VXR8 Traction Issues

[MrLOL]

Quick question.

What causes the traction issues that the VXR8 has ?

You see supercharged corvette's doing 1/4 miles in 11 seconds, but 600 bhp + wortec VXR8s struggle to get bellow 13 seconds.

is it just down to the extra weight of the R8 and the corvette will have similar grip issues as the R8 ?

or is there more to it than just weight differences.

[ARAF]

Aerodynamics as well, once you start moving.

[IanJ]

Quote from Wiki about the ZR1



"The rear wheels are the largest ever mounted on a production Corvette with 335/25 Michelin Pilot Sport PS2 tires on ultra-light 20 in (510 mm) wheels."

[Mystvxr]

Quick question.

What causes the traction issues that the VXR8 has ?

You see supercharged corvette's doing 1/4 miles in 11 seconds, but 600 bhp + wortec VXR8s struggle to get bellow 13 seconds.

is it just down to the extra weight of the R8 and the corvette will have similar grip issues as the R8 ?

or is there more to it than just weight differences.

Ask a physics professor for an exact answer, you can start by calculating the coefficient of rolling friction, there are many variables, fast vets can have up to 335mm of rubber, but that's just one part of the equation, there's so much physics going on, that's what makes it such a challenge for a human to try and get right, all cars and drivers must succumb to the laws of physics.

[napa1985]

Ask a physics professor for an exact answer, you can start by calculating the coefficient of rolling friction, there are many variables, fast vets can have up to 335mm of rubber, but that's just one part of the equation, there's so much physics going on, that's what makes it such a challenge for a human to try and get right, all cars and drivers must succumb to the laws of physics.

nutty professor

[Phantom Mark]

Its the whole package, weight, weight distribution, aerodynamics, suspension geometry, gear ratios, tyre compounds, tyre contact patch, rim / tyre weights, rotational inertia, drag............but to name a few

I am not a Physics Professor, but I am the Physics Director for a Vehicle Simulation company

FWIW I think my VXR8 has astounding traction, I never really have a problem getting the power down even in damp conditions, I was pleasantly surprised and expected the car to be far more slippery when driven aggressively, the major factor for the R8's lack of quarter mile time compared to the Vette is absolutely the weight, these are fat pigs, even if it doesn't feel like it when your driving along.

Mine weighed in on the local weight bridge at 1840kg, quarter of a tank of fuel, I weight 75kg, to compare how fat these cars are my old BMW E60 530d M-Sport weighed in at 1720kg all up with a full tank of juice !!!

[S2000GT]

Ask a physics professor for an exact answer, you can start by calculating the coefficient of rolling friction, there are many variables, fast vets can have up to 335mm of rubber, but that's just one part of the equation, there's so much physics going on, that's what makes it such a challenge for a human to try and get right, all cars and drivers must succumb to the laws of physics.

you canna change the laws of physics.

[ringram]

You see supercharged corvette's doing 1/4 miles in 11 seconds, but 600 bhp + wortec VXR8s struggle to get bellow 13 seconds.

Why the surprise? PD supercharging is pointless on the stock engine. Ive been well under 13 sec with "600bhp" on stock tires. I keep telling everyone this but everyone acts surprised when the results fail to meet the hype.

Sure there are some traction issues, but there are also the issue of decreasing torque and lack of high rpm power, hell I was breaking traction at 100mph shifting into 4th! Add that all up and the PD is torquey sure, but just doesnt stack up on many levels. I've spent about 20 years modifying various Chevrolet V8's and have been through the thought process around performance mods many times, seen reports of others results, issues, costs etc. And while the decision can be close in some instances in my opinion on a stock engine there is no point supercharging.

I beat HarryOz's 1000bhp Monaro over the quater mile. Down to traction yes, but whats the point in all that power if a non supercharged car can beat you to over 100mph!? I think Jez and Harry will tell you thats not important to them and they are after raw top speed. But thats a pretty specialist requirement. For 95% of people being fast off the line and up to road legal speed is what counts. Well ok, maybe some like the off idle torque of the supercharged cars, but just dont mistake torque for power.

Look at all the top sports cars. How many use forced induction? Lambo, Ferrari, Zonda etc. Sure for supermental power forced induction is required. But you are talking north of 600bhp, by which time your stock engine is well dead anyway.

[MrLOL]

so the reason why the big power cars arent putting down massively quick 1/4 mile times is down to the power delivery of the FI setups ?

And in terms of comparisons with other cars (such as the vette) its down to the size of the rear tyres and the extra weight.

[Phantom Mark]

Well you absolutely have to have the power/torque in proportion to the weight, its pointless for example having 600nm of torque and 450bhp in a car which weighed 500kg, you would never be able to get the power down............and in this example the PTW ratio is more suitable in the Vette because the R8 is just overweight basically.

[ringram]

so the reason why the big power cars arent putting down massively quick 1/4 mile times is down to the power delivery of the FI setups ?

And in terms of comparisons with other cars (such as the vette) its down to the size of the rear tyres and the extra weight.

Well its all in the combination in either instance really..

[MrLOL]

so the power delivery of the FI setup doesnt suit the weight and tyres of the R8

but may suit other cars better ? hence why the ZR1 can get sub 11 sec 1/4 mile times, despite having a very similar engine ?

[ringram]

Not even that. A PD blower is not ideally suited to the stock engine. It runs out of airflow at higher rpm so power falls away. Dont forget the LS9 is designed around the blower.
Forged pistons, dry sump, 9:1 compression. LS7 spec duration cam, but with milder lobes. 211/230
If you could cam the stock engine and it had forged pistons and a lower compression, then it would wind out better with the right sized blower and not die off. In effect you would build to the same guidelines as the LS9.
Sure tires would help down low, but not up higher rpm when its dead anyway. Low down power is not required with the V8 stock cars will struggle for traction in the first 2 gears in any case, so why make it worse?

[MrLOL]

ah so the american FI setups that get the low times (theres one on youtube of an 8 second supercharged Zo6) supercharge the engine, but take a completely different approach to what we do ? which is just banging the supercharger on the stock engine ?

Sorry for asking lots of questions, just trying to further my knowledge

[ringram]

Almost certainly, yes.

If you are going to do it, do it properly