I'm at 9-9.5 air pressure on the 14.5x32 M/T.
I pulled power out and tightened the bottom knob 2 clicks after this pass and it spun pretty bad. Took one click out and removed more boost for the 3rd pass and it spun bad again but I think the track went away a little. Then loaded up and went home. I'll be back out Sat. to try again. Hope to get a go pro under there to have more info.
I have video of all three runs I'll load up to YouTube in a few and start a new post.

I think I had less then 5psi of boost at launch and for the first .5 seconds after the 1st pass.

Can't see the tire tracks at the hit in above pic, but what we can see is that at this point it has the tire paddling BAD.

If you square up the tire at the hit, you will NEVER hit it hard enough on out to stand it up. You MUST make wheel speed early. I suspect you are WAY soft early........Most turbo guys are

I added 200 rpm to the trans break launch number and it didn't shake anymore, but it didn't hook any more either lol

Removed 100 rpm after 2nd hit and still had trouble hooking. The track may have went away some. I'm going to try to get more data tomorrow.

I seem to have the best results by taking sweeps out of the top of the rear shock. I'm going to try 1 more sweep loose before the 1st pass tomorrow..

my struts fail your floor jack test so I might have them revalved this winter. There dbl. Adjustable Strange with the koni cartridge on bottom and the hex head on top. Has 2 flats from full right hand rotation on top, bottom is about middle of adjustment.

Has me confused good lol. I pull boost out and it spins more. It's goofy.

FastmOp is this after your gear change? It might need more boost on the hit

Monte: I am going to try my new boost controller next Friday. Previously with no boost contoller, it would initially hook on 5 lb but then start to spin 5 feet out. I realize the boost controller can help with this.

But, what would you suggest I set the rears at? They are Menscer dbl adjustable AFCO. The front's only have single Strange. Tires are 315 on 12" rims at 15 lbs.

Also, I am going to add 80 lbs of rear ballast this time (2 bags of fill dirt...I mean it is a truck!)

For me... there are a few things to consider on the launch.

1) The limit of how hard you can accelerate the car forward, is directly related to the traction available at that INSTANT in the run. Don’t think that traction is the same 0.1sec into the run, as it is 1.0sec into the run. It is NOT consistent through the run…

2) The traction available on transbrake release, is totally related to how hard you hit the tire. The harder you hit the tire (up until a limit of the tires ability not to deform), will give you the most initial traction. The more initial traction you have, the harder you can initially accelerate the car.

3) The traction available shortly after the car starts to move, is totally related to how much weight you were able to shift (through acceleration) to the rear tire right after the hit.



What I mean by these is this. The more downward pressure you put on the tire to plant it, the more traction you have. The more traction you have… the harder you can accelerate the car. The harder you accelerate the car, the more weight shift you have from front to back, causing more downward pressure on the tire… this added pressure from acceleration, allows you to accelerate the car even more!

So lets look at the “stages” of a launch with some basic examples.

Stage 1 – Tire Hit
Car #1 - Lets say a car with 100% stiff rebound on the shocks (ie doesn’t move), has a given “dead hook” ability to accelerate the car at 0.5g’s forward. If you put power to the car on trans brake release to accelerate at 0.5g’s or below, you will not spin the tires. If you put power to the car on trans brake release to accelerate it above 0.5g you will spin.

Car #2 - Now let’s consider a car with a tuned shock. Let’s say you let go of the transbrake. The axle is thrown to the ground, planting the tire. This tire is pushed into the ground, and can now has more traction then it normally would, so it can now accelerate the car forward at MORE then 0.5g’s. Lets say it now has the ability to accelerate at 1.0g’s.

Stage 2 – Hit transition
Car #1 – As your converter starts to couple, and the car starts to accelerate forward, if you stay under the 0.5g limit threshold of spin, you will start to accelerate. As you accelerate, weight shifts to the rear of the car. Again adding more pressure to the tire. Lets assume that weight transfer gained you and additional 0.5g’s of possible acceleration + the 0.5g’s of dead hook tire traction, you can now accelerate the car 1.0g’s at this moment in the run.

Car #2 – Because this car has had the rear axle thrown to the ground on the hit, this added pressure from the hit already starts at the ability to accelerate forward at 1g. As the converter starts to couple, the car starts to accelerate. This acceleration can happen at a higher rate then Car #1, because the available traction from the hit was much greater. The harder you accelerate the car, the more weight shift you have. So now if you accelerate the car hard, you may gain another 1g of pressure from weight transfer, plus the 0.5g’s of dead hook, plus the 0.5g’s of tire hit. You can now accelerate at 2g’s.

Stage 3 – Acceleration
Car #1 – With a limit of 1g, you can continue to slowly add power as long as you stay under the available traction power limit.

Car #2 – At some point the suspension will run out of travel, and the “hit” pressure will be lost. This is a point where you are solely relying on your previous acceleration for pressure on the tire to accelerate you forward. If you failed to accelerate harder then the 2g limit during the Hit transition, and you have now lost your 0.5g’s available from the hit… you will only have 1.5g’s from your previous acceleration.


There are a couple other aspect to this that I have purposely ignored to simplify this. First of all… nothing actually happens in “stages” as I outlined above. There is a crossover of these things, but these are the BIG events that happen. Also chassis setup (instant center, anti-squat, etc) will effect the downward pressure on the tire. The point I’m trying to make though, is that it is good for people to understand the concept of downward pressure on the tire vs. traction vs. ability to accelerate.

Monte preaches “tire hit”, “wheel speed”, and “Getting up on the tire”. These are exactly what car #2 above is doing. Wheel speed is an indication of acceleration, it allows the tire to reform itself round after the hit, and also on a slick wheel speed (slightly spinning) can actually create more traction (and less motor load), then dead hooking.

But the bottom line is… You can see how the launch “feeds” on what you did early in the run, on what you can do next. If you don’t take advantage of the traction you have, at the INSTANT you have it… you will suffer later in the run because of it.

I sure am glad I raised an engineer.
Doug

Great stuff! Thanks for posting.

That slow motion is super slow What brand and camera settings are you using for that? Video taping, even using Super 8 film on cars on the starting line have really helped me over the years

My Saturday just got fubar. Will try to test soon at bowling green.

Diz, thanks for all the info. I hear what you are saying.

With all that in mind, do you have a baseline setup, or should I go with what I have? Of course, I can't find my log files right now to tell you what they are set at. My fronts were at full loose (Strange Single), but I changed them to +5 from full loose tonight.

Bada$$!!!!
Maybe one day I'll make enough power to need to learn more about this...best read in a long time...

On a slick tire car with power, you have GOT to spin the tire a little to go fast. Dead hook, or "stick" the tire early and it squares the tire up and NO AMOUNT of power applied after this will "stand" the tire up, until the car gets enough momentum that it stands up on it's own. That point is generally past 60ft, depending on how hard the car is moving.

The GOAL and I preach this to guys all the time on slicks, is to MAKE the car spin the tires. I don't mean shake your azz off, make it hop up on the tires and spin. That is NOT tire spin......that is shake INTO spin. What I try and have guys do is apply enough power early, to "set" the tire and suspension, make some wheelspeed early and have that wheelspeed become great enough to narrow up the tire and blow it off. More or less white smoking the tires. Then you back it off from there.

Most guys that complain about "blowing the tires off" are doing no such thing. Most are too soft, they square up the tire, it paddles and THEN it spins. Nothing on the planet, NOTHING, not even a top fuel car will knock the tire smooth off at the hit. All you have to do to see this is watch the super slo-mo of a fuel car during a race on TV. It hammers the tire initially, setting the tire and THEN either gets round or stays square. How to FIX it after the hit is one of the hardest things in the world to do on a fast slick tire car............Under powered and over tired bracket cars that just go out there and dead plant the tire and motor down through there are a different story. Very few have enough power to snap up on the tire and they use the dead hook thing for consistency, but that is NOT the FAST way down the race track.

1st, 3700rpm launch. This is the tire shake pic
https://youtu.be/_ir8fG4WmlA

2nd 3900rpm launch, 2 clicks tighter on bottom knob rear shock
https://youtu.be/ly5TI6MC528

3rd 3800rpm launch, 1 click looser on bottom knob
https://youtu.be/ly5TI6MC528

Do you data log? The reason I ask is because I'm suprised it can get up on boost that fast before the light comes down. Maybe part of the problem is inconsistent boost on the launch?

The other thing is if it spins right at the hit like that, I would be adjusting rebound (top adjustment), not compression (bottom knob). But without seeing either the data log, or a better slow video from the side, I'd be purely guessing which way to have you go.

Monte, do you consider a Hoosier quick time pro a slick? if not, than whats the method for quickest way down the track with these tires?

I have almost all the boost pulled out of it to not blow the tires off. It's only making 2-3 pounds on the break. 1st pass was more boost then the other two. I sat there on the last pass to make sure it built boost before I let go of the button.. the first pass had more boost then the 2nd pass and the 3rd pass had least. I was trying to tame it down to get it past 60 foot. Then I was going to poor the boost to it.

Yes I changed gears. It feels a lot stronger with the new gears. I also put the new motor in it this year.

FastmOp, what are you using for a boost controller?

Here will be my initial settings. The track will be ok at Houston's Royal Purple Raceway.

Weight: 3,500 lbs with 80 lbs rear ballast for about 53/47 weight dist
Front shocks: +5 from full loose
Rear shocks compression: +10 from full stiff
Rear shocks extension: +15 from full still
Rear tire psi: 17 lbs
Launch rpm on brake: 3200 lbs
Boost controller: 5 lbs at launch progressed to 15 lbs at 40 mph
Shift: 6,000

Thoughts?

AMS 1000, it's a CO2 on the waist gate system.