High stall converter affect on dyno numbers...

[RECHRGD]

Just curious about this.  What affect does converter efficiency have on rwhp results on a chassis dyno?

[flyinlow]

 I would think the initial torque numbers would improve due to the better torque multiplication in a high performance converter as the turbine accelerates from zero RPM.  At peak HP RPM's as the turbine starts to catch up with the impeller I don't think it will change things much. Depends on what you mean by efficiency ? Some converters have a lock up clutch. When engaged it is like a manual transmission with no slippage, 100% efficient. The converter lock up clutch is not normally engaged at WOT.  If you install a high stall converter they slip more in normal driving and make more heat. Less efficient. 

Converter selection sometimes seam more Voodoo than camshaft selection.

My new Hughes converter is waiting to be installed. This is the first high performance converter I have installed in 30+ years. It will be interesting to see how it drives compared to the older design. It is a lock up converter.

Hope to see some improvement off the line....but if it adds 50 HP, I will take it.  

[RECHRGD]

I had been told at one time, that if you calculated your percentage of converter slippage, then added that percentage to the rwhp on the dyno it would equate what the rwhp would be with a manual trans.  Not sure if that's true but it makes sense to me.  Say your converter slippage works out to 8%.  If you put down 350 on the dyno that would equate to about 380 hp with a manual trans or lock up converter.  Probably useless information, but could be helpful in trying to calculate flywheel hp.......

[c00nhunterjoe]

Best method is take it to the track and note the mph clocked and the weather conditions at the time. Specifically density altitude, humidity, temp, and vapor pressure. From that, you can calculate your correction factor to about a 1 hp variable. If you dont have access to all the numbers, just get mph and density altitude and that will get you within 5 or so. Way simpler then trying to play the dyno correction game. Besides the converter, the gear ratio and tires will affect it as will the dyno operator. You can make anything look good depending on how you load it.

[flyinlow]

I always wondered if it was a wash.

At initial stall some torque converters can put 2.5 X the torque out that you put in. as the turbine starts up from zero rpm at WOT the stator acts to boost the flow and pressure returning to the intake side of the impeller. More output torque temporarily  at the expense of heat production.

Lets say your engine makes peak HP at 5000rpm.  You are on the chassis dyna running  5000rpm. The impeller in the converter is going 5000 rpm, but the turbine going to the transmission input shaft is only going 4500rpm.  10% less , but are you still getting some torque multiplication? If so the extra torque helps make up for the lower rpm in the horsepower formula. Since automatics are considered to have higher drivetrain losses it must be at least a slightly losing proposition at high rpm. It can't be just the losses from driving the transmission pump.