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Converter slip under power #2777797
05/24/20 08:09 PM
05/24/20 08:09 PM
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Oregon
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AndyF Offline OP
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Anyone with a driveshaft speed sensor care to share some converter slip numbers? I've been out driving the Duster and watching the driveshaft rpm on the data logs. Going down the freeway I get a few percent slip but at WOT the slip increases up to around 10%. I haven't made a full throttle pass down the track yet since the tracks are closed but I've made some part throttle blasts down the freeway and recorded the numbers. While I'm accelerating the slip is up around 10% but it drops as I get out of the throttle and then goes negative as I decelerate.and the driveshaft spins faster than the engine. I'm trying to figure out what gearing I need to put in the car. Obviously I don't want to gear it like a stick car but I'm not sure if I should add the full 10% in or not. Most calculators don't use anything close to 10% for converter slip. I think the old Mopar calculator assumed around 3% slip.

Re: Converter slip under power [Re: AndyF] #2777834
05/24/20 09:49 PM
05/24/20 09:49 PM
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Frostbitefalls MN (Rocky&Bullw...
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I had a 10 inch"medium stall" from A&A behind a 408 in a 3450 lb car with 3.55 gears. It would flash to 4000 when i went WOT but would settle in at about 10 percent slip at cruise of 65 to 70 mph. A stock converter would probably slip 7 percent under the same conditions. At least that is what i saw in my dart. I had a lockup trans in it with the same gears and would see over 200 rpm slip at cruise speeds when not locked up.


8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
Re: Converter slip under power [Re: gregsdart] #2777850
05/24/20 10:15 PM
05/24/20 10:15 PM
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dvw Offline
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What RPM? You need to look at slip at WOT at the top of the RPM Range. Just because is shows slip doesn't mean it''ll be slow. Less gear ratio tends to show more slip. Its all a function of load.
Doug

Re: Converter slip under power [Re: dvw] #2777887
05/25/20 12:43 AM
05/25/20 12:43 AM
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AndyF Offline OP
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I have 4.56 gears in the car right now which are too steep. I was going to change to 4.11 gears but with this much slip I think I'll go with 3.89 gears. I haven't used WOT throttle yet. Today I hit if from a roll with 3/4 throttle. It went from 60 to 105 in three seconds and then I backed off. The converter slip went to about 30% when I rolled into the throttle and then gradually tightened up to about 10% by the time I started to lift. I suppose I won't know exactly what it does at the track until I do it but the data is telling me that it is going to be slipping at least 10% near the top end of the track.

Re: Converter slip under power [Re: AndyF] #2777905
05/25/20 03:34 AM
05/25/20 03:34 AM
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Andy, do you know which converter company and model yours is?
I had Chris at Contintental converters make me a custom 10 inch street and strip converter for my old pump gas Duster, that converter would foot stall right at 2300 RPM before pushing the 165x15 front tires through the staging beams, it would flash stall around 4200 to 4400 RPM depending on the track elevation and weather conditions.
I broke it and install a Turbo Action 8 inch SS/AH Hemi foot brake converter I had in stock and that converter was way better on the street and at the track shock That change pick up my car at Madras .2+ ET and over 2+ MPH in the 1/8 mile shock, a little more gain at Woodburn also up
It drove real nice at light part throttle on the street and at the track and would flash stall up around 5200 RPM in high gear at WOT from a 35 to 45 MPH roll work
I think it had around 9% slippage across the finish line in the 1/4 mile up

Last edited by Cab_Burge; 05/25/20 03:35 AM.

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Re: Converter slip under power [Re: AndyF] #2777940
05/25/20 09:18 AM
05/25/20 09:18 AM
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Mt Morris Michigan
mopar dave Offline
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Andy, I use a Dynamic 8" with a 4.10 gear and a 28" tire. I think the combo is real good for street/strip unless you do a lot of long distance driving. My car with the 511 also runs about 60-105 in 3 seconds judging by my video timer. Couple days ago on the freeway I checked it again with full exhaust at 5.5 seconds from 55-117 using my speedo for mph and the video timer for time. My vert has since been recalibrated by Lenny and seems a little tighter. It used to be 6% slip and when I checked it last year was 4.5% tru the traps. The car drives real nice on the street and the trans temp barely goes above 180*.

Re: Converter slip under power [Re: mopar dave] #2777983
05/25/20 10:40 AM
05/25/20 10:40 AM
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the beauty of a loose converter on the street. they're very inefficient. I use a converter that's a little tight for the cam and no way i'd use anything looser.

Re: Converter slip under power [Re: Cab_Burge] #2778067
05/25/20 02:11 PM
05/25/20 02:11 PM
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It is a Trans Action 10 inch converter. Part number is 17805ST. It is what they call a tight converter but I think "tight" is a relative term when it is behind 600 ft-lbs of torque. I don't have any issues with the converter, it seems to be a pretty good match for the way I drive the car. I just didn't know what to expect in terms of slip while under power. My guess is at the track this converter will never catch up to the engine. It will slip a lot off the line and then gradually close the gap in high gear but looks like it might go thru the lights at 10% slip. Guess I'll just have to do it a few times and keep track of it.

Re: Converter slip under power [Re: lewtot184] #2778086
05/25/20 03:05 PM
05/25/20 03:05 PM
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Dont worry about any slip numbers that are not in the top of high gear, max RPM. Otherwise its just not accurate data. Here is a screen pic of one of the runs in the Vette 8.01 170.. The red line is engine RPM, the green line is driveshaft RPM, yellow is accel G's It is slipping 9% at the stripe. Don't read a ton into converter efficiency IMO we have been as fast at 10% as we have been at 1% overdrive with more power after making changes last year to a lock up converter. This year is a new pump design, gearset, and new stators from this. We shall see if we can make the lockup deal run faster than the slipping stuff, but so far not happened. I have often found "less efficient" converters to be faster than super tight efficient ones.

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Re: Converter slip under power [Re: Al_Alguire] #2778090
05/25/20 03:10 PM
05/25/20 03:10 PM
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AndyF Offline OP
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Thanks, that is very close to what my curve looks like. The throttle position is a square wave and RPM is almost square but the driveshaft RPM is a triangle. I understand what you're saying about not knowing how it is going to work until you test it since it all changes depending on the power and the load. At this point I'm just trying to figure out which gear ratio to use. I think I'm going to go with a 3.89 rear gear and assume 10% slip at WOT in the lights.

Re: Converter slip under power [Re: AndyF] #2778093
05/25/20 03:15 PM
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We have noticed no real change in slip % using various gear rations. We used everything from a 5.00 to a 5.48 in the car depending on the weather conditions and track. Stator changes will affect it but minimally. The lock up deal certainly changed the slip% but does not show on the time slip. Well that's not entirely true. We run the back half better with the lockup but we are much worse down low 0-60-330 which is where all the ET is. We used to have to run 5.09-5.12 to run 8.0's we now are running 8.0's going 5.18-5.20. We also have a high speed dump in the trans to drop the line pressure once out of low gear. We are changing the gearset in the trans this year as well as pump and stator combo to try and get back to 1.10-1.13 60' and 5.0's in the 1/8, but we may not get a chance to see if any of the engine and trans changes do anything this year.


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Re: Converter slip under power [Re: AndyF] #2778719
05/27/20 12:44 PM
05/27/20 12:44 PM
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Frostbitefalls MN (Rocky&Bullw...
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Since you most likely have a converter with as big a core and a tighter setup than my 10 inch AA, 3.55 or 3.73 gears with 27.5 inch tires should work fine. I sold that Dart, and the new owner drove it home 300 miles without any issues. 3.55 gears, 27.3 inch tall tires.


8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
Re: Converter slip under power [Re: gregsdart] #2778766
05/27/20 03:15 PM
05/27/20 03:15 PM
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I doubt the 4.10 vs 3.89 gearing will have much affect on either the track ET or street performance, other than perhaps very light throttle cruising rpm being slightly lower.
The converter just slips more with that taller gears, so the speed vs rpm hardly changes.


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Re: Converter slip under power [Re: fast68plymouth] #2778803
05/27/20 04:53 PM
05/27/20 04:53 PM
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I don't have any experience on street driving, but on 1/4 mile passes I have had a converter at over 11% and my last combo 9 inch (getting a new motor and converter) is somewhere between 3 and 4%. Don't remember exactly. The high slip converters were 10 and 8 inch.


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Re: Converter slip under power [Re: AndyF] #2778842
05/27/20 06:38 PM
05/27/20 06:38 PM
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Re: Converter slip under power [Re: Mattax] #2778870
05/27/20 07:52 PM
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That is correct. The S-800 tight converter for street/strip big block.

Re: Converter slip under power [Re: fast68plymouth] #2778871
05/27/20 07:54 PM
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I ordered a set of 4.10 gears from Doctor Diff for my existing S60. I figured I should do the easy swap before I spend the money for the major change. We'll see how the car drives with the 4.10 gears and then I'll make the decision on which gear set to use when I switch to a 9 inch.

Re: Converter slip under power [Re: AndyF] #2778885
05/27/20 08:34 PM
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If your driving is mostly around town, I think you'll like the 4.10's and you'll keep your performance too. Like I said before, if you do a lot of freeway driving, you'll want the 3.73 gears or the 3.89 you mentioned.







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