Question for: PTC converter users

[TurboBuRick]

How does shift 2-3 shift feel? Do the gears feel like they blend instead of hit. Almost feels like clutch slipping but no flair. Bizarre Thinking that I'm blowing through the converter but Dusty says if anything it would be too tight.

On a log when I punch it, the rpm flat lines around 5000-5200 while speed goes from 70 to 100 mph.

Trans was just freshened up. I don't know if that good or bad but none the less I have this issue. Not letting full power get to the wheels. Thats for sure.

 

[Dusty Bradford]

What does the rpm do on a WOT pass? There should be drop on each gear change. The only way to properly evaluate a converter is with WOT data, preferably from a track so you have traction, and room to run the mph up.

A 70-100 pull is a lot like a dyno pull if you just go WOT in 3rd gear. The converter is flashing to 5000 rpm and is continually coupling which is why the mph is climbing but the rpm is not. It will reach a point where the converter is fully coupled, then the rpm will begin to rise more rapidly.

 

[TurboBuRick]

Thanks for the reply Dusty. Thats exactly what it feels like. (Flashing to 5000rpm) I think thats a little high for my combo. Can you adjust that to say 3800-4000?

 

[forcefed3.8's]

The converter will flash from a roll. You need to start from a dead stop, which is impossible on the street.

 

[TurboBuRick]

Here is a log with a third gear pull.

 

[Dusty Bradford]

Thanks for the reply Dusty. Thats exactly what it feels like. (Flashing to 5000rpm) I think thats a little high for my combo. Can you adjust that to say 3800-4000?

Roll data in 3rd gear is no good, just as a lot of info from a 3rd gear dyno pull is no good. It makes the converter flash and the engine just rides on it. The rpm needs to go to the shift point before anything can be evaluated.

The true flash stall of your converter will most likely be in the 4800-5200 range. I'll need WOT data from a track or good road test pass before you can make a good decision on what sort of adjustment the converter may need. The true flash stall is also what rpm it will fall back to on a gear change. If I built it to flash to 3800 rpm, you'll have a 2,000 rpm drop at the gear change and it will spool so slow, it will be of no use.

To evaluate a converter when a track isn't available. I roll into the throttle in 2nd gear, pull it to the gear change and then see what the rpm drops. If your going to shift at 5600-5800, make a pass doing this and then see what the converter tells us.

 

[DCVING 6]

Rick,
Head out to Central ave just south of 183rd, you should be able to make full hit there.

 

[bison]

How does shift 2-3 shift feel? Do the gears feel like they blend instead of hit. Almost feels like clutch slipping but no flair. Bizarre Thinking that I'm blowing through the converter but Dusty says if anything it would be too tight.

On a log when I punch it, the rpm flat lines around 5000-5200 while speed goes from 70 to 100 mph.

Trans was just freshened up. I don't know if that good or bad but none the less I have this issue. Not letting full power get to the wheels. Thats for sure.

Most that run a 9.5" arent shifting at 5200. My converter flashes to 5400-5500@26psi. Therefore if im in second and shift at 5400 the rpm will not drop at all. My peak torque is at 5600 rpm based on injector dc. If i shift at 6400 it drops to 5400. That flat line of rpm is good after ratio change. I have tremendous g force when during that time. Then before you know it the engine rpm is climbing rapidly as the converter couples and the slip % drops. Mine goes under 5%

 

[bison]

Thanks for the reply Dusty. Thats exactly what it feels like. (Flashing to 5000rpm) I think thats a little high for my combo. Can you adjust that to say 3800-4000?

Looks like it might be about 100-200 rpm low for your combo to be honest assuming the parts i see in the sig. 3800 will kill the performance. You should be able to rev to 5800 and still make power with those parts. I had a tiny 212 hydraulic roller in one that pulled to 5800 and the converter flashed to about 5200 at 28+psi. The engine turned out to be one of the quickest and fastest stock bottom ends ever. The converter made a huge difference. Slip was only about 3% at 134mph in 3rd. Another nice thing about the converter when dialing in a car with fuel maps is that you dont have to waste many cells below the flash rpm unless they are being used for drivability. You can use them where the engine is spending most of its time.

 

[Dusty Bradford]

The other thing to look at is overall rpm. If it never climbs over 5200, your springs are shot. I never ran less than 981's on a flat tappet cam because the spring pressure after several heat cycles wasn't enough for boost and rpm. I sent 3 boxes of 981's back when I did my last flat tappet motor. Very few of the 3 boxes were close to the advertised spec. Had I not checked the spring pressure myself before putting the engine together, I would have had rpm issues.

I started using a Sealed Power spring from the local parts store. They all checked between 100-110# at 1.7 installed height.

 

[Chrisk]

Here is my log from last week. I have a PTC NL and just had jimmy fix my flaring 2-3 shift.

 

[TurboBuRick]

Here is my log from last week. I have a PTC NL and just had jimmy fix my flaring 2-3 shift.

Looks to me like you have the same problem Chris. 2nd to 3rd blended together. No rpm drop. I bet my log will look alot like this. I don't like it.

 

[TurboBuRick]

The other thing to look at is overall rpm. If it never climbs over 5200, your springs are shot. I never ran less than 981's on a flat tappet cam because the spring pressure after several heat cycles wasn't enough for boost and rpm. I sent 3 boxes of 981's back when I did my last flat tappet motor. Very few of the 3 boxes were close to the advertised spec. Had I not checked the spring pressure myself before putting the engine together, I would have had rpm issues.

I started using a Sealed Power spring from the local parts store. They all checked between 100-110# at 1.7 installed height.

Hydraulic roller here. I'm not seeing a rpm problem. Just have not pushed that far. I'll get a good log today and we'll take it from there.

 

[TurboBuRick]

Looks like it might be about 100-200 rpm low for your combo to be honest assuming the parts i see in the sig. 3800 will kill the performance. You should be able to rev to 5800 and still make power with those parts. I had a tiny 212 hydraulic roller in one that pulled to 5800 and the converter flashed to about 5200 at 28+psi. The engine turned out to be one of the quickest and fastest stock bottom ends ever. The converter made a huge difference. Slip was only about 3% at 134mph in 3rd. Another nice thing about the converter when dialing in a car with fuel maps is that you dont have to waste many cells below the flash rpm unless they are being used for drivability. You can use them where the engine is spending most of its time.

Thanks bison, I appreciate your input. Here is the problem IMO, My car makes a ton of power between 4000-5000 rpm. If the converter is not coupled hard to the trans at that point, It just dumping the power off as heat.

 

[TurboBob]

Thanks bison, I appreciate your input. Here is the problem IMO, My car makes a ton of power between 4000-5000 rpm. If the converter is not coupled hard to the trans at that point, It just dumping the power off as heat.

Not entirely true.

Below the point where the converter 'couples' part of the 'slippage' is generating torque multiplication.

The only way to know the true efficiency is with a torque converter dyno.

 

[TurboBuRick]

Not entirely true.

Below the point where the converter 'couples' part of the 'slippage' is generating torque multiplication.

The only way to know the true efficiency is with a torque converter dyno.

Thanks for chiming in Bob. So what do you think of Chris's log?

 

[Dusty Bradford]

Thanks bison, I appreciate your input. Here is the problem IMO, My car makes a ton of power between 4000-5000 rpm. If the converter is not coupled hard to the trans at that point, It just dumping the power off as heat.

The 70mm will never spool with a converter that couples tight at 4000rpm.

Get the log shifting at 5600-5800 and we'll look at the rpm drop. It should drop to 5000 rpm, give or take a couple hundred. If you want it to pull the engine back farther than that we can tighten it 400 rpm or so.

 

[Chrisk]

The last time i was at the track my 2-3 shift flaired so bad that it redlined and actually did not shift. Jimmy the trans guy said its probably burned up. So he mentioned about a fix that forces more or all of the fluid to the 2-3 shift rather then some of the fluid. Jimmy mentioned he and Chris from CK Performance came up with this.
The log I posted was with the "fix" installed.

Prior to this PTC NL i have now I had a lock -up and i blew right thru that thing.

 

[TurboBob]

Thanks for chiming in Bob. So what do you think of Chris's log?

if you look at the RPM trace you will see a point where it stops being a flatline and starts to climb again. This is the coupling point where the stator sprag uncouples and you are no longer multiplying torque. Below this point, the torque coming out of the converter is higher than the torque going in. Slippage above this point is true efficiency.

The coupling point RPM changes with the square root of applied torque. If you increase boost and raise your torque 10%, your coupling RPM will go up 4.9% (1.0488 is the square root of 1.1).

You must shift above this RPM, and the RPMs will drop back to about this point.

The converter looks like its doing its job to me.

Bob

 

[Chrisk]

On my log it shows 4*knock and the very top. Dont know if its false? I did up the boost 1 psi and turned the alky down half a notch since i was very rich last trip at the track.
I just want a 10sec run before the season is over. Guess I need to use the trans brake next time.