Swapping Gearboxes

[Dave DND]

Whilst most of us spend all of our time tinkering with various aspects of the chassis or upgrading our engines, it seems that very little thought is ever given to the gearbox and the different types that are available to us. There is plenty of information out there with regards the different internal gear ratios, and if you are like me, then you may have found a lot of it quite difficult to understand, and as a result, we tend to stick with the box that we already have. However, if you actually want to change your gearbox so that you can get some more speed, or be able to cruise the motorways with a better fuel economy in mind, then at some point you are going to have to start looking at some figures

For those of you that wish to work it out for yourself, you may find this formula to be a good starting point:    

MPH = (Tyre Profile(mm)*Tyre Width(mm)/100+Rim Diameter(inches)*25.4/2)*2*3.14159*Engine RPM*60/(Final Drive Ratio*Gear Ratio*1000000)*0.62137

Or . . . . .

Here's one I prepared earlier - If you are trying to compare different gearboxes, then have a look at this "live" spreadsheet   


www.beachbuggy.info/DNDGearboxCalc.xlsx     


Open it up with Microsoft Excel and "ENABLE EDITING" - You will then be able to play around with different wheel and tyre combinations and quickly see from both the live data and the graphs how it will affect your Buggy right across the range.


Important things to consider:

Look for the engine revolution speeds where you would normally change gear, and make sure that you can still potter about town or country lanes in your chosen gear.

Be mindful of what power your engine can actually produce as there is no point gearing your car up to do 100 mph if your engine runs out of steam long before you can get there.



Our good friend Julian also has some very useful links over on his website

http://www.partsemporium.co.uk/rpm&speedcalculator.htm

http://www.partsemporium.co.uk/Gearboxcodes.htm

[snoopy]

Nice job there Dave the line graph makes understanding the difference simple.

[Testa]

Good work there Dave.

Vw Rancho Transaxles also has a calculator on their site, Mike there is very helpful and quick to reply to questions.

I ended up going for the pro street I think in the splity, get some very strange look when overtaking people in the motorways in the fast lane.

Testa

[farmer rob]

Mine is geared for 138mph, is that too high 

Rob

[Mickyb]

Dave

I have an AC 1500 box in my buggy with the 1800 type 4 engine. I found a 1200 engine topped out at about 65 and the 1500 topped out at 75.
I haven't found the top end with the 1800 but will pull 85 easily. Around town 30 if ok in top.
I have a webcam 86a cam shaft which gives about 80 bhp at 4500 revs on a single 36/32 carb.

Micky

[Dom]

Cool I have play with the formula nice work were would a good recon box from and would it need to rancho pro street box / Hevey duty or would standard be engine 1776cc
Dom

[Dave DND]

a 1776 would be fine on an ordinary 1500 or 1600 box - remember the tyre sizes also have a lot of influence too