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aitch_de

Engineering diagrams / technical drawings for rear-end or chassis?

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Hi all,

 

I'm about to embark on a build of a 240/260 (tbd) and have been searching in all the forums for any engineering drawings of the underside at the rear... or the chassis geometry in general.

 

I have an ambitious engine conversion in mind, and I'm just trying to find out some aswers to questions such as:

 

  • depth of the tunnel and the profile
  • inner dimensions of the rear running gear (namely the geometry of the half shafts and diff)

 

Additionally I'd love to find info on the weight distribution of the car, and similar.

 

I'm actually looking for a rolling chassis that is more or less complete, but with no running motor as I don't to go aggressively cave-manning a prime specimen!

 

Can anyone help me out with some search terms or suggestions on where to look? My other avenue is buying up every CAD model I can find and hoping that I can divine some half-way reliable dimensions from them; that said, many of these models are of the top surfaces of the body only.

 

kind regards,

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1 hour ago, Neverdone said:

Whatever "ambitious" engine swap you're planning on, has more than likely already been tried. Sometimes just asking, "Will 'X' fit?" is sometimes the quicker way to go.

 

Tesla Model S rear drive unit (incl. diff and inverter) image with halfshafts and subframe/etc attached .. fortunately there are sub-millimetre 3d scans of these available so the modelling part can be quite accurate.

 

Thanks so much for the resources you provided, I'll examine them with fresh eyes tomorrow!

Screenshot from 2019-06-26 22-39-03.png

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Posted (edited)

There's another way to fit this motor which involves separating the motor and invertor and not using the diff from the Tesla, but using an adapter plate and mounting this motor in the engine bay and using one or both of the original transmission and/or the rear diff (or another suitable rear diff with more appropriate gear reduction)

 

The cv joints in the tesla motor integrated diff have extremely wide geometry as they also work in SUVs, so with appropriately short half shafts it's not totally infeasible to cut a lot of the width out..

 

I'm also not wedded to the idea of using the whole tesla subframe, it's just one options, most used motors ship on the subframe, minus the suspension/hubs/etc

 

I just took a quick look, unmodified that rear subframe in its entirety from Tesla is 77.3 in (1,964 mm) (ex. mirrors) wide, and the S30 family are more like 1,626 mm (64.0 in)

 

I'm not sure the 6 inch fender aesthetic is what I really want, but I it should be possible to take some width out of the Tesla unit, or split it and mount it in the engine bay and run a drive shaft and use the (or a) rear diff with suitable gearing.

Edited by aitch_de

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Posted (edited)

Considering how much engineering went into the suspension geometry, the structural design and so forth, it seems to be sensible to swap the entire subframe into the Z, without redoing anything "inside" of the subframe itself... even if this means incongruously-looking wide rear track.  BTW, what actually is the difference in rear track width?

 

For a "straight" rear subframe swap, you'd "only" need to engineer hard-points that receive the rear subframe, and connect them to the stock unibody.  While it is intellectually satisfying to do this in CAD, then maybe CNC-cut the resulting parts, this seems like a misallocation of resources.  Maybe it is better to employ the shadetree method, of first bracing the inner fenders and so forth with temporarily welded-in members, then taking a sawz-all to the stock structure, leaving a gaping hole into which to trial-fit the Tesla components?  

 

Also, considering that you're in Germany, how will you get this through your TUEV inspection and so forth?  And what is your strategy for mounting the battery packs?

Edited by Michael

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Posted (edited)
14 hours ago, Michael said:

Considering how much engineering went into the suspension geometry, the structural design and so forth, it seems to be sensible to swap the entire subframe into the Z, without redoing anything "inside" of the subframe itself... even if this means incongruously-looking wide rear track.  BTW, what actually is the difference in rear track width? 

 

I've seen builds done both ways, converting from a Model S drive unit. There's an Audi RS5 conversion with the Quattro drive system in-tact because the builder mated the Tesla motor and inverter in the engine bay and hooked it directly into the Audi transmission.

 

As much as I love some of the ultra widebody early Z builds, as you picked up on, I'm in Germany, and I'd love to be able to use this car on the road, so things like reengineering sub frames may be out of the question, but keeping "stock" (or at least e-marked and certified) suspension, subframes, etc, etc may allow me to restore the car as a motor-swapped restoration vs. an entirely custom build, if I deviate too far from the original designs then I could be looking at 7-10k EUR in costs to have a special inspection performed and it'd be counted as a one-of-a-kind build and essentially treated as-if I'd done a clean-room build from sheet metal in my garage.

 

For what it's worth the track width of the Z is 53" (1346mm) 66" (1699mm) - but I think that the TÜV (vehicle inspection authority) will look unfavourably on serious mechanical modifications.

 

14 hours ago, Michael said:

While it is intellectually satisfying to do this in CAD, then maybe CNC-cut the resulting parts, this seems like a misallocation of resources.  Maybe it is better to employ the shadetree method, of first bracing the inner fenders and so forth with temporarily welded-in members, then taking a sawz-all to the stock structure, leaving a gaping hole into which to trial-fit the Tesla components?   

 

Whatever I pick-up will likely be rusted to shit, so I'm thinking of building a full cage, and bracing the frame whilst I cut out the floor and sills. That would have given me the option to do-away with the tunnel, and modify some of the floor pan to take batteries, but sends me firmly down the "one-of-a-kind" route in the eyes of the TÜV. Alternatively with a forward mounted motor directly onto a modified drive shaft leaves plenty of space in the engine bay for a few batteries, not to mention the former home of the fuel tank and the spare wheel well.

 

The complete Tesla Model S battery pack with 85kWh weighs a stonking 1200lb (540kg) but is modular, comprising 16 modules each giving about 5kWh and weighing in at 55lbs (24kg). They're fairly manageable sized too, 26.2×11.9x3.1" (78×302×665mm). Given the weight it seems wise of Tesla to have mounted it in the floor!

 

I'm yet to look up weight distribution figures on a regular 240Z, but it shouldn't be toooo difficult to fathom where the centre of gravity would fall if I went with say, 50kWh of batteries (at 550lb/240kg) (which would run me about 10×1200EUR for the packs, and give me something like 180 miles of range) and the Tesla drive unit (295lb/133kg) which can be sourced for 5-8k EUR plus 2-4k in ancillaries (controllers, etc).

 

It's perfectly plausible to split up the battery packs, they need high voltage cable, and coolant running to them, but that's the most basic of basic plumbing. I expect the plumbing and wiring to be easier than dealing with the plumbing and wiring for an ICE.

 

The money aspect felt quite interesting to me, I've followed the Mighty Car Mods 240Z build (well they think it's a 240!) where they motorswapped for an RB26, but sourcing those motors in Europe now also begins at 15k, and that's "original" status, where they still need a modern turbo upgrade, upgrades to proper modern fuel injection, modern coils, and electronic management, new exhaust manufacture, etc, etc, etc.

 

Even with higher than average costs to get a permit to use it on the street here, I can imagine that a Tesla conversion and a modernized RB26 upgrade would come in at roughly the same price. Starting costs for the drive train alone are 15k EUR with a 5k "adaptation" budget.

 

To touch on the CAD aspect momentarily, I'm a software engineer by trade, so the idea of managing a build and designing my own parts requirements comes more naturally to me than sitting with a sawzall and hacking at it. I can weld, but not excellently, and certainly never tried to weld Aluminium, which is a skill I'd need to pick up.

 

Land prices are so high in my home city that if I want to rent access to a shed with a bay and some tools it'll easily add 500EUR/month to my costs for this car, which pushes it almost to the point where I can't justify the cost. At least I can't justify dragging the build out over a year, and being 6k EUR out of pocket for having had the luxury of taking my time.

 

So my "plan" (in so far as I have one) was to find a (complete) rolling shell, get it stripped and start bodywork and chassis changes on it, but try and get it back to stock.

 

Get it dipped to strip the old paint and misc and then anodized and protected. From there I wanted to get the chassis and fenders/etc scanned with hand held 3d scanner, I think a clean scan of a 240Z chassis would be a valuable resource for the community in general, and would allow me to plan the rest of the build virtually whilst getting all the parts made up.

 

Hand-in-hand this approach may actually help me keep costs and timeline short, but it depends on my abilities in software more than my greasemonkey skills...

 

The whole thing may turn out to be prohibitively expensive in Germany, right now a rusted out shell in piss-poor condition is selling for 6-8k EUR (for e.g this one).

 

I was hoping to get close to running and driving for circa 30k EUR within 1-1.5 calendar years, but with a 3 month active build time of real workshop time.

index.jpg

Edited by aitch_de

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It sounds like a good strategy would be to first make a list of proposals, from the very mild to the egregiously aggressive, and submit them to a TÜV inspector.  That would ultimately bracket the possibilities.  Is there some option where you first run your freshly-built car on race-tracks only, then obtain some endorsement of safety and reliability from the track officials, and use that endorsement to solicit approval for usage on public roads?

 

If, as seems to often be the case, it is unlikely to source an S30 Z in decent condition in Germany, and your project becomes part swap/grafting, part rust-abatement, part reconstitution of the interior and the supporting mechanical/electrical systems, and part welding of a new chassis-frame, then perhaps there’s merit in reconsidering your options entirely.  One possibility, again depending on what the TÜV people say, is to start with a complete wrecked Tesla, harvesting the front and rear clips, a portion of the battery and the battery control system.  You would then build a custom sports-car from scratch, but would register it as a “Tesla”… except that it would be considerably lighter, more compact and therefore sportier.  You could also do the opposite, of calling your new creation a “Z”, registering it as a Z, but using only a smattering of Z-sourced components, such as maybe the windshield and windshield frame, the roof, A and C pillars… and making everything else custom.  Lastly, you could do the aforementioned for some other car, that’s also a 2-seater sports car, but is more common in Europe, for which components are easier to source.  One possibility is an even older car – maybe something from the 1950s? – which might be subjected to less stringent requirements on safety and so forth, and would therefore be easier to register?

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