Acceptable Converter Slippage

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Seanh832
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Acceptable Converter Slippage

Post by Seanh832 » Wed Dec 23, 2015 5:56 am

I had a Hughes Pro IV 8" Race converter built for my Hydraulic Roller SBC 406 combination a while back and was told that it would slip 4-5%. With all the basic parameters input the Wallace Racing Calculator says im getting around 8.6% slippage. That extra 3.5% slippage puts me on the rev limiter 125-150 feet before the finish line in the 1/4 mile and limits my max mile per hour to 136 instead of pulling to 142 at 7000rpm. I typically run 1/8 mile due to my work schedule but the car was set up to run 1/4 mile and be driven on the street. The cars best 1/4 is 1.31 60' and 9.85 @ 136.6mph at 7000rpm on the rev limiter with a 3.90 gear and 28 x 10.5 Hoosiers behind a TH350. What is and acceptable % of slippage on a custom built race converter? Anyone have any solid data? Preferred brand of converter?

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Re: Acceptable Converter Slippage

Post by Greenlight » Fri Dec 25, 2015 3:37 am

I have Racepak (and other datalogger systems) data on several cars that run in NHRA Stock, Super Stock, Super Comp., Top Dragster, and Comp. Eliminator.

4% to 5% slippage is typical on a VERY good Stock eliminator converter. Super Stock cars range in the 5% to 7%. Lighter cars tend to have more slippage. I have seen values as high as 11% in some dragsters.

I am reluctant to name which converter companies I prefer, but there are several good converter companies that build quality pieces.
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Alan Roehrich
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Re: Acceptable Converter Slippage

Post by Alan Roehrich » Fri Dec 25, 2015 11:36 am

For most bracket race combinations, 8% slippage is "in the ballpark".

You're talking about a really good and well developed combination when you talk about 5% slippage.

But yes, some companies build more efficient converters.

Actual slippage should be calculated, using an engine RPM signal and and an output shaft or driveshaft RPM signal. If you're looking at your tach and using the MPH on your time slip to calculate it, you may be off by a significant amount.

It's hard to get a low true percentage of slip with relatively low RPM and a taller gear. Most 8" converters are going to want to see 7500 RPM + and around a 4.56:1 gear for 1/4 mile racing.

You might do it with a high end converter that will cost $800 to $1,000, and you may have to send it back once or twice. And you might not get slippage down to 5% without hurting your 60' times, and possibly your reaction times.

Seanh832
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Re: Acceptable Converter Slippage

Post by Seanh832 » Sat Dec 26, 2015 1:38 am

This converter was a $1200 custom built unit but i haven't pulled it out to have it adjusted. I just expected it to be a little closer to what i was quoted in regards to slippage on the first shot. Thanks for the input guys..
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