I want to hit a sub 5 sec 0-60 at trax this sunday. Last year i managed a 5.36 at the FCS at Bruntingthorpe. Since then I've saved more weight and have adjustable suspension (raise / stiffen the rear).
The 5.36 run was done on shagged out yokohama a539's that have gone very hard, I still have the yoko's but am unsure on the following, do I
A) get some tyre softener and treat them b4 the weekend
or
B) buy a pair of Toyo R888's?
Any advice or people with experience appreciated. :beer:
Tathan, it does indeed increase your in gear aceleration if you go ligther, thats the main reason why ligther is better on trackdays as you dont launch at all on most trackday but you spend the whole time acceleating and decelerating in gear.
Noticeably? I didn't notice a difference between the same model of car, one with about 3 or 4kg less once it was in gear. Revved nicely in neutral though
Don't see how reducing the rotating mass off and engine can be worth horsepower that you'd realise? It's only a few kg, granted it's a foot or so from the centre so needs more force to accelerate but surely not more than a couple of lbft are needed?
But when you are at 4000rpm in 2nd and want to be at 7000rpm in second, that means you have to put energy into:
a) building up the extra energy in the car
b) building the the extra energy in the flywheel
So the less weight the flywheel has the less energy is wasted that can get used to accelerate the car instead.
In lower gears it a bigger effect of course.
You see figures bandied around like "1kg off the flyhweel = 10kg off the car in 1st gear" in terms of acceleration difference but i cant comment on the accuracy as ive never done the maths on it TBH
But as you can see from those "figures" it would only be like losing 30kg anyway and only 15kg in 2nd etc, so its not going to make *that* much difference.
Steve, im sure 200bhp in an E30 is great fun, still feel pedestrian compared to some of the astras and novas etc that ive driven though, lol
Sp30-94 is a centrifugal charger, effectively its like a turbo compressor but driven by a gearbox driven off the crank instead of by exahust gasses.
This means it doesnt make masses of boost at low rpm, which means you can get away with fairly high compression, so you could do it on a standard M50 lump without lowering the CR etc IMHO, but ive not tried it yet, its on the list of projects i would like to do one day
I've read and understood your points about having kinetic energy in the flywheel on launch and therefore the bigger the flywheel the greater the KE at launch, BUT this is only of benefit until you need to exceed that launch RPM. i.e until the clutch is fully engaged and you then want to increase the RPM, at that point the effects of the greater mass of flywheel are negative.
The heavier flywheel KE at launch can be easily countered on a car with a lighter flywheel by increasing the RPM, as the KE is obviously relative to the rotation speed and the mass. So reduced mass coupled with increased speed can have the same KE as heavy flywheel at lower speed.
On the previous topic of clutch slip. With stickier tyres and greater launch RPM the slip encountered will be more detrimental as obviously higher RPM and more torque will produce more heat at the flywheel/clutch face, but I still believe that the clutch slip will be for a reduced amount of time and therefore the resultant clutch abuse may not be as great.
I am aware that all my sides to this discussion are theory based and that theory is usually proved wrong, so I'll see what happens on sunday. If i come back with a fried clutch, I'll happily say 'Chip was right' :beer:
We're not talking about in gear times, we're talking about launch times.
If the flywheel's too light, when you pull the clutch up, the engine goes "****, WTF?" and gets stuck down at 2000rpm, trying to fight against it's own torque curve.
If the flywheel's too heavy, when you pull the clutch up, the engine's got loads of inertia and the wheels just spin.
So, I think the point chip is trying to make is that it's trial and error to find a flywheel that's perfect for launching.
But then he also says it would be too heavy for track use, since you only launch once on a track, and even then it's not vital to get a good launch as long as there's a nice straight to build up some in-gear speed.
I've never heard of tyre softener, does it condition the rubber or what?
If the flywheel's too light, when you pull the clutch up, the engine goes "****, WTF?" and gets stuck down at 2000rpm, trying to fight against it's own torque curve.
If the flywheel's too heavy, when you pull the clutch up, the engine's got loads of inertia and the wheels just spin.
So, I think the point chip is trying to make is that it's trial and error to find a flywheel that's perfect for launching.
But then he also says it would be too heavy for track use, since you only launch once on a track, and even then it's not vital to get a good launch as long as there's a nice straight to build up some in-gear speed.
But when you are at 4000rpm in 2nd and want to be at 7000rpm in second, that means you have to put energy into:
a) building up the extra energy in the car
b) building the the extra energy in the flywheel
So the less weight the flywheel has the less energy is wasted that can get used to accelerate the car instead.
In lower gears it a bigger effect of course.
You see figures bandied around like "1kg off the flyhweel = 10kg off the car in 1st gear" in terms of acceleration difference but i cant comment on the accuracy as ive never done the maths on it TBH
But as you can see from those "figures" it would only be like losing 30kg anyway and only 15kg in 2nd etc, so its not going to make *that* much difference.
Sorry, I didn't mean to imply it gave you horsepower, just that it's "worth" horsepower if ya seen what I mean
I understand the theory or reducing rotating mass takes less energy to spin it up to a given revs, I just think that even your "1kg off the flywheel = 10kg of the car in 1st gear" won't be noticeable. Maybe in 1st, but in a high gear? "1kg off the flywheel = same as driver having a sheeit out the window before booting it?"
CP tried tyre softerner, on slicks with naff all pressure in them and wondered why he couldnt launch lol. Too many revs and spins, not enough bog tastic.
also its worth noting that most tures "grip" better with a small ammount of slip
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