Calculating HP loss due to converter slip ?

[forcefed3.8's]

It is tough to not to get slip from a converter on the dyno. Starting in 3rd at low rpm and hitting it with power will not allow coupling. I was seeing mph in the 11x on the dyno at redline, but the car traps 152+ with around 3% slip. Not what you are asking for, just some info. You might not see anymore dyno hp with the PTC, but the track will tell the story.

 

[Mike T]

It is tough to not to get slip from a converter on the dyno. Starting in 3rd at low rpm and hitting it with power will not allow coupling. I was seeing mph in the 11x on the dyno at redline, but the car traps 152+ with around 3% slip. Not what you are asking for, just some info. You might not see anymore dyno hp with the PTC, but the track will tell the story.

Rob, after reading your reply I went through all of my log files including 2 dyno pulls. Using 93 MPH as a marker found that 18-20 percent was the slippage range on all of them. Power was in the 395 range.


On the dyno we opened the exhaust which netted an additional 50 HP. In comparison to all of the other files slippage went up 6-8 percent. Would this be considered normal for only 50 HP?

 

[TurboBob]

The MPH signal in the stock ECM has some lag, so in the PL I recalculate it based on the raw measurements and then filter both the MPH and RPM using the same factor. So the lag will not affect the reading (or at least minimized).

After the 2-3 shift most converters are multiplying torque, thus the high "slip" numbers are not truly lost power. As the converter couples the amount of multiplication tapers off and at the top end you are left with just the efficiency (which gets better with more RPM/MPH).

From run to run, converter to converter, pick a MPH to compare them at. The PL data is reasonably accurate presuming the parameter is set correctly for the detected gear.

Bob

 

[TurboTnZ06]

I think the engine makes more power, slips and goes past peak hp, so it wasn't ever really measured. Just have to do back to back pulls/track runs with different converters and that's all you can get for real numbers of hp "lost".

 

[Mike T]

Bob this is a nice feature that I only recently heard about. It has allowed me to go over old logs with an additional perspective on things. I'm going to help one of my friends set his up and I would like to know if I've already calibrated his PL for taller tires would we use the normal values in the three adjustment boxes?

 

[TurboBob]

if I remember, the converter slip factors are independent of the tire size correction.

Bob

 

[Mike T]

Your data looks flawed. Post gear ratio and approximate mph.


Sent from my iPhone using Tapatalk

Your right, something is a little off. With 0% slip RPM @93 would be around 4303 and this would work out to 23-24%. Still not good though.

 

[Mike T]

The math is dead on here showing 29% in the 430 HP range. Most frames in the PL are working out mathematically. Looking at the dyno chart after 420 the line gets a little rough so I'm thinking the converter was ballooning or the trans was starting to slip.

Do you guys have any slip data to share from the dyno for comparison? Are these numbers typical?

 

[murphster]

Like was said before, a dyno pull in 3rd gear may exaggerate slippage as they roll along in 3rd and just mash it for a couple sec. Do a mock pass thru the gears up to 90mph on the hwy and record it on PL. Should give more accurate results to compare to.

 

[bison]

Just did mine. 82-84lbs/min. Approximately 700whp. 5500rpm, 27.3" tire , 3.42, 1:1 86% at 70mph. 30.6@100, 13.6@115. Beyond that it starts to pick up rpm. 5800 @125 10.23%, 6300@140 6.9%. This engine needs taller gearing to run its potential.


Sent from my iPhone using Tapatalk

 

[Mike T]

Good stuff Bison, interesting how it stayed around the 5500 RPM range while gaining 45 MPH. If you went with a 3.08 for the top end how would you expect it to affect the area that your seeing 5500 at now, more or less slippage? BTW what converter is this?

 

[TurboBob]

the point at which the rpm starts to rise is where the stator comes off the sprag (if you have one), past that point all your slip is real slip. Before that, some of the RPM differential creates torque multiplication and is not just slip.

Bob

 

[20psiofevil]

I just got off the rollers with mine and found some issues. 15psi gate pressure it put down 398rwhp but rpm would not go above 5300 (flat lined), the converter was slipping 1700rpm. mph would increase but not rpm. Hit it with some more boost (17psi) 445rwhp and got rpm to 5500(flat line) but would not go higher from there, again converter slip was 1700rpm. Anyone ever seen this before? I'm thinking something is seriously wrong in the trans. Unlocked converter of course.

 

[achalmersman]

the point at which the rpm starts to rise is where the stator comes off the sprag (if you have one), past that point all your slip is real slip. Before that, some of the RPM differential creates torque multiplication and is not just slip.

Bob

Thank you for this. I have seen you post about this torque multiplication before but thua statement helped me understand a little better

Sent from my VS990 using Tapatalk

 

[achalmersman]

Just did mine. 82-84lbs/min. Approximately 700whp. 5500rpm, 27.3" tire , 3.42, 1:1 86% at 70mph. 30.6@100, 13.6@115. Beyond that it starts to pick up rpm. 5800 @125 10.23%, 6300@140 6.9%. This engine needs taller gearing to run its potential.


Sent from my iPhone using Tapatalk

How are you collecting this? I assume Xfi and driveshaft speed sensor? Cool!

Sent from my VS990 using Tapatalk

 

[bison]

How are you collecting this? I assume Xfi and driveshaft speed sensor? Cool!

Sent from my VS990 using Tapatalk

Not on this car. Just mph data from a GPS. I'm sure there's some error there but not much. Probably a little lag in the GPS and a little tire growth.


Sent from my iPhone using Tapatalk

 

[achalmersman]

Not on this car. Just mph data from a GPS. I'm sure there's some error there but not much. Probably a little lag in the GPS and a little tire growth.


Sent from my iPhone using Tapatalk

Oh ok I was just curious if xfi has a lag on the mph like the stock ecm

Sent from my VS990 using Tapatalk

 

[bison]

Good stuff Bison, interesting how it stayed around the 5500 RPM range while gaining 45 MPH. If you went with a 3.08 for the top end how would you expect it to affect the area that your seeing 5500 at now, more or less slippage? BTW what converter is this?

Keep in mind I would never be in 3rd at 70mph on a quarter pass and I'd be using a different gear ratio (3.23) and or a 29" slick that would grow. Taller gearing would take even more road speed to couple but I wouldn't be shifting till higher road speeds. It's a 17 blade 9.5" PTC.


Sent from my iPhone using Tapatalk

 

[bison]

I just got off the rollers with mine and found some issues. 15psi gate pressure it put down 398rwhp but rpm would not go above 5300 (flat lined), the converter was slipping 1700rpm. mph would increase but not rpm. Hit it with some more boost (17psi) 445rwhp and got rpm to 5500(flat line) but would not go higher from there, again converter slip was 1700rpm. Anyone ever seen this before? I'm thinking something is seriously wrong in the trans. Unlocked converter of course.

You probably need more road speed to couple.


Sent from my iPhone using Tapatalk

 

[20psiofevil]

You probably need more road speed to couple.


Sent from my iPhone using Tapatalk

Dyno's are weird with turbo cars. Looking back now I wish I had just dyno'd in 2nd gear because really only wanted to see where this combo stopped making power. Took it out for a spin tonight and 2nd gear 6100 rpm converter slip was 655rpm.