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Black magic Mk5 GTI track car

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fuscobal:
Osir told me their bonnet is under 7kg wich is very good compared to Seibon but the vent is in the wrong position and the price is also much higher than Seibon + bringing it from US would add 50% to theprice from shipping and taxes !

phrozen:
loving the audio!!

are the mids in the door cards sealed or venting into the door??

fuscobal:
The mids are on the dash. The midbasses are venting into the door because the Microprecision 7 are infinite baffle drivers. A sealed enclosure for 2 x 16.5 drivers would need a volume that cannot be obtained inside a door (I mean the door has the volume but it's impossible to seal it as you have the windows and water that has to drain on the lower part of the door) !

This is what Osir offers right now > http://www.osirusa.com/mm5/merchant.mvc?Screen=PROD&Product_Code=VGTI-CFHGT1-DCF&Category_Code=VJETEB

I'm a bit confused as of wich one is the lightest of all, wich one can be painted and does the vented one have any real benefit of cooling the turbo knowing there is positive pressure on that area pushing the hot air back (not allowing it to exit from under the hood) ?

fuscobal:
Ok, found some info that I've missed before > http://www.osirdesign.com.au/GTI_CFH.htm

CFH GT1 and CFH GT2 offers 2 versions, single sided and double sided

CFH GT1 and CFH GT2 uses special reenforce compound coating which can withstand high pressures

This special coating keeps your hood in shape all the time

CFH GT1 and CFH GT2 lets you use the factory latch and hood stand with no modifications needed

Factory hood weight  13.6kg

CFH GT1 and CFH GT2 Single side (carbon out only) weight less than 7kg

CFH GT1 and CFH GT2 Double sides (carbon inside out) weight less than 8kg Looks good even the hood is opened

Knowing the weight is my main purpose, the single sided wich is much cheaper and a little lighter also would be my main bet. Now...can it be painted black and would be any real benefit to buy the vented one (same price vented or OEM like) ?

Yesterday I've removed the rear seat belts assemby wich was a 2Kg saving



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fuscobal:
Because I got bored today, I made some aerodynamic calculations for the Hungaroring track today :

- Car's weight > m = 1450Kg
- Car weight + downforce > N = 1520Kg (OEM car has 0kg front@160kmh and -20kg rear@160kmh. I've considered an addition of 20kg front brought by an air dam/splitter and 70kg rear from an 1400mm span wing with 225mm width and 10deg AOA. On the rear I've substracted the 20kg lift of the OEM car from the 70kg addition brought by the wing so I've got about 50kg left. The wing considered was the Reverie 225mm wich is a moderate downforce wing (wouldn't want something too big wich would hurt the car's look or bring too much rear downforce wich may cause front lift). N@160kmh resulted by adding the downforce to the car's weight, so 1450+20+50 = 1520kg, from wich only1450kg will generate inertia and centrifugal force.
- Hungaroring length> 4381m
- Hungaroring cornering length> 675m (15 turns)
- medium cornering radius R = 55.5m
- Friction coeff between semislick and asphalt > u = 1.2 (Don't have an exact value so this is an approximation. However, even with a different value, the difference would remain because it would appear in both formulas and deduct itself)

The car's equilibrium at the limit would be Fn = Ff

Fn = u * N (for OEM car N1 = m = 1450kg, for the car with downforce addition, N2 = 1520kg)

Ff = m * V^2 / R

In the 2 situations, the car's speed on a circle with 55.5m radius would be :

1) OEM car > v1 = sqrt(Fn1 * R / m) = 8.161m/s^2
2) Aerodynamically enhanced car > v2 = sqrt(Fn2 * R / m) = 8.356m/s^2

Knowing the cornering total distance of the track is  L = 675m, at the 2 speeds, this would be driven in t1 = 82.71s by the OEM car and in t2 = 80.78s by the aerodynamically enhanced vehicle. From here, we can see there's a 1.93sec improvement in lap time wich is not negligeable at all.

Considerations :

1) The cornering length and medium radius were taken from a database but for accurate calculations each corner would have to be accounted separately with its radius and arc length. I supposed the car is spinning inside a 55.5m radius circle for a distance of 675m
2) The aerodynamics of the stock car was approximated from Bruce's post on ''improving aerodynamics with OEM parts'' topic !
3) I did'n consider my car's riding height wich is probably about 30mm lower than OEM. Normally this should bring extra downforce by increasing the undercar air speed and decreasing pressure but as I don't have any data, I can't approximate the addition
4) I didn't also account for the chassis body roll and different tire loads.
5) I didn't take into account the effect of the greater corner exit speed on straights wich would bring time improvement on straights also (maybe another 1sec even !!!)

To follow :

- 30mm wider Kerscher wings > maybe 1-2kg weight reduction being they are ABS as opposed to iron sheet
- Odyssey ER40 deep-cycle > - 15Kg
- Carbon Osir hood > -7Kg
- VwRacing air dam > +2Kg (don't actually know the difference between the OEm one and this)
- Rear carbon wing > +3Kg (same as above)
- Maybe another set of fixed Recaro sidemounts for track days (or custom made ones) wich will replace the sliding rails > - 12-14Kg

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