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Hello , it is my first post on the board and i like that place ! im currently searching for info to build my own BEC conversion. I used the search but didnt found much of what im looking for.

I have access to lots of VAG parts and i been looking at the Quattro diffs , they come in two ratios 3.89 and 4.11 , was wondering if any of those ratios are worthy or just not driveable with a bike engine.

Any opinions? What ratios should i look for ?


Thanks

here i crushed some numbers in a calculator

seems like i would lack torque in order to push the gears , 4.11 seems not short enough for the task.

Trying to find a good rear diff with axle shafts . would adapt the output shaft of the GSXR1000 engine to the diff with a super short driveshaft for a mid engined light car

here are the crushed numbers

One thing to remember with a BEC is that a bike engine has a primary reduction ahead of the transmission.
You wouldn't happen to have an 02M you could take apart would you?
I've been wondering if I could delete the 1-4 gears and plug the bike engine output into the trans input fairly easily.

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"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

Welcome, Letomoto.
It will depend on your application, and your engine, but in general, the sport bike engines (R1, GSXR) are geared fairly tall. Mine is a 05 R1 and the final drive is about 2.64. So I went with a 3.27 ratio (94 Ford Mustang). It works out to be about a 24% reduction, which I hope that will keep the RPM at cruising speeds at a reasonable level. (about 6,500 at 120km vs 5,000 for the bike) Here is a good reference http://www.gearingcommander.com/

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Martin


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

The gixxer primary reduction is 1.553 so....
10,000 engine rpm is 6439 rpm at the transmission input shaft.
5,000 engine rpm is 3220 at the transmission input shaft.
etc, etc.

_________________
"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

oh , i may be calculating my stuff wrong then , i thought the FD of the bike transmission was the actual front and rear sprokets with the chain . even with a Miata 4.3 diff the end speeds were off the roof .

on the chart below i was comparing a VW trans and the GSXR tranny gears applied to a car diff without knowing about the actual final drive of the gsxr... this explains some stuff...

This is to be put into an old Beetle wich is about 1000lbs with the engine removed , i want it to be snappy

I do have a 02J transmission and another VW cable trans in the garage that i could tear apart

so how do you guys calculate all the reductions combined then ?

here is what my data looked like

http://www.teammfactory.com/gearcalcula ... on+1+%26+2



So now with the added reduction the maths are getting way more plausible

10k rpm with 3.89 diff and 1.55 reduction , now may be a bit too short for highway use
1st : 70kmh
2nd :92kmh
3rd :112kmh
4th :130kmh
5th :145kmh
6th :157kmh

Thanks for your answers , this project is very exciting

The primary reduction is quite literally between the clutch housing and the transmission input shaft so you can do the division and enter the corrected number as the engine rpm variable.

_________________
"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

So now with the added reduction the maths are getting way more plausible , i just replaced the 10k rpm with the 6439 reducted rpm in the calculator

10k rpm with 3.89 diff and 1.55 reduction , now may be a bit too short for highway use

1st : 70kmh
2nd :92kmh
3rd :112kmh
4th :130kmh
5th :145kmh
6th :157kmh

7k rpm in 6th cruises at 109 kmh slightly high rpm for long rides but the 1st and 2nd are so long that a longer FD like the old bimmer 2.89 would kill the launch and accell


old bimmers do have a 2.89 final drive

1st : 95kmh (1st and 2nd looking pretty long to me to have some fun launching)
2nd :124kmh
3rd :151kmh
4th :176kmh
5th :195kmh
6th :211kmh

Take a look at the B-3 thread, he did some ratio juggling and discusses his results. IIRC he's happiest at about a 3 to 1 FD.

_________________
"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

trying to search for it but the search tool is askling for at least 4 characters and the "-" in B-3 acts as a" dont search for this character"

it doesnt finds anything searching for B-3 user

a link to the thread would be awesome

thanks

He's half a dozen topics under here now in the "active topics".

I like the transaxles and middy designs, though it's hard to get them to look right. If you're considering normal IRS diffs, the Ford one is light and has the advantage of many ratios available.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
SketchUp collection for LocostUSA: "Dream it, Build it, Drive it!"
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i think i found the thread while reading some posts in the BEC section , Robbovious mentioned his B-3 and then found the build link in his signature

is it the one youre talking about ?
viewtopic.php?f=36&t=13941

Yep

_________________
"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

woah this is an insane thread ... 93 pages ... im gonna spend a month reading hah !

i want to build a rear engined old beetle , im starting to think i will take a good LSD diff and encase the diff itself in a bell to keep the grease in and mount bearings to the frame and use a chain and sprokets in between engine and diff... would give me more FD options in the case i dont like the gearing ... just replace sproket instead of the whole diff and refabbing mounts and stuff.. would also give me more options on the engine's placement but ill keep reading maybe ill find an easier scenario down the line.