sdh2903
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| posted on 25/7/16 at 10:05 PM |
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Uprated clutch in a 7
I'm currently shopping for a clutch for my new build. It's a 2.0 turbo with 250 ish bhp and 300 torques. Engine is mated to a mk3 mx5
flywheel and box.
There are couple of off the shelf options from competition clutch and action clutch however thought I'd email helix today and the helpful chap
said I wouldn't need a clutch rated for 300lbft in a 600kg car. I did reply and ask if there was a rule of thumb for speccing a clutch for a
relatively light car but it was late in the day so didn't receive a reply yet.
So my question is, how have people specced their clutches in their cars that have upped the power?
Cheers
Steve.
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Andy D
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| posted on 26/7/16 at 05:42 AM |
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Have never fitted anything other than a standard Clutch in my car up to recently. Fair enough it's no power monster at 170bhp (Pinto) but
that's about 60% more power over standard .. 105bhp? Only used on trackdays, so gets a bit of grief, been no trouble. I've always presumed
in a light car, you'll lose traction before the clutch slips?
Recently fitted a Caterham box so needed a different clutch, and the only one I could find was a Helix uprated one.
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chris
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| posted on 26/7/16 at 06:19 AM |
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I run a st170 engine on a 1.8 zetec clutch and flywheel to a type 9 box and had no problems so far
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JAG
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| posted on 26/7/16 at 09:17 AM |
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The torque that the car can transmit to the road (and hence the torque that the clutch/gearbox must handle) is limited by the tyres and the weight of
the car.
A very light car can transmit much less torque and hence the clutch doesn't need to be re-specified when you up the engine power output -
especially if the clutch came from a much heavier production car.
Justin
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Bluemoon
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| posted on 26/7/16 at 10:23 AM |
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^^ ditto,
Comes down to:
http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/frictire.html
if you can spin up the rear wheels with the current clutch fully engaged with no clutch slip, then there is not more to gain (apart from a different
bite point feel).. It's likely that the standard clutch is rated at twice that need for the standard engine as the car's weight has
probably half the "standard" dooner car weight.
300ftbl == 400Nm
Assuming wheel diameter of 60cm
then limiting traction torque at the wheels, assuming friction coefficient of 1 and LSD would be:
600(kg)*9.8(N/kg)0.6(Meters)/2 = 1,764.0
Assuming a type 9 gear box and 3.14 differential, coefficient of friction of 1, the wheels will break traction (clutch fully engaged) at the following
engine torques:
1st 1,764.0/(3.36*3.14)=167 Nm
2nd 1,764.0/(1.88*3.14)=298 Nm
3rd 1,764.0/(1.26*3.14)=445 Nm
4th 1,764.0/(1.*3.14) = 561Nm
5th 1,764.0/(0.82*3.14) = 685 Nm
As the tires coefficient of friction is less than 1, it's likely you wheels will break traction in 1st, 2nd 3rd and maybe 4th..
Dan
[Edited on 26/7/16 by Bluemoon]
[Edited on 26/7/16 by Bluemoon]
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Ben_Copeland
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| posted on 26/7/16 at 11:17 AM |
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Mines over 300lbft of torque going through a standard clutch through a standard type 9. Been in there 2 years and still ok.
I think it's likely to depend on how you drive the car, what your doing with it etc.
Drifting / donuts / drag starts is going to knacker a clutch much quicker
Ben
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sdh2903
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| posted on 26/7/16 at 02:16 PM |
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Thanks chaps, some very in depth info there!
Car is going to be a mix of road / track but biased more to the road. I just didn't want to fit a standard clutch for it to start slipping 6
months down the line. However I'm also mindful of not wanting to spend extra cash on a heavier more hardcore clutch if not necessary.
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