FrontEngineDragsters.Org Forum
Technical => Roo Man's Room => Topic started by: ricci32 on August 10, 2015, 06:49:13 AM
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My friend has a former tf 2001 sterling chassis dragster he has raced the car for several years , this season he stepped up his engine program using a blown bbc 496 inch engine the car has always had a problem with tire shake but this year has been horrible. he runs a large rear tire set up, I will get the exact size. with the prior engine he ran mid 6's with a top speed of 210mph the car has always run a big block chevy. any idea on thing we could try or look for. the car looks like the tire rolls over its self and has bent and broken the wheelie bar in the past. the tire shake is so violent that it has damaged the car on several past runs. there is no driving through the shake. any suggestions would be appreciated.
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Clutch or PG ? Waiting on tire size(manuf) and rim width and tire pressure, launch RPM's?
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hoosier 33.5 17 16on a 16x16 rim 6psi launch 2500
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powerglide trans
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Dont know about Hoosiers, but 1/2" increments with Goodyears is a door car tire, but besides that, trying to run a fuel tire combo on a light weight dragster with a PG and low RPM launch does not work. Too much tire and no bottom end HP (@ 2500 rpm) is the problem. I always recomend 12" on the tire width and keep the rim 2" narrower. He's not going to like what I said because it means he is going to spend money on rims and tires and will just try and make what he has work instead of fixing it. With todays racing surfaces and prep an tire compounds, 12" of rubber is more than enough.
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Larry I am guessing that you are talking about Charlie Bensons car ? That is a really big tire that he runs . Dose it shake right at the hit or dose it spin into a shake . A lot of the guys with big HP Top Dragsters are running that Mickie Thompson tire with a lot of success . It would be nice if he could borrow a set from one of the Pro Comp guy's at Epping . What low gear dose he run .
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not sure on gear but it shakes right at the hit violent shake.
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He likes the top end speed with the larger tires if he gets a good launch. Charlie does an amazing job for a guy who builds everthing himself motors trans and rears and the speed he runs is mind blowing. but he is still a budget racer pushing his equipment to the max.
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Larry It sounds like it is dead hooking . The only thing that I can think of would be to lower the rear tire pressure like a 1/2 lbs and try it . The reason that I mentioned the Mickie's is we tried a set on my sons Top Dragster when we out at Norwalk I know it is not the same as Charlie's but we were spraying with 2 kits at 300 hp each and brought the m both in right at the hit and the tire was smooth as can be . It dose not wadd up like the Hoosier . He ran his quickest ever e.t. at 6.54 with no shake or Quiver . Scott Hall would be a good guy to talk to . He might have some good idea's . See you guy's at the Hot Rod Reunion we can b.s. a little !
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Rear motor top dragsters have different dynamics then a Front engine dragster
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I agree with the "dead hook" assessment. That is a lot of tire to get slipping with 2500 rpm at the hit. Pump the tires up and / or lower the wheelie bar to get some wheel speed leaving (or do as Bruce suggests and put the right size wheel/tire package on the car). Bigger is not necessarily better.
Roo
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Rear motor top dragsters have different dynamics then a Front engine dragster
I understand that but they both need wheel speed to go from a to b and the Mickie Thompson tire that I suggested is narrower than the Hoosier I think the tread width is 14 1/2 wide but I think the big difference is the side wall with the same air pressure as the Hoosier they are much smoother .
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Rear motor top dragsters have different dynamics then a Front engine dragster
Would it make sense to think that, for comparable tires shakes, it would be felt more strongly in a FED than in a RED?
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Has nothing to do with it. RE dragster has all the weight in front of the rear axle and further out along with a much stiffer chassie because the rails are further apart. Tire plants harder because the chassie is stiff, Try pushing down at the motor and see how much chassie flex, again at the rollcage, again at the front of the footbox. Now with a FE dragster the motor is out the same (relative), but nothing ahead of the motor and a fat ass driver counter-balencing the front weight by sitting behind the rear. Frame rails at the motor are narrower and the chassie will flex more. At the hit the tires are trying to drive under the engine on both cars, The FE will flex and arc in the middle to a point to where without enuff HP the flex will reverse itself and spring back unloading the rear tires, then tires catch up and frame flex/arc happens again, then guess what, back it goes into reverse and so on. If you have enough hp to maintain the arc till top HP is acheaved and carry it through its a good pass. A RE dragster does not flex as much so it does not unload the rear tires because the weight to the front is constant
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Has nothing to do with it. RE dragster has all the weight in front of the rear axle and further out along with a much stiffer chassie because the rails are further apart. Tire plants harder because the chassie is stiff, Try pushing down at the motor and see how much chassie flex, again at the rollcage, again at the front of the footbox. Now with a FE dragster the motor is out the same (relative), but nothing ahead of the motor and a fat ass driver counter-balencing the front weight by sitting behind the rear. Frame rails at the motor are narrower and the chassie will flex more. At the hit the tires are trying to drive under the engine on both cars, The FE will flex and arc in the middle to a point to where without enuff HP the flex will reverse itself and spring back unloading the rear tires, then tires catch up and frame flex/arc happens again, then guess what, back it goes into reverse and so on. If you have enough hp to maintain the arc till top HP is acheaved and carry it through its a good pass. A RE dragster does not flex as much so it does not unload the rear tires because the weight to the front is constant
Thanks for the lesson Bruce. Keep 'em coming.
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I agree with Bruce, those tires are too big for your combo/ HP, and not enough launch RPM to get "up" on the tires.
I don't know the compound of your tires, but the size is the size Pro Stock run, and they are shifting twice as much as you, so the compound is likely to be softer that what you should be running. Pro Stock launches, hooks, shifts, hooks, shifts, hooks, shifts. With a PowerGlide you to need to keep the tire speed up so the slicks don't pull the motor down below your power range.
i just called Dennis Murphy that races a blown alky 426 style Hemi, with a PG in NHRA Heritage A/FD, he is the only guy I know that runs a PG, all the rest of the A/FD run Lenco, with either a clutch, CrowerGlide, or converter. Dennis uses a 9" converter, 33x14.5x15 GoodYears with 4.56 rear gear and a 1.58 1'st gear, running about 1700 hp and 6.40's at 220 mph. The other fast teams use N/TF 12" wide 16" M&H tires with good non-shake most of the time runs. Like Bates/ Adams injected nitro early Hemi runs 6. teens and their best MPH is 230mph acouple of weeks ago in Sonoma Ca. One of the other fast A/FD's is Bill Wayne running a blown alky Alan Johnson Chevy, also running the N/TF 33x12x16 tires, but with a converter. The exception is Davenport, the 2014 Champion, racing his 369 ci Late Hemi, and 33x15x15 tires. You see the Heritage rules have a fuel pump limit, and Davenport is very smart building a small motor to better match the fuel pump.
What you might try now is lower the tire pressure to 5 or 5 1/2 to reduce the bite, but I don't think that's your long term combo. You can also try some of the smaller 12" M&H, they make a couple of the 12" NTF tires, that way you don't have to buy new 15" rims, which will give you allot more options. But you may need to contact your wheel guys to see if they can narrow you wheels to what the tire guys say will work with your combo.
Did you break your wheelie bar because of tire shake or because the front end came up fast and hard there-by unloading your slicks, if so put at least another 40 lbs on your front end. I have often suggested to other racers to add some front weight and they do run quicker.
In our Heritage JrFueler we had bad tire shake a few years ago, and broke our rear motorplate, steering, fire bottle mount, and a winshield. We have fixed most of the shake by adding more tubing in the chassis between the rear motor plate and the rear end because we think the chassis was moving too much with the added power and traction.
Good Luck with your project.
Jon Hansen, Hayden Wheels, JrFuel Dragster Association, and Hammer-Hansen-Hook-Ramay JrFuel
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Dennis Murphy is also gets into a lot of shake, Its hard to help when one did not build the car and all you can do is repairs.
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My friend runs 14x32x15 hoosiers on his fed and it will not make a pass without tire shake above 6psi. 5.5psi is the limit. So that said I would not recommend to up the air pressure as for it will get worse with higher pressure. And by worse I mean break every weak link/part on the car. He is going to change slicks due to the shake problem. It has been a struggle for us and the hoosiers... without mistakes we never learn.
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What kind of FED is your buddy running the 14x32x15 Hoosiers on ? I think if he is making less than 1200 HP, that tire might be too big, it's hooking up too good and then shakes. Pro Stock run 33x14.5x15, and shift 3 times ??, and run 6.50's at 212-213 mph.
I also wonder is that tire is designed for a race car that shifts more than a PG. When Goodyear 1'st let me know that they were going to put a number of tires on an "inactive" list, and with no production schedule. So I called all slick manufactures looking for the JrFuel sizes, 31x12x15, lucky for us racers I talked Goodyear into making another batch of the light weight [ 22.6 lb] 31x12x15 tires as long as I gave them a solid order for 150 tires. In my search, Hoosier told my not to run their 32x12x15, because it has a much softer compound and designed for cars that shift more than twice [PG] so they would hook, shift, hook, shift, etc, but a FED with a PG needs to get and keep the tires spinning some so they don't pull the motor down below it's HP range.
Cheers,
Jon
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Yes his dragster is less than 1200 hp. It is a mild steel 185" chassis with a 565 bbc. Leaves at 6200 rpm on the brake, 5800 on the chip. And yes he is looking into different slicks for his fed. Maybe Scott will chime in...Love this site for all the great info. Thanks everyone!
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John, This is Scott with the big ass hoosiers. What size rim do you guys recommend with the 12" slicks? Also, do you still have some left?
We have narrower our tire shake down to tire pressure and anything over 6.5 lbs (except at Bakersfield) will shake hard.
Our last time out the car shook 3 times, off the line and then had to hit again twice before it settled down. The shake was so violent it broke
wheelie bar
front axle got bent
broke float bowl
cracked a valve cover
broke crank mandrel
broke ignition box
just in one pass, not to mention when the floats broke it flooded the motor with alcohol and blew out both head gaskets.
Wish I had this info when I was buying slicks last year.
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i prefer a rim thats 2in narrower then the tread width, because it stands up square on the burnout and gets even temps across the surface. To run a matching rim to the tread the tire crowns and the center gets hotter and the edges dont get any heat.
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Scott if you can get a set of the Good years from Jon they would be your best choice for your car . If you can't get a set Hoosier makes a 12x33 co9 tire 18350 part number . I have run them before and it is a pretty decent tire . Like I said the Good year would be my first choice .
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Two questions if I may:
1) When troubleshooting tire shake, is it valid to skip burnout and see how it goes?
2) Generically speaking, what's the lowest acceptable horsepower to successfully run the Goodyear 31x12x15 tires? (alky FED, PG, ...)
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Most any time I have had shake problem more power was key to curing it. IMO the 2500 leave on OP is biggest issue.Shake is basically tire not knowing if it wants to spin or hook.let it spin a little and your brain and car parts will think you.Now by spin I mean a little and there is good margin between little spin and spinning to point of loosing ET.At 2500 I'm pretty sure you are way below powerband , heck thats street car powerband and with smaller tire and way low HP.
While I agree tires maybe bigger than norm.I am not sure that changing is only way around problem. tire compound and power at hit would seem to the way around it.I know the hoosiers I have on mine are way soft and will not be hitting track on car.I going with harder compound M/T's for first run's and working from there.Power wise I should be around 1100 and running 6600 stall.Wish I could say that it works but have no idea yet. first fire up is in week or two .Doing assembly and wiring now.
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NEEDS MORE WHEEL SPEED..dAVE
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Sorry Ricardo, I missed the post, I think 600 hp may be the low end. I know Bob McKray/ Don Enrquez running an all iron non-raised runner 23° SBC is running a 750 hp. And they ran a 7.16 at the 2016 March Meet.
Part of the problem is not allot of choices of tires, the 10.5 tires are made for door cars, stiff sidewalls, or 29x11x15, or 29x12x15 Goodyear, which of course lowers your clearance and total gear. For many years Enriquez ran a 30x12x15, but it's no longer made and Bob McKray is making more power.
I have found if I need more tire speed, ie less grip, I lower the tires pressure, like as low as 5 lbs. Lower if you run bead-locks.
I hope this helps,
Jon
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I keep seeing lower pressure for less grip. I always thought slicks were opposite passenger tires and would lay down without cupping to create more grip at lower pressure.
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It's easy to prove, if you have an infared temp gun. With lower tire pressure you will get higher temps on the edge of the tires. When you take a shot after a run, just shoot the temps across the width of the tire. I always take a reading of tire temps after a run so I know how much it's spining. The reason why you get more tire speed is it concaves in the center. Now keep in mind if you want more bite, raise the pressure. Granted my advantures are with mostly 12" tires, but I think it's the same with wider slicks.
Jon