Posts: 196
Threads: 36
Registered: August 21st, 2016
Member Is Offline
Location: Kalgoorlie, WA.
Theme: UltimaBB Pro Grey
Mood: Hey, look, a SQUIRREL!
posted on May 14th, 2017 at 11:04 PM
Gearbox rebuild question.
Hi all, I'm keeping Frank as a swingarm rear end, but upgrading the engine from the 1300SP to a 1600DP from a 73 Superbeetle.
My question is it worth, or am I able to, use the internals from the IRS 73 box and put it in the 66 swingarm case? My aim is for longer gearing
(it's 600k's to Perth from Kalgoorlie!) not after a drag racing monster! But if possible, use the shorter first gear and longer 2nd,3rd and 4th?
Please advise if it's possible or if I'm dreaming!
Cheers, Greg.
modnrod
Fahrvergnugen
Posts: 978
Threads: 50
Registered: March 17th, 2011
Member Is Offline
Location: Midwest, Westoz.
Theme: UltimaBB Pro Blue
Mood: Old School Volksies!
posted on May 15th, 2017 at 10:31 AM
Gday Greg.
My Super has stock ratios with a closer 3rd, it ended up 3.78/2.06/1.35/.93. I went for a closer 3rd to reduce the rev drop from 2nd to 3rd, which
gives me a better rev range at about 60-80kph on the dirt and at 40-50kph thru towns (and a tenth or two at the track........not that I would do that
of course!).
The stock ratios, especially 3rd and 4th being close, are actually really good for the highway. The fact is that 1600s don't have the torque to push
a Beetle around a 3-dog Road Train quick enough by just accelerating from top, but if you drop it down to 3rd then you spend at least 5 or 6 secs LESS
time on the wrong side of the road, a stock 1.26 3rd is an almost perfect rev drop to get you around the trucks. Annoyingly far away from 2nd, but
it's all a compromise.
If you keep your 4.375:1 diff ratio and stock 3.78/2.06/1.26/0.89 ratios from your 1300, then on the highway at 110kph your little 1600 will be
happily humming away at 3500rpm on stock tyres, which is fine but you don't want to cruise at speeds much higher, the revs will stress the poor
little thing out a bit!
If you transfer the 3.875 diff AND all 3.78/2.06/1.26/0.93 ratio gears from your Super into the swing axle case, then you will have cruising revs of
3280 at 110kph, which to be honest for our highways is just about the perfect compromise between cooling airflow, torque needed for the aeros and
longevity. You will now also have an even closer 3rd gear to top, which means longer legs when going around trucks in 3rd gear. The downside is a
noticeable drop in acceleration off the lights, after all you've just lost 13% torque to the tyres (4.375/3.875), although it also feels much more
relaxed which is nice sometimes.
Some early 1300s had a 1.32:1 3rd gear, I dunno if yours does though, others will know better than me, I just know what they drive like on our local
roads with different gearing. The early gears and the gears out of your Super have different set-ups where they mount to the shafts inside (again,
others are MUCH better at this than me) so they are NOT directly interchangeable, at least they weren't for mine, but the whole complete set as a
changeover IS possible I think.
Remember that up to 200rpm can be easily taken away or added just by playing with tyre heights, but also remember that less than 3000rpm at 110kph in
our part of the world is just asking for the little thing to pop a boiler and overheat all the time, so keep the highway revs between 3000 and 3500.
modnrod
Fahrvergnugen
Posts: 978
Threads: 50
Registered: March 17th, 2011
Member Is Offline
Location: Midwest, Westoz.
Theme: UltimaBB Pro Blue
Mood: Old School Volksies!
posted on May 15th, 2017 at 11:55 AM
Oh, I forgot (it happens.....).
We are lucky to have some excellent gearbox builders in Oz, as good as anyone anywhere and better than most.
Luckily in WA we have 2 that I know of at least, so if you don't feel like rebuilding it yourself you have options.
1st is a retired gentleman that goes through Veedub Centre in Osb Pk, 9242 2808.
2nd (who built mine) is Country Chris in Mirrabooka, 9209 2010, he does most of the Offroad race stuff over here.
