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Author: Subject: Smart Car as Donor
Replicar328

posted on 6/2/20 at 01:25 PM Reply With Quote
Smart Car as Donor

I'm planning to build a replica 1936 BMW 328 and have a donor MX5 in the garage. But using the MX5 is proving to be complex as I need to maintain the width of the original car which is 1,550mm. I have GRP body panels made from a buck which was made from an original car so no way to change this.

The MX5 is wider, with correspondingly wider track. Although I'm told that using a Smart Car is complicated because of the electronics, it has a width very close to the BMW. So I'm hoping to use the rear subframe essentially as it is, and the front suspension and sterring rack all mounted on a space frame chassis. The wheelbase of the replica is significantly longer, which will be a problem for ackerman but otherwise I think this will be an easier way to go, although I'm sad about losing the front engine rear wheel drive setup.

I'd welcome some advice on this project.
1. Has anyone built a spaceframe chassis to take the smart car subframe, suspension etc?
2. Whilst I'm at it, should I use a different engine/drivetrain
3. Can I get away with moving the steering rack forward or back to change the ackerman angles
4. Is there a better solution than using a smart car donor?

Cheers
Adrian

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minitici

posted on 6/2/20 at 01:55 PM Reply With Quote
Just narrow the MX5.
You would need to move suspension points inboard and fit narrower drive shafts and a narrower steering rack.
Bound to be a lot better than using Smart Car parts.

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Replicar328

posted on 6/2/20 at 02:20 PM Reply With Quote
quote:
Originally posted by minitici
Just narrow the MX5.
You would need to move suspension points inboard and fit narrower drive shafts and a narrower steering rack.
Bound to be a lot better than using Smart Car parts.


Thanks for your thoughts. This has been my plan from the beginning but it isn't easy. At the rear, I can probably use the lower wishbones although the inboard pivots would be close to the diff. I would need to fabricate rear upper wishbones so the inboard pivot points go either side of the diff anchor points. Bringing front suspension points inboard clashes with the engine although the wheelbase of the replica is 135mm longer than the MX5 so I may be able to get around this by moving the lower wishbones left to right - or replacing the front suspension altogether. Shortening the steering rack and drive shafts all possible, but the simplicity of just bolting the smart car subframe and front suspension and steering components to a space frame. I've been planning this for too long, need to get it done!

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Mike Wood

posted on 7/2/20 at 08:26 AM Reply With Quote
Wax an old 3 Series BMW seen as an option?

Ford live axles come in a range of widths from Anglias, Escorts to Capris and Cortinas and a range of diff ratios and options to upgrade.

Cheers
Mike

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Mr Whippy

posted on 7/2/20 at 08:36 AM Reply With Quote
everything I've ever read about the smart car paints its drive train as utter junk can't think why you'd want to use it for the basis of your car

wiki says the 1936 BMW 328 has a width of 1550mm, the 1950's Ford Anglia has one of 1537 mm, why not base the car on something like that? it will drive much more realistic and spares will be easy to source. You could pick up a rusty old donor for peanuts, sell the savable bits and make some money?

[Edited on 7/2/20 by Mr Whippy]

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Replicar328

posted on 7/2/20 at 06:24 PM Reply With Quote
Thanks to all for your thoughts. I must admit, a 3 series BMW would be nice, especially with a straight six engine. And I'd be happy with a solid axle, but it seems to me that old for Anglia's are now viewed as classics, with silly prices - I blame Harry Potter. I've heard the same about the Smart Car drivetrain but I'm not looking to make a racer, just a runabout for sunny days - the thing I like least about the smart car idea is the engine in the back. I've actually thought of using the smart rear subframe/suspension assembly and putting a front wheel drive engine and transaxle in the front - it'd need to be inline to fit comfortably, with transaxle forward of the engine - any ideas on suitable engine/transaxle?. The Smart Car rear suspension is kind of weird, somwhere between trailing link and De Dion, with a semicircular hoop coming forward around the engine but with a rubber bush in the centre, so no easy way to use this with a propshaft going forward. Woe is me...
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JC

posted on 8/2/20 at 07:16 AM Reply With Quote
There have been 3 Smart based kit cars as far as I recall: The Michelak C7, a version of the MEV Exocet and the Banks Europa. The latter featured in TKC recently I think, so it might be worth a look.
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PorkChop

posted on 8/2/20 at 08:28 PM Reply With Quote
I think going the Ford route would be your easiest option at the rear, or using a Volvo rear axle like theduck has on his 105e.

Would Escort front suspension and steering be an option since they aren't that much wider than a 328? Using Locost geometry might get you into the right ball park for setting up the suspension too.

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Mike Wood

posted on 8/2/20 at 08:39 PM Reply With Quote
Could use 1960s Ford Anglia rear axle casing with the appropriate diff ratio combined with Triumph Herald Vitesse front hubs (and a converted to Ford PCD using an adapter from Merlin Motorsport to match rear axle).

Key would be suitable steel wheels of correct diameter, PCD, offset, width and look. If it was not for the too small diameter, 13" Weller Formula Ford steel wheels might be a start (or Triumph Vitesse steel non-Rostyles wheels matched with a BL/BMC axle)

Put in a Ford Mk9 gearbox and a Fiat Twincam.

Google Dwornick Engineering Vincent MPH for inspiration for producing 1930s inspired replicas using later components.

Cheers
Mike

[Edited on 8/2/20 by Mike Wood]

[Edited on 8/2/20 by Mike Wood]

[Edited on 9/2/20 by Mike Wood]

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Replicar328

posted on 9/2/20 at 12:36 PM Reply With Quote
Lots of helpful posts, Iím responding to all in this post.

To JC, thanks for info on Smart Car based kit cars Ė I will google and investigate these. Same for PorkChopís suggestions.

Mike Woodís suggestion to google Dwornick Engineering Vincent MPH lead me to https://www.vincent-mph.co.uk/rolling-chassis.htm which looks like a really easy way for me to get the job done. Not my original intention as I wanted to do a lot myself, but a complete rolling chassis for around £3,000 with dimensions which are near enough makes a lot of sense. I will telephone early next week. Concerned that the last update on this site was in July 2016 so hope they are still active.

Altogether, nice ideas, more research needed, Iíll post the results sometime soon.

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Replicar328

posted on 29/2/20 at 10:52 AM Reply With Quote
Quick update. After much deliberation and web search Iíve decided to stick with the original plan and use my MX5 as a donor car for my 1936 BMW328 replica. Iím now pretty sure I can use the suspension uprights for both front and back, and the only wishbones I will have to fabricate are the rear top ones, to avoid the inner pivot points clashing with the diff anchor points.

The key to this decision was the discovery of: https://grabcad.com/library/miata-rear-suspension-1 and https://grabcad.com/library/miata-front-suspension-na-1 which you can view in 3D online and measure between two points. This has given me all the dimensions I need.

I will have to shorten the steering rack and the drive shafts and modify the original Ron Champion chassis to make it a little narrower and follow the Haynes Roadster suggestions for adapting the chassis to suit the MX5 donor, but this should, as recommended, be a much better solution than using a smart car.

Thanks again to all contributors
Adrian

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Mike Wood

posted on 29/2/20 at 12:11 PM Reply With Quote
Adrian

Good to hear an update on your interesting project. Pleased you are going for front engined and rear wheel drive to follow the original.

Some nice pics of an original car for sale - pics probably worth saving for future reference/inspiration: https://www.carandclassic.co.uk/car/C1203445

Key to getting the look will be steel wheels, hopefully of similar diamater. MX5s were available on steels (14inch?) might be tricky to track down a set, but may not still not give enough of correct look as the originals would be larger diameter with higher profile tyres.

Cheers
Mike

[Edited on 29/2/20 by Mike Wood]

[Edited on 29/2/20 by Mike Wood]

[Edited on 29/2/20 by Mike Wood]

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Replicar328

posted on 29/2/20 at 06:49 PM Reply With Quote
Thanks Mike,

I've copied these pictures - I've now got quite a gallery which really helps to understand the detail. I bought the book "BMW 328 vom Roadster zum MYTHOS" - (from Roadster to Legend) https://www.amazon.co.uk/BMW-328-Vom-Roadster-Mythos/dp/3613039133 which actually has some amazing pictures, even photos of drawings with some key dimensions.

The original has 16" wheels, with the outside diameter of the tyre being 680mm. So far I've found https://www.oponeo.co.uk/steel-wheel/alcar-kfz-9507 which are close enough with the correct 4x100 PCD and they are 6.00J - hard to find narrower. I'm thinking of reducing the tyre O/D to 650mm as the wider wheels/tyres than original fitting under the front wings will limit the turning circle.

Central bore may not be quite right, may need spacer ring. Need to think about wheel offset to minimise scrub. It seems that van tyres with higher profile can give me the necessary O/D. My favourite tyre and rim size calculator is https://www.wheel-size.com/calc

Knock-off wheels would be nice if available at all, but not legal on a modern vehicle?

Just giving you a flavour of the complexity of this project, as I can see from your post that you've been thinking about it!

Once again, most grateful for your inputs.

Adrian

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