hi all, I am turning my bug in to a toy for playing on the drag strip, I currently have a 1776 twin weber and lots of other bits, happy with the engine

I have a 1300 box at the moment and wondering if there is a better box for speed over a quarter mile, not fussed about cursing speed just the power at the strip, im not the good with understanding ratios and all that confusing stuff!!!

cheers

oli

so the general is going lower to a major as the reduction hubs will not like drag racing + a top speed of 70 or something is not much good.
1300 box will do best try it out first then make decisions based on fact where it is lacking.
you would be better off dragging the rod.

not the general Keith the hot rod! the general is going up to field marshal, the beetle was running 18 second quarter with a 1200 motor last year

Sort yourself a rancho or speak to cogbox dude 

The best 'stock' box for drag racing is a GT gearbox, but these days those are as rare as hens teeth.

The things you need to know are the gearbox internals, your rear tyre diameter and the power band of your cam (min and max rpm at which it makes power).

Looking at your buggy I will assume about a 27" diameter rear tyre.
Based on your 1776 engine, I will assume an Engle W110 cam with a max rpm of 5500 and max HP of about 70, these are the figures I will use for the various calculations.

A stock 1200/1300 gearbox has the following gears:
4.375 Ring and Pinion, then 3.777, 2.058, 1.261, 0.889 (1st to 4th)

Assuming a gear change at 5500 you will be shifting at 26, 49, and 80mph with a theoretical top speed of 114mph

a 1500 box changes the R&P to 4.125 giving shift points of 28, 52 and 85mph and a top speed of 120mph

a GT box changes the R&P to 3.875 giving shift points of 30, 55 and 90mph and a top speed of 128mph

a 1600 box changes GT 4th gear to 0.931 giving shift points of 30, 55 and 90mph and a top speed of 120mph

The top speed is theoretical since it is unlikely you will reach 5500rpm in 4th gear without a very long run up (several miles).

In reality when using a stock gearbox on the drag strip, 4th gear is a waste of time, you will drop too many revs shifting from 3rd to 4th (5500 to around 4000) and you will have run out of tarmac by the time you bring them back up, so just keep your foot down in 3rd.

As such you are optimistically looking at a 1/4 mile speed of between 80 and 90mph depending on your gearbox and how well you have driven.

Based on a guessed weight of 1600lbs (730kgs) and 70HP at the flywheel you would be looking at an ET of about 17-18s for the 1/4 mile.

The first thing you will break will be either the differential or the ring and pinion.

The 3.875 R&P is the strongest one there is for a type 1 box, anything else is weaker.

A stock gearbox only has 2 spider gears in the differential, a super diff has 4.

Dropping the clutch at 3000rpm will place huge load on the gearbox, eventually something gives.

Pete at Cogbox built all of my various drag racing gearboxes, I cannot recommend him highly enough, he will custom build whatever you want, but his services are not cheap (I still broke all of mine several times)

Rancho boxes are more of an off the shelf item that sit between a stock box and a custom one.

Remember "drag racing costs money - how fast can you afford to go?"