Aluminum vs Magnesium Gearbox

[Stan Clayton]

As I 'restomod' my '75 Zink Z-10B/C for FSV I'm considering a new aluminum gearbox main case as I upgrade the existing box from Mk9 to Mk5. Is there any consensus that the aluminum case is a worthwhile upgrade over the mag case, or am I just spending money?

[Daryl DeArman]

If the Mag case is up to the task, why wouldn't it be a better option over the aluminum? If it's dimensionally identical it would be much lighter. It could be a bit beefier and still be both lighter and stronger.

[Stan Clayton]

Thanks Daryl. My magnesium "Rhino' bare case weighs 11 lbs and afew ounces, versus 4 lbs more listed for the OEM aluminum 'White Rhino' case. One website page I read stated that with the mag case the Mk5 is good to 180 ft-lb of torque, but that it's good to 200 ft-lb with the aluminum case. Hewland's website just says 180 ft-lb, with no comments about the transaxle case material. Just wondering if anyone here has any insight into the question. Thanks

[Daryl DeArman]

Thanks Daryl. My magnesium "Rhino' bare case weighs 11 lbs and afew ounces, versus 4 lbs more listed for the OEM aluminum 'White Rhino' case. One website page I read stated that with the mag case the Mk5 is good to 180 ft-lb of torque, but that it's good to 200 ft-lb with the aluminum case. Hewland's website just says 180 ft-lb, with no comments about the transaxle case material. Just wondering if anyone here has any insight into the question. Thanks

Assuming the Al case is 11% stronger and the Mg case is 30+% lighter I guess it depends on which you can afford to sacrifice, the strength or the weight.

If it were me and I had a good Mg case, I'd stick with it before I spend $ on a new Al. What's a really good FSV engine produce 140-150 ft/lbs?

[Garey Guzman]

Stan,
Do you already have a motor? If so, what does the dyno say you need?

As you probably know, Vintage is allowing up to 2.0 a/c engines now. If you're going that route, the extra capacity will likely allow better longevity and durability. Since you're not restoring an existing car to an original spec, it would seem beneficial to go with the Alum.

If you were worried about weight, skipping a couple pizza's and desserts will likely loose the 4 extra pounds from the case! (Unless you're already an endurance runner with nothing extra to lose!)

[Stan Clayton]

Thanks Garey. My car currently has a 1835cc Bertils water cooled VW engine, which i suspect is right at the max for its Mk9. I didn't get a dyno sheet with the car. Since the car has no FSV provenance it will have to run exhibition in Vintage, but it is allowed 2135cc in SCCA, which implies nearly 180 ft-lb. The gearbox case in it is at least 25 years old, so I though I'd ask about the aluminum case.

I used to be a skinny long distance runner, but my last marathon was 30 years and 70 lbs ago, so it's for certain I am not concerned about the 4 lb weight difference!

[Daryl DeArman]

Since the car has no FSV provenance it will have to run exhibition in Vintage, but it is allowed 2135cc in SCCA, which implies nearly 180 ft-lb. The gearbox case in it is at least 25 years old, so I though I'd ask about the aluminum case.

I used to be a skinny long distance runner, but my last marathon was 30 years and 70 lbs ago, so it's for certain I am not concerned about the 4 lb weight difference!

Sounds like your answer is simple. Not worried about the weight and suspect at/very near 180ft lbs .

[RussMcB]

My magnesium "Rhino' bare case weighs 11 lbs and afew ounces, versus 4 lbs more listed for the OEM aluminum 'White Rhino' case.

Is that for sure apples to apples?

I was just wondering if your current case might have a few pieces of steel it in, like studs, bearing sleeves, etc., bringing the weight up.

Just curious.

[Garey Guzman]

Is that for sure apples to apples?....

Mag is about 34% lighter by volume than Al so it's probably correct.

[Bob L.]

I went shopping for a Rhino case (over in dune buggy world) to recase my March SV, 2 yrs ago. Saw mag listed several places, yet no one had one. Make sure supplier can really put hands on a mag. rhino case, before you get too excited about your find. Found many listing, but most got their's from same place....... just resellers.

I went with alum. as I figured: less brittle/proned to cracking from impact, cheaper, likely easier to repair, and was available. Still not cheap (shipping wasn't kind either....none free). I did the cutting/mods. Had William do setup, used their fancy black coating, inside and out. Came out well.

Bob L.

[Charles Warner]

Stan,

It also depends on the stress vectors for the box. Case in point: the 1989/90 Reynards came with a mag case. However, with the shocks pivoting at the bottom and the rockers at the top, the stresses tended to pull the side plates away from the case. Result was a new CWP every race. Fix - go to an ally case.

So, not just a matter of weight.

[Stan Clayton]

Is that for sure apples to apples?

I was just wondering if your current case might have a few pieces of steel it in, like studs, bearing sleeves, etc., bringing the weight up.

Just curious.

Thanks Russ. My case actually weighs 11 lbs 10 oz with sideplate suds and a few sleeves, so i wrote 11 lb and a few oz to (sort of) account for the difference. In any case, I saw websites that stated a 4 lb difference, which is close enough for conversation's sake. And honestly, the weight is not a factor in my decision making.

Now that I've read the thread I've settled on an aluminum case for the longevity, reliability, and ease of access. When I upgrade to the permitted 2135cc (for the SCCA FA class) the engine should make about 170 ft-lb, extrapolating from its current 140+ ft-lb as a 1.8L. 170 ft-lb is way over the Mk9 recommended max of 150 ft-lb. The old box ran without a single issue for 20 years, but I'm not interested in finding its weak spot. And the extra $150 is hardly a deal breaker.