darren s

iTrader: (1)

I took my car to the track for the first time today and now that all the excitement is wearing off and I have had a little time to think about things I am worried I may have some converter issues. I think the car ran good but I noticed that I was crossing the line in the 1/8th at 7k rpm at only 101mph. With 28in tires and a 4.56 gear I should be good to around 128mph ( I know it will be a little less due to normal slippage). I'm going to call the guy that built my converter next week to see what he reccommends. It's a 7.75in converter that flashed to 5500 and will transbrake to about 5700. Crossing the line at 7k I'm seeing about 26% slippage. That seems pretty high to me but I don't have a lot of experience with auto race transmissions so I was hoping to get a few unbiased opinions before I talk to my converter guy. It's a powerglide behind a 500hp ls engine in a car weighing less than 3k. Thanks for any help,



Darren

mrvedit

There is no way 500HP in a 3000lb car is going to hit 128 mph in the 1/8 mile.
You might hit it in the 1/4 mile though.

There are some handy online calculators available to help you figure things out.
To calculate ET/MPH from HP and Weight (and vice versa):
http://www.wallaceracing.com/et-hp-mph.php

To calculate 1/4 mile ET/MPH from 1/8 mile ET/MPH:
http://www.wallaceracing.com/8th-quarter.php

Many additional calculators including for converter slippage:
http://www.tciauto.com/tc/racing-calculators/

darren s

iTrader: (1)

I am aware of that and will be running 1/4mi tracks too. This was my first test session at an 1/8mi track. The car has a 250shot on it too I'm not using yet. I already used the tci slippage calculator to get the slippage numbers I listed above. Anyone have any real world experience or advice?

jimmyblue

iTrader: (11)

I don't think that's high, given how tiny and how
high a stall-speed the converter is. My 3500 will
stretch past 5500 at full pedal.

What you care about, if anything, is how much of
the slip results in/from torque multiplication (win) vs
how much goes to waste heat (lose).

darren s

iTrader: (1)

I know it throws out a TON of heat if I try to street drive it. From dead cold I have about a 10mi range before the trans fluid is up to about 230. I know a lot of that is due to it's small size and loose nature. I have a large B&M cooler on it now but it's not enough. I have bought a tru cool 40k cooler and two 8in fans that I am going to install on it in the next few weeks to see if that helps with the heat issues on the street. I don't want it to be a daily driver but I would like to be able to cruise at about 55mph for 20-30mi at a time. I'll worry about all the street manners later, I'm just trying to get the track times figured out for now.

darren s

iTrader: (1)

FWIW yesterday the car ran a 6.71 at 101 with a 1.46 60ft.

darren s

iTrader: (1)

I figured out the trans heating issue, there was a hole missing in the seperator plate in the valve body causing fluid to deadhead and heat up the trans. This was also spiking my line pressure and ballooned my converter. I have the trans fixed and the converter repaired. I had it tightened up some, now it transbrakes to about 5200 instead of 5700. I toook it back to the track expecting the times to improve but everything was .1 off, 60ft and et. The MPH was the same. I crossed the stripe at 6500 as opposed to 7000 and my slippage is down to around 17% but that still seems kinda high to me. The converter builder says it should be around 1/2 that by 7k rpm if I were to run it out the 1/4mi but that seems like a lot to tighten up in 500rpm. I do not think the car is spinning, feels like it hooks right up and goes. The car is 90 mustang and I listed all info I feel would be relevant below. I ran 3 1/8mi passes and the 60ft times were all around 1.53 . ET's were 6.81, 6.82, and 6.92. I tried coming off the transbrake with the 2step set at 3600, 4000, and 4500 with no difference in 60ft or et. I really haven't ever had anything at the track other then 90% street cars so I'm not sure what I should expect. I did tell the guy that built my converter that while it will be N/A most of the time for bracket racing I will spray it on occasion just for fun so maybe that has something to do with it. I did not get to make a pass off footbrake but the car will footbrake to about 3200 with manual brakes before it starts to push. Every pass off the brake the car came out clean and straight with both front wheels about 3-4in off the ground. I have only been to the track 1 other time with the car a few months ago and it was pulling consistent mid 1.4's but it was also 20deg cooler than it was today.

90 mustang 3030lb with driver
glide w/ 8in stall-will transbrake/flash to 5200
4.56 gear with 325/50/15 radials
6.0 LS LQ9/vic jr carb intake/850 quick fuel carb/1 7/8 longtube headers to 3in exhaust
cam is a hyd roller .24x @ .050 int/ex, 112 lsa, .61x lift
Front suspension
lakewood 90/10's, aje k member and a arms, coilover kit with 130lb springs
Rear suspension
solid upper and lower arms in stock location, QA1 single adjustables w/ 130lb springs, anti roll bar.

Any opinions on the new slip numbers and if it would be worth much et or mph to try for the tighter top end?

slow67

iTrader: (2)

It can be difficult to get a converter locked down in the 1/8. What RPM are you shifting at? What is your max RPM?

darren s

iTrader: (1)

I'm shifting at 7k, rev limiter is set at 7300. First outing I was crossing the line at 7k and had 26% slip. After the converter was tightened I went back and crossed at 6500 with 17% slip so it is better, just seems hard to believe it's going to tighten up that much more in 500 rpm. I'll give it try in the 1/4 when I can and see what happens but it may be a while. I'm going to try a buddies 9in 3600 stall soon to see if it picks up or drops off. Keep in mind I still haven't sprayed it yet either.

slow67

iTrader: (2)

If it is going to 5200 on the transbrake, it should be locked down by 7000 rpm.