ajrothm

I'm trying to figure out how much my converter is hurting me..(or helping for that matter)

I just switched from a stick to auto, first time out was Friday night..I really only got one decent pass in but I got data off of it.

Using my "ricer math", I calculated my exact trap RPM from my data log by adding my 9.35 ET my launch starting point in secs, to pin point my exact trap speed/rpm, which is 6714 rpms@145.5 mph(trap speed on the slip, log showed 147 but I know my speedo is 2 mph fast everywhere), so this is pretty damn close.

The online converter slip calculators are giving me 11.1-11.5% slip depending on which one you use.

So I guess my question is, what is a good slip % for a 1/4 mile car.... One that is street driven often?


The car trapped 149mph with the stick on a soft launch and lift shifting. I was hoping the auto would trap the same, even with the additional weight and given parasitic loss due to more efficient launching and no loss during shifts.. But it seems to have killed about 4 mph... 1 mph I can account to a much worse DA but...

It just seems like I should be trapping more mph for the HP it makes, I'm wonder if the converter is eating up mph.




STATS:
1900 rpm launch, flashes to about 5100-5200....Shifts at 6600 and recovers at 5850 rpms.... Traps at 145.5 mph @ 6714rpms with 3.42 gears and 28" tires. (88" circ).. 11.5% on the high side.

Thoughts on converter slip in a 1/4 mile street car?

RENE'S RAGE

iTrader: (96)

From my understanding 6 speeds will trap alittle higher.
Did the auto knock .6 off the 1/4.
As far as slip, I don't have a clue, but what I've read is 10% or less.
I'd be pretty happy with that time slip!

studderin

iTrader: (28)

mine is zero, is that good?

RENE'S RAGE

iTrader: (96)

She said, you don't have one!

rex388

Your stick shift will have more MPH over an auto and that is just the way it is. But as for slippage that seems a little high.

Just a question, why did you want to run a 4l60e over a th400/300?

ajrothm

Damn.. So I guess a lot of these hardcore drag/turbo guys here are not measuring converter slip... There has got to be some mph found here.

I'm gonna talk to the converter company (Coan) and see what they say...

I'd like to keep the flash but have it tighter down the track.. Not sure if that's possible or not. Guess I'll find out.

Ed Wright

iTrader: (1)

That converter is fine. Guys talking about chasing MPH with converter slip are missing the point. Much more to going fast than that. Coan is one of the good converters.

c0ncEpT

iTrader: (4)

Agreed.

If your looking for MPH just buy a triple disc converter and lock it in high gear. Not much ET to gain but it will show a few MPH higher from what I've seen.

Call Coan and discuss it with someone there. If they think they can help they will.

Ed Wright

iTrader: (1)

I have seen turbo and nitrous cars pick up a little with lock up converters. Certainly not all. Never saw an NA car pick up with a lock up converter. They are heavier, and for NA cars most always slower.

Mystery Bird

iTrader: (7)

Just out of curiosity, how does a car run more MPH (faster) but not less ET (quicker) by locking a converter? Forgive my ignorance but I just don't understand.

Ed Wright

iTrader: (1)

I tested that with several cars at the track. I have never seen an NA car gain or lose when locking the converter near the 1000' clocks. Unless it's making good power locking it sooner usually costs some et.

My NA 383" was over 530 rwhp and for a while had a 4400 RPM Vigilante lock up converter. I tried locking it a couple of times in high gear. Pulled the RPM way down when it locked. First time, before I picked up my time slip I was sure it would be worth some MPH. It was worth zero. Same ET & MPH. Suprising.

Often lighter nitrous or turbo cars pick up when locking the converter. At least that is what I have found.

John02SS

iTrader: (47)

Most the converters are gonna be 8-12 % unless your buying a high dollar billet converter like Ultimate, Neil Chance, etc. The car picked up 29 from 660 to 1320 which shows the converter is doing pretty good. A shitty converter will lay on its *** in high gear normally.

87silverbullet

iTrader: (11)

If you look at your second slip you got to the 60ft faster than the 1st slip. With that happening there is less time to make mph from the starting line to the finish. For example Toyota supras run 12.0@ 152mph. They have all the time in the world to make that 152 mph because the 60ft might have been a 1.89. Plain and simple when you cut your 60ft your mph will go down.

ajrothm

Good information! Thanks for all of the feed back fellas..

Yeah I wasn't necessarily thinking about locking the converter, but maybe just having it tightened up some so it's more efficient.. My back half gain of 29 mph is average, but my MPH as a whole just seems low for the power it makes... So I was looking for places that I could be losing mph/power, the converter was my first thought because I know loose it feels.

The car dynoed 900rwhp with a stick and an aggressive tune up. It made 840 rwhp on a street tune up and thru the air filter, this setup trapped 149 mph with the stick. I converted it to the auto and I know it gained about 100lbs with the auto swap and 70lbs with the roll bar..

So when it ran 145.41 mph the other night, that was with 170lbs of additional weight, a little worse DA and the same "840hp" tune up... I was thinking I would lose mph due to the weight and slip, yet gain mph from better front half numbers and efficiency...(faster shifts).

I weighed the car on CAT truck scales the next day and it was 3600lbs with me in it and 1/4 tank.. 145mph @ 3600lb is no where near 840 rwhp.... Maybe 750rwhp... So it has definitely lost some power, my guess was the converter.


Ed you're right about the turbo cars gaining a few mph when locked up. A guy on the Vette forum locks his converter at 120 mph and picks up 4mph (146 up to 150 mph when locked).. That's on a TT C5..

I don't think it will work well on a blower car that needs the rpms for power... But reducing trap rpm down to 6500 from 6700 may be beneficial on my setup....less power loss thru slip... Who knows....

87silverbullet

iTrader: (11)

You need to leave this dyno hp mumbo jumbo and mph to hp ratio stuff alone. You ran a better ET with the auto creating a better 60ft. Then, in the process you didn't lose much mph, which is the way it is supposed to be.

It picked up almost 30 mph in the back half which is good for a converter. I would be happy with your timeslip

ajrothm

Well.... Maybe it just needs more power then.... Lol

I want it to trap 150 mph regardless of what it ETs...

We do lots of street/roll racing down here and it needs to have a decent trap speed..... LOTS of cars here trapping in the mid 150s...

I do like a killer ET but, I really will only drag race it at the strip a few times a year.... So mph is a little more important too me then 1.20 60's.

87silverbullet

iTrader: (11)

Well, you need to put the stick back in it then. Manuals are better suited for roll racing then autos.

ty_ty13

iTrader: (42)

mine only slips about 3% to the 8th... but it needs a heavy load on the motor.
its also a 4.30 rear gear with a 275 and a 2speed th400. spin it upwards of 8500rpm

BAIN

iTrader: (5)

Don't heat up your tires and spin through 2 gears and you will pick up mph

Ed Wright

iTrader: (1)

The more power it makes, the less difference you will see. Can't tell it effects my car at all, if it blows the tires off & dead hooking runs about the same MPH.
My old stock '95 F body test mule would vary almost a MPH.