Billet Ali Rear Subframe

[BlackBeaut]

Hi Guys,

 

I spent a fun few hours on Saturday tearing down my rear end, amazingly no bolts sheared and only one head had rounded. I still managed to swear a bit though to keep up appearances

 

Anyway I've been blast cleaning the parts these last couple of days and frankly I think they suck, lots of rust means lots of weak looking pitted steel now. Given that I'm putting in a short nose R200h with a large finned back cover (from an S12 Silvia, think it's the same as Z31) I'll need to create some kind of rear brace anyway, so I started thinking that why not go the whole hog and create new upright sections as well.

 

Here's some idea of what I'm thinking:

gotta dig those camera angles

 

and a little Flash animation here:

http://www.equiview.co.uk/240z/anim.html

 

Now I'm always a little wary about aluminium due to it's fatigue life issues but it's been years since I've been involved in real engineering and materials so maybe it's not so much an issue now. The 3 alloy options I'm considering are 2014, 6082 and 7075 all T6 treated. Spec details here:

http://www.metalfast.co.uk/stocks.htm

 

Also any design critique would be greatly appreciated, are my webs too thin at 5mm or too much even? I want to keep as much space as possible around the top mounting bolt heads so that it's as easy as it can be to get spanners on them, as that was something I discovered to be a lot of fun on the tear down. Admittedly with the R200 moustache bar being behind the uprights this should be a lot easier.

 

BTW, does anyone know of any freeware CAD software? I do all my 3D stuff in an ancient animation package, on an ancient Mac, dimensions are pretty difficult to get right.

 

cheers,

Rob

[johnc]

Considering that 7075-T651 has a tensile strength on par with annealed 4130 Cro Moly steel I don't think you will have any issues with the strength of what you're building. Cost might be an issue, but not strength.

[JMortensen]

I think the main force that these parts face is a lateral force. This comes from several discussions with racers who had cracked the stock pieces up at the top, or had seen damage around the bolt holes. I braced mine at the top with a piece of angle across the top and some gussets as well. Looks like the majority of your strengthening is geared at the bottom end. There was some pretty good discussion of this on the rear toe adjuster thread here: http://forums.hybridz.org/showthread.php?t=89111&page=1. Basically we all thought that the structure needed to be improved on. I went to the top to strengthen, Terry had already replaced everything back there with a single aluminum plate, and Jeromio braced across the bottom.

 

Mat is right, your uprights will definitely interfere with the mustache bar, as there is only ~6 or 7 mm clearance there.

 

If I weren't modifying existing uprights I think I'd end up with something like Terry has. That has got to be a HUGE improvement over the stock setup.

 

Here's another link to the original thread on the toe adjuster: http://forums.hybridz.org/showthread.php?t=88572

[auxilary]

If you're planning on mass producing them, you may want to look into suspension techniques rear sway bar mounts, and incorporate them into the design.

[BlackBeaut]

Thanks for the thoughts guys!

 

JohnC, if you were considering making these which alloy would you opt for? I know ArizonaZ uses 6061T6 for their moustache bars (pretty much the same as 6082 over here) but of the three options that's the weakest. Of course material costs are always an interesting diversion!

 

JonM, I've been reading through the 'toe adjuster' posts for a while now soaking up as much info as possible. For my uses though I'm probaby going with ArizonaZ adjustable arms as my existing arms are a bit knackered and with the exchange rate as it is at the moment it just makes sense.

 

Regarding strength at top verses bottom, I'll draw up a new design that uses a double vertical web but should still allow easy access to the bolts. The reason for all the extra meat at the bottom end is that I'm thinking that the bolts from the lower cups and the rear brace will just screw directly into the upright. Must check dimensions to make sure two holes don't intersect! Of course I could loose a lot of material here if I just went with a bolt and nut arrangement as with the existing uprights, my thinking against this is that that adds another end to the bolt that can corrode and make disassembly all the more fun. I'd love to hear your thoughts on that, just don't forget the weather in the UK sucks 99% of the time

 

Good point about moustache bar clearance, I'll look into that!

 

Aux, I'm not considering mass producing these, the market in the UK is far too small and the exchange rate is against me for selling to the big US market. In fact I'd be more than happy for someone to just rip off the idea, it's not exactly breath taking in it's conception Adding in extra mount points for rear roll bars is a nifty idea though.

 

Cheers,

Rob

[S15 200sx owner]

Hi Guys' date='

 

Given that I'm putting in a short nose R200h with a large finned back cover (from an S12 Silvia, think it's the same as Z31) [/quote']

 

Hey Rob,

 

I am also planning to swap in a short nose R200 (MLSD from R32 GTR) What are you planning on running for a front mounting system for yours, i havnt got that far yet! But am very interested to see if you have come up with anything yet?

[BlackBeaut]

Hey Rob' date='

 

I am also planning to swap in a short nose R200 (MLSD from R32 GTR) What are you planning on running for a front mounting system for yours, i havnt got that far yet! But am very interested to see if you have come up with anything yet?[/quote']

 

I'm in pretty much the same boat as yourself at this moment in time. I've got some ideas bubbling in my head but nothing definite. My main idea at his point it to run a couple of beams from the rear uprights, close to the underside of the car. Have them attach (somehow!) to the either the front diff cross member or something similar to the Ron Tyler mount and then hang something from that the diff can bolt on to. Boy, that makes so much sense!! I can probably come up with an illustration for that if you'd think it would help.

 

The other option of course is the one that Ross at Modern Motorsports is developing with Rick Bowers (Speeder):

http://forums.hybridz.org/showthread.php?t=97369&page=2

This will no doubt be a great and well researched product.

 

Cheers,

Rob

[BlackBeaut]

OK, here's a couple more variants with 2 central vertical webs, also more material has been removed to give better clearance for the moustache bar. The other major difference is that I've turned the upright around, so the milled pockets face the rear of the car. I figure that made production sense as then all the milling work would take place from just one side of the billet. The blue surface is the area where extra material has been removed to give the moustache bar clearance.

 

Slightly more radical material removal here, does mean that the top bolts would be easier to access from the front.

 

 

I'm not suggesting this as a production colour scheme of course

 

cheers,

Rob

[JMortensen]

On the stock setup the flat part of the uprights pretty much lines up with the end of the frame rail. So if you flip them around then the rear control arm bushings would be located too far forward by the thickness of the angle, if that makes sense.

 

So your above idea would work if the bolt mounting flange faced forwards, then your vertical braces faced backwards. They can't both face the same direction, because then either the bushings will be located in the wrong place or the mustache bar will be interfered with. If you have a second look under your car and I'm sure you'll see what I'm talking about.

 

EDIT--I'm partially wrong in the above statement. I'm still stuck in my own project I think. I needed the verticals to line up with the end of the frame rail so that the bushing cup pieces could line up where they were needed as well. Your design does not need the verticals to line up since you can put your cups wherever you please with respect to the uprights. So as long as the bushing cups end up below the bolt holes at the top and you have room for the mustache bar you should be OK.

[ZHeadV8]

Hi Rob,

 

Glad to see you here

 

Nice plans, wish you had published them a little earlier, we spoke about your front mount which looked excellent but I have now sorted other ways to do the job (Arizona Z billet front and rear).

 

The guy building my car would most probably be interested in this when it is finished - you know who he is .....

[tube80z]

OK' date=' here's a couple more variants with 2 central vertical webs, also more material has been removed to give better clearance for the moustache bar. The other major difference is that I've turned the upright around, so the milled pockets face the rear of the car. I figure that made production sense as then all the milling work would take place from just one side of the billet. The blue surface is the area where extra material has been removed to give the moustache bar clearance.

[center']

[/center]

 

Have you considered an X bracing for the verticals? It would need to be spaced out to clear the Diff but I think there is space. This should be stiffer.

 

Cary

[JMortensen]

There's a good idea! Space it out about 2 inches and run a big X from the top to bottom. Then just forget the link at the bottom, you don't need it at that point.

[johnc]

Regarding material choice:

 

I would look for an aluminum alloy that is easy to machine, has a tensile strength around 50ksi., a yield strength around 40ksi. and good fatigue resistance. In the US, that material is 2024. 2017 would also be a good choice. 2017 also has better corrosion resistance then 2024 which has to be anodized or clad if in an industrial or marine environment.

[BlackBeaut]

Hi Rob' date='

 

Glad to see you here

[/quote']

 

Hi Andy, I get around you know. Sure beats working

 

Hi Rob' date='

Nice plans, wish you had published them a little earlier, we spoke about your front mount which looked excellent but I have now sorted other ways to do the job (Arizona Z billet front and rear).

[/quote']

 

Hot of the brain press this last couple of days, sorry for being slow You can always retro fit something like this though once your beasty is on the road.

 

No probs on the diff mount, I've actually gone cool on the idea, bit overly complicated. For every day use the mod to the stock mount - bolting the L bracket and rubber shim to go under the diff cross member - seems pretty spot on to be honest.

 

Cheers,

Rob

[BlackBeaut]

Hi all,

 

Thanks again for the responses, all good stuff.

 

Yup Jon, lining up the verticals with the end of the frame rails isn't essential with this design. As long as the top bolt holes are in the correct location relative the bushes below then it should be fine. At the moment I'm designing the uprights to be 36mm thick which seems to be roughly the thickness of the stock bearing caps on the back. I need to dig out my poly bushes and double check that dimension though. That and every other dimension!!

 

Cross bracing is an interesting idea, I'll mock up a design. Not too sure if there's space at the top to clear the moustache bar at the top, or if there would be any issues with the petrol tank - that's pretty close up there - or if I've even got my head around what exactly you mean. Worth looking at though. Feel free to scribble on my pics.

 

Thanks for the material suggestions John, no doubt I'll be anodizing or powdercoating for protection anyway but better corrosion resistance is always good.

 

 

Just to recap on my idea for mounting the short nose diff, here's a couple of shots of what I've been thinking on. To be honest I'm not 100% sold on the design, I'm sure it would work, but whether it's too complicated for it's needs is another question. I do like to go a bit Heath Robinson on my designs at times

 

Billet front diff cross member with twin exhaust hoops anyone? You gotta love shiny bits of metal

 

Cheers,

Rob

[BlackBeaut]

 

Is that the sort of thing you meant?

 

Cheers,

Rob

[JMortensen]

That's what I meant. I don't know if Cary was on the same wavelength.

 

It still appears to me that you'll have an interference issue with the mustache bar and the uprights. Which got me to thinking about the mustache bar. You could eliminate the stock bar, and integrate a more modern design of a shorter bar into your framework. You'd need to beef the frame up on top I think, but the other advantage would be that you could move the diff forward, giving better weight distribution. As long as you're running CV's in back the halfshaft misalignment won't be a problem.

 

Making the subframe instead of modifying an existing setup gives you so many possibilities. Talk about "outside the box"...

[blueovalz]

Why use a mustache bar at all, and instead, integrate the rear diff mount into the cross bracing?

[BlackBeaut]

I've thought about moving the diff forward, it would make whatever bracing that happens between the uprights easier as there'd be less interference with the diff cover fins back there. Just not too sure how far it can go without affecting CV angles too much, and how far forward it can go without causing issues with the front cross member. If I can move the diff forward say 4" then I'd get CV angles around 15 degrees (possibly, if my maths is any good!) is that an acceptable value, the CV joints I'll be using from a 200SX are tripod type like the 280ZX, but sightly larger.

 

As for getting rid of the moustache bar, I take it you'd have to really beef up the actual body work that the uprights bolt into? I'm concerned that the 4 bolts that hold the uprights in are somewhat weedy in comparison to the 16mm bolts that hold the moustache bar in. Terry, in your solution I see that you have addition wings that locate on to the moustache mounting bolts, did you add those so you could mount the sway bar or because you felt the four upright bolts weren't enough? Also raised is the question of vibration, I guess it would be possible to bush the cross brace/rear diff holder on to the uprights to help reduce transfered vibrations.

 

At the end of the day I'm building a weekend streetable fun car with good track capabilities. It would be nice though to arrive at a design that others can use, should they wish, with minimal alterations to their cars, for whatever purpose they drive their cars for.

 

Cheers,

Rob

[blueovalz]

When I was investigating the use of CV joints back in the late '80s, the consensus I received was that, about 13 degrees of angle, under "significant" torque (whatever significant meant), was the safe limit.