"Rule of thumb" power / weight vs CV size?

[vwjim]

Evening,

I've found suggested power/weight vs clutch strengths before, but wondering what the consensus is for what power/vehicle weight bands require what CV sizes? ie at what point do Bug CV's become too small and 100mm CV's become a requirement and also 930 108mm CV's?

I'm converting my 1914cc turbo Samba from SA to IRS. Its always had CB race axles since I broke axles on the drag strip, but with the new IRS setup I'm considering the options for CV sizes.

I own 100mm 924 stub axles already with the 100mm CV's & 924 driveshafts. So I would just need the conversion gearbox output flanges, (type1 to 100mm), if I were to go that route on the Samba.

I also already own a 915 gearbox, which is destined for a turbo Oval. So that project would need the 930 adapter stub axles & some sway-away driveshafts I suspect.

Thanks

[Bruce.m]

Can’t help much except to say, it’s torque that kills CV / transmission/ etc, rather than BHP. And the weight (inertia) involved (both the vehicle & for a drag start, the highly energised spinning flywheel/engine on the other side)

[Ol'fogasaurus]

Especially "shock" torque loading as in "side stepping" (slipping your foot sideways off the clutch pedal as the start light went on) the clutch pedal. Years ago, the idea was to preload the clutch ("IOW" let the clutch pedal out enough (or the gas pedal preloading the auto trans) so that when the clutch was finally let out fully the (shock) loading on all the components would be less severe.

I haven't been on the track since '86 and things have changed a lot since then but in the mid-60s this was the thing to do.

Lee

While looking for something in my old stack of things I found a shift knob with the line lock button still in it. If interested I will take a pix of it.

Lee

[vwjim]

Morning,

Yes I appreciate that its torque & weight related as well as tyre / track / road grip levels. Also how you drive / abuse it.

Just interested if there's a guide value, ie over 200bhp then 100mm then over 300bhp use 930 CV's etc.

I've fitted plenty of Bug CV's to early buses with up to 150bhp and they've all lasted so the power value must be higher that that.

[Ol'fogasaurus]

Morning,

Yes I appreciate that its torque & weight related as well as tyre / track / road grip levels. Also how you drive / abuse it.

Just interested if there's a guide value, ie over 200bhp then 100mm then over 300bhp use 930 CV's etc.

I've fitted plenty of Bug CV's to early buses with up to 150bhp and they've all lasted so the power value must be higher that that.

A very complicated question.

Since I posted on this already, I did a search on CV joints (for facts) and there are a lot of (let's say) limitations such as angles, hours of use, HP and so forth. The subject based on the posting question itself can get a linear answer rather than an answer with a lot of necessary accompanying information.

There are some ads that are hard to not realize that they are ads and are not necessarily factual.

I'll keep at it as it is an interesting question in itself.

Lee

[Ol'fogasaurus]

See if this helps.

https://www.bing.com/search?q=strength+ ... bc&pc=U531

Lee

[Bruce2]

..... tyre / track / road grip levels. Also how you drive / abuse it.

Just interested if there's a guide value, ie over 200bhp then 100mm then over 300bhp use 930 CV's etc.

930 CVs are only needed for the angle. If you have a stock suspension, you don't need them.
100mm CVs are all any street/strip car needs. Richie went deep into the 9s with stock Bus CVs.
My local speedster builder used Beetle CVs on every 4 cyl build. All the way up to 250hp turbo Subaru power.
One of the last cars he built laid down 360hp to the ground on a chassis dyno using Bus CVs. This was through a converted Subaru trans where you can't buy anything smaller than 100mm flanges.

The limit for a Beetle CV is met with drag slicks. If using slicks, you must use 100mm CVs.

[Wally]

..... tyre / track / road grip levels. Also how you drive / abuse it.

Just interested if there's a guide value, ie over 200bhp then 100mm then over 300bhp use 930 CV's etc.

930 CVs are only needed for the angle. If you have a stock suspension, you don't need them.
100mm CVs are all any street/strip car needs. Richie went deep into the 9s with stock Bus CVs.
My local speedster builder used Beetle CVs on every 4 cyl build. All the way up to 250hp turbo Subaru power.
One of the last cars he built laid down 360hp to the ground on a chassis dyno using Bus CVs. This was through a converted Subaru trans where you can't buy anything smaller than 100mm flanges.

The limit for a Beetle CV is met with drag slicks. If using slicks, you must use 100mm CVs.

Yeah, I agree with all of that and can add a little to it that supports the above even more:
I run 100mm T2/T3 CV's (actually they are partly new, but partly still used ones from an old T3 Vanagon shaft, including the shaft itself) and recently did a 10,5 in a heavy 1303 street beetle on a proper drag strip with a 1,6 60ft.
Car makes 475 engine hp when I ran the above number, about 600Nm engine torque.
So, a 100mm CV is obviously very very strong. Gearbox is a G50. I'am nt sure how far beyond 350hp a 915 will hold...

I have seen many 90mm original T1 CV's blow up at around 200hp in drag racing situations, so unless you just use original CV's for street driving only (where I beleive 250hp should be possible if you roll into the power), 100mm's are advisable for most wilder applications

[Bruce.m]

If it’s helpful.
I’m just in the process of fitting driveshafts before my EFI 1641 gets installed. I could go with 100mm but I’d need to source the shafts (guess old 924/944 would be the right length). I do have 944 stub axles but not the gearbox flanges.

Either way, for now it’s getting stock shafts and 90mm CVs. The only quirk, is I’m using inner CV joints from a Polo 9N.

Old early 911s use 90mm CVs (up to about 1968), and the original version is very hard to find unless you buy a complete driveshaft set. People have tried Beetle CVs & they fit but do not last very long. This might be due to poor quality CVs or the distance being slightly out of beetle spec putting the joints in a bad orientation. The trick is to use the Polo CV instead (used in a number of models in early 2000s). The extra benefit is they come with a grease seal, new bolts, new spreader washers, etc. unfortunately those joints are also becoming harder to find & GKN don’t sell them any more.

[H2OSB]

I recall discussing this with you, Bruce, so time ago. In the 90s I had an '86 VW Gti. This car had 100mm CVs, the non-Gti/Gli cars of the time had 90mm CV. Later, when I got into Beetles (I only had IRS Beetles and had no idea SA cars were different), I always wondered if the inner end watercooled car CVs could be used on an IRS trans. Anyone ever explore this? Bruce? Seems like something you'd play with.

H2OSB

[Bruce.m]

I did pick over catalogues & look at various versions. Still took a bit of a risk because the inner cage spline length is rarely specified. It’s needs to be 24mm on the bug driveshaft although the overall width is 32mm. Main reason for looking at non stock items was the questionable quality of bug items from empi etc.

[H2OSB]

I agree with your last sentence. The ones I always got for my Gti were Lubro(I think), and my thinking was VW still supported those models, so factory parts should be available. With the aircooled aftermarket offering questionable quality, I was hoping to decent parts

H2OSB

[Ian Godfrey]

I have found the folks at GKN (Lobro) motorsport division very helpful. Scroll down to the CV page in this brochure :
https://www.gknautomotive.com/globalass ... nglish.pdf
They take the standard CV's, lighten them, hone them and hand fit the balls for least resistance. I have a set of 100mm in my car
Soooooo much better than Empi

[Bruce.m]

Look like they do a beetle sized CV too. Checked & available from typical motorsport suppliers for a fair price. Lightweight version is quite a bit more.