Hi

I've been fiddling around with ratios for David's bug. What do you think?

I realise that it will be slower off the line with the tall 1st but after that I think it will works well.

Car now has a pretty tame 1904 cc (9.8 1/8) but were going to a 2442 Oxyboxer in the future.

The gears should be much more useful on the track.

In my old yellow car I ran 3.55 1st 2.00 2nd, 1.30 3rd and .93 4th, in a heavy 1302/Superbug I didn't even notice that the 1st was taller.

The G50 in my other bug @ 6000 rpm does 1st 37.5 mph, 2nd 63.3 mph, 3rd 93 mph, 4th 121 mph and 5th 152 mph

Steve

Stock 1303 L bug transmission below, what I'm thinking about using at the chart at the bottom of the page

The Gear Ratio's And Tire Size For This Chart Are

1st 2nd 3rd 4th R/P Tire Size

3.78 2.06 1.26 0.930 3.880 24.00

MPH PER EACH GEAR

RPM 1st gear 2nd gear 3rd gear 4th gear

3000 14.61 26.81 43.83 59.39

3200 15.58 28.60 46.75 63.34

3400 16.56 30.38 49.68 67.30

3600 17.53 32.17 52.60 71.26

3800 18.51 33.96 55.52 75.22

4000 19.48 35.75 58.44 79.18

4200 20.45 37.53 61.36 83.14

4400 21.43 39.32 64.29 87.10

4600 22.40 41.11 67.21 91.06

4800 23.38 42.90 70.13 95.02

5000 24.35 44.68 73.05 98.98

5200 25.33 46.47 75.98 102.93

5400 26.30 48.26 78.90 106.89

5600 27.27 50.05 81.82 110.85

5800 28.25 51.83 84.74 114.81

6000 29.22 53.62 87.66 118.77



Taller 1st & 2nd, lower 3rd stock ratio 4th

The Gear Ratio's And Tire Size For This Chart Are

1st 2nd 3rd 4th R/P Tire Size

3.11 1.86 1.30 0.930 3.880 24.00

MPH PER EACH GEAR

RPM 1st gear 2nd gear 3rd gear 4th gear

3000 17.76 29.69 42.48 59.39

3200 18.94 31.67 45.32 63.34

3400 20.13 33.65 48.15 67.30

3600 21.31 35.63 50.98 71.26

3800 22.49 37.61 53.81 75.22

4000 23.68 39.59 56.64 79.18

4200 24.86 41.57 59.48 83.14

4400 26.05 43.55 62.31 87.10

4600 27.23 45.53 65.14 91.06

4800 28.41 47.51 67.97 95.02

5000 29.60 49.49 70.81 98.98

5200 30.78 51.47 73.64 102.93

5400 31.96 53.45 76.47 106.89

5600 33.15 55.43 79.30 110.85

5800 34.33 57.41 82.13 114.81

6000 35.52 59.39 84.97 118.77

Gday Steve.
I'm going through this at the moment with my '73 Super, but a bit different to your plan, I'm chasing a good overall rev-drop per change, and when combined with the 205/70R15 tyres I'm considering for the back on the street. keeping highway cruise revs to about 3600 max, but in conjunction with the deepest diff that will last. Then when I get to the drags I can throw on 185/60R14 to drop the gearing down big-time, and the spin will make it live........hopefully!
It depends what you're after I guess, but with that size motor would you think a taller 4th or taller tyres would be of benefit for the highway? I don't know you're combo obviously, but there's a heap of torque in that motor, it might pull better with a slightly taller top.
Eg. 3rd as a stk 1.26 and 4th as 0.89, standard gearsets, so you only need to buy the 1st/2nd. With 1.86 2nd/1.30 3rd, changing at 6500 drops the revs back to 4545, with 1.86 2nd/ 1.26 3rd, the revs drop to 4405, nearly the same. With 1.30 3rd/.93 4th, changing at 6500 drops the revs to 4650, using 1.26 3rd/0.89 4th the revs drop to 4590. Almost the same drops, but no need for extra gearset purchases.
I rekn either gearset stack will work really well, the rev drops are nice and progressive for most street rev-ranges, I'm looking at very similar gearsets for mine.
With mine however, I'd like to use a 4.375:1 diff with 3.78/2.06/1.34/0.89. This will give me a BIG jump out of the hole for when I play at the street drags to try to keep the LSx crowd honest for the first 100m (lol), but with the bigger tyres still keep my highway revs around 3500 for the long 350km trip home (between 100-110kph). I'm a bit concerned that the 4.375 might be a bit fragile if I get carried away (uhmm, as you do sometimes.......), so still considering a 4.125:1 diff, but with 3.78/2.06/1.39/0.93. I lose 6% wheel torque off the jump, but it might mean the difference between driving home and catching the bus with the Bug at my daughters house!
Any idea how much weaker the 4.375 is compared to the 4.125? A lot, not much?

PS OOPS! Just saw tracvk, sorry man, my dumb moment for the day!
What about a 1.41 3rd, with a 1.00 or 1.04 4th? Make the top 3 gears a bit tighter, and for the trip home you could taller rear tyres on it. But really the torque would be good enough to pull a sailor off your sister, so they aren't needed probably!

Hi

I want to keep my 4th a .93 with the 3.88, its OK for highway.

I just want to bring 1st & 2nd up closer to 3rd & 4th, I might even stick with the 1.26 ratio 3rd.

1st is over so quick now its nearly useless, a taller 2nd would have been useful at Raleigh and it might be useful through the fishhook at Wakefield.

In my old 2.1 yellow bug I ran a 3.00 1st, 2.00 2nd, 1.30 3rd & .93 4th with a 3.88 box. Driving it you wouldn't notice the taller 1st & 2nd.

An explanation of my gear chart,

24 inch tyres, 3.88 C&P 0.93 top in all examples

(1st 3.11) (2nd 1.86) (3rd 1.30) (4th 0.930) blue lines
(1st 2.82) (3rd 1.09) orange lines, considering a 2.82 1st & 1.86 2nd

Stock 1303 trans ratios (1st 3.78) (2nd 2.06) (3rd 1.26) black lines, same 4th 0.930

Steve

Looks like a good spread steve, if you think the 3.111 will be OK for you.(should be with 24" tyre)

I would not use the 1.09 third however, it is far to big a % drop from the 1.86 second.
Stick with the 1.30.

1.26 will work, but sacrifices your 2nd to 3rd sweet spot for a very close 3 to 4 step.
...which may suit your proposed tracks/driving style, which only you can decide.