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 Post subject: Bathurst Diff Ratios
PostPosted: Tue Dec 23, 2008 6:09 pm 
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Got a MK2 gti track car. Stock cultus redlines @ 8500rpm.

I might be going to bathurst soon. I suspect this track will be mostly 4&5th gear.

Has anyone run bathurst? How were the std ratios?

Are there any off the shelf options to decrease diff ratio. (higher top speed).

Modena Engineering can make me a crown and pinion.

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Eastern creek 1.54.10, Wakefield 1.12.60 Bathurst 3.05


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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Tue Dec 23, 2008 8:07 pm 
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bdmotorsports

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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Wed Dec 24, 2008 9:13 am 
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markymark wrote:


bdmotorsports dont have what Im after.
Unless im reading info wrong the ratios on the site are reverse of what im after.

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Eastern creek 1.54.10, Wakefield 1.12.60 Bathurst 3.05


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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Wed Dec 24, 2008 9:15 am 
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racer5 wrote:
markymark wrote:


bdmotorsports dont have what Im after.
Unless im reading info wrong the ratios on the site are reverse of what im after.


Ooops :oops: then your only other option is to use a diff from a cino, which i believe are 3.52:1. Better yet use just change your gearbox over to a cino gearbox.

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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Wed Dec 24, 2008 9:27 am 
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The two easiest solutions would be using a Cino or 1600 gearbox.

Cino box pros: Cheap and has taller ratios than GTi box
Cino box cons: Weak diff, but less of an issue if you weld it up and use power steering.

1600 box pros: Stronger diff, and gearset is interchangeable with M series gearboxes to tailor ratios for your specific needs.
1600 box cons: Requires a heap of modifying to make it fit.

End of the day I'd probably go with the Cino box to save hassle. I do think that your "mostly 4th and 5th gear" assumption is slightly out though. Sure, you'll be using 5th down Conrod, but the rest of the track is so bloody steep that you'll be in 2nd and 3rd most of the time, especially with a Cino box.

-edit-

Would be interesting to know if Mark Brame made any ratio changes to his Swift for Bathurst - I doubt there was allowance for it in production car racing.

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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Wed Dec 24, 2008 2:45 pm 
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The Group E cars made changes by altering tyre sizing, i.e. running 185 or 205/60/14's to change gearing.

Dattman on here has a lot of information on gearing changes. Try giving him a PM. If you can max out your rpm's in 5th down Conrod, you're probably doing well on your stock engine and going higher would likely negatively affect you on the rest of the track, as Yldboy has suggested.

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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Wed Dec 24, 2008 6:30 pm 
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Iknownothing??? should be Iknowquiteabit, I agree, just spotted this topic, I'm on holiday so don't have my spreadsheet to work it out but a standard gti box at 8500 in 5th will probably give you 230-240kph depending on tyre size, even downhill you'll be doing well to hit the rev limiter in 5th, a swift simply doesn't have the power to overcome drag at that speed, haven't been to Bathurst personally but I hear it's really steep so you'll only use 5th gear once.


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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Wed Dec 24, 2008 6:50 pm 
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DIY :wink:

215kph in 4th and 254kph in 5th with standard gti box and 175/60/14

PM email address and I can send you the excel file to do calcs

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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Wed Dec 24, 2008 8:46 pm 
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I lived in Bathurst for 30years and only moved to Canberra 4 months ago.

Anyway good luck with only using 4th and 5th. You will be more likely to down to 2nd around forest elbow, you'll likely make 4th once you go over the crest on mountain straight but you'll be back to third until skyline.

I dont know about yours but my GTI does at least 110 in third and if you check the speeds of even the V8's you'll soon see how far down the cogs you'll be.

Bathurst is very steep and everybody who drives the track for the first time says it does'nt look so steep on TV. The inside of the corner on the dipper is about 75 degrees.


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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Thu Jan 15, 2009 7:59 pm 
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Just wondering if you've been to Bathurst yet and what you thought of the track.
And were my comments right.


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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Fri Jan 16, 2009 7:00 am 
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Thanks for input. Running standard diff and gearbox ratios is probably best.

I have since defered entry in this years event and will enter for 2010.

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Retired the gti after 12000 track kms of fangin around.
Eastern creek 1.54.10, Wakefield 1.12.60 Bathurst 3.05


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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Fri Jan 16, 2009 8:36 am 
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racer5 wrote:
Thanks for input. Running standard diff and gearbox ratios is probably best.

Actually you're better running a 4.389 diff.
I worked out that with your tyres in 5th at 8500rpm you would have a theoretical top speed of 247kph using the 4.1 diff, of course drag would stop you doing any more than about 220kph.
Changing to a 4.389 would give you 230kph so you would improve acceleration in all gears.


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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Fri Jan 16, 2009 10:06 am 
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That is interesting. I will consider that as an upgrade for use on track days.

What is your experience?

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Retired the gti after 12000 track kms of fangin around.
Eastern creek 1.54.10, Wakefield 1.12.60 Bathurst 3.05


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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Fri Jan 16, 2009 9:19 pm 
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racer5,

Interesting question raised earlier, and I was thinking on the way home today whether any of those computer games would be any good for you? 8-[
What I mean is that several have Bathurst, Oran Pk, Eastern Ck tracks. And also some allow you to do configuration adjustments to your car. If you found something that was a bit Swift-ish (a Focus XR4 perhaps?) then you might be able to roughly experiment at no cost!!
That is assuming they are at least reasonably accurate...

Just a left-field sort of thought!!

Can I ask a track day question too - how much of a difference do slick tyres make compared to street tyres? I am going to do my first track day next weekend at Wakefield! :D Trying to get a feel for it all!!

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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Fri Jan 16, 2009 9:39 pm 
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stay away from pure slicks if this is your 1st day at WP.

Semi slicks are the way to go. Yokohama AO48 or similar, alternatively Toyo RA1
road tyres are good starting point intially to get a feel for the track but you will go to semi slicks pretty quickly anyhow.

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2006: Mk1- yeah well at some stage to go on track...
2003-2005 Mk3(retired)- EC 1:54.6 , Wakefield 1:13.14 , OP (short) 52.00 , OP GP 1:24.40


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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Fri Jan 16, 2009 10:19 pm 
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tekkie wrote:
stay away from pure slicks if this is your 1st day at WP.

Semi slicks are the way to go. Yokohama AO48 or similar, alternatively Toyo RA1
road tyres are good starting point intially to get a feel for the track but you will go to semi slicks pretty quickly anyhow.


Thanks Tekkie!

Sounds great!! That will be next I'm sure!! They look like the grip is really something :twisted:

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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Mon Jan 19, 2009 7:22 am 
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Capt_Gherkin wrote:
racer5,

Can I ask a track day question too - how much of a difference do slick tyres make compared to street tyres? I am going to do my first track day next weekend at Wakefield! :D Trying to get a feel for it all!!


If you have expensive tyres on your car consider changing them.
They will probably be wasted after a day on the track. All the edges of the tyre blocks will be torn off. Street tyres will probably only handle about 4 laps before they overheat and you will experience slidding and understeer. When you experience this just come in and let them cool a bit and go again.

My 1st track day ripped my street tyres to shreads.
So copying what others had done before me, I got some 13" x 5-1/2" rims and bought some second hand formula ford tyres (not for street use) for $30 ea.
You need accurate air pressures to get correct tyre operating termperature, use a Go kart or Racing Quality air gauge. If pressures are not right the car will have no grip .

Alternatively 2nd hand Yokohama AO48 (these can be used on the street $220ea new) are a good option. Call Gordon Leven Motorsport Tyres (Bill) and ask for availability and cost(both formula ford and yokohama tyres). ph 02 47354500.

I have only run slicks once, I wasnt very experienced at the time and had trouble getting the air pressure (temp) correct, therefore I had erratic grip.

Ive done about 5000km on Wakefield (and my car is relatively stock). It is a good track for a GTI, plenty of run off, good pit area, tight and twisty, most walls are a long way off the circuit. Ive seen plenty of GTi street cars there and they all handle it without any problems.

Front brake pads-Take a spare set you might need them to get home. Check your pads before you go. Bleed brake lines so new oil is in system, Check engine oil level or change before you go.
If you have a floor jack at home take it with you. Have a good look over the car before you go and tidy up any loose ends (otherwise you might spend 1/2 the day fixing little things that could have been prevented before you got there, eg check & tighten engine mount bolts, Wheel nuts, suspension nuts, exhaust rubbers, no loose wires etc in engine bay, battery tight)

Whatever tyres you use, you will have a great day.

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Retired the gti after 12000 track kms of fangin around.
Eastern creek 1.54.10, Wakefield 1.12.60 Bathurst 3.05


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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Mon Jan 19, 2009 10:39 pm 
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Thanks racer5,

I was initially thinking that I'd do my 1st track day on street tyres, and upgrade to semi-slick (A048 look great) on my next outing.
However I take your point that I may have shredded some expensive tyres by then!
So I am going to call that guy & some others about options for some second hand semi-slick tyres & rims (hopefully fairly lightweight).

I did buy a Michelin digital tyre pressure gauge today, and also a helmet - woohoo!!!

I also worked out how I can successfully mount a camera (in video mode) by gaff-taping a mini tripod to the back of one of the headrests on the back seat!!

Is it worth getting nitrogen in the tyres? Is that a gimmick, or is it because nitrogen is more inert so therefore does not respond as much to being heated up? :?

Yes, I heard Wakefield is a great track for GTis - nice and windey, and nothing to hit!!
5000km on Wakefield - man, that is incredible!!! :shock:

Great tips about spare brake pads & checking the car over too.

Sorry to hijack your thread a bit too!!

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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Mon Jan 19, 2009 10:46 pm 
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Capt_Gherkin wrote:
So I am going to call that guy & some others about options for some second hand semi-slick tyres & rims (hopefully fairly lightweight).


Let us know what you find out. I'm interested in a set of used Avon's, but I need the skinny set off the front of the Formula series, whereas most people want the wider rears.

Also, the air you breathe is 80 nitrogen, so for everyday use I don't see a lot of point in paying for pure nitrogen inflation - but for the track I guess every little bit helps. ;)

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 Post subject: Re: Bathurst Diff Ratios
PostPosted: Tue Jan 20, 2009 5:58 am 
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Capt_Gherkin wrote:
Thanks racer5,

Is it worth getting nitrogen in the tyres? Is that a gimmick, or is it because nitrogen is more inert so therefore does not respond as much to being heated up? :?



I wouldnt use nitrogen, you will be adjusting tyre pressures throughout the day.

Save your money. Spend it on track tyres.

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Retired the gti after 12000 track kms of fangin around.
Eastern creek 1.54.10, Wakefield 1.12.60 Bathurst 3.05


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