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Interesting Converter Information (Stall Speed) #1904899
09/02/15 01:01 PM
09/02/15 01:01 PM
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Oakland, MI
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dizuster Offline OP
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Just thought I’d post some information about converters that I learned this summer from testing. Sort of interesting stuff that flies in the face of everything I ever thought I knew about stall speed.


My car has a small cam… 230@.050”, and really shows it. It absolutely just doesn’t want to make power above 6000~6200. Anytime I shift it higher than that, the car loses ET.

Last year I ran a converter that would stall at about 5600~5800… I would guess right around the peak HP (or maybe even a touch over it). The slip on the big end wasn’t all that great either coming in at 13%. Way too much stall speed from what anyone would normally tell you to run on a motor that only pulls to 6000rpm.

With the turbo and small cam, this thing makes MEGA torque at low RPM. So I bought a new converter this year to tighten things up and hopefully take advantage of my power curve RPM band.


Same exact tuneup as last year. Same weather, Same boost, same jetting, same timing, everything… 100% the same except for the converter.

-Stall is down to 5200~5400, which should be a good thing since this motor doesn’t like RPM.
-Slip is down to 6%. Which should couple the motor better to drive the car forward.
-Finish line RPM dropped from 6500 down to 6100, which again should be good since the motor doesn’t like RPM.


Here is the kicker… 60ft times stayed the same, but the car slowed down. Lost at least 3mph at the finish line, and roughly a tenth in ET.

How the HELL can I make a converter change that brings the RPM back towards where the motor makes more power and more torque, have less converter slip %, and slow the car down?!

The only thing I can think is that this particular converter doesn’t multiply torque like the old one. So during the shift fallback while it’s back on stall speed, it’s just not multiplying torque to accelerate the car like the old one.

Pretty crazy stuff…

Just goes to show there is a LOT more to converters then slip and stall speed…

Re: Interesting Converter Information (Stall Speed) [Re: dizuster] #1904907
09/02/15 01:09 PM
09/02/15 01:09 PM
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Portage,michigan
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It might also show that convertor makers dont quite have the touch regards making the right piece for a Mopar small block that has a turbo on it. Just probably not a lot of similar builds out there that a guy can look at his notes/ others he has built to get his setup right.
Likely going to be a trial and error thing I would guess.


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Re: Interesting Converter Information (Stall Speed) [Re: dizuster] #1904921
09/02/15 01:31 PM
09/02/15 01:31 PM
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Oakland, MI
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dizuster Offline OP
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Well I should clarify something else... I was trying to be generic about that stall speed and slip isn't everything.

As slow as this converter is... I absolutely love it... and here is why.

The old converter would stall about 2500 on motor, and 5800 on boost. It would take me about 2.5 seconds to go from 0psi of boost to 10psi.

The new converter stalls around 3800 on motor, and 5400 on boost. It will go from 0psi to 10psi in about 0.9 seconds.

Whatever it lost in ET/MPH is well worth the ability to stage/bracket race the car now... so it was a trade off for me.

Re: Interesting Converter Information (Stall Speed) [Re: dizuster] #1904931
09/02/15 01:51 PM
09/02/15 01:51 PM
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Columbia, CT
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Are you leaving under full boost or off idle?


Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.
Re: Interesting Converter Information (Stall Speed) [Re: dizuster] #1904936
09/02/15 01:58 PM
09/02/15 01:58 PM
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Not surprising that a looser converter is quicker. People get caught up in converter efficiency thinking that will make the car quicker. That is seldom the case. Lower slip numbers generally equal slower ET's, but they put less heat in the transmission and are generally more consistent. Generally speaking looser less efficient converters are quicker in the car, put more heat in the transmission and are less consistent.


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Re: Interesting Converter Information (Stall Speed) [Re: dizuster] #1904946
09/02/15 02:08 PM
09/02/15 02:08 PM
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I'm thinking there is more to it slowing down than the convertor, boost likes tighter convertors with the boost ramping up faster has to equal to faster ET maybe your motor isn't putting out the same HP it did valve springs getting weak maybe some of the valves are leaking check into the motor make sure it performing correctly on all cylinders.
I’m not disagreeing with Al loose convertors makes cars faster but with boost your car should of pickup more et and mph at least mph something is wrong with the motor in my opinion.

Re: Interesting Converter Information (Stall Speed) [Re: dizuster] #1904947
09/02/15 02:08 PM
09/02/15 02:08 PM
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Milwaukee WI
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It would have been nice to have logged exhaust pressure with the old converter. I would suggest doing it now for a baseline for future changes. Tighter converter equals more exhaust energy. You may be peaking to soon now.
I do agree with Al. I also know what you mean about staging with it. Give and take...


"use it 'till it breaks, replace as needed"
Re: Interesting Converter Information (Stall Speed) [Re: dizuster] #1905063
09/02/15 04:16 PM
09/02/15 04:16 PM
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Oakland, MI
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dizuster Offline OP
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I actually suspected the valve springs, so I put new ones on about 3~4 weeks ago. I also shimmed the hydraulic lifters near solid just incase it was collapsing the lifter. Removed air filter just in case it was dirty.

None of the above did anything to the ET/MPH. The only thing that happened this winter is the trans came out, new converter went in.

Overlayed the data logs from last year to this year, o2 readings are identical.

All very strange if it's down on power, I don't know why.

Yeah I don't log exhaust pressure, I should probably do so.

That being said, I added 2psi this week and the car picked up more then 2 tenths and 3mph, so I don't think it's choked on back pressure or it wouldn't have reacted so well.

Last edited by dizuster; 09/02/15 04:17 PM.
Re: Interesting Converter Information (Stall Speed) [Re: dizuster] #1905283
09/02/15 09:00 PM
09/02/15 09:00 PM

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I lost a lot of footbrake races with a converter that was looser and faster but could not hit the tree--went to tighter converter same 8 in--car slowed but I could KILL the tree every round--no big about RPM at stage etc--just dead on
Got a mystery 8 in in my small block dragster--box was marked 6200
loosest converter I have ever seen--soft and loose as you can imagine--car is wicked fast , RPM drop at 7500 shift is barely audible Car is fantastic!!!! This thing feels like it has water for fluid and it is just super happy at all times and MPH so big it is crazy--so....all the conventional wisdom is out the window

Last edited by crabman173; 09/02/15 09:01 PM.
Re: Interesting Converter Information (Stall Speed) [Re: dizuster] #1905353
09/02/15 10:20 PM
09/02/15 10:20 PM
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It's ALL about the stator and pump fin angle. The stator in the new converter is much more aggressive, as shown by reduced slip, lower rpm and mph at the stripe. Once the converter welds itself to the motor, you simply don't have enough grunt to pull it up top. You probably lost most of your ET and momentum at the 330. Check to see if it is running the backhalf the same. If you have more, turn the wick up after the 60ft and make it run to 330 and it should be quicker.

WAY more to a converter than where it stalls

The converter doesn't know if it's a small motor or a big motor, nor does it care if it's a Mopar, Ford or Chevy. It simply knows torque

Last edited by Monte_Smith; 09/02/15 10:23 PM.
Re: Interesting Converter Information (Stall Speed) [Re: dizuster] #1905805
09/03/15 04:54 PM
09/03/15 04:54 PM
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fredericksburg,va
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Im thinking you engine likes that higher rpm, if you could put a stiffer gear to get back to the target rpm, might run faster. Tighter means more drop between shifts, your looser conv. probably didn't see much rpm drop at all. Think of a PG, all converter. Just thinking.

Re: Interesting Converter Information (Stall Speed) [Re: dizuster] #1905834
09/03/15 06:23 PM
09/03/15 06:23 PM
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Dayton, OH
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Converter=voodoo

Re: Interesting Converter Information (Stall Speed) [Re: ] #1905836
09/03/15 06:29 PM
09/03/15 06:29 PM
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Taxes & Virus's R-US, NY
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I would think it went a little lean on top...Just a guess, and hopefully you have the log, but a loose converter can mask a lean spot....I would think since it was loaded sooner, its struggling a little more to pull into the power band. Need to see some time slips and understand your setup more, but that would be my 2 cents off the top of my head...The proof would be if it gets back to its old et...Maybe the logger couldn't see the difference....not sure.

If that's not it, maybe the valve seats if the springs are new....Eventually you get enough mileage on them, they need resurfacing and a valve job....

Last edited by Dragula; 09/03/15 06:35 PM.

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Re: Interesting Converter Information (Stall Speed) [Re: dizuster] #1905844
09/03/15 06:38 PM
09/03/15 06:38 PM
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Basically, with higher rpm your energy production increased at a faster rate than your energy losses.

Think of it as a balancing act, balancing power production against power loss. The higher rpm converter simply allowed the engine to produce more net energy over a given time period. While converter slip/heat buildup were increasing as well, you had not yet reached the break-even point and ended up with a net gain.

Last edited by weedburner; 09/04/15 12:49 PM.
Re: Interesting Converter Information (Stall Speed) [Re: dizuster] #1905869
09/03/15 07:23 PM
09/03/15 07:23 PM
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I'm glad somebody is figuring this stuff out!

Through a series of missteps - I've basically gone backwards while trying to fix things that weren't broke. LOL

I thought my converter was too loose or hurt because the math kept working out to more and more slip. The last pass it maintained the same rpm from the 660' mark to the stripe - but gained 25 mph. So I pulled the trans and went through it, and had the converter gone through and de-stalled some at the same time. It's a heavy "street truck" with a lockup 4,000 stall converter and it appeared to be stalling to 4800 and flashing much higher. It had traction issues at times - and mistakenly thought it would be "happier" with a little softer leave. WRONG!

The trans was hurt - which probably produced ALL of my slip. All the clutches were smoked and the steels were burned black with the pressure plate now cone shaped. (internal leakage problem)

Now that I've had the converter made tighter, and the trans gone through and repaired - it won't 60' anymore. The trap speed went up and the RPMs went down - but I believe that was a function of the trans problems. Now the converter only stalls to 2,800 instead of 4,000 and it's a pig down low. Yeah, it picked up a couple of MPH - but I'd rather be hanging the hoops!

So - converter is coming out again - and hopefully they can put it back to what it had BEFORE I had them mess with it. Maybe, just maybe - it'll 60' again AND make some MPH?







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