launching an AUTO

[kenneth]

Just wondering what would be the best RPM to launch at the track with an auto.
Currently I'm power braking and bringing RPM's up to 1700 the best 60' so for is 1.9 I know it should be better than that with my mods
I want to go to the track tomorrow if the weather will hold out on us.
Any suggestions PLEASE

Also using BFG G force R1's Drag tires

 

[kenneth]

I just went try it out again and at just over 2000 RPM's with the street tires they start overpowering the brakes.

 

[psfracer]

I know on a common sense level this doesn't add up---but I consistently get my best 60' times when I leave off idle. It just seems like the converter flashes quicker and higher for some reason vs preloading it.

 

[kenneth]

I'll give that a try tomorrow.

 

[Charlie Sheen]

I know on a common sense level this doesn't add up---but I consistently get my best 60' times when I leave off idle. It just seems like the converter flashes quicker and higher for some reason vs preloading it.

That's what I've been doing now on the cooler track surfaces.

 

[kenneth]

Well I tried it out (launching at idle) and ended up with low 1.9's and high 1.8's Thanks psfracer and Mister Roper for the advice.
A little more practice and I should be able to 1.8 steady with occasional 1.7.

 

[ixtlan]

Here is small article I wrote that may explain why the idle launch was better.
A bit more info than applies but for what it's worth.


Here is quick rundown on TC basics.
Number one you need to decide what you want.
Mileage and drivability or Torque and raw acceleration.
You cannot get without giving.
Number two you need to match your cam and TC stall.
You will need to know your Cams torque and Horsepower curves.
(Dyno 2000/2003 is perfect for estimating this)
For "Acceleration" you will need to determine where your peak torque occurs in relation to RPM. ​

Also you will need to determine where your Peak Horsepower occurs in relation to RPM.
As an example:
In RatStang's 289 and cam the Torque peaks at 5500 RPM and the Horsepower at 7000.
Horsepower will "Pull you thru" the loss of Torque. This equates into acceleration. If you have a cam with a flat torque and horsepower curve then you will not accelerate because the torque is acceleration. If you reach your torque and flatten out you will not continue to accelerate. Your engine will "Bog" at this point because you do not have torque continuing to rise.
(Yes I am going to hear about this)
Here is where the TC comes into play.
All TC's are rated at Flash Stall. This is the RPM that the TC slips to before it starts its lockup. The actual Lockup occurs appx 500 RPM lower after it Flashes to the rated RPM.
So during your shift from gear to gear you Flash to the RPM. What you want the TC to do is to Flash about 1000 RPM below your max Torque. ​

So in my example I would want my TC to Flash about 4000 RPM. ​

This way the Torque after the shift will continue to accelerate my vehicle as opposed to flattening out.
The Horsepower will carry me thru the shift until I reach my Flash again.
Now that is Pure continued acceleration.
Here is the give and take portion.
If I have a 4000 RPM Flash Stall then my actual lockup would be appx 3500 RPM.
If I am using the vehicle as a daily driver the lockup of the TC at 3500 RPM would place me at what speed while I am piddling around town? With my setup of a 3.55 rearend in 3rd gear (1:1) with a 26 inch diameter tire this lockup of the TQ (3500) does not take place until 76 mph (use Virtual Engine Calculator to figure this).
This does not equate into mileage and drivability at all.
So I must compromise.
I want my lockup to occur around 40 mph (which is the average speed I will be driving around town). For this to happen I will have two choices.
Lower my Lockup RPM with the TC which will affect my acceleration performance.
Or lower my rear-end gearing.
Or Both.
It is a compromise situation.
The best all around compromise for my example I feel would be a 4.11 rear gears and a 2800 RPM Flash Stall TC.
That places me at appx 40 mph lockup for drivability at the cost of max acceleration.
​

Give to Get.​

 

[andyman]

I know on a common sense level this doesn't add up---but I consistently get my best 60' times when I leave off idle. It just seems like the converter flashes quicker and higher for some reason vs preloading it.

Maybe the engine side has more momentum and hits the tranny side harder....
I'll have to try it

 

[Charlie Sheen]

Here is small article I wrote...​

Very nice!

 

[US-1]

I have found that my auto car leaves harder when the rpm's are around 1200-1400. If I take it up around 1700 it doesn't jump out there as quick. I believe the car reacts better to flashing the converter instead of pushing it.

 

[Rangersfan]

I know on a common sense level this doesn't add up---but I consistently get my best 60' times when I leave off idle. It just seems like the converter flashes quicker and higher for some reason vs preloading it.

Same deal here. Anytime I try to preload it, my 60ft suffers for it. Now if I could just flash it at a consistant rpm off idle, I'd be good.

 

[terry5357]

I have been preloading to about 2k my 60' times are in the 2.05 range, but the car runs faily well off the line. I am turning 8.06 @81.5 mph at the 1/8 mile track. IF I just nail it off the line I have to contend with a .5 second or so hesitation.
IF I am sitting still and stomp the pedal to the floor I hear the sucking of the intake before the engine responds.

If I take the R's up to 2k I get "intant" response. I have asked Diablsport to look at my tune but never really get any response from them, I believe I will just go to a Diablo guy here in the DFW are and just have them tune the car so it is at optimum performance.

HPP only does SCT so does anyone know of a DiabloSport guy in the DFW area that is anygood.

 

[2k05gt]

I have found that my auto car leaves harder when the rpm's are around 1200-1400. If I take it up around 1700 it doesn't jump out there as quick. I believe the car reacts better to flashing the converter instead of pushing it.

I have the same experience, If I try to launch at 1800 my 60' is around 1.99-2.05 but when I launch from about 1000-1200 my 60' is 1.90-1.95. not sure why that is.

 

[marcspaz]

I can tell you what I think. If I am way off, some one please let me know, but how I understand it...

At an idle, you have a high 60' due to waiting for the clutches and bands to engage on the rev up.

At low rev RPMs (but above an idle) the clutches begin to engage slightly, lowering the vehicle response time. As you speed up the clutches slip, torque builds quickly and forces the clutches to slip a bit more prior to full lock-up. Puting you closer to the power band as the lock-up occurs, giving you a better 60'.

At higher RPM, the closer to lock-up you are, the less the clutch packs slip and the more the car bogs down because you are not in the power band at lock-up. It like popping the clutch at an idle in a stick and trying to floor it.

This is the science behind high RPM stall converters. If your car doesn't have full lock-up until about 4K, the clutches are slipping into higher revs allowing you to be deeper into the power band when you start moving.

http://auto.howstuffworks.com/automatic-transmission.htm