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Old 09-06-17, 08:03PM   #1
73ta
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Default Stick shift launch technique

Going to take my track car to the 1/4 mile track this weekend. Can anybody give me some pointers on launching my stick car? Running a R compound tire with about 550 hp in a 4000 pound TA.
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Old 09-06-17, 09:49PM   #2
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Ideally you want to bring it up to were the motor is making peak torque, dump the clutch. With out spinning to tires, if you played around on the street, you'll have some kind of and idea. What rpms, but the track going to be allot sticker then the street, so if 1500 on the street worked with out spinning the tires, I'd start off at 2500 on the track. By sping I mean just sitting there for those split seconds and going no were.

You'll know what rpm is best, because your 60' will pick up.
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Old 09-06-17, 09:51PM   #3
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550 hp, I guessing around 3500
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Old 09-07-17, 01:29AM   #4
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Take a lesson from the top fuel guys:
Think of the clutch as an infinitely variable dry torque converter.
You can vary the apply at launch by slipping the clutch.
Left foot to brain & vice versa!

This does three things -
1- it lessens the shock loading to the drive line parts as opposed to just revving up and side stepping the clutch at launch rpm.
I've done it both ways and side stepping the clutch pedal at the hit just breaks stuff eventually especially if you are just using street grade components.

2- Your tires will not go up smoke at the hit/excessive wheel spin.

You will actually feel the car move out better . No bog, rpm's stay up as you (QUICKLY) ease into it while applying full throttle.
3- cause more frequent inspections for accelerated clutch disc/ pressure plate & flywheel wear wear due to the extra heat created when slipping the clutch .

Slipping the clutch just enough takes practice.
The time line for all this to take place is maybe 1 second (if that) and change
Just watch your 60' time and you will know when you have it right . Deft left and right feet , good seat of the pants driving instinct, a sharp eye on the tach & a keen ear on the engine.
A G meter/accelerometer with playback/data recording will show it up.
So will the incremental times on the time slip.

Do not hot lap the car.
Give the clutch sufficient time between runs to cool. 20 minute minimum.
Jacking the car up and ducting a fan/blower towards the bell housing/ clutch can will Help speed the cooling process ( do not chill shock clutch components with CO2 or N2O .Cool air is best) especially if you are going late rounds and getting hurried up by staging bosses.

Certain race clutch pressure plate assemblies are engineered to slip at the hit ( as opposed to a street type clutch) and as rpm's go up centrifugal force causes fly weights on the clutch fingers in the pressure plate to increase the clamping force on the disc.
Those type clutches are engineered for the purpose of drag racing.
They can be custom tailored to HP level and race car weight and gear ratios in the trans & rear.

Are you currently using a single disc or twin disc clutch system?
If you plan on racing a lot , a twin disc requires less pedal effort and offers more clamping force/ friction surface area than a single disc unit.

Practice , practice & practice.
Have fun.
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Old 09-07-17, 08:19AM   #5
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Do you have a 2 step rev limiter? If you do put it on the 2 step where it likes to launch, as Gach said, the track is stickier than the street. You might have to put more rpm in it at the track.
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Old 09-07-17, 11:22AM   #6
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Hope you got good U joints. You will find the weak point of your driveline.
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Old 09-08-17, 01:57AM   #7
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If the U-joints are the tough ones they will hold up .
The shaft should be a minimum 3" dia. and incorporate stronger yokes too.
Raced all the time? If the joints have a grease fitting pump fresh grease into them before race day.
Always inspect them after every race for looseness/slop in the cups/yokes & binding.
The needle bearings in the cups will eventually get hammered flat from violent launches and bind. Anything that does not check out OK pitch it and get a new part.
The receivers on the yokes that hold the cups can eventually get distorted and the cups will be loose fitting in them.That will cause a bad vibration. If that is the case time to have a new shaft built.

Where I have had stuff go away is in the differential/carrier.
Stock ring & pinion gears & spider gears are made of hard material so they will wear longer and give quiet service for a long time but they do not handle high shock loading for very long. They will eventually shatter at the worst possible times. Same deal for axles.



Race gear sets and spider gears are made of softer more ductile steel alloy material that will not shatter (usually 9310 nickel steel alloy).
It handles shock loads better but does not wear well on the street and tends to be noisier.

If you put wider,taller or just stickier tires out back that will put more stress on parts at the launch if traction is exceptional. You may have to raise launch RPM to compensate that change.

There has to be a slip point somewhere in the system to protect the rest of the parts ,let it be the clutch.
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Old 09-08-17, 08:33PM   #8
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Thanks Sprint. Here is my setup: 550 Hp & 600 Ft Lbs., Nitto R spec radials, TKO 600 Prepped by Liberty Gear, solid u joints, 3:42 stock gears with cap brace/girdle rear diff cover, welded fully axle ?????, C clip stock axles with disc brakes, Centerforce dual friction clutch, Hays billet steel flywheel, Quick Time bellhousing. Used to drag race the car 40 years ago with the stock 4 speed. It's set up to autocross/track race. I have never had any tire that would hookup enough to cause any breakage. Usuall don't get traction until 2nd gear about 60 mph.
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Old 09-09-17, 03:57AM   #9
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No trouble at all .
Sounds like a stout setup to begin with .
If Liberty built the trans it can stand the extra abuse.
Fully welded axle???= whoever set up the housing put a 360 degree weld where the axle ????? join/insert into the center section.
On stock production housings the ????? are only spot/puddle welded to the center section through holes in the tube socket on the center. Basically tacked in place.
With high power abuse those puddle welds have been known to fatigue, shear and rotate which will cause all kinds of issues. The spring perches are probably/should be gusseted too?
I've seen stock perches (un-reinforced) distort & collapse on high power/high torque cars that launch hard have good traction at the hit.
If that happens the housing will rotate up ( go positive) and if the rotation is severe enough it will pull the slip yoke completely out of the trans. Not a fun day. LOL
Traction bars will help to limit the rotation but even so I would also install an adjustable pinion snubber as insurance. There is a location for that on the 2nd gen F cars wher the stock pinion bump rubber goes. May need to be re-inforced though.
Leave a good inch between the snubber and the pinion shaft part of the housing to allow for suspension travel. It can adjust all the way up for more suspension travel on the street or just remove it when not racing. Left in a race setting can cause it to bottom out and make for a real rough ride on the street.
Drive shaft loop? If not, get one installed.
Stock axles- are stock axles. If you start chasing 60 foot times & hooking hard be prepared for an upgrade.
C-lip eliminators? If you had drum brakes yeah. With disc brakes the rotor/caliper assembly provides a sort of positive axle retention should a clip-button failure take place.
Should and axle actually break in the housing it will do some crazee stuff but the rotor/caliper assembly will hold it in the housing(still gonna be a wild ride till it gets stopped. That's why ultra high power cars are using full floating axles.
Stock gear set -same condition that applies for axles. A little slippage will make them last longer.

Hope it all goes well on race day.
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Old 09-09-17, 02:51PM   #10
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Axle ????? are fully welded to center section, has a driveshaft loop, spring perches are gusseted with stronger U bolts.
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Old 09-09-17, 06:43PM   #11
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Do not worry about what everyone is saying, GO AND HAVE FUN. The car will be fine, if you go to a track rental, you have time to get the launch down. Even if you leave soft, check your mph at the end 1/4. It will tell you what you should be running in the 1/4. Have fun, post time slips!!!!!!!!
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Old 09-09-17, 10:58PM   #12
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Quote:
Originally Posted by JSPONT View Post
Do not worry about what everyone is saying, GO AND HAVE FUN. The car will be fine, if you go to a track rental, you have time to get the launch down. Even if you leave soft, check your mph at the end 1/4. It will tell you what you should be running in the 1/4. Have fun, post time slips!!!!!!!!
Could've said it better, all great advice though.
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Old 09-09-17, 11:36PM   #13
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I had a TKO 600 third was a bitch... Always hit fifth or nothing going for third haha . Had to shift third easy..

Good luck and have fun ....
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Old 09-10-17, 02:19AM   #14
sprint250
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Default PZ auto censoring of words/text

Hey Gach,
Every time I spelled the word tube in that last post (SOUNDSLIKETOOB) it displayed as 4 question marks. WTF?

TUBE TuBe tube tube tuber tuba tubular tube like tubing toob

Guess its fixed now? Wierd.

73ta,
That'll do nicely.
Go burn some gasoline.
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