So I just realized you can measure converter slip with calculator lol.

my car did a 10.5 @135 with a 3.37 gear, 3500lb car.

yes it’s a lot of gear but I wanted some highway driving and was not focused on 1/4 mile at the time. That gear worked great on my manual trans.

anyways car is now t56 but I was always curious why it felt so slow automatic. Posted my dyno information. It made the peak power at 138 mph at the stall. About 3900 rpm. I went through the traps on the stall so the speed makes sense with rpm.





what would the negative 30% slip do for my cars performance? I still have the auto setup in the garage. Took it out because just felt slower than should.

 

It means the front turbine blade in the converter is spinning 30% more than the than the driven blades. Its hard to describe how the inside of a converter works without a lot of animated pictures but its fluid coupled and the force of the fluid being pushed by the drive side spins the driven side, the fluid makes a 180* turn between the two halves and there is some fancy hydraulic magic that happens to multiply the torque output through the converter. This is why a converter in an automatic can deliver like 800lbs of torque to the gear train from an engine that only makes 400ft/lbs and which is why they can have the gear ratios they do vs. a manual that only delivers what ever torque the engine makes through a clutch.

So with a clutch, if it slips like 30% you would smell clutch for the next hour because that sucker would be nearly on fire. Clutches 100% lock up, no slip. Lockup converters have a wet clutch inside that also locks them up and delivers a no slip power transmission. The converter in my th400 is not a lockup type, th400's don't have the option to run a lockup like a 4l80 or 4l60 do. So I always have some slip because its always fluid coupled.

For you that's all just a long winded explanation to say that your converter is spinning 30% faster on the engine side then it is on the transmission side. If you had a lockup converter that means it could either be bad and not grabbing like it should or you have to much HP and are well past the wet clutches HP capacity. Does it slow you down vs. a manual? Maybe, maybe not. Depends on if the slip loss was made up for in less and quicker shifts or not.

This is basically why auto's never put as much WHP down as manuals, with the trade offs being that autos are more durable(sometimes), less prone to user error, and generally speaking shift much faster(.4sec to change gears, drop RPM and start climbing again in my th400) than a foot operated clutch and manual shifter. Also in my experience much cheaper to build. So you try to make up for the power loss by having the whole deal work quicker and have less gears to shift through.

In stuff like 600-800hp street cars auto's tend to feel softer to me where as manuals tend to feel like they snap my head back more but in a 1/4mi run they both end up being the same times and speeds. The auto just tens to feel like it walks into the power where the manuals just jump into it.

 

everyone I speak to says the magic inside converter lmao. Guess it’s ok to chalk it up to that.

I had built rmvb th400 with 3800rpm stall from UCC ($1700) in the car. So do you think the car would’ve been faster if it was closer to 0% slip ? Drastically different or slightly?

I wanted be auto but hated the sluggish feeling car had after 2nd gear. Wondering if this is why.

 

A TH400 can never have 0% slip. There is a fluid passage that facilitates the clutch operation inside the converters on the newer transmissions that the th400s just don't even have.

IMO autos always feel sluggish compared to dropping a clutch hard because the high stall just won't let you slam the power in like that. It's just soft until the stall speed because its the equivalent to feathering a manual clutch on an engine that would "stall" if you let the full clutch out before the given RPM needed. Would it be faster with a 4l80 vs a th400? That I'm not experienced enough to say really but I would imagine so. Will it be faster with a manual? Again I don't know, that's also calling for a different suspension setup and other tweeks to get it to hook different. The car will probably like different gearing depending on which transmission is has too.

There are a lot of changes to be made between setups, which changes are responsible for making it faster are kind of a mystery when you make them all at once.

 

Math is wrong somewhere....Never negative, and 30% positive, you're not moving much.

www.wallaceracing.com/converter-slip.php

 

You've input 3900 rpm @ 139 mph 3.39s and 28 " tire should be closer to 6000 rpm , that's why the negative # . Double check your rpm @ mph data and try to calculate again

 

that’s what the dyno read. That mph at that rpm.

 

I've never seen a torque converter multiply engine rpm. The driveshaft would need to be spinning at >5600rpm to to go 139 with a 3.37 gear and 28" tire. As mentioned above, verify engine rpm and speed.

 

Ok. Was just curious if it would affect performance but seems like not even possible.

 

The name of the game, whether it’s manual or automatic, is to keep the engine in its “happy Zone” as much as possible during a pass. Either with the converter, trans gearing, rearend gearing, tire height, etc or a combination of all of the above.

 

Your RPM is wrong. There's no way you went through the traps at 3900 RPM.

 

Must have let off.

 

Or the displayed RPM/Signal was incorrect. I agree... negative slip isn't possible. It's either locked or its slipping.

Problem was the trans side couldn't ever catch up to the engine side due to the gearing and power you were making. An auto/converter is sensitive to the gear gear/tire/rpm range. You can't just run what you want and expect any converter to work. Well, not work optimally as it should in a 1/4 mile race scenario anyway. My car did similar with a 3.10 gear and 30" tire. Less weight... but more load due to taller gear and tire. Converter won't ever be happy like that. Mine basically rode the stall point and the trans side of the converter couldn't ever catch the engine side. So it just hung at the stall point and slowly accelerated. Get a 3.90 in there and rev it to 7600 with the correct converter and it would be a night/day difference I'd say.

 

+1

And for 640rwhp seems accurate. I'm guessing it 60'd in the 1.55-1.59 range.

 

Not sure if anyone noticed that his dyno is highlighting Max values for each hp, tq, and rpm. Not when those values occured. Based on the sheet shown he's at 6500ish at 138 mph, which makes sense.