Leaving on a chip/regulated air throttle?

Hello all,

I tune an alky dragster 526 14/71 high helix glide. We run a 44 mag with the 8973 box pulling timing and performing the shifting duties. We also run an air throttle and leave off it at around 3500-4000 RPM.

We match race sometimes but mostly run a 6.40 index class (4/10ths protree closest to 6.40 without going under wins ) however its a quick 8 format and the last round is heads up, no 6.40 limit.

My question is this, dependent on temperature air etc the launch RPM varies 100-500 RPM. What I would like to do is to set the air throttle so that it opens the trottle to a point where it would be at say 5000 RPM and then use the 8973 launch rev limit to control it to say 3800 just shy of making the car push through the brake. I would like to do this for 2 reasons one to hit the tires a little quicker than just using the air throttle, the second to make the launch RPM as close to identical run to run since we are running a dial most of the time.

I know that leaving wide open on a limiter is hard on the crankshaft but my thoughts were that tailoring the RPM by this small an amount would probably be pretty harmless. Hell every nitrous car with a converter does it wide open but with no juice.

That said we had a crank in the car that had cracked through the 7/8 rod journal after 10 runs and we were ever so lucky to catch before it came apart so the car owner is naturally a little gun shy. We have a new Bryant in the car now so weak parts are not a concern.

Looking forward to hearing your feelings on this ( Chuck D and Mike C , I know you are out there) Particularly anyone who has done it before.

Richard Gavle

 

There are a few pro mods in the Sacramento area that leave on a two step (blown alcohol). I've wondered how it works without wanting to cough the blower. I leave on a air launch, and it does vary, but it is activated when I'm on the transbrake, so my RPM is usually pretty repetitive. The brake tends to load it and keep the launch RPM about the same (i believe).

 

Been doing this for the last two years. Can get a very consistent launch for tuning. I launch at 3 or 35. The other thing we use on the launch control is how fast the butterflies open. Will leave the launch RPM the same and slow down the butterfly opening speed on slicker tracks. The real nice thing about doing it this way your throttle is only part way open, not wide open. With the 8973 box and throttle launch, auto Trans, you can make the car haul! O buy the way, When Mike’s Transmission ran his 5 second run in his dragster, he had this set up. (8973 box, throttle launch, Power Glide).


Mack

 

Thanks for the replies,
We have been 6.20s and sub second 60s on a marginal track. I am hoping that by increasing the initial wheel speed we can get it on the tire a little quicker on a good track and with a little attention to mid and big end tune-up get into the low teens without having to lean on it too hard.
Richard Gavle
Chuck D and Mike C still hoping to hear your input.

 

glide on a 2 step

We also run a set up like that, but just a 2 step in the 8147 box with a 44 amp mag,BBC 500 inch motor, 206d rotor screw, we open the blade on the 2 set to .125. and run from 3000 to 4000 at the hit, it keeps the motor from getting to much fuel, and we can tune our 60 foot time to the .01 the same per round, and have quite a few passes in the 6.0's, hope it helps and good luck

 

How do you get around using a pro trans brake when you hit the trans brake to back up or as in my case a bruno you hit the trans brake to put reverser in forward or reverse. do you have to run a toggle switch to turn off air throttle so you dont rev to 3500rpm as you back up, or as me going to forward. sure that will wake up your crew chief.

 

Hello H Brown,


Are you the guy thats been talking to Mike G in Maryland? I am the guy who set up his air throttle and the time window circuit on the MSD 8973 shifter output.

On our car we use two buttons on the T-brake one to back it up and another (or the MSD 8973) to apply it on launch. Then you simply wire the air throttle switch with a standard bosch relay like you use for nitrous through the contacts which are marked N/C - Normally Closed so that the relay will allow current to pass normally. Then you take the wire that goes to your back up button and splice it into the activation terminals of the relay and when you energize the circuit when you back up the N/C relay contacts are open so that no juice goes to the air throttle.

If this is hard to understand I can draw it on paper and fax it to you in the next day or two.


Richard Gavle
[/I]

 

Richard thanks for the reply.
no I have not talked to anyone, just asked a few questions on here. I really want to do this two step set up, but also keep it safe on the line so I dont run over my only helper. I would appreciate a drawing if you dont mind. I want to keep it simple in the car and just need to figure out if using a toggle switch and a light, or two transbrake buttons is the way to go for me.
Again I use a bruno/lenco which requires you to activate the transbrake to lock the input shaft to shift out of neutral to go forward or reverse, not just to reverse.
thanks for all help to get this pig off the line.

 

Greg,

We are 1 of the teams that use the 8973`s 2 step function on our car, Randy Kays 63 Vette. AJ 481X, PSI C Rotor, and a Bruno-Lenco. How exactly it doesnt send the blower to the moon, i dont know. We tried the air throttle, but it was pretty inconsistent for us.

 

Wiring air launch so you can back up safely and quickly

O-K here goes,

First off you will need to use 2 switch()buttons, one to back up the car and another to launch it off the brake. In addition you will need two bosch relays.

Whenever 12v is mentioned it means a switched positive battery voltage.


12v to one terminal of backup switch the other terminal on switch connects to one terminal of the transbrake solenoid the other terminal of the transbrake solenoid connects to ground.

12v to launch switch the other terminal of switch connects to the 86 terminal of both relays. Connect both 85 terminals of both relays to ground.

12v to both relays 30 terminals. Connect one relays 87 terminal to the transbrake solenoid ( the terminal that you previously connected to the backup switch not the grounded side). Now connect the other relays 87 terminal to the air throttle solenoid and connect the other side of the solenoid to ground.

When you press the backup button the juice will only go to the transbrake solenoid and the 87 terminal of the one relay since the 87 terminal is normally open it will have no effect on anything and only apply the transbrake solenoid. When you press the launch button it will energize the pull in coils on both relays and both relays will transfer 12v power from the 30 terminals to the 87 terminals therby energizing both the transbrake and the air throttle solenoids at this point the Co2 will enter the air throttle slave cylinder extending the cable to whatever amount you have set it at so that you can mat the gas pedal and the throttle will open partway. When you release the launch button the relays will deenergize and the contacts will transfer and the transbrake will release while the throttle snaps open.

You could do this with one relay and a diode but diodes fail and the throttle would snap open while backing up....A second relay is cheap insurance.

Good luck to all

Richard Gavle

I have drawn this on paper tonight and will make a better drawing in the morning and try to scan it to PDF and will then be happy to e-mail it to anyone who feels a picture is worth a thousand words..and if you do you sure ain't seen one of my drawings

 

We use 1 relay to a toggle switch to back up. The throttle will not fly open backing up if you don't have the pedal pressed down. Idle back to the starting line. Been doing it this way for 5 years with a 8973 box.

 

Just in the interest of balance here. We have been using the MSD 8973 for two years with absolutely no problems. It has worked great, but is somewhat more difficult to program than it needs to be. The documentation could be better, and it does take a little time to make a change. We don't use a transbrake, but Will is right that the voltage spikes have bothered many electronics.

 

Will,
I agree with you 100 percent, I used a diode to prevent flyback voltage on every coil in my car, nitrous transbrakes etc. In addition the big capacitor that MSD sells works very well at suppressing transients on the voltage supply to the MSD.
Pete9857,
We used one (relay) on our car but the way we use it may not be compatible with everyones car. Also the way this one is wired up you can apply the gas normally backing up or any other time, I am not sure if that is how yours is set up or not, but the guy at the company who sold the air cylinder said the only way to wire it up was so you could idle safely to back up.
The other problem we had is we use the 8973 to shift the car and sometimes it would shift prior to the launch of the car and the driver would be unaware until he hit the transbrake and the car pushed through the lights in second gear To cure this problem I have set up a "time window circuit" that only allows the MSD to communicate with the shifter from .8 seconds to 3 seconds after the launch.
This has solved all of the problems we have had ( so far ) with our 8973. It should be noted that we have it mounted 6 feet from the motor so the EMI is not a big problem if you are mounting it or any other computer equipment near a magneto I would suggest shielding it.
PS if anyone wants PDF's of either mickey mouse workaround just shoot me an e-mail and I will send the files.

Richard Gavle

My e mail address is my first and last name as one continuous word followed by @gmail.com
The reason I posted it like this is so that web crawlers can not harvest it and add it to thier spam lists .

 

Bottlefed, I hear ya. we use the msd shift controller on our lencodrive. I also put LED's in dash telling my son what gear it's in. Believe it or not, our 8973 is right next to our points box which is right below the mag on the frame. No crank trigger, mag 20. we also use the V300 with no issues.

Glenn

 

well certainly there is alot more knowledge here than what I have but I will post my results.
I run a MSD 10 plus and the 8977 controller and have had great luck with it. YOU CAN NOT use this as a RPM limiter you need to use a standard CHIP in the MSD and not the controller. I use a standard chip for the RPM limits and all the timing functions with this box with great success so far.
I will say that the RPM limit on the starting line when used with the LAUNCH retard and M5 VP fuel makes a real PRETTY flame show from the mufflers under the car.. Keep in mind PRO TREE your only on the limit for a brief moment so far I have had no ILL EFFECTS.. I just switched my standard roots to a 14/71 Kobelco k8 hihelix so I am using alot more launch retard for the moment untill I get this thing sorted out on the fuel system.