I'm trying to track down some problems and figure out optimal gearing for trap speed, but I don't fully understand slippage. I'm trying to understand how torque converter slip effects MPH and gearing. I've looked around but if anyone could briefly explain it, I'd appreciate.

For context this is a TH400 with 3500 stall:
How does the slippage affect gearing ratio?
Does it numericly lower it and thus make a given ratio reach higher mph?
If a converter is very inefficent and slips a lot, will the car be able to trap higher at the same RPM?

In calculating mph to ratio I've found that with a Th400 (2.48,1.48,1.0) and 3.42 gears that second gear is good until 100mph at 6500rpm. And in third gear it is good for 147mph at 6500rpm.

With these numbers would a "loose" or inefficent converter with a lot of slip allow for 105MPH in second or 95mph in second? (Just throwing out numbers)

 

The more the converter "slips", the lower the mph for the same engine rpm. Unfortunately, there is a basic relationship between stall speed and how "loose" a converter is at the top end. Each manufacturer will try to tell you they have discovered some secret that allows the converter to effectively "lock up" at the big end while being loose enough at the start of the run to allow the motor to jump into the powerband and effectively multiply torque. But from what I have seen, TINSTAAFL in converter design and the basic design of all of them is the same.

Rich

 

So using my 100 mph in second gear example...a very loose stall would only reach 95mph before running out of gear?

How much varience is possible 0-5mph or 5-10+?

And thank you for the explanation.

 

Reviving an old thread

I'm interested in hearing people's opinions as well.
I'm trying to track down whatever gremlin is killing my 1/4 times.
I suspect that either the tranny or TC is slipping excessively.
I've been told that 10% is too much.

 

What is your combo...gearing, weight, converter stall/converter maker, rpm you shift at and estimated power level? Very important for any real help.....

I will say that a good loose verter will generally lose peak hp but will make most of that loss up with more average horse power from extension to shift point rpm. This is really why an unlocked Big verter can dyno bad but make great mile an hour where it counts, street/strip. Then there's a bad converter or bad converter design that has very little efficiency and not that great of extension..

My PI 3200 verter took a crap a a few weeks back..There was little warning sign and felt great. Got a little flashy for a few minutes..then it came apart taking the tranny with it....so, you never know...Most people say they tend to get flashy when the clearances go bad. So, unless your verter feels real odd I would not think it's gone bad. It may however be a poor design or poor mismatch for your combo...

Yes, 10% at your peak is alot..But that's not set in stone! You may make it up with better extension and such...(especially useful with cars with peaky power bands) and better launch (more flash stall). In the real world though, I look for something with 93-95% at peak horse power. My PI had 93.5% at peak power and 95% at 6800rpm's. Verified by locked vs. unlocked numbers. With about 89% at my extension.

 

93 Firehawk, leather, ac, ttop.
LE2 heads / LE1HL CAM + boltons.
3.73
Stock weight
ProTorque 3200 (purchased used, yeah I know ... bad idea)
6375 shift point
380rwhp/340rwtq through the 3200 stall.

Car should run migh 11s at 118 or so.
Car is running 12.3 @ 110 with 1.7 60'

I even let a more experienced (and lighter weight) driver try. He was only able to pull 12.2 @ 111.
(So at least I know it's not me)

I suspect that I'm slipping in 3rd gear.
I'm considering replacing the TC with a Yank 4000 stall and having the tranny rebuilt to handle more TQ.
I don't know if it will fix the problem, but I suppose it's not a bad idea.

Complete mods list : http://www.cardomain.com/ride/2297151
Heads/Cam install details : http://www.cardomain.com/ride/2297151/4
Dyno/Track Results : http://www.cardomain.com/ride/2297151/3

 

OK, you got pretty good info there with dynos and time slips...I will say one thing first..I used to run a manual in my car with full weight (minus jack and spare tire) and back when it was making 408ish at the rear I ran about 118mph...I then added roll bar, ET streets (a little rolling resistance) and when I converted to an auto my trap speed went down to 112-113 MPH And, dyno went to 365 unlocked (lost over 40rwhp)... So, if your full weight and your converter looks locked? then 350-360 is what's really at the rear unlocked?

Now, Looking at your 1/8 mph vs, your 1/4mph I would say your not slipping 3rd gear. It would really show up with a bigger spread then what your seeing. In fact that 23 mph gain from 1/8 to 1/4 is right on with an "AUTO" car with the weight and power level (when I slipped 3rd gear I noticed right away that the car went from accelerating in a linear fashion to a big jump in rpm, and felt disconnected....). What I think is happening is your not using your available power curve...Looking at your power curve I would shift at 6600 rpm. Right before your valve train looks unstable. This will give you more extension on your shift and way more average power. Ed Wright taught me a while back that the power at your extension is what's important for auto cars, not peak power. I bet right now with that tight converter and shifting at 6375 rpms you next pull (extension) is like 4500-4600 rpms? You can raise that extension some by shifting higher...(although, it's not a direct correlation, something like torque at the point the converter stops slipping) or by getting a looser converter (like you described). A SS4000 yank will drop your extension to about 5400-5500 when shifting at 6600rpm. Or, if you want to just shift at the same 6375 it will be some where in the 5300-5400 range. Now that converter (because of it's efficiency loss) may or may not gain mph..(compared to say a 3200). I bet it will though, as your 10% loss stated had to come from dynoing? locked vs. unlocked on your old converter.....you'll 60 foot a ton better for sure. You also might try a SS3800 (it will act like a 4k behind your extra power) and your extension should still be in the 5100-5200 area shifting at 6375...I would call Yanks number though, to find out exactly the stall and extension number with your power level...If you can keep the efficiency up and make better use of the available power you might pick up a few mile an hour. That combined with a better 60 foot (1.60) should pick up 3-4 tenths in the 1/4.... My guess is 11.9-12.0 @ 113-114 mph...

 

I appreciate the analysis and advice Jimbob.
That makes sense now that I look at it.
It's just weird that it's costing me that much in the 1/4.

I beleive the dyno numbers are with the converter locked.
Ed has it set to lock at 95mph. (I'm not familiar enough with how that all works
to give you any better answer).

I really want to replace the TC, I just don't trust it.
Besides, I think you are right about the benifits of the higher stall and extension.
The built trans .. I don't know. It's not like I have $1400 to throw at it if I don't have to.

 

Converter is a huge deal for autos....
I have seen a lot of racers get atleast 3 plus converter re-stalls/replacements to get their combo right...So, it's not easy on the first try. I bet you would be real happy with an SS3800 (stall like a SS4000 on your combo). If you were going all out racing a Thruster Pro 4000 will give awesome extension and good efficiency but it will be stally on the street..and not like juice at all...My SS3600 should flash to 4100-4200 rpm (similar to my old 3200 VIG) but have more extension...I was thinking of going SS3800 in my combo but I want to shoot a 150 shot, and with the power my combo makes that shot may not work...I know LS1 402ish stroker guys with same power on engine love the SS4000 but can't shoot any juice....

 

Yeah, I've been on the fence between SS and the PT models.
I've heard a lot of guys tell me how much they prefer the PTs.
At the same time, I drive this car to work every day and I may want to do N20 someday
(granted, by the time I decide, I will probably have to take the tranny out and have it built
up a bit anyhow, so changing the TC wouldn't be a big deal)

 

I had a PT4000 on my engine with similar horse power to yours...I had a small 305 comp cam in there at the time and only needed to shift at 6k rpm (after that the power took a dump). Anyway, the PT4000 could hardly get me up a hill without riding at 4k rpms. The stall had a flash of about 4600-4700 rpms and an extension of 5700, with a 6k shift point...(Not good for my combo back then). I had it destalled to about a 3800 stall, with 5000 extension after. I then traded off to "Twofast4lv" and that converter is still in there with a big 225+shot of juice...If I were buying one for a daily driver/strip car the SS line is way more streetable and should allow you some room for Juice (SS3800 and less)...I think with your power level the 3800 might just be what your looking for... The SS3600 would for sure work with Juice but will slow you down maybe a tenth "NA" (that's a big maybe too) and lose 300-400 extenion over a SS3800. Just remember that any off the shelf converter is going to flash 200-300 more with your engine, weight and gear...The higher the stall the more it will flash on your combo..

 

As and FYI to what my problem was, I had my torque converter come apart. It was slipping a crazy amount. Pieces of it went through my transmission.

It cost a good amount to get it all repaired.

For your problem, I would send your converter in for a restall. It will be cheaper in the long run. And while your trans, is out have it gone through.

Just out of curiosity, what were your unlocked dyno numbers? I have a feeling they were closer to 360? Unless you are locking your converter like on the dyno, it wont run like the dyno numbers. It will be hard on the converter, but you might try locking it up sooner?

 

Fortunately, my fluid looks pretty clean. Not that that guarantees that nothing
is broken. But it does make me feel a little better.
But I will certainly take a closer look when the trans is out of the car.

I think when this one comes out, I'll sell it cheap to someone who wants to restall it.
Protorque quoted me $276 to refresh it.
I'm really more comfortable with Yank anyhow and I don't want my car down for a week or two while they restall it.

I don't know what my unlocked numbers are (or if the ones I have are locked)
I just let Ed run the dyno and tune the car and try not to get in his way.
I didn't actually realize that the graph started so late until after he shut the
dyno PC down.

I do know that I asked him about locking, and he said that he set mine to lock
at 95mph (vs stock 75mph) and that in his own tests it didn't seem to make
a difference at the track. He also offered to burn me a new chip with any
lockup setting I wanted so I can try it for myself.
I may take him up on that at some point.

 

That sucks about your tranny and converter...As you can see the same thing happen to me...The damn metal from the converter (looks like one of the berrings went out in the converter) went thru wiping out both my 5 pinion plantaries, sprag, pump, 2nd gear Red band, 3/4 Zpack, some assembly that holds the clutches (Reaction shell....The beast maybe). I believe some valves in the valve body need replacing. Replacing all those parts plus replace the B&M 28000GVW cooler...(can't trust to get all the metal out...). And can't forget the new SS3600 Converter I just had to buy... I'm sure glad Ellis "Twofast4lv" is hooking me up on this...

I use to lock my converter at the track years ago. I would gain about 1 mph locking at 100mph (remember, good extension) so, had to wait...I did try different mph lock points but that mph gave me the most 1/4 trap speed. However, I never could notice a ET difference Locked vs. unlocked. I figured it was so late in the run (locking it) that it just didn't give me enough time to help me before the 1/4 came by. I stopped locking to keep the stress down on my old converter clutch when I saw no difference in ET. Some guys say it helps ET, some guys say it doesn't...Seems to help less with the Yanks .....Never tried it on my VIG3200....

 

On the other end of the spectrum, the PT4000 in my 6800 RPM shift point car is doing the trick

The 5700 extension keeps the car nicely in the powerband. Like you said, it's all in what the car needs!

My PT4000 still creeps at idle and can actually pull the car uphill at idle! Around town driving leisurely I wind it up to about 2800 rpm to briskly run w/ traffic.