How much rpm vs driveshaft rpm should you have at the stripe. I am having a big issue with my dragster not the mph and et. I changed converters and it has lost 6 mph and a lot of et. Not sure how to post the graph from the racepak.

At the 1-2 shift the difference is 3800 rpm difference. At the stripe it is 700 rpm difference.

Racepak also shows your the Ratio between the two. It will be 1.00 to 1.20 most likely. 1.00 means no slippage, 1.20 means 20% slippage.

time slip. You loose et in 60 and 300'? Most of et is first half of track. Thats part I would be looking at. What 60 rpm compared to old and same with 330. MPH I would be looking at top end slippage more,but then we don't race mph and once you find et you will find mph for most part. JMO

The engine rpm at the shift is 7680 and the driveshaft rpm 3996. SO it is actually 3684 rpm different. the ratio is stating it is 1.92 at the shift and 1.11 at the stripe.

quote:

Originally posted by S/C718:
At the 1-2 shift the difference is 3800 rpm difference. At the stripe it is 700 rpm difference.

The driveshaft RPM should be a lot slower in low gear due to the transmission gear ratio. I assume the 3800 RPM difference is still in low gear, just before the shift?

700 RPM at the stripe doesn't seem too bad. The exact slippage % depends on what RPM numbers we are talking about, but using a typical finish line RPM, 700 is about 10%.

quote:

Originally posted by S/C718:
The engine rpm at the shift is 7680 and the driveshaft rpm 3996. SO it is actually 3684 rpm different. the ratio is stating it is 1.92 at the shift and 1.11 at the stripe.

Guessing this is a 1.80 low gear transmission? If so, you are looking at 11-12% slippage in each case.

Lenny,

You are correct. It is a 1.80 low gear.

Just checked a pass i have here on this laptop and Im at 1.97 at the shift, 7572 rpm 3839 DS, and im about 1.12 i believe at the 1/4 mile. The run i have here is 1/8th.

quote:

Originally posted by S/C718:
How much rpm vs driveshaft rpm should you have at the stripe. I am having a big issue with my dragster not the mph and et. I changed converters and it has lost 6 mph and a lot of et. Not sure how to post the graph from the racepak.

You're going to get differing opinions here because it depends on the combination and how people like to run them. But I’ll share some of what I’ve learned.

The torque converter is going to dictate your top end slip percentage, along with engine power, rear gear, tire rollout, and weight. In your case the only thing that changed is the converter. Generally a converter that has less slip people call “tighter” and usually will have a lower first gear flash and shift fallback RPM.

With our stuff, 7.40 dragsters, we see about 9-10% slippage at the stripe. My old converter slipped 6% but it wasn’t as consistent, nor as fast. Usually, looser is faster and more consistent.

You should be able to figure out where the ET/mph went with the race pak. If it slowed down that much the converter must be way wrong. Usually, a looser converter runs the front half real good so the ET is quicker even if the mph is down. A tighter converter will 60’ worse but mph a little better since it slips less up top. Of course the RPM range where the engine makes power matters too. For yours to lose that much mph and ET it has to either be so tight the engine is way out of its power band or same thing on the loose side. But if it was too loose I would suspect your post also would have mentioned a very high stripe engine RPM.

I would not get too caught up in converter slip numbers unless they are way out in left field, just my 2 cents

Roughly 7267

quote:

Originally posted by S/C718:
How much rpm vs driveshaft rpm should you have at the stripe. I am having a big issue with my dragster not the mph and et. I changed converters and it has lost 6 mph and a lot of et. Not sure how to post the graph from the racepak.

At the 1-2 shift the difference is 3800 rpm difference. At the stripe it is 700 rpm difference.

send me your two graphs and i'll post them. #21 explains how to email a log

quote:

Originally posted by S/C718:
The engine rpm at the shift is 7680 and the driveshaft rpm 3996. SO it is actually 3684 rpm different. the ratio is stating it is 1.92 at the shift and 1.11 at the stripe.

For quarter mile racing at the stripe, 11% is high. Normally 4 to 8 is typical. If your current converter lost you all that MPH and et it's either broken or not fitting your combo!

Greg,

I will send the graphs to you later tonight. Thanks for the help. After reviewing the graphs the car isn't coming up clean on the chip. I am checking into that now.

quote:

Originally posted by S/C718:
Greg,

I will send the graphs to you later tonight. Thanks for the help. After reviewing the graphs the car isn't coming up clean on the chip. I am checking into that now.

I had a converter once that was so tight it wouldn’t let the engine get to the rev chip. That could be your issue!