I had a Precision Vigilante '2800' that would flash over 5000 at 18 psi boost on my 383 LT1. The engine was turning 6200 rpm at 135 mph with 2.73 gears and 25" tall tires. Do the math and that's alot of slip. With no slippage, it should have been going 170 mph. It would only foot-brake stall to 2100 rpm.

So, I talk to Precision and they assured me they can fix it. I sent it back and they reportedly tightened it 500 rpm and installed a "turbo stator" that should allow it to build more boost on the line against the foot-brake. I got it back and it will build much more boost on the line, but it also foot-brake stalls to 3600 rpm (yikes!). Now, it only drops 200 rpm on the shift. I logged a run the other day it at 6200 rpm, it's only doing 105 mph (double yikes!). Calculate the slip on that one! What a turd. >

And to top it all off, Precision isn't being very cooperative in fixing this.

Mike

 

i went thru 4 with Viki at P.I. until she told me she couldnt make it work for my turbo ls1. I talked to Carl ROSSLER and he said to call viki and get a 10" or 10.5" ...i forget which and that would hold.....she knew what i was talking about when i called back but i had already ordered a converter from another company

 

Well, if it makes you feel any better, I have a similiar situation. At 6350rpm, 25.75" tire, and 3.27 gears, I am at 126 mph. My math shows that to be right around 18% slip. I get about a 700rpm drop on shifts. I ask my converter guy about it and he basically buffalo's me telling me that either my math isn't right, or the rpm or mph is off and that there's no way the converter is slipping that much. Unfortunately I don't know enough about it to know exactly how a semi-high stall turbo converter *should* work, but I'm pretty sure it is slipping to much.

How much rpm drop on shifts did you get with your first converter? How much do you/everyone think is optimal? I guess haveing a converter a bit loose is better than a bit tight and breaking input shafts and what not.

Troy

 

If your getting 700 rpm drop on all the shifts then it's OK. I assume your shifting it in the low 6k range. If it dropped 1k it might be too tight depending on where you want to shift. It might be possible to get it to lock more in high gear depending on what kind of guts you have in the converter. Nobody can tell you for sure except your supplier unless it's opened up and looked at. Loose is better than too tight in the converter world

Engineermike. Like was said. If PI has your converter as tight as they can get it and it only drops 200 on the shifts then you need a larger converter. Like swap from a 9.5 inch to a 10.

A converter can be tricky especially in a difficult turbo application. We had hell getting the turbo V6's to work. You only have a 274 or less inches to spool as large as a 88mm turbo but it makes well over 1000hp. It requires a loose converter for spooling yet it has to be tight on the high side. I have worked with PTC for years with different Turbo applications and have a handle what's required. If any of you are interested I'm a dealer for PTC and can get you one of their pieces.

Here's one thing a lot of companies won't tell you. It is a bit of a guessing game and unless an identical combo to your's is on file the first converter can be off a bit. I have been through as many as 5 with a new unique combo to get everything right. This is why most companies offer 1 free stall change so there is a baseline to go by to get it right.

 

Hey Dustin... Have you ever heard of a "spragless" converter offered by Transmission Specialties.. They can convert someones converter to spragless.. And it's suppose to slip less, and eliminate the chance of sprag failure..

Opinions ??

 

All converters for a performance app should be spragless. Eliminates any chance of breaking it. We tried a new converter from the real Art Carr in cali a few years back. Broke the sprag on the first pass....Not to mention it had a stock c4 stator in it with what checked out to be a toyota pump. We had it rebuilt to be spragless and put a steel stator in it instead of the aluminum it came with.

 

Someone please explain the math. I get 563 rpm drop on the 1-2 shift and 511 rpm drop on the 2-3 shift. This is with 28" tire and 3.55 gears at 130.6 mph in the 1/4. I have a Art Carr AODE with a 3000 stall converter. My 60' are 1.6 to 1.9 foot braking in a 3650lb car with driver.

 

That is EXACTLY the problem with turbo cars. Gotta be loose enough to spool the turbo but couple on the top end at a relatively low RPM. I have seen loose coverters on the dyno and as soon as you come up on boost, the engine hits peak RPM instantly regardless of roller speed and will hang there for as long as you want to keep the throttle down. It gets scary when you have a heavy hitter combo and it's pegged on the rollers for 5 seconds or better trying to find the top of the HP curve! The cars do drive better in the real world than the dyno would suggest but a Dynojet really unmasks a problem converter with the heavy rollers and a 3rd gear pull. I had the perfect TCI converter for my car till it blew up. It was a BREAKAWAY for a TH 400 and was a "gross misapplication" horsepower wise as quoted by TCI. Hah hah, oops! It stalled 3000 at12 psi on a 2 step and showed 4% slip on top. What we need CAN be built but it takes some forward thinking by converter manufacturers to build what is essentially a mild stall, saturday night special converter that is BULLET PROOF. I tried to get TCI to duplicate the breakaway converters recipe only in a heavy duty configuration and they claimed it couldn't be done in that shell and diameter. They did offer to sell me some tiny 9 inch converter that they THOUGHT might do the job for 1100 bucks. I have heard great things about PTC having the combo's that work and when i get the cash, that's where im goin!

 

The first converter dropped about 400 rpm on the shift. I've heard that 600 is optimal, which is why my current 200 is way not enough.

 

What transmission fluid are you using? What kind of transmission is this? fwiw, with my c4, and my 125-127 in the quarter power level, when I switched from regular type F to John Deere Hygaard transmission fluid, my rpm drop went from about 500 rpm to 700 rpm. Something to think about if you think the converter is close....

Troy

 

Cool info, That rocks!

 

edge converter?

 

While PI does a very good job with specific chevy LT1, LS1, and buick T6 combos, they know absolutely zilch about anything else. If I needed an off the shelf converter for my LT1 or LS1, I'd be calling them. But anything else and it's outside their realm of understanding. Mike, do yourself a favor and send that converter to someone else........Lane at PTC, Lenny at UCC, or even Steve at TransKing. All three do very well with turbo combos.

 

Shane, believe me, I thought long and hard about buying a new PTC before deciding to have PI re-stall mine. After talking to another turbo owner with a PI and Jack at PI, I figured I could get a re-stall for $225 rather than paying $800 for a new PTC. Guess I was wrong. . .

I'm going to try to get PI to re-stall it tighter (again) for free. If that doesn't work out, I'll send it to PTC.

Thanks!
Mike

 

You would think that with the proliferation of turbo chevy's and ford's that PI would have learned something in the past 6-7 years. But damnit, if they haven't! Like I said, I would use them for specific applications. But not this one. They restalled my vigilante 9.5 three times before I finally let someone else work on it and then picked up almost .3 in the quarter.

 

Not edge converter. I'm not going to say who as I could very well be in the wrong. (It is someone that is supposed to know how to do turbo converters though) Shane, what do you consider the optimal rpm drop during shifts? Does this amount change, depending on whether or not you are shifting at 6000 or 7000 rpm? I believe you once said that in your testing if converter slip was either higher or lower than 10% you lost e.t....?

Thanks.
Troy

 

Sorry, troy, I never said anything about 10%. What's optimal is different depending on the car.

 

I had a similar experience with PI... I "worked" with the tech on the phone when ordering my 9.5 converter. I made it very clear what the application was, 600RWHP, Turbocharged, 4r70w w/3.55's in a 3500lb car, I mentioned that I'd like it to stall at around 3000rpm. They were convinced that they'd get the right converter for me.

I installed that converter, put the car on the brake, and it immediately went to 6800RPM, where it held... I called them, and they verified that I had the correct part number, and preceeded to tell me that the car was making *way* more than 600 to the wheels (which it wasn't). Long story short, they said they had room to make it tighter, "tightened it up", and now the car sits at a tick over 3k on the tbrake... I'm not sure what the original converter was set up for, but it was almost undriveable... just getting the car moving from a stop was pretty incredible. I can't say that I'm convinced these guys know what they're doing, seems kind of like trial and error to me (which sucks when you've gotta take the trans out every time to try it out...)

IMHO, skip PI...try something else...

Justin

 

What are you guys using with a PG in a 3300 lb car and 331 gears?
I was thinking 3500 10" with my t76 combo. 336ci Rblock all the good stuff.
I do want to be able to street drive as much as possible and get good sixty's on the Brake.
Thanks, Brian

 

My current converter is a 4800-5000 stall from artcarr (Was supposed to be 4000) on a 9" converter.

I'm going to go turbo soon, i am wondering if this is going to be completely wrong for a turbo setup, and i'm sure it will be.

It works great on my N/A stock block motor, because i get to launch at my peak torque and it works very well will the trans-brake. but i'm not so sure on a turbo...