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Playo

6th gear mod

Hi Doug

Could I get a price on  the 6th gear mod for the B5's please, both supplied price and how much labour to fit  is?

Thanks
Doug

£385+vat

around 3 hours to fit plus gearbox oil
Playo

Excellent! I'll be in touch soon
samj

What is a 6th gear mod???
BennyBoo

samj wrote:
What is a 6th gear mod???


It gives over 200mph at about 7k rpm in the 01e box..  
mad-for-tar

Right here:

http://www.mrctuning.com/index.ph...mp;id=37&Itemid=59#drivetrain
StumpyRS4

But primarily I would assume for better cruising ability...?
pjbRs

I was going to ask similar, what difference does it make to normal cruising, lower revs? so better mpg?
Doug

Lucas ran the diesel 6th gear so he could do 202mph:

http://www.youtube.com/watch?v=rPBl_g1GMAY

but it took ages to get there and was too long for just hitting 200 mph - top speed in that gear was 230+.

Lucas specified a custom 6th gearset to be made so at 7000 rpm IIRC a b5 rs4 would hit 200 mph. I ran this gear at bruntingthorpe to hit 202mph. If it was longer it would not have hit over 200 in that distance.

If you want one for super long 6th put the diesel one in, although it is much the same price.
cos

Hi Doug(I had some health problems so I'll contact you for the tune) may I ask how much hp you need to hit the 200mph in that custom 6th gear?Thanks (Doug I
BennyBoo

cos wrote:
Hi Doug(I had some health problems so I'll contact you for the tune) may I ask how much hp you need to hit the 200mph in that custom 6th gear?Thanks (Doug I


I got to the rev limiter in 6th in a stage 1 remapped car.. So i'd guess not that much more.. Maybe under 400hp?
cos

So if it is  possible to hit 200mph with a 400-450hp s4 in that custom 6th gear ,that will be great because many cars can't do it that easy although having arround 400+ hp!
musty

Hp only gets you to 200 quicker if your car is geared to 200 it will get to 200 hp only determines how quick you reach it
loomx

Not really, it a world with wind resistance maybe...

A 100bhp isnt going to reach 200mph, even if it is geared to it, infact if it was geared to 200mph its top speed would drop significantly, due to a lack of power to overcome the resistances.
S4Player

Can this be done on my b7 Doug?
kookies4

loomx wrote:
Not really, it a world with wind resistance maybe...

A 100bhp isnt going to reach 200mph, even if it is geared to it, infact if it was geared to 200mph its top speed would drop significantly, due to a lack of power to overcome the resistances.


Just straying OT a little...but it's fascinating...trust me..  Jonny's right - let's not forget the impact air resistance has at speed...
If you don't believe my sums...there are quite a few US forums dedicated to the 200 mark and have calculations there...

Using the old power required to overcome drag formula:

Where F is the drag force, v is the speed, p is air density, A is the frontal area and Cd is the drag coefficient....



Remember - This is just the power required to overcome the drag
...on top of this you'll need to overcome drivetrain, friction etc etc....so you'll see that it's not as easy as it might appear at first...air gets very heavy the harder you hit it!    Hell you need an extra 120hp to combat the additional drag between 180 and 200...

All the 200mph+ sites say that a rule of thumb is around 550hp upwards
ruxy

i'm quite interested in this, obviously the 200 capability is a good enough reason but the plus of better mpg on a long run i'd never really thought of. What does the engine rev at when cruising at say 90 to 100. Be good if it was around 2k?
kookies4

ruxy wrote:
i'm quite interested in this, obviously the 200 capability is a good enough reason but the plus of better mpg on a long run i'd never really thought of. What does the engine rev at when cruising at say 90 to 100. Be good if it was around 2k?


More sums..
I've done this based on my own stock tyre/wheel combo (225/45/17) - so even a few mm will make some difference.
Hope I've grabbed the right ratios....
Below shows the revs at certain speeds across the range of 6th gear options.

BennyBoo

I may be wrong but 190mph for hitting the rev limiter in a standard 01e isn't right is it..??

If so, my stage 1 remap gives me 190mph, so your previous data could be wrong for saying 190mph needs 380hp..
kookies4

BennyBoo wrote:
I may be wrong but 190mph for hitting the rev limiter in a standard 01e isn't right is it..??

If so, my stage 1 remap gives me 190mph, so your previous data could be wrong for saying 190mph needs 380hp..


Rev limit as standard on S4 is lower than I have used - think it's more like 7050.  All I can say is that my revs/speed is pretty much spot on to the first column in 6th.

The air resistance calcs I have looked at again - I realised that I have calculated PS instead of BHP...plus by assuming that the air temp might be 15C...it brings the numbers down a little.  The calcs match up almost perfectly to something similar done in US on a Camero (yes...they might have screwed up... ) - but they used all non metric figures all the way through, yet our final HP numbers really do correlate well.  Look on any 200mph site - this air resistance thing is almighty  

To overcome effects of air resistance:
SR71

Often peak power is not at the rev limit (my 540hp car actually makes peak power at 6600rpm although the graph is essentially flat between 6-7000rpm...lucky me).

So the gearing should ensure that you achieve the speed you want at the rpm associated with max power rather than just the rev limit.

If you do the latter, one of two things will happen:

1) Although you may ultimately achieve the speed you're looking for, you're "wasting" power and could have gone even faster if you'd geared the car down a bit further.

2) Having reached the rpm associated with peak power, the car will not/hardly accelerate further because drag continues to rise with the square of the velocity but the power the engine is actually developing is now reducing.

So using kookies4 tables, what you want to do is make sure that the rpm at 200mph corresponds with the peak power rpm on your dyno plot.

This obviously assumes that the distance required to achieve the speed is not restricted. I call this "autobahn willy-waving".



If this is NOT the case (like VAMX) then the problem is more complicated.

That said, Doug has done the work for B5 S4 boys already, although IIRC the exact power the car was developing on the day is a bit of a mystery isn't it because it was being tweaked between runs?
SR71

Out of interest, here is a B7 RS4 dynoed at 438hp doing a GPS verified 187mph:

http://www.youtube.com/watch?v=VH7obaj5Ekw
loomx

kookies4 wrote:
loomx wrote:
Not really, it a world with wind resistance maybe...

A 100bhp isnt going to reach 200mph, even if it is geared to it, infact if it was geared to 200mph its top speed would drop significantly, due to a lack of power to overcome the resistances.


Just straying OT a little...but it's fascinating...trust me.. †Jonny's right - let's not forget the impact air resistance has at speed...
If you don't believe my sums...there are quite a few US forums dedicated to the 200 mark and have calculations there...

Using the old power required to overcome drag formula:

Where F is the drag force, v is the speed, p is air density, A is the frontal area and Cd is the drag coefficient....



Remember - This is just the power required to overcome the drag
...on top of this you'll need to overcome drivetrain, friction etc etc....so you'll see that it's not as easy as it might appear at first...air gets very heavy the harder you hit it! † †Hell you need an extra 120hp to combat the additional drag between 180 and 200...

All the 200mph+ sites say that a rule of thumb is around 550hp upwards


But for what co-effecient of drag are those figuers for, the S4s is pretty good iirc.

my car can hit the limiter in 6th, which is around 7300, which with 18s on 225/40/18s i seem to remember to work out to be around 196, My car should be around the 500hp mark, but I dont think it will be higher than that.

Infact iirc the Cd of the S4 is lower than a BMW M6, and that managed 204Mph with 507ps/500bhp.
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