got a notch fox street/strip car (don't really drive it on the street) 302, e303 cam, 70mm turbo, making 8 -12 psi boost, c4 trans, 3.27 gears. Sorting thru many issues with this car I purchased as described. I had it dyno tuned, the tuner said it's a pretty loose converter, attached is the dyno sheet and a video at the track. Could not launch the car hard because of tire spin and missed 2nd gear in the attached video. But during that shift from 1st to 3rd the tach only drops to 4,800 - 5,000 rpms. the converter, i was told it's a 3500 stall?
My questions are...does the converter act like a 3500 rpm stall unit? Is this to loose of a converter for this car? a newbee C4 turbo v8 guy

/www.youtube.com/watch?v=8sgh-jvOzzA

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What are you shifting at? If you are shifting at 6000 and its pulling back to 4900-5000 I'd say that's not too loose. What does it flash to?

 

Calculate the converter slippage, that also will give you some good info on the converter.

 

did a few from my dyno charts...5K rpm's...50% slip at 6K rpm's it's 14% slip, on another dyno session it was 4950 RPM's...61% slip, at 5300rpm's it's 34% slip, per the internet calculator used.

50% at 5K...that seems like a bunch of slip???? yes?

 

Never really pushed it to the limit or tested this...have seen 3500 rpm on transbrake with a real rich (9.5:1 AFR) tune on car.

the reason I'm asking all these questions about my converter is...I think it is to loose (50- 60% slip at 5K rpm's) for a turbo application....and the transbrake stopped working, so I had to pull the transmission. So, thought I'd post on the subject.

 

How in the world are you coming up with this "50%" slippage number???? Do you have a sensor to measure the driveshaft speed and compare it to the engine RPM?

 

[h=4]Conv Slip% = [((RPM * Tire Height) / (Rearend Ratio * Trans Ratio * MPH * 336)) -1] * 100[/h]
http://www.tciauto.com/tc/racing-calculators/

Jess

 

Here's the deal the calculation is only valid in high gear ratio 1:1

So, in your video it looks like you were +- 6000 rpm's at the finish line ; I need to know how tall your tires are and MPH but here's an Example: 3.27 X 122 X 336= 134043.84 /28.0"= 4787.28 BUT THIS REPRESENTS ZERO slippage not representing the total including the converter contribution. After finding the standard or base calculation of ZERO slippage you compare it to the observed RPM.
4787.28/6000= .79788 which is the reciprocal of the converter slippage. Now just subtract: 1.00-.79788= 0.20212 or 20.2% converter contribution/slippage

In all honesty it's not horrible but definitely not an efficient converter by any means. A tight converter may have between 3%-8% slippage, many converters show 10%-14%, IMHO anything over the 14+% is a loose converter and needs tightening or replacement to gain lost ET/MPH.

In the video it looks like you loaded the converter to 2000 rpm's then flashed pretty close to 3500-3700 rpm's then it climbs rpm. It may be possible the converter you have isn't built for a boosted application with the proper stator and anti-ballooning plates? JD

 

https://www.theturboforums.com/members/46122-Pete-Hughes

i would talk with Pete from Hughes see what he has to say,

 

55Chevy...thanks for the fine review of my video!...as a newbee, been looking at the video many, many times. I did think it was about the 3500'ish rpms for a flash, thanks for confirmation. So, I think the flash rpm is good, but the high RPM and speed in third gear seems loose.

My tire size is 26" dia...also measure the circumferance 81.6 inches. Using your calculation and the 26" tires....14% slip. Using TCI formula get the same, 14% slipage with my dyno sheet (attached). Using the online calculator on TCI and my dyno number I get 5.8% slip, using Wallace Racing online calculator, the results are 13.4%, TeamCSR calculator...5.8% WTF one word "Bonjour"

I guess I"ll have to believe the 55Chevy and TCI manual formula! I think the stall/flash rpm is good, just too much slip after that? does that make sense?

The converter does look like it's got anti-balloon on the outside. BTW...It's going for a ride to the converter folks for them to take a look.

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Dyno sheets...speed and rpm numbers...then calculate

 

Man that looks good in the video to me. It's going from 6100 to about 4800. I'm having this same loose stall, but mine is only dropping 300 rpm between gears.

 

He missed second gear on that shift.

Jess

 

oh okay, how do you miss a gear with a auto trans though

 

Good question. Stock shifter? IDK.

Jess

 

converter is way too loose. you should see at least 1000 rpm drop on the shift with a good converter

 

You got it...a stock prnd21 shifter....it's now gone!

 

talked with the convertor person, Tim at PTC. He opened it up and asked if this was built for a nitrious car? I said IDK bought the car as is. He said that I can see that it would now hold the power of a turbo car! So, the bottom line is for $XXX they can get it fixed up for the torque for a turbo motor. It like going to the doctor for an illness...you tell them the symptoms...the run some tests...advise on the cure/solution. you got to trust them!