Broekens
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| posted on 22/3/09 at 07:00 PM |
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Suspension setup for a BMW E34 based Roadster
Hello,
I´m pretty much new here, I´ve been reading about the locost scene for the last few months and trying to get a picture of my future car. I´ve already
selected an engine, the M50 from BMW. This will give me something like 200 hp, sufficient for my use. Secondly, I like to use a E34 525i, because they
are cheaper than a E36 325i.
Because the M50 is a pretty long and wide engine, I´ll use the McSorley 7+442 design as a basis. But the next thing I'm trying to figure out is:
what rear suspension configuration is the best choice?
Obviously, BMW has engineered a very good rear suspension on the E34, I know Aerosam is reusing it. But I think it isn't the best option,
because the 525i weighed nearly 1600kg. Using the BMW rear suspension would be a bit overkill for a 650kg car. Could I adapt the rear axle to make a
double wishbone suspension set up?
Or should I use the BMW setup?
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zilspeed
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| posted on 22/3/09 at 07:23 PM |
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quote:
Originally posted by Broekens
Hello,
I´m pretty much new here, I´ve been reading about the locost scene for the last few months and trying to get a picture of my future car. I´ve already
selected an engine, the M50 from BMW. This will give me something like 200 hp, sufficient for my use. Secondly, I like to use a E34 525i, because they
are cheaper than a E36 325i.
Because the M50 is a pretty long and wide engine, I´ll use the McSorley 7+442 design as a basis. But the next thing I'm trying to figure out is:
what rear suspension configuration is the best choice?
Obviously, BMW has engineered a very good rear suspension on the E34, I know Aerosam is reusing it. But I think it isn't the best option,
because the 525i weighed nearly 1600kg. Using the BMW rear suspension would be a bit overkill for a 650kg car. Could I adapt the rear axle to make a
double wishbone suspension set up?
Or should I use the BMW setup?
Everything about the E34 running gear is to suit a 1600kg 85mph cruiser.
As you rightly say - not completely suitable for a relatively light sports car.
The other thing is, you're more or less on your own with the suspension design.
Rare as they are getting nowadays, Sierra bits are way better supported in terms of wishbones and rear hub carriers.
By al means, use the M50 engine and relevant box, but otherwise, maybe best to avoid the BMW bits.
(Personally, it would be a mid engined RWD car for me using a FWD donor, but that's not the question you asked  )
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Broekens
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| posted on 22/3/09 at 07:46 PM |
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Yeah, a mid engined one will be very cool car, but probably too much of a racecar for me. But using the BMW engine and a Sierra(Cosworth?) rear axle
could be another option..
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mr henderson
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| posted on 22/3/09 at 07:54 PM |
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Zil's advice is spot on. I will add a piece of my own, and that is that the BMW engine is too big and far too heavy for the power that you can
get out of it. It's OK in a heavy saloon, but inappropriate in a light weight se7en
John
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zilspeed
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| posted on 22/3/09 at 08:07 PM |
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And if I may add.
All that weight up fron has got to mean understeer.
(All Rover V8 users can stop jumping up and down, I know they're light 'for what they are'.)
When it comes to engine choice, the first thought of a heavy engine makes me think of hairpins where all the nimble cars with light engines will get
into the corners better.
I know plenty of throttle will get the back end out and sort of balance it out, but it's not fast. The guy with the K series / Zetec SE / tuned
xflow or bike engine will gain 2 or 3 car lengths at this point.
Mid engined V8 is a different ball game here IMHO. I look forward to seeing V8Kid's car proving this theory at events this year.
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Miks15
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| posted on 22/3/09 at 08:34 PM |
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Ive used an E36 donor, ok im only using a 1.6 so not as much weight up front as yours would be (or power for that matter)
But im re using the rear end, well partly. Im reusing the diff, drivehafts and hubs, with fabricated uprights and using the roadsters rear setup and
bones.
I dont know how effective itll be but its saved me having to get new diffs etc
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Broekens
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| posted on 22/3/09 at 08:34 PM |
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The BMW M50 is weighing 195kg , but it kicks out nearly twice the power of the pinto. I couldn't find the weight of a Pinto engine, but a crate
zetec 2.0 is 168 kg. I'm not sure, but 25 kg isn't that much for 40 horses extra?
And besides that, I ain't going on the track, so a bike engine is a no go for me. The BMW engines are one of the smoothest running engines that
I know.
About the Rover V8, I think it is a bit old fashioned, the design is dating from the 50s.. Also I'm affraid of a high fuel consumption when
using a V8.. And besides that, there are many people (especially in the US) who fitted a Small Block Chevy.. Or are they all driving a uncontrollable
understeered lump of metal?
I 'm trying to get about 200 horses from under the bonnet without emptying my bankaccount. Do you people know an alternative to this engine?
[Edited on 23/3/09 by Broekens]
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ettore bugatti
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| posted on 23/3/09 at 10:46 PM |
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You will be fine with the engine, otherwise throw some bricks in the back
You might consider a deDion setup, easy to manufacture. The suspension geometry is also understandable for a novice designer (compared to double
wishbones)
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Broekens
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| posted on 24/3/09 at 10:15 AM |
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Yeah, your namesake did put straight 8s in his racecar, so a straight 6 should work
With the suspension, I think I'll stick to the IRS design of the roadster, maybe with some adjustments.. Does anyone know a book where
suspension design is comprehensively adressed?
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ettore bugatti
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| posted on 25/3/09 at 12:48 AM |
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Try Staniforth or Milliken.(Bol.com )
Also a member called Rorty made drawings of a IRS and deDion for a locost. There are somewhere here...
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Broekens
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| posted on 25/3/09 at 07:03 PM |
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Thanks, I'm certainly gonna buy one of these books.. Which one do you advise? Miliken is twice as expensive, but if it is the better book, why
not?
[Edited on 25/3/09 by Broekens]
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ettore bugatti
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| posted on 26/3/09 at 08:14 PM |
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LOL, I cannot advise you since I dont own any of these books
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Broekens
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| posted on 26/3/09 at 09:40 PM |
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Ok thanks for your help.
I like your design, it reminds me of the Alfa Romeo RZ/SZ fron the early ninetees
But does anyone know which book is best when designing a suspension for a roadster?
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mr henderson
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| posted on 26/3/09 at 10:31 PM |
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quote:
Originally posted by Broekens
But does anyone know which book is best when designing a suspension for a roadster?
Have you read Chris Gibbs (Haynes Roadster) book. Not so much about actual design, which has he has already done, but it is very usable.
If you are still thinking of using the BMW parts then your problem is more to do with converting them to usability in this situation.
For instance, if you make your own rear uprights, which you would need to do whether you did IRS of De Dion, you will have to make housings for the
bearings, as the BMW units are probably pressed into the trailing arms, unlike the Sierra ones which bolt on (one of the reasons why the Sierra is so
popular as a donor)
John
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Broekens
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| posted on 27/3/09 at 09:00 AM |
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Yes, I'm still sticking to the BMW engine. I'm going to correct the understeer with my foot..
But has anyone used the BMW E34 hubs before?
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