Ratman
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| posted on 12/3/10 at 07:40 AM |
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I guess, when I started this thread, I had hoped that someone would have some actual hard evidence comparing like with like. In UK I think there are
some kit manufacturers who make both front engine and midi versions of cars that are designed and built with very similar concepts and perhaps with
identical engines. Then (this is stretching things a bit) maybe they have tested them at track days on the same track and can pass on their
experiences. My own experience is pretty much just one short wheelbase (2100mm) midi with 66% weight on the rear wheels. This gives a real advantage
off the line and very responsive handling, but it is twitchy and spins do happen. Building again I think I would make the wheelbase longer, and if you
are doing this, then it must be six of one and half a dozen of the other for front or mid engine. As soon as the straights get to be a decent length
then the biggest difference is probably aerodynamics, and a midi can generally be built lower because the driver doesn't need to be able to look
over the engine. I think this is really what caused the shift in the early sixties with F1. All up, I think mid engine is more entertaining, and
that's what it is all about..
Here's one of my spins.. What I think happens is that although the midi tends to more likely to spin, it is more likely to stay on the road when
it does it. Watching Porsche races on TV, the same seems to happen with them.
http://www.youtube.com/watch?v=UkKSIFUctPc
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iank
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| posted on 12/3/10 at 07:53 AM |
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I think that video demonstrates why reverse is now required for IVA. Nose first into a cliff on a blind bend wouldn't be a good place with
other traffic around.
Back on subject, I think I probably agree with the aerodynamic argument for single seaters, which seems pretty logical with 20:20 hindsight. Also
running a propshaft to the back past the driver requires a wider car in that environment.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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cymtriks
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| posted on 20/3/10 at 11:16 PM |
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quote:
Originally posted by Alan B
quote:
Originally posted by Doug68
quote:
Originally posted by Ivan
Cymtrics has raised a vital point about keeping the COG low and the problems with modern FWD drive engines where COG plays a secondary consideration
in design
This arguement is good in theory, but then you need to explain the Lotus Elise.
Beat me to it Doug....I'd forgotten just how s**t the Elise was.... ......could it be better with lower CoG...sure, but we are taking road cars
and the Elise aint too shabby......
But we will never know two impotant bits of information:
1) would a front engined Elise (if a suitable drivetrain had been available to lotus) have been just as good or better?
2) how much better would the Elise have been if Lotus had managed to source a purpose designed (i.e. lower CoG) drivetrain?
Saying the Elise makes me wrong is nonsense. You could just as well say that road tests in favour of the MX5 over the MGF prove that front engined is
better.
I suspect that as long as a FWD driveline with the typical higher CoG is used then the advantages are very small or possibly not there at all.
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Doug68
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| posted on 20/3/10 at 11:49 PM |
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quote:
Originally posted by cymtriks
FWD driveline with the typical higher CoG
Examples please.
I've looked at Toyota's and a few others and I'm not finding engines on top of transmission's they're next to them as per
this Mitsubishi one...
 
Rescued attachment Box.jpg
Doug. 1TG
Sports Car Builders WA
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kb58
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| posted on 21/3/10 at 02:27 AM |
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quote:
Originally posted by Doug68
Examples please.
I've looked at Toyota's and a few others and I'm not finding engines on top of transmission's they're next to them as
per this Mitsubishi one...
Agreed, much like the Hondas. What are some modern examples of high-CG FWD drivetrains that render them unusable as a group? I don't see any.
[Edited on 3/21/10 by kb58]
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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Doug68
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| posted on 21/3/10 at 03:45 AM |
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Ok so how about we clear this up with some dimensions?
Using the bottom of the chassis for reference so to take ride height out of the equation.
For my longitudinally mounted V8 I get the following dimensions from underside of chassis to...
1. CL Crank height. 225mm
2. Top of cam cover height. 595mm
Also the fuel tank is typically 40kg of weight or more and compared to a 7 it seams to be very easy to get the fuel tank in a middy in a better
location so from underside of chassis to...
3. Underside of fuel tank 28mm
4. Rough fore aft distance of CG of tank to CG of car. 0mm the CG of the car is inside the fuel tank.
So what do other peoples cars measure and how do the number above compare with a 7?
(CG measurements taken from my CAD model which has proven accurate to date)
[Edited on 21/3/10 by Doug68]
Doug. 1TG
Sports Car Builders WA
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kb58
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| posted on 21/3/10 at 05:18 AM |
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I'm not sure how useful this'll be because it depends if the builder is fine with the oil pan hanging down below the frame rails.
I'm not, so I'll come up with one number, but if another builder's fine with 75mm ground clearance, he'll get a much
"better" number. Never mind the pan may get removed by a speedbump.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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cymtriks
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| posted on 21/3/10 at 01:10 PM |
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quote:
Originally posted by Doug68
quote:
Originally posted by cymtriks
FWD driveline with the typical higher CoG
Examples please.
I've looked at Toyota's and a few others and I'm not finding engines on top of transmission's they're next to them as
per this Mitsubishi one...
Your photo actually shows the engine crank to be several inches higher than the axles.
On a typical FWD the engine crank is a bit forwards and a bit upwards from the axle line.
This is largely to fit in crumple zones, emissions stuff and manifolds. The modern FWD car tends towards tall and narrow engines.
Now look at a purpose designed transaxle. Often they are inverted (axle above engine input) which, with a small bell housing and low sump, can put the
CoG much lower. There are also transverse gearboxes available for longitudinal engines (as on the McLaren F1) which also put the CoG lower.
I suspect that we are trying to compare very similar numbers here and that choosing specific cars could be very misleading. The differences between
one manufactures list of priorities and parts bin compared to those of another manufacturer are probably far greater than the differences that we are
discussing.
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kb58
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| posted on 21/3/10 at 04:05 PM |
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quote:
Originally posted by cymtriks
On a typical FWD the engine crank is a bit forwards and a bit upwards from the axle line.
Now look at a purpose designed transaxle. Often they are inverted (axle above engine input) which, with a small bell housing and low sump, can put the
CoG much lower. There are also transverse gearboxes available for longitudinal engines (as on the McLaren F1) which also put the CoG lower.
But virtually no one uses purpose-designed drivetrains for a Locost/middie street car. Most builders don't have formula car budgets.
In a middie, tyre diameter dictates nearly everything since it defines axle alignment. Since we use street tires and not low-profile racing slicks,
tyre centerline (and therefore the axles) end up about where we want. As long as ground clearance of ~4" is acceptable for a street car, modern
FWD drivetrains work just great.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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MakeEverything
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| posted on 21/3/10 at 08:07 PM |
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Mine uses a renault Transaxle, which has aproximately 30 degree angle of the driveshafts. It was fixed to a renault engine which was in line (as per
the original car) and is soon to have the cosworth engine mounted the same way.
Personally, i think the car is very well balanced, and the paperwork at SVA (at the time it was done) said that the weight distribution was 55% to the
rear from memory - Almost a perfect balance.
The car is noisy, as the exhausts and the engine are only about 6" from the back of your head, behind a flimsy firewall. I like it, its like
russian roulette with pistons rather than bullets! 
If this post is out of context, its because i got bored with some of the detail of the above, and thought id post anyway!! 
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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Doug68
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| posted on 22/3/10 at 06:23 AM |
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quote:
Originally posted by cymtriks
Now look at a purpose designed transaxle. Often they are inverted (axle above engine input) which, with a small bell housing and low sump
The inverted units you refer to are Porsche G50 units which are way expensive. A lot of people myself included use Audi or Renault units which are
not run inverted. Hence the limiting factor on how low you can go is the bottom of the diff.
Also to run a low sump you're basically going to have to go dry sump, so to take advantage of the potentially much lower CG your going to have
to spend serious money.
You'll find most GT40's et all are not running dry sumps. On my car the sump protrudes maybe 1/4" beyond the bottom of the chassis,
but its the diff really thats stopping me from going lower.
The driveshaft angles at normal ride height are ~7 degrees which is fine IMHO.
Doug. 1TG
Sports Car Builders WA
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