Help with tire shake.

Ok, After running consistent 7.50's in my 63 T/S vette all year, we decided turn it up a little & see what would happen. Running a 540 KB/Olds/big chief, 1471 hh retro at 25 over,25lbs boost, bruno/lenco, 2.08 1st, 1.44 2nd,3.90 rear gear, M/T 33x16.5x15. 30 degrees timing, pulling 10 degrees for 1.2 seconds at the hit. The tires shook right from the hit until about the 60 foot mark where i pulled 2nd & it made a hard move right & had to lift. running 6.5 lbs of tire pressure, leaving on a two step at 3500 rpm. Any Ideas? I'm not sure what to do next.

thanks, Jason.

 

tire shake

i run m/t tires + brunos and they don't shake - my 1st thought is too much air pressure and you are really bouncing the tires - with that short of a tire and a 2.08 1st gear you should have plenty of wheel speed. you'll probably need to give more information - beadlocks? - did you make any suspension changes from your previous baseline? where are the wheelie bars set? where is the converter set up to stall? 6.5 lbs of air hot or before the burnout cold air pressure? my m/ts gain almost .5 pound of air from cold to hot - if you are starting out at 6.5 and gain .5 pound you are way over what they want.

 

No beadlocks, tire press. is set at 6.5 cold, no chassis adjustments from the previous baseline,wheelie bars are 65 inches long & 6 inches up to the axle of the wheelie bars. I was thinking that too much wheel speed or too much air pressure would result in smoke & not shake. We did make a second pass leaving in 2nd gear, 1.44, and no problems but only a 1.10 60 foot.

 

If you are running the same tire pressure as before and you are making more power now and shaking the tires, I would INCREASE the tire pressure. Go up .5 at a time and see what happens. I would not be surprised if you ended up at 8 lbs.frank

 

Mike, we are running a Bruno with a converter. But I think that basically you are saying that I am not leaving with enough power to get up on the tire, obviously I cannot change any clutch setting, but would changing the launch rpm help?

 

Higher RPM = More Boost, fuel and power.

 

I agree with Mike on this one and I might take it a step further in saying that you might want to adjust your 1st gear ratio. With the motor making power and your shocks adjusted, if you bring your launch RPM's up with a slightly taller 1st gear, you will really notice the results of the added power. Getting down the track is one hell of a balancing act and if you change one thing, you will have to adjust others to compensate.

 

Can you recommend a better first gear ratio for my combination?

 

not always true

you are answering your own question here




i will probably get stoned for my comments but here goes…

question for ya warrior:
-are you running an air throttle controller?

if so good… if not buy one. as long as the rules allow it they are definitely one of your best allies with a converter car and better than the 2-step deal imo with a converter set-up. and i know the 2-step deal ‘works fine’ but a converter is very sensitive to the speed at which the motor accelerates ‘into’ the converter because that torque gets multiplied.

i’m getting the impression from things you said that you are being too aggressive and blowing thru the tire into shake.

another question warrior:
-do you video your runs? and do you run any data acquisition?

if you’re not video taping your runs… start NOW. drivers LIE! (i can say that btw cuz i are one)

look back at the video in slow-mo and you won’t have to guess what is happening.

another question for ya warrior:
-are you tuning this car from the driver’s seat or do you have a crewchief?

if you are… then absolutely video the runs… cuz drivers that tune REALLY lie (again i can say this). video the run AND have a crew member shoot detailed pics of the footprint your car leaves. these two things will tell you every thing you need to know and where need to be headed.

talking to clutch guys does you NO good… and i’m not knocking the clutch guys as i have played both games. in a converter deal it is really easy to blow thru the tire and into shake and not be able to tell that is what happened unless you have a good video (or graph) to refer back too. and raising the stage rpms (throttle controller… not your inaccurate foot) will typically soften the hit… lowering the stage rpms will typically hit the tire harder.

so since you said the leaving in first gear was violent (hell the thing probably wanted to defy gravity?!) and leaving in second gear it was well behaved but soft… i would lean toward these things

for now…
-moderate blade opening speed
-stage rpm very close to converter rpm
-3/4 to 1# less tire pressure
-timing controller… gonna have to see what your deal likes (that is more track dependent/condition imo)
-maybe leave in 2nd gear (last resort i know)

longer term if you keep it all hopped up…
-re-gear your lenco to soften the first gear ratio and make even transitions
or
-higher ring/pinion ratio to keep it from knocking the tires off (the little tire cars are very sensitive to too much gear in a hi hp combo because the little tire just exaggerates the overall ratio)

just talking from my experiences with blown alky and nitro converter set-ups… best of luck bro

 

Ok, I do not run an air throttle , but I do have one in the trailer, so I will be installing it. No data aquisition yet, we do videotape every run, so I should be looking for the car to get up on the tire right away & then go into shake? after examining the tire marks on the track, the car moved forward about 5 or 6 feet before we started to see the shake prints. The track owner said he could see daylight under all 4 tires.
I do tune from the drivers seat.
So by raising my launch rpm closer to converter stall speed, it will actually hit the tire softer, even though the boost output will be higher?
And when you say to regear lenco for softer hit & even transitions, should I keep the 1.44 for a second gear ratio and go to a 1.80 or so for a first, or should I change both & get rid of the 1.44 alltogether?

 

I agree with everything that Sean (altered boy) is saying....as he drives my car and makes good calls on this stuff....and we have a solid suspension car (125" altered)....
Your overall first gear ratio is 8.11:1 (2.08 X 3.90) and it has soooo much torque multiplication with the ratio and converter - no wonder it's so violent at the line....now maybe thats the way the door cars are setup...but in our world a 6.50-7.00:1 overall first gear seems to get the car to launch smoothly and the 60' times actually get better when the car calms down at the hit....
I know it's a few things to look at....but overall first gear....controlling the throttle blade opening with the air cylinder and timing retard at the hit are my votes...

 

Ok , I am planning to change the gear ratios in the trans. If I replace one of the 1.44 gearsets with a 1.25, it will give me a 1.80 first gear. which ratio should I use for second. the 1.44 or the 1.25?

 

i’m gonna take an educated guess (based on your statements) that if you go frame by frame on the video you’ll see the car up on the tire immediately, a very round (and spinning) tire, and then it will keep growing until a short distance out it has grown sufficiently to propel the car ‘off the ground’ (or seem too) at which time it’s gonna start shaking because it’s no longer fully in contact with the ground… poof… spinning into tire shake. and you’ll get the ‘daylight under all 4’ and ‘dude your car took off’ comments.

btw... to the naked eye the above scenario 'looks like violent underpowered shake' so most guys just keep hoppin the damn thing up and it gets ugly from there

i also tune from the driver’s seat… it’s a bitch but i’m the designated nut behind the wheel and i’m very happy being it (it’s kinda fitting too… ha ha). but as the driver my ass also becomes the ‘data recorder’… about 90% of the time my scrawny ass can tell whether i get:
-‘shot up’=blows the tire off
-shaken like a baby=shake at the hit
-pushed back/down before the car ‘hops up’=starts to get up on the tire but can’t then it shakes

but i usually keep that data to myself until i see some video so i don’t look like a blatant liar… so i have a crew guy shoot pics/vid of every run and both of the cars footprints

do you know what you are looking for in the footprints? it would be worth taking one of your guys up to the line when some big tire cars run (quick series, dragsters, whatever) and spend 30 minutes just looking at the footprints they leave and see if you are both on the ‘same page’ as to what you are seeing.

what happens 99% of the time… your time flashes up on the board and EVERY crew member turns and walks away!! never even looking at a HUGE piece of data written on the track… what a loss!

you are working with a type car than i’m not all that used to… doorcar vs altered/fc but the principles are similar. with your weight you may find that your deal does likes and tolerates more final ratio than what we run in our deal. but if i had to guess (and it’s just a guess bro) i’d look for a 3.73 or 3.50 ratio to TRY (the beauty of a 9” ford assuming you have one in your deal). you really won’t know until you try... and swapping the pumpkin if you can find one to borrow for a few runs is the easiest and cheapest way. there are gonna be some guys tell you that ratio is ‘way to hi’ or ‘will never work’… but you’ll find most the time they’re not swinging the kinda hp that you are or not working with a little tire. and the roll out on a little tire at the hit makes a huge difference in the final ratio.

as for the staging rpm question… will boost be higher? maybe… but probably not much. especially if you go to a air launcher. why? i’m gonna guess on your 2-step the blades are wfo? they won’t be on with an air controller… they’ll only be cracked. that is one factor. other thing… and this is what REALLY matters… the farther the stage rpm is from stall speed the bigger ‘run of torque’ the engine has that is gonna be multiplied… or ‘flashed’. if you bring the motor up and just ‘touch’ the stall… the converter has already begun to ‘tug the motor’ and won’t let it hit the tires with a running start.

 

well some things that didn’t get discussed or brought into this discussion are actual car weight and bore/stroke combos as well as actual converter stalls. all are variables that are gonna affect this situation.

if this were a 1.5 second quicker car on a big tire (ie promod) i’d say yep… bigger gear and spin that thing up ($$)… but this ain’t a pro-mod. if you find you sacrifice hi-end boost due to the gear change BUT it gets the car to go 100ft and be drivable then you may end up having to play with your blower o/d a little to wake it up down track. bottom line is if you have a car that is unmanageable or undrivable to 100ft what have you gained? but with a 540 in a car like this i’m gonna say that spinning it’s brains out on a little 15” tire isn’t the answer

and while i agree that the promods are quickly trying to become left-side steer f/c’s i don’t think any sanctioning body has let that actually happen yet have they? is adrl allowing it? i know one team very well that is trying to make their car ‘think’ it’s a solid car. i bet mike is right on tho and this is on the horizon.

for reference sake we are launching around 3,000rpm and weigh 2,000#

 

ah ha!! very cool!! did not know this was already happening. was it kuhlman that tried it years ago leading to the 'four corners suspended' rules? seems like i remember something like that but can't recall for sure.

anyone running a truly 'solid promod' at this point? and who's got the best chassis combo out there for these deals?

 

think Scotty Cannon's superbird was running a solid rear end in ADRL when it ran into the 5s?