How to set up a chassis for drag racing?

[j-f]

Hi there ,

What are the basic knowledges to know, and understand, to tune a drag race chassis?
I feel I can do better with my car regarding ET, 60ft and consitency.
But, as it is totally new for me, I'm not sure what to do?
Car is the Fourplay gasser.
Stock front shocks.
Stock spindles
lowered on adjuster

Old koni yellow rear shocks
28mm sway a way torsion bars
RLR spring plate cover with empi inside urethane bushing
Empi Adjustable spring plates
Phoenix 26.6x15 slicks.

best ET so far is 11.65s 1/4m with a 1.52sec 60ft.
Best 60ft is 1.51 with a wheelie.

Thanks guy's 

[richie]

Hi J-F

thats cool you got that car and are racing it   Is it ball joint or king and link front end? am sure better shocks at both ends would help.  Really to analyse it some more info would be needed, do you know gear ratios? and ring & pinion? some engine spec? and rpm you launch and shift at? maybe weight of car?
Any video of it launching?

cheers Richie

[PPRMicke]

Hi there ,

What are the basic knowledges to know, and understand, to tune a drag race chassis?
I feel I can do better with my car regarding ET, 60ft and consitency.
But, as it is totally new for me, I'm not sure what to do?
Car is the Fourplay gasser.
Stock front shocks.
Stock spindles
lowered on adjuster

Old koni yellow rear shocks




28mm sway a way torsion bars
RLR spring plate cover with empi inside urethane bushing
Empi Adjustable spring plates
Phoenix 26.6x15 slicks.

best ET so far is 11.65s 1/4m with a 1.52sec 60ft.
Best 60ft is 1.51 with a wheelie.

Thanks guy's 

Hi Many people forget how important a shock absorber is
Especially on a drag racing car
Front is good if you can adjust so you can change how much the front part lifts so the weight distribution from the front wheels to the rear tires
Rear is even more important that you have adjustment in the return side and pressure side
In the UK there is a shock absorber manufacturer called AVO who are cheap and work well for a sportsman car
Many people forget how the weight balance is late whether it is a Volkswagen or ProStock car
Many in the Volkswagen world lighten the car like crazy at the front then the balance becomes incorrect
In my world it is better to put a few kg of lead far down as far forward as possible because the weight balance on the car should make the car go forward as fast as possible Not high up in the sky for every inch it goes up how much slower it gets 60 F
/// M

[j-f]

Hi J-F

thats cool you got that car and are racing it  Is it ball joint or king and link front end? am sure better shocks at both ends would help.  Really to analyse it some more info would be needed, do you know gear ratios? and ring & pinion? some engine spec? and rpm you launch and shift at? maybe weight of car?
Any video of it launching?

cheers Richie

Hi Richie,

Yes, I'm glad I got this car, that's a long time dream of me.

Front beam is balljoint, stock spindles, lowered on adjusters.
I don't know my gear ratios. I cross the line a bit less than 7700rpm. I tried with the rev limiter at 7500 and I hit it just before the finish line. It got a spool and weddle straight cut gears, that's all I know.
I have the dyno sheet of the rolling dyno, I'll post that later.
Car should be less than 600kg. I can weight it a some friends farm, they got a balance for cereals, I don't know where else to weight it. I could ask the MOT station if we could weight front and back to have some more usefull data, but I don't know if they will do a car without registration.
I installed a 2 steps for the last race at clastres and tried to launch at 5.000 and 5.500. 60ft were 1.54 and 1.51. It either spin the tires, do small wheelies or a bigger wheelie.
I do have vids, I'll try to upload that.

Sorry to be as usefully acurate as a hammer in a matches building contest, but I want to learn and improve.

[j-f]

Hi there ,

What are the basic knowledges to know, and understand, to tune a drag race chassis?
I feel I can do better with my car regarding ET, 60ft and consitency.
But, as it is totally new for me, I'm not sure what to do?
Car is the Fourplay gasser.
Stock front shocks.
Stock spindles
lowered on adjuster

Old koni yellow rear shocks




28mm sway a way torsion bars
RLR spring plate cover with empi inside urethane bushing
Empi Adjustable spring plates
Phoenix 26.6x15 slicks.

best ET so far is 11.65s 1/4m with a 1.52sec 60ft.
Best 60ft is 1.51 with a wheelie.

Thanks guy's 

Hi Many people forget how important a shock absorber is
Especially on a drag racing car
Front is good if you can adjust so you can change how much the front part lifts so the weight distribution from the front wheels to the rear tires
Rear is even more important that you have adjustment in the return side and pressure side
In the UK there is a shock absorber manufacturer called AVO who are cheap and work well for a sportsman car
Many people forget how the weight balance is late whether it is a Volkswagen or ProStock car
Many in the Volkswagen world lighten the car like crazy at the front then the balance becomes incorrect
In my world it is better to put a few kg of lead far down as far forward as possible because the weight balance on the car should make the car go forward as fast as possible Not high up in the sky for every inch it goes up how much slower it gets 60 F
/// M

Shocks are definitively necessary. I ask GAZ shocks, but they don't do dual adjusters ones.
I'll will have a look at AVO.
Car is basically set up as a gasser, without lot's front weight.

[j-f]

[ Attachment: You are not allowed to view attachments ] Here is the dyno sheet

[richie]

Hi Richie,

Yes, I'm glad I got this car, that's a long time dream of me.

Front beam is balljoint, stock spindles, lowered on adjusters.
I don't know my gear ratios. I cross the line a bit less than 7700rpm. I tried with the rev limiter at 7500 and I hit it just before the finish line. It got a spool and weddle straight cut gears, that's all I know.
I have the dyno sheet of the rolling dyno, I'll post that later.
Car should be less than 600kg. I can weight it a some friends farm, they got a balance for cereals, I don't know where else to weight it. I could ask the MOT station if we could weight front and back to have some more usefull data, but I don't know if they will do a car without registration.
I installed a 2 steps for the last race at clastres and tried to launch at 5.000 and 5.500. 60ft were 1.54 and 1.51. It either spin the tires, do small wheelies or a bigger wheelie.
I do have vids, I'll try to upload that.

Sorry to be as usefully acurate as a hammer in a matches building contest, but I want to learn and improve.

Ok cool   Here is my launch theory, and this is clutch dependant, you need launch rpm high enough so that as clutch pulls rpm down as it launches it stays above peak torque, usually 2 step around 6300-6800 rpm, you are trying to get clutch to slip a little ideally and it needs enough hp & rpm to do that   Never been to Clastres so no idea on what track prep is like, if it spins tyres then work on tyre pressures and when you go some better shocks adjusting them as well.
Get a really good tyre gauge, needs to measure at least as small as 0.1psi increments, and you might need different pressure side to side to compensate for driver weight:o

[j-f]

Hi Richie,

Yes, I'm glad I got this car, that's a long time dream of me.

Front beam is balljoint, stock spindles, lowered on adjusters.
I don't know my gear ratios. I cross the line a bit less than 7700rpm. I tried with the rev limiter at 7500 and I hit it just before the finish line. It got a spool and weddle straight cut gears, that's all I know.
I have the dyno sheet of the rolling dyno, I'll post that later.
Car should be less than 600kg. I can weight it a some friends farm, they got a balance for cereals, I don't know where else to weight it. I could ask the MOT station if we could weight front and back to have some more usefull data, but I don't know if they will do a car without registration.
I installed a 2 steps for the last race at clastres and tried to launch at 5.000 and 5.500. 60ft were 1.54 and 1.51. It either spin the tires, do small wheelies or a bigger wheelie.
I do have vids, I'll try to upload that.

Sorry to be as usefully acurate as a hammer in a matches building contest, but I want to learn and improve.

Ok cool   Here is my launch theory, and this is clutch dependant, you need launch rpm high enough so that as clutch pulls rpm down as it launches it stays above peak torque, usually 2 step around 6300-6800 rpm, you are trying to get clutch to slip a little ideally and it needs enough hp & rpm to do that   Never been to Clastres so no idea on what track prep is like, if it spins tyres then work on tyre pressures and when you go some better shocks adjusting them as well.
Get a really good tyre gauge, needs to measure at least as small as 0.1psi increments, and you might need different pressure side to side to compensate for driver weight:o

Clastres is a good prepped track.
I tried between 0.9 and 1.1bars, I use a karting tyre gauge.
If I launch at 6300 rpm, I think it will wheelie pretty hard.
I read the article that John Connely from aircooled.net wrote a while back, it seems to be a good honest base line.

[richie]

The idea is more rpm/power helps clutch slip at hit and it wheelies less As Micke mentioned you may need to add a little weight to front of car to help balance it better

[PPRMicke]

Hi I don't know what you know about clutch adjustment
Have you heard of breaking loose when adjusting the clutch
to set a controlled slip
Tools you need to have an input shaft from a gearbox with a sleeve (1/2 socket) that is welded to it A flywheel lock then a torque wrench
How to do it You start by locking the flywheel then you insert the input shaft into the disk then you pull with the torque wrench in the opposite direction to the engine goes to the disk release the grip then you get a torque
You should be 5-10% less than the maximum torque that the engine has
How to get the pressure down in the pressure plate you shim between the flywheel and the pressure plate so you get what you want for the start to be optimal You always have slip in the start if you want to get a good 60 F
/// PPR Micke

[j-f]

Hi I don't know what you know about clutch adjustment
Have you heard of breaking loose when adjusting the clutch
to set a controlled slip
Tools you need to have an input shaft from a gearbox with a sleeve (1/2 socket) that is welded to it A flywheel lock then a torque wrench
How to do it You start by locking the flywheel then you insert the input shaft into the disk then you pull with the torque wrench in the opposite direction to the engine goes to the disk release the grip then you get a torque
You should be 5-10% less than the maximum torque that the engine has
How to get the pressure down in the pressure plate you shim between the flywheel and the pressure plate so you get what you want for the start to be optimal You always have slip in the start if you want to get a good 60 F
/// PPR Micke

Hi Micke,

Yes, it is done. Clutch is set at 250nm.
Seems to work well that way.
Kennedy stage2, exedy disc.

[PPRMicke]

 Hi
One question Can you measure in any way how long your clutch slips
We usually slip around 3-4 tenths in 1st with the combi you have in clutch on a good track
The weight balance in the car is often what does the most good
If you put a 5kg lead bar in front of the front car it usually works well for 60 F so the weight balance makes the car go forward instead of up with the front wheels
90% of those here in Sweden who are fast have a lead battery in the spare wheel well then      Good shock absorbers front and rear On my pro mod I have 120kg lead in the front If you were to look at US Pro Stock they have at least 20-40 kg in the front
PPR Micke

[j-f]

Hi
One question Can you measure in any way how long your clutch slips
We usually slip around 3-4 tenths in 1st with the combi you have in clutch on a good track
The weight balance in the car is often what does the most good
If you put a 5kg lead bar in front of the front car it usually works well for 60 F so the weight balance makes the car go forward instead of up with the front wheels
90% of those here in Sweden who are fast have a lead battery in the spare wheel well then      Good shock absorbers front and rear On my pro mod I have 120kg lead in the front If you were to look at US Pro Stock they have at least 20-40 kg in the front
PPR Micke

Hi Micke,

No idea how to measure clutch slippage? I stage using the stage brake, leave the clutch slightly engage to preload the gearbox a bit, put gaz and lift the clutch, smiling and hoping for the best  
Barely anything in front of the car. Battery is on the passenger floor and even the fuel tank sits above the driver knee. I believe it was set up for show and go rather than chasing time.
I will change that,

Thanks,

JF  

[ Attachment: You are not allowed to view attachments ]

[PPRMicke]

There are different ways to measure slippage in the clutch
A friend who films the rear tire is the cheapest way Then you paint a triangular line on the tire then you watch the film and see how much the tire is slipping It should be a maximum of one lap then you listen to the sound of the engine The old trick I started using in the 90s before computers came into the picture
Auto meter has a tachometer with memory and a channel for measuring drive shaft speed
If you use Wideband lambda, there are data loggers for them for reasonable money (wideband lambda is a very good tool for adjusting the carburetors and ignition)
The thing with safety and how the thinking is in Europe is a very big difference A battery inside the car is a big NO NO here in the Nordic countries Same with fuel If you bring it up here in Sweden you are banned from racing for a year
/// PPR M