converter slipping

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70wayfarer

70wayfarer

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ok....apart from my turbo oil leak it feels like my converter is slipping. when I took her for the first rad test I thought the trans needed more fluid, but no that was all good. the shifts are softer than I would have expected also.
my converter is a 9.5 ptc 3800 stall. 410 sb, s475 turbo, 727.
the rear gears are 3.5 and a 28" tire.
at 60 it mostly sits around 2200rpm but sometimes gets uo around 3000 but mph does not change much. when I give some gas it reacts like a manual with a f#@ked clutch. give her a big foot full and around 3500- 4000 it explodes into life, boost coming on strong too.
i'm running a large cooler and it does not seem to be getting hot at all.
I read somewhere that sliping and softer shifts go hand in hand. higher rpm the shifts are firm.
what gears and tire are you guys using for a street stripper. maybe I need a higher numerical gear like 3.25 or 3.5?

cheers
 
I might be off my rocker, but I believe I read somewhere that with a turbocharged application you don't need as high a stall, I could be wrong.

I'm guessing you had the converter built specifically for your car? Any changes?

If not, it might be advantageous to call PTC and see what they have to say.

Hopefully someone can shed some light on it for you.
 
the converter was more for strip than street hence the hi stall. I went over my specs with Lane at ptc, but I had told him 3.5 gears. I have put 2.75 gears in for road brke in miles not thinking it would have the effect it has.
the fluid seems not hot at all after 3o mile drive, but will put a temp guage in to be sure.
at 3500-4000 the boost and converter seem to come on at around the same time and things really get interesting. loving boost already.
 
70wayfarer said:
the converter was more for strip than street hence the hi stall. I went over my specs with Lane at ptc, but I had told him 3.5 gears. I have put 2.75 gears in for road brke in miles not thinking it would have the effect it has.
the fluid seems not hot at all after 3o mile drive, but will put a temp gauge in to be sure.
at 3500-4000 the boost and converter seem to come on at around the same time and things really get interesting. loving boost already.
Click to expand...

That might be the issue right there, your not staying up in the power band like you were, and the converter is probably slipping. I would for sure add a temp gauge.

Did you add the boost after you got the converter?

I'm just spit balling here, but like I said, I swear I read that with a turbo you don't need the high stall.
 
nah...converter was specked for turbo. the high stall is to be able to bring rpm up close to boost coming on when staging.
 
70wayfarer said:
nah...converter was specked for turbo. the high stall is to be able to bring rpm up close to boost coming on when staging.
Click to expand...

Well the only thing left is the gear change. Your RPM's are way lower at part throttle than they were, leaving you down off the converter while cruising. Either way, I think you would be experiencing this even NA.

I know when I went the other way, from 2.76 to 3.55, the difference is quite a bit in RPM's at 55-60 mph.

Now that I think about it, perhaps it was lower compression for boost.
 
That's just about where mine went, right at 700 increase. I know it made a huge difference in the way the car drove. It was an absolute dog down low, it in no way compares to your power plant, but I would have to think the same theory applies.

I dunno, if that's the only change you made, and it wasn't doing it before....

Maybe there's a certain point where that converter locks up for part throttle, so to speak, and you're just below it.
 
ok, you had the verter speced for the 3.5 gear and changed to a 2.75, this changes everything about the verter, it's just not going to react the same like was mentioned at the lower rpm's cruising. when you kick it in the *** it does just like it suppose to.
 
yeah....thought the 2.75's would make brake in miles easier on the wallet. did not expect the effect it had on driveability. not driven a car with such a converter before now.
are the soft shifts at lower rpm a result of the slip as I've been told? at upper rpm they were firmer.
have solid engine mounts and oem style trans mount. did notice a shudder at medium to heavy acceleration. could this bi the trans mount. trans is new build.
 
If I'm reading this right, you're planning on going back to the 3.50's sometime soon. If that's the case, just try and keep the trans cool & live with the "slip" for now, and get back to those gears as soon as possible.
 
OldmanRick said:
If I'm reading this right, you're planning on going back to the 3.50's sometime soon. If that's the case, just try and keep the trans cool & live with the "slip" for now, and get back to those gears as soon as possible.
Click to expand...

trans fluid does not seem to be hot at all.
this is my first turbo build and to be fare I'm not sure of what gears will work best on the strip with a 28" ET Street tire. last thing I want is the turbo to run outa puff 3/4 track.
cam is hydraulic flat tappet and good for 6500.
 
70wayfarer said:
trans fluid does not seem to be hot at all.
this is my first turbo build and to be fare I'm not sure of what gears will work best on the strip with a 28" ET Street tire. last thing I want is the turbo to run outa puff 3/4 track.
cam is hydraulic flat tappet and good for 6500.
Click to expand...
Well, 120 mph is 5121 rpm with a 28"-tall tire and a 3.55 at 120 mph... if my math is OK.
That, plus 5% slippage for the converter would give you 5,377 @ 120 mph.... not an over-rev situation at all with 3.55's.

Sounds like a good combination for street/strip car.


Check my math; I haven't done this for a long time...:eek:ops:
 
the 3.5's will go back in before it goes on the dyno, which hopefully will be before Christmas. will post results when it does.
where is the best location for trans temp sender ?
 
70wayfarer said:
the 3.5's will go back in before it goes on the dyno, which hopefully will be before Christmas. will post results when it does.
where is the best location for trans temp sender ?
Click to expand...

Seen B & M's work well with 727's,personally. Don't know, if you have a deep sump transmission pan. Sure would help, on trans fluid temp control.
 
Ive not had a lot of experience with hi-stalls. The few Ive driven felt,on the street, like big old rubberbands.Until they got close to their rated stall, then hang on! Even stalls around 3000 felt strange to me. But then, Ive been a stick man since 1970 when I bought my first Mopar; a Swinger340. Panther pink no less.
From what Ive read here amongst the turbo crowd; Most say they go faster and quicker with the lower number gears. I have no experience. Yet.
 
I put the 3.5 gears back in a couple of weeks ago and the difference was night and day. rpm at 60 is around 2800 but drives on the open road sooo much better.
had her out to 120mph with 10 psi boost and **** loads more in her yet.
 
70wayfarer said:
I put the 3.5 gears back in a couple of weeks ago and the difference was night and day. rpm at 60 is around 2800 but drives on the open road sooo much better.
had her out to 120mph with 10 psi boost and **** loads more in her yet.
Click to expand...

Sounds awesome , post a video if available .... Fwiw : Full synthetic automatic trans fluid doesn't break down until 450-500 degrees farenheit. Normal automatic transmission fluid, starts breaking down quickly about 220-250 farenheit. You may know this already. Went through this , with a over loose converter years ago.
 
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