LocostUSA.com

Hello,

I am currently building a mid engined BEC with an engine from a ZX14

there are several differentials available but they all have different reduction ratios, form around 3.5 up to 8

I really have no Idea which ratio to choose? What does it even mean really?
All I know is that I do not care for top speed, but want to accelerate as fast as possible.
I also think it would be nice to being able to drive along to motorway at around 3000rpm in 6th gear for 60mph / 100km/h
-> thus saving fuel and reducing stress for longer motorway journeys.

can you help?

many thanks!!

Google "transmission gear calculator."

Honestly, you're getting way ahead of yourself. Much of building a car is planning, which means first teaching yourself what's important. Google is your friend. Between engine speed, gear ratios, and tire diameter, it's very straightforward. It concerns me a little that you keep asking for "as fast as possible", or "the best available", or "the lightest." Yes, all that's out there but it will cost a fortune, yet you also require it to be very inexpensive. My advice is to spend a lot more time reading about BEC cars to learn about the various compromises that have to happen, and there'll be plenty.

There's an old saying about cars, "There's fast and there's cheap, pick one." Another is, "Speed costs, how fast do you want to go?"

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Are you really building or just thinking about it? If you're already building, and you are asking these questions, you'll be in for some surprises. Also, it would be polite, to provide a bit of an introduction, before shooting off all these questions.
Anyway, the gearing commander is very helpful, because you can enter all your parameters, and come up with some guidelines. http://www.gearingcommander.com/. I doubt you'll be able to gear it for 3,000 rpm at 60 mph. For my R1 it will be closer to 4,500 rpm at that speed. I am using a Ford 7.5 with a 3.21 ratio, which is about a 17/55 in bike sprocket ratios (stock is 17/45). You will need to gear it shorter than stock, to compensate for the greater weight. If you want super acceleration, you will need to go even shorter, but you'll be at 8,000 rpm at 60 mph. No free lunch.
Check my build log for a reverse set-up. Cheaper than a Quaife. Reliable? Don't know yet. Does it work? Don't know yet.
There are many bridges to cross in a build.

_________________
Martin


My build log:
viewtopic.php?f=35&t=14520&start=0
My build video:
https://vimeo.com/143524140 password "matovid"

I have used a 04-05 ZX10r. My car weighs under 475kg wet and I used 3:00 (15-45 sprockets) diff ratio. Made easier since I have used a chain driven diff. With 215/45/17 tyres, my car is doing 5900-6000 revs at 100kph. If I swap the 15 for a 17 tooth it drops the revs by approx. 500 at 100kph.
With the 15-45 gearing, my car is great around town. 6th gear is very usable. As my motor is less than 500mm from my head and totally exposed, the noise from the motor is very hard to tolerate at 100km hence the two sets of gearing. Ear plugs are still a must at all times.