I was looking at some data on my last 8.33 Pass and noticed the RPM Drop from Low to high gear went from 7300 to 5800 on the 1 to 2 shift. It's a 1.76 first gear.

I was curious to see what some of you guys are seeing. Isn't there a certain % you like to see? I know the converter is pretty tight

Thanks,

Tim

 

Most of the good tuners are looking for an 800 rpm drop on the shift. Depends on where your torque peak and horsepower peak are too. On our mod motor, we pull the engine out of it's power band with a tight converter and a glide so we went to a T400.

 

1000-1200 is what marty chance told me. mine drops about 1200.

 

Thanks for the input...

 

Tim,
Mine is a 1.80 glide, but drops 800-900 on the shift is all. Converter efficiency is about 6% or so best I can tell.

Craig

 

Thanks Craig, My data Logger is telling me that converter slippage is 3 to 4% on the big end and when I shift into High gear the converter really pulls the RPM's down. I wouldn't have known any of this without the Data Logger. This also explains why I am not running out of RPM with 4:10 gears in the Back end; the converter is coupling really hard, which is not necessarily the optimum for ET. I explained in the other Topic how I am going to try and overcome some of this.

Trying to optimize all this stuff for ET is difficult, especially when we keep adding Power (Timing) to the engine and it makes a 100 or more horsepower, obviously the converter is going to react differently at different HP Levels. Honestly I could probably change the converter & Rear Gear in the car and get a new converter and be done with it but this gives me something to tune and I like the idea of having a tight converter for the Street Driving I do.

 

If you keep spining the blower, or adding timing at the time of the gear change, that could push the converter harder, not letting it fall back. I know on slicks my car would benifit from more gear. It is just about right on radials. I don't have a good data logger to know for sure how much the drop is.

On the gear change how much boost drop do you have?

 

I don't have my Data log in front of me but I think the boost drops from 28 to 23 or 24 pounds. As far as timing, all I'm using now is the Boost curve and not any of the gear retards which may be the next step after we max out our engine tune utilizing the Boost curve / MAP sensor / timing control.