what ratio for 3rd & 4th

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MarkMc

Guest
I have recently broken the gear box (in half) :( . I am looking at after market gear boxes and was wondering if anyone has changed the gear ratios in the boxes when they get them rebuilt? I ask this because I think 3rd and 4th may be a little too high for the quarter mile. I am crossing the traps at 111mph 12.6. 60 foot 2 seconds way too much wheel spin in first.
Is it worth changing the gear ratios :?: Will it improve the quarter times :?: Should I stay with standard ratios because motor is not completely tuned and more power will bridge the gap( lack of go in 3rd and 4th) :?:
On road I notice my car in 3rd gear does not start to pull(well) until about 90 to 100 kph. On road 4th gear starts to pull(well) at about 110 to 120 kph. I would prefer it if the boost point were moved to 3rd 80 to 90 kph and 4th 100 to 110 kph.
The motor is not tuned to full potential yet. Supposed to make about 190 kw(1bar) at wheels(guess 320 to 340hp at fly wheel). The tuners say it should make a bit over 200kw at wheels when tuned with a bit of octane booster.
Do you need good clutches(twin plates) for dog boxes :?: I have brass button clutch at the moment and its a bit worse for wear. But will cost alot less to fix than buying new twin plate.
My fly wheel is supposed to be a bit worse for wear too. How important is the fly wheel with a dog box :?: how good are remachined flywheels :?: Are aftermarket fly wheel just lighter for better response :?: Or do they work better in other ways :?: What so special about after market fly wheel :?:
 
Fast Guy

Fast Guy

Moderators
Staff member
How are you launching to get too much wheel spin? I can't get any :wink: (try using less revs or better tyres :p )
It probably depends how you want to drive your car as to what gearing you want. You could put a longer :?: ratio diff in to cut the wheel spin in 1st, but it willl raise the speed in every gear when you come on boost unless you drop the ratios abit.
A close ratio box would drop the speed you come on boost at in gear, but then you'll loose top speed and I (having one) don't think it's worth it, unless you only drag the car. If you're having problems with wheel spin now, a close ratio box will make it worse.
 
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MarkMc

Guest
I let out the clutch at between 5000 to 6500 rpm estimate(hard to tell exact revs) and then putting the foot down. Wheels spins into second (newish tires too). I got my best time for the quarter shifting up early into 2nd . How do you get no wheel spin :?: . launch control device.
I was not thinking of getting all the ratios changed(low ratio gearbox or diff change) just 3rd and 4th to be a bit lower(not by much). 1st and 2nd and 5th gear seem fine for the road.
I think on road it would be better to have a lower 3rd and 4th and over the quarter would be faster too. If 3rd gear is 150pkh at 7500 rpm now and 4th gear is 200 kph at 7500 rpm(this what I think my standard gear box used to do). I was thinking of changing 3rd gear at 140 kph at 7500 and 4th gear at 190 kph and 7500rpm.
Was wondering if anyone has had these gear ratios changed? My gear box is broke so if I’m going to change anything now is the time.
I am only having problems in first with wheel spin.
Thanks for the info. I’ll try less revs next time, but nothing really happens until about 4500 to 5000 rpm(may bog down a bit, but give it a go :wink: ).
 
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skiddusmarkus

Active Member
I've got shorter 3rd,4th and 5th gears.I went for 90mph max in 3rd,115mph max in 4th and 145 max in 5th,so approx 10% shorter than standard.Ivan Tomic figured out the ratios for me if you want the same.
I chose this gearing as it's in between Dakar and normal gearing for the R so should be a good compromise between track and strip.When I picked them though I wasn't planning on having an engine rebuild which is now underway so I may have to raise the revlimit by 500rpm(not for everyday use) to get the most out of the power on the strip.I aim to cross the line in 11s at 120mph so would need a change to 5th which isn't ideal and will cost me time.
If you use the gearbox manufacturer I think you will then make sure they fit the gearset themselves,or Sasha/Ivan has a hand in it.
 
Fast Guy

Fast Guy

Moderators
Staff member
No launch control, must just be a good technique :wink:

Skiddus, I'd have maybe gone for about 120 in 4th, cos if you have abit too much power you're gonna need to change to 5th to cross the line :?
 
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skiddusmarkus

Active Member
Carl-I wasn't planning on rebuilding the engine and only going for around 350bhp-that wouldn't have seen 120mph terminals,whereas new spec should.That's why I want to have the revlimit inreased to 8000rpm to allow another 10mph or so in each gear,namely 4th.
 
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MarkMc

Guest
How do you find the lower 3rd, 4th, 5th ratios(better, or no real difference perceived). Did the lower 3,4,5 gears improve your times(lower ET) :?: ? Did they increase your mph crossing the line or reduce your mph crossing the line :?: .

3rd 90mph, 4th 115 mph and 5th 145 mph was this with 7500 rpm :?: ?

Whats fuel economy like with lower 5th. I get about 12.8 L/100km now. Do you think it would be 20% worse :?: ?

11s at 120 mph what BHP you looking at :?: ? (350) or

The tuners indicated that my car should make early 200 to 220 kwaw when finished running in and tunned up. Would this power level be better suited to standard ratios or lower ratios like yours 3,4,5. For quarter mile use. My car revs to 8000rpm I know I should stop at 7500 but it just wants to go.

On road is 3rd and 4th better. One of the other reasons why I was thinking of getting lower 3rd and 4th is that I drove an sti earlier this year and it seemed to respond well in the lower gears. Want my GTIR to respond better too. The sti did not feel more powerful, just better geared and at certain speeds felt like it would leave my car behind a bit too easily. From a stand still in a straight line the GTIR is probably faster.
My car is now producing boost later in the rev range and the issue does seem to be a bit more pronounced(until boost comes on of course). know you can’t have it all with bigger turbo you must get more lag, but lower 3rd and 4th would help mask lag.

I have already gone with another box not the one you indicated, but they would have built the complete box for me. I have read some of the previous remarks, but they seemed reasonable to me and would have used them, but for the fact that the box I will have fitted will replace everything(so they tell me(billet)). (billet)Not foreign exchange students either. Does any one know where Trust get their gear boxes from. Do they do GTIR boxes. Does any one know if they have in the past sourced them through Vic(Aus) The tunning company indicated they do, can’t remember name of company(might have start with M or N).

Fast Guy

Good technique for launching.
What revs do you hold on the line :?: ? Do you dump the clutch or slip :?: ? Do you then put your foot flat to the floor or do you hold back :?: ? Do you have special tires :wink: ?

Thanks for info much appreciated
I thought someone must have tried to reduce 3rd and 4th it seemed logical(sorry about all questions just curious ,and about to invest a far bit into new box)
 
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skiddusmarkus

Active Member
Phew,you out of breath :lol: ?

I only drove the car for 500miles before the engine died,so didn't really get much chance to push it-I wanted to run the gears in for a few hundred first.Then I drove it to the drag strip(100 miles each way)and did 3 runs-the engine broke on the 3rd run but was still driveable.
It was also running like an absolute pig so my times were appalling,running up to 3secs slower than my PB with 15mph lower terminals.
The speeds I gave were at 7500rpm yes.
For 11s I'll hopefully have approx 400bhp.
Shorter gearing should help with lag,even better with a lightened flywheel.
 
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