Drag racing techniques and car setup

A few comments on this article. These are my own opinions so may well conflict with others

Original article in red, my comments in black

When building a drag car it needs to be as light as possible and as powerful as possible, weather it handles and goes round corners is not important but you do need maximum traction at the driven wheels. If you wheel spin you loose time.

Handling is VERY important:

1. Acceleration off the line depends on both driven wheels gripping and this requires a well balanced car.
2. Each gear change can unbalance the car so, again, it needs to be balanced.
2. Top speeds can exceed 150mph in a road legal car so good handling is required at this speed and when slowing down.

It is not possible to build a car specifically to do both and you cannot run a strip car round a circuit because it won't corner,

My Elan is being built primarily for the drag strip, but will also be used for hillclimbs and sprinting.

but you can run a circuit car down the strip it just won't be as quick as a purpose built drag car.

But this article isn't about building a purpose built drag car, is it?

b) Get the car of your choice, put bigger brakes on it and put the engine in.

For a drag car, bigger brakes are not necessary. In fact, they can be dangerous as slowing from 150mph plus needs to be done in a controlled manner so as not to destabilise the car.

c) I wouldn't bother lowering your car but I would put harder shocks on it to hold the wheels more firmly on the ground so they don't spin.

What? Harder DAMPERS will result in tyre judder and LESS grip. Softer and progressive suspension is required so that the car squats on initial acceleration thereby pushing the tyres into the track surface.

 

So, and to put this gently, in your opinion OG, the article still needs some work?

 

IMO, yes.

 

This would be a VERY difficult guide to write and get right from the first draft.

Something that is not mentioned is weight transfer / preservation. By that I mean a RWD or AWD based on a RWD layout requires a good amount of weight transfer to get good traction off the line. Conversely a FWD or AWD based on a FWD layout requires weight preservation up front, or put another way it needs to resist weight transfer.

For weight transfer to happen, the rear shocks need to allow the car to squat and the front to lift / shocks extend but without lifting the front wheels off the ground. Maybe even preload the rear by having zero or even negative rake i.e. nose up slightly when stood on a level surface.

To preserve weight and resist transfer can be helped in several ways besides selective weight reduction or adding ballast. Adding rake (raising the rear or dropping the front) can really help as can shock setup. Setting the rear shocks to hard with maximum damping to resist squat and having the fronts sprung softer (less spring assistance when the front lifts) to keep the nose down all help to preserve weight over the front wheels.

To explain what I meant earlier by an AWD based on a RWD layout a typical example would be a Skyline GTR where the gearbox is in line driving the rear wheels and the transfer case throwing power forwards to the front wheels. An AWD based on a FWD layout would be along the lines of a GTO or EVO, transverse engine and gearbox where the front wheels are driven straight off the gearbox akin to a FWD; the transfer case (mounted on the side of the gearbox) throws some power towards the rear.

In the case of an AWD based around FWD weight transfer unloads the front wheels (primary driven wheels) which will spin like crazy. As the (typically) viscous diff struggles to lock up sending drive to the rears a huge load is placed on the transfer case which can fail quite spectacularly, as can things like UJ's and rear driveshafts depending on power levels. Even if there is no failure, there is a huge waste of power and traction. So you can see weight transfer / preservation is quite an important consideration.

This subject leads quite nicely onto alignment. Quite simply straight is fast! By that I mean that when you need the greatest traction (i.e. at launch) all wheels need to be as close to zero camber and zero toe as you can get them. This might require negative camber up front and positive camber at the rear to allow for lift at the front and squat at the rear. The amount will be determined by how much suspension movement you have on launching with your particular setup.

I hope people find this helpful and food for thought.

André

 

Good post. My only caveat is re launch camber. IMO it is more important to have the correct camber at the end of the track rather than at launch. I would not be happy trying to stop from 160mph with a positive cambered rear end. Better to have a rear suspension geometry that doesn't go into positive camber when compressed. My system, although with only 50mm of travel, increases negative camber on compression (which also aids cornering).

PS. That is one hell of a car you have there, any photos on here? How much does it weigh? Is that time on street legal tyres?

 

Thanks for the compliment.

OG I take your point, I can only add my personal experience which is by lifting off gently and smoothly and applying the brakes in the same way, I have never had the car become unstable even in winds exceeding 20 mph!. I just commented on your 'chute post too.

Yes it was on R888s. At the time it weighed in excess of 3500 lbs, last time I weighed it it was 3256 lbs with me in it but it is currently in Greece having every body panel replicated in carbon kevlar honeycombe. We should save 2-250 lbs with any luck. For exaple, a stock door weighs in excess of 30 kgs and my new ones (without lexan or glass) weigh 2.3 kg each. We are also adding another 150-200 hp to it LOL.

 

Wow, that is some serious weight reduction, and I thought that I was obsessed

1250bhp and 3000lbs = 933bhp/ton - impressive.

 

It is a little OCD isn't it LOL. Shooting for 1000bhp/tonne ultimately but the real driver for the weight reduction is to lower the moment of inertia and give the transmission a little bit on an easier time. Too many of these.

 

Yeah, that is my concern as well. To that end I am fitting an adjustable flow valve (to my spec) in the clutch pipe. This will allow us to reduce the initial hit on the transmission but still allow an almost instant hook up (hopefully). Removing the gearbox requires engine removal as well so I want to avoid this if at all possible, or at least reduce its frequency

 

We had a Tilton clutch flow control valve in there! I have had smaller inserts made for it now and will also be fitting a variable control as well. Great minds lol.

André

 

Your cars are FWD so the experience I have drag racing really does not apply . I will say I have tried alot of clutch systems and parts trying to keep my Type 1 tranny from exploding every race . I found that getting my clutch right changed everything . My 60 ft times were consistent 1.35 with NO burnout and ET's were 6.30s in the 1/8th and I credit most of that to my clutch. Here is a vid of my old bug (red car) leaving the line , notice no burnout and I also shifted to second gear in the air( it goes higher up when shifted ) I broke the wheely bars. Mike

 

Nice run. We mainly run the 1/4 over here (UK) so I calculate that you would be running mid to high 9s.

What makes you think that our cars are FWD? PG's GTO is AWD and my Elan is RWD.

 

Andre, any runs this year? Did you get the Kevlar panels fitted?

 

I stand corrected, LOL . I have never run 1/4 mile track but only because most of our tracks are IHRA 1/8th mile but I look forward to running my street car 1/4 mile . Mike

 

Can't you run the VW on the 1/4? Gearing issues?

I went to Irwindale a couple of years ago. Initially disappointed that it was only 1/8 mile, but we had a good time and you get to see the whole run and more of them It was difficult, however, to compare the times to the 1/4 mile I am used to.

 

I will be able to run the 1/4 at a few tracks but the majority of the tracks near me are 1/8th . The two tracks that run 1/4 are Rockingham and Kinston , if I get the chance I will give you a report on the outcome. Mike

 

Yes, please do. What's your start line ratio?

 

The transmission is geared pretty low , 3.88 r/p 3.78 , 2.31 , 1.58, 1.21 On 26x 8.5 tires . My street tires and slicks measure the same specs. I believe I will change the gear ratio down the road but right now it works.

 

OG, I just got the car back after most of my season has been missed. We are trying to see if we can get it together to run this weekend.
It has been claimed (tbc on a weighbridge) that 140 kg was saved.
We had the engine on an engine dyno but the operator didn't tighten his intercooler pipes properly and during the session the inlet pipe blew completely off causing the compressors to massively over spool and buckling brand new compressor wheels. He also didn't have the correct filtration on his setup AFAIK because I ended up with a brand new injector developing a high pressure drip. Most likely cause is contamination!
Still we smashed the dyno record before and even more after the compressors buckled!! 1035 hp before, far from maxed out. 1095 hp after but had to ease through the surge before we could boost, however the torque numbers and therefore the hp numbers were well down due to only loading in the last half of the power band.
Turbos are fixed, injectors rebuilt, fingers crossed for this weekend
The picture below is without an engine or gearbox so it sits a little high.

André

 

Thanks, not far away from finding out. New fuel pump as mine has died, new rear lower control arms, new powered steering pump and the engine / gearbox are good to get fitted. Already mapped to 1095 hp (not fully maxed) so just tweaking then off to the track.