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Shorter 4th Gear

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sander288 "Bolt-on Master"

1,404 posts · joined Aug 2008 ·

#806306
After ringing out the 1300 a bit over the last year it becomes really apparent how overdriven the standard 4th gear is.

Its great for street driving but on the track it just dies.

What ratios would be best for a 4th gear for racing?

at the moment I change into 4th at about 110 - 115kph and it takes quite a bit to get up to 120 - 130kph.

I know the motor doesn't have much poke but i'd like to make lemonade from lemons as the box is due for a rebuild in the next 12 months.

Cheers

Shaun
BMW R65 LS
1967 1300 Deluxe
Swing-axles FTW ❗

Sides Veteran Volks Folk

2,220 posts · joined May 2007 ·

#806335
Ooo ooo - this could become a nice little dsicussion methinks....

Some more info might help tho:
[*]What are your current 1st,2nd and 3rd ratios ???
[*]What ring & pinion do you have ???
[*]What's your tyre size ???
[*]What rpm are you happy to spin to ???
[*]What type of events are you doing, which tracks, and what sort of top speed do you want ???

Seems to be more common for people to bring 3rd gear closer to 2nd, but it all sorta depends on the above list I think...

😵‍💫
VWDCQ vice pres & web dude - vwdcqinc.org.au
Join a car club - get car peeps

My toys
'70 Hillclimb Bug 'Jezebel' w/- Haltech EFI - http://bit.ly/VwTNtQ
'60 KG Coupe - resto kinda started
01 New Beetle - gf's car, but I turn the spanners

68AutoBug Beetle Restorer - Experience over 138\% - YIKES --

11,654 posts · joined Aug 2002 ·

#806421
sander288 wrote:After ringing out the 1300 a bit over the last year it becomes really apparent how overdriven the standard 4th gear is.

Its great for street driving but on the track it just dies.

What ratios would be best for a 4th gear for racing?

at the moment I change into 4th at about 110 - 115kph and it takes quite a bit to get up to 120 - 130kph.

I know the motor doesn't have much poke but i'd like to make lemonade from lemons as the box is due for a rebuild in the next 12 months.

Cheers

Shaun
yes
as its an overdrive....
its not good for a small engine going up hills etc....

you probably have 4.375 to 1 diff ratio...

using 14 inch wheels will make it better all way round....

Lee
- Helping keep Air Cooled VWs on the road - location: SCONE in the Upper Hunter Valley - Northern NSW 320 kms NNW of SYDNEY---

sander288 "Bolt-on Master"

1,404 posts · joined Aug 2008 ·

#806513
Gearbox Ratios

1st: 3.80:1
2nd: 2.06:1
3rd: 1.32:1
4th: 0.89:1

Ratio: 4.375:1

Tyre Size: 165R15

Happy to spin to what the engine will go to, I don't have a tacho but I would guess it is going to 5000rpm or a bit more.
Not sure how to work it out but what revs is 115kph in 3rd gear?

Type of Events: Hillclimb, Tarmac Rally, tracks would be Winton, Wakefield Park, Eastern Creek, Bathurst. But to be honest I'll take what event is running.

As far as top speed goes... well what ever I can get up to really. I suppose is 150 - 160 kph was possible at Wakefield I would be happy as that is what the MGB's were getting to down the straight the other weekend. But After advice from Greg, i've decided drafting is a very good way of increasing ones top speed....

👍

That should be enough to go on...
BMW R65 LS
1967 1300 Deluxe
Swing-axles FTW ❗

1303Steve Scirocco Rare

8,650 posts · joined Aug 2002 ·

#806538
Hi

If you go smaller rolling diameter you will worsen the handling.

Steve

sander288 "Bolt-on Master"

1,404 posts · joined Aug 2008 ·

#806539
Yeah i'm going to keep the 15" wheels, it was made for 15" and runs well with them.

I worked out my RPM at 115 in 3rd gear, 5500rpm - i'm not sure if a stock motor should be rev'd so high but thats what it goes up to.

I used a gearbox calculator on CSP's website.

Cheers

Shaun
BMW R65 LS
1967 1300 Deluxe
Swing-axles FTW ❗

Sides Veteran Volks Folk

2,220 posts · joined May 2007 ·

#806613
Holy cr@p... 5500rpm with a standard donk !!!

😵

I reckon grab yourself a copy of Wes's spreadsheet and have a play.... http://www.offroadvw.net/exceldyno/index.htm. I modded my copy to also show % rpm drop between gears, which is kinda useful.

Your current gearing should give 172 km @ 5500rpm in 4th... I think only place a 1300 would pull to that would be down Conrod Straight with a tail wind. So.. maybe a 1.0 4th gear instead... then top speed would be 153 (still doubt a 1300 would get there). Obviously it'd bring 4th MUCH closer to 3rd, but still be reasonably streetable with 3600 rpm @ 100km/h (current would be 3200rpm). If you're shifting from 3rd at 115... then revs would drop to 4200, compared to 3700 with your 0.89.

Of course if you're going to change much engine wise factor that in too to save doing it all over again...

😉
VWDCQ vice pres & web dude - vwdcqinc.org.au
Join a car club - get car peeps

My toys
'70 Hillclimb Bug 'Jezebel' w/- Haltech EFI - http://bit.ly/VwTNtQ
'60 KG Coupe - resto kinda started
01 New Beetle - gf's car, but I turn the spanners

Craig Torrens 6 times Australian, 7 times State Hillclimb Class Champion

8,040 posts · joined Jan 2003 ·

#806625
Put some twin carbs on it and I think you will be surprised with the extra pulling power. 👍

You can get a .93 4th in VW (I know my 76 box has it)....its a fine tooth gear, but you are only running a 1300 !!