hi all, I experimented with luanch rpm on the weekend, 67 cuda 440, 610 dyno horse at 574 foot pounds of tourqe at 4700 rpm, with a 4600 8 inch stall. Previous set up was launching off the stall at 3800 rpm, calvert bars just touching and in the lower hole. Car ran a consistent 10.23 with low 1.4 60,s. Set the launch at 4400 rpm, 60,s fell off to high 1.4,s and the odd 1.55 and 1.557,s, but i still managed some 10.22,s and the odd 10.3, car seemed very inconsistent. I never experimented with the bars at all and by pure luck I went into the semis, with a 90 or so car field. Any ideas on what I should try with the bars next time out or go back to the way I had it. I should state i,m using 29. by 12 15 good years with 11 psi and 471 moser gears.Just trying to get a little more out of the package, thanks Tim

Tim, you have a lot going on here. At first glance, bumping the rpm up with the same track conditions and experiencing what you did is consistent with a track that may be getting too hot. The hotter the track gets, the softer the hit should be to the tire to maintain traction. This will incorportate different shock settings, and the such.

Or another version of the above could include a 'poorly prepped' track vs. a 'well prepped' track. Poor prep = softer hit (rpm, shock settings, preload) Well prepped = harder hit (more rpm, stiffer shock settings, less preload)Caltracs' baseline settings are typically designed for the street strip footbraker. My

I see you have a 4600 8" stall, but do you know what the converter will flash too?

Tell us more about your combo:
shocks and if adjustable, what settings
your tranny
How much travel in the front end
I expect you are using a spool
Car weight
And not to cause any debate, but what is your pinion angle set at?

To get back to your question though, I would put your launch RPM back to 3800. Make changes of 200 RPM increments (My opinion).

I think a 1.4 60 with your combo and first time use with caltracs/transbrake are pretty good numbers!

good advice plumcrazy, i should astate that i,ve had caltracs on for awhile with the mono leaf , trans brake is fairly new last year but only 3 races. 727 with all the good parts, caltrac front shocks on the front, rancho on the rear set at 7, car weight of 2800, not sure what flash stall is , tried to figure it out but just don,t get it ,lol.Can,t remember pinion angle but it was good last time i checked, thinking 3 degrees down was it.

Way to go! The 1.4 60 makes alot more sense now! My Rancho's are the older 5 ways. On a good track I can run them on 4 or 5 and the launch at 4400, not too much difference between those two shock settings. But when the track heats up I have to drop down to 3800 and run the rear shocks on 2. 60's will stay really close but the reaction time will be affected. I was educated on this by Phil Mandella in Ca. He is quite the Mopar Chassis man.

As far as the flash is concerned I can explain how I do it. Some may or may not agree, so ask around and make an educated choice.

First for safety, a lot of tracks prohibit testing the brake in the pits. So, find a place that you can control the car and not jeapordize anyones safety. That said:

If you have a two step adjust it so it does not activate until say 6000
Place tranny in first gear and set transbrake.
Press the foot brake pedal down very hard for added safety.
Give the motor full throttle as if you were going to launch the car.
Watch tac and as soon as the tack stops climbing, that is your flash stall speed.
Let off throttle. No need to keep it there any longer.

If you have a play back tac that will give you a good reading while launching the car. Also much safer.

Also, I am assuming that based on your comment you have not been shown. So I mean no offense by giving the above outline.

Good luck.
Steve

no0 offence taken yes i did that with my 2 step, that,s why i stated 4600, that is the stall.

With the HP and torque you have, you may be hitting the track too hard/quick with your 471 gears to get a good consistent bite.

It is likely you would get a more consistent launch without hurting ET's with a 4.30 gear or even a 4.10. You already have a converter getting you into the power band of your motor with the 4600 stall. .

Your car (67 A-body) should be light enough you can use the torque of the motor to get you off the line hard rather than the rear gear. I know I had real good luck getting a consistent launch with my big block (512cid) #2850 70 Cuda with 720hp running a 3.89 gear and a 32x14.5 tire. 1.21-1.23 60' times.

With more gear, an "iffy" track can get real tricky in the first 60'.

I was playing with mine on the week end seemed to like 1 turn of pre load and 9 way ranchos set at 3 where I usually run them 7 or 8 for foot breaking??

funny you should mention that, before I put the brake in,I was foot breaking, with a 4.56 gear I was low 1.4,s and the odd 1.39 on my 60 foot. I was consistent 10.15 and 18,s.I anialated my 8 3/4 on the line and the only moser unit to go with the 9 inch i put in at the time had the 4.71,s, that is why they are in the car now.