For those who are using a swtich pitch, i would like to know if anyone has figured the total slip % in low stall mode and high stall mode, above the stall points. IE, what is your calculated rpm vs the actual rpm driving above the rated stall speed in each case. I heard there is 4% in transmission, not including the converter.
I think that will vary according to the converter you are using. I have a modified 12" that stalls 3000-3200 high, and ~1800 low stall. At the track, I launch in high stall and switch to low stall about 3 seconds out. My trap speed is about 107 MPH, and with a 26" tire, I should be going through the traps at at 4729 RPM without slip. Next time I'm at the track, I'll have to take a look at the actual RPM, but I think it is pretty close.
Converter Slip It is dependant on the whole combination. Weight, amount of torque being generated, gearing and aerodynamics all play a large role. The same converter in two different cars can have two very different amounts of slip. This applies to WOT as well as cruising. Does this answer your question? No. But it is something to keep in mind. Also, once the transmission is in gear I don't think a good one should be slipping at all.
Once you are above stall speed it shouldn't be slipping, you better hope it slips at a stoplight. All of them are going to slip but most reach about 98% through put very rapidly after reaching the "Stall Speed".
All Torque converters will slip some. The only ones that won't slip are the lockup ones, and that is with the clutch applied. You won't be able to feel it, but if you calculate what the engine will be spinning at a particular road speed and compare that to the actual observed RPM, you can calculate the amount of slip. 336/tire diameter X rear ratio X MPH = RPM My car has gone a best of 12.45 @ 106.80 MPH. I have 26" drag radials and a 3.42 rear. 336/26 X 3.42 X 106.80 = 4720 RPM. That is with 0 slip. Next time I go down the track, I will see what the engine RPM's through the traps and compare.
slip The higher the quality of the converter (more $$$) the more efficient it is. You are still talking about a fluid coupling though and in my own personal opinion I don't think most higher than stock stall converters reach 98% efficiency. Unless maybe in something with the aerodynamics of a Bonneville land speed racer running at 55-60 mph. What do you think Larry?
Don't really think I could put a number on it, but if OEM could get to 98% efficiency, they would hardly need the Torque converter clutch. The torque converter by it's very design would never get to 100% lockup without a clutch.
don't you mean switch-pitch? That was put there for the other guys debating whether or not they slip at all. In principle, you are correct, it should give you the characteristics of both converters described in the write-up. I agree they still work good on engines that operate within the rpm-range of a correctly built VP converter. I've had 3 VP transmissions myself. Pay close attention to the portion of the write-up that discusses changing the pump vanes; some VP builders do it that way to extend the stall-speed of VP converters too. The VP also can have trouble with the extreme thrust forces when used with a real high-hp engine. The owner of Yank previously worked as an engineer for the Hydramatic division of GM; he agreed the VP is a good converter, but has its limitations like everything else in this world. At the time several years ago when I bought my 200-4R converter from him, he told me he had just finsihed building a VP for an off-road racer. I am also interested in how much slip is gained/lost between a pass using only high-stall vs using high/low stall.
Yes i read the article stating that bending the blades makes the converter very inefficient. The switch pitch is actually doing the same thing if you think of it, but since i have a turbo car once i get the turbo spooled, i can switch to the low mode and hopefully maintain the power still at the lower stall. I know Jim from PAe has put some better parts in them now, so i hope thrust issues don't show up. What exactly goes wrong?
You are confusing the pump vane angle with the stator blades. My limited understanding tells me that it's never a good thing to fool with the pump blades (as the YANK carticle indicated), and the stator blade angles can only be modified to increase high-stall by a certain amount. Do your research before you buy. I don't know what Jim Burek puts in his coverters now, so you will have to talk to him and his competitors about what the differences in their products are.
I have a 12" Tri Shield VP converter(3200/1800). There are two other N.E. guys with this converter. We all are very satisfied with the converter. Stalls where it needs to without loosing efficiency. Yesterday at Atco, I went 12.57@105.48 MPH. Mathematically, I should have been turning 4658 RPM through the traps. I glanced quickly at the tach as I was at the end of the 1/4 mile, and as near as I could tell, my tach read somewhere around 4900 RPM. I'd say it locks up pretty good.
Larry at what point do you switch it to low stall, and have you raced it one pass leaving it in high stall?
I have a Poston switch pitch controller box.(I hide it in the center console) It has a digital timer. Very simple to connect, 4 wires, 12 volts, ground, switched side of the brake pedal, and transmission. You set the timer (0-11 seconds) for the time you want high stall. When your foot is on the brake pedal, the converter is on (hi stall). When you let go of the brake, the timer counts down to 0 and turns the converter off. I set it for 3 seconds at the track. 0 seconds on the street. There is no advantage to using high stall for the entire run. Everything I have read says that it results in lower trap speeds. The way to use a switch pitch is to launch in high stall and switch to low stall 60-100' out. The controller has a manual mode also.
