mile converter slip??

#4 Post by Marty Chance » Tue Nov 26, 2013 7:38 am

sorry it took me so long to reply
i will be happy to look at the video\
the reason the rpm drops to the same thing no matter how high you shift, is the engine is not making any more power when you take it higher than 7000.
Marty
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Marty Chance
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Re: 1/4 mile converter slip??

#5 Post by Marty Chance » Tue Nov 26, 2013 7:40 am

could you give me some specs on the car
dyno ???
cubic inch
bore
stroke
compression
transmission ratios
cylinder heads
carb size
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wheels
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Re: 1/4 mile converter slip??

#6 Post by wheels » Tue Nov 26, 2013 8:13 am

Thanks Marty,

The car is a '67 Chevy 2 race weight is 3100, 355 10.1:1, 260@.050 .555 lift solid flat tappet (comp cams 306S), 4.56 gears, TH400 stock gearing, 8"converter (supposed to flash at 4500), pro-systems carb, 1.75" fender well headers, 255/60 drag radial. Heads are modified Dart 2 sportsman iron, 2.05 intake 1.625 exhaust valves, 65 cc chambers. The guide area has been turned down, and the intake port matched. Runs on 91 octane.
Now the bottom end is old and the ring seal is not great, so I think that would change things once it is freshened.

Here is the link to the tach playback.

http://www.youtube.com/watch?v=iAOiPyuwX5M

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wheels
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Re: 1/4 mile converter slip??

#7 Post by wheels » Tue Nov 26, 2013 8:15 am

Oh the carb is a 750 base, not sure of actual cfm. The bore and stroke is 4.030 x 3.48.

bracketracer
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Re: 1/4 mile converter slip??

#8 Post by bracketracer » Thu Dec 05, 2013 7:14 pm

Marty, What are you calling "low" torque motors and same for "high" torque motors?
Another words what torque # range do you consider high torque?

I am looking at some log graphs and most it seems like my rpm drop is 670..

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Marty Chance
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Re: 1/4 mile converter slip??

#9 Post by Marty Chance » Fri Dec 06, 2013 1:00 pm

Wheels i would recommend you shift at 7000 and raise the stall on the converter so it drops to 6200 on the shift. This will also help the car be more consistent as conditions of the air change.

Bracketracer - the terms i used "low torque" and "high torque" are very vague and variable. A "low torque" motor would refer to a power curve that relies more on engine speed and HP to accelerate the car, this is usually found in short stroke motors or motors with large runner heads and big cam shaft (ie sbc w/ SB2 heads)
"high torque" motors refer to longer stroke motors with small cylinder heads that produce high velocity at lower rpms . These motors produce power curves that rely more on torque to accelerate the vehicle (ie Pontiac 455)
These are very generalized terms and there is an infinite amount of variations that make each application unique. I hope this helps
Marty Chance
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jmarkaudio
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Re: 1/4 mile converter slip??

#10 Post by jmarkaudio » Sat Dec 07, 2013 2:05 pm

I resent that SB2 comment, my 461 CI SBC with SB2's makes over 700 ft/lbs of torque... :mrgreen:
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wheels
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Re: 1/4 mile converter slip??

#11 Post by wheels » Sun Dec 08, 2013 7:44 pm

Thanks Marty great info.

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Marty Chance
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Re: 1/4 mile converter slip??

#12 Post by Marty Chance » Mon Dec 09, 2013 8:03 am

Mark good to hear from you, I have an SB2 motor also
wish you and yours a very Merry Christmas
Marty
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jmarkaudio
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Re: 1/4 mile converter slip??

#13 Post by jmarkaudio » Tue Dec 10, 2013 8:30 am

Thanks, Merry Christmas to you as well. Have a safe holiday! Sorry I'll miss you at at PRI this week, maybe I'll get up there next year.
Mark Whitener
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