Stressed vs. Non-stressed Engine/Gearbox

NewyorkKopter · 06-08-2006, 07:48 PM

Hey, you know how some supercars have the engine bolted directly to the chassis? What are the advantages of doing that? Also how come some cars like the F50 have it while others like the McLaren F1 don't?

Moppie · 06-08-2006, 08:03 PM

In the case of the F50 it was a good marketing trick.
The Mclaren was a little more converntional, it also used an engine from another manufactor, that possibly wasn't able to surport the weight of a road cars ass.

By useing the engine and gearbox as part of the chassis, you do away with those parts of the chassis, and so save weight.

UncleBob · 06-09-2006, 12:26 AM

the engine/tranny/drive train is a rather large solid chunk of metal that is very rigid. If you incorperate it into the frame design, it will make the frame more more solid without adding any material to the frame.

Where as a rubber mounted drive train is the opposite. The frame has to be boxed in and reinforced to deal with all that weight and torque movement acting apon it, so the frame will be much more substantial. The advantage to rubber mounting is less vibration transmitted to the frame, which will not only make the car more creature friendly, it will also reduce metal fatigue.

Motorcycles, for example, use the engine assembly not only for a large portion of the frame, but in some examples will also make it the pivot for the rear swingarm and base for the front steering assembly. One of the most extreme built in this way was a race bike made by John Briton. It literally had no frame, everything was built off the engine/tranny assembly.

NewyorkKopter · 06-09-2006, 06:07 AM

o, so thats why the F1's chassis is so long at the back, while the F50's just stops infront of the engine. I was looking at the F50's engine and the R390's engine...the F50 has two rods connecting the chassis to its rear subframe, while the R390 has to rods cennecing the chassis directly to the engine. Is there any reason why one's bolted to a subframe while the other's bolted onto the engine?

Also how come car's like the F50 have only two connecting rods from the chassis to the subframe while others like the Koenigsegg have like 6? and just one more thing, can you use a stressed engine layout with a tubular chassis?

NewyorkKopter · 06-14-2006, 02:01 PM

yea so why do some manufacturers bolt the chassis on to the engine, while others do it to the subframe?

drunken monkey · 06-14-2006, 03:47 PM

packaging and space involved.
it's common sense.

NewyorkKopter · 06-15-2006, 07:21 AM

oo, I thought it was for performance reasons. Thanks for that

drunken monkey · 06-15-2006, 07:47 AM

in a sense.... but in a round about way.

the less metal there is, the less weight there is and hence the faster you can go.
however, in some race formats, some things are regulated such as air intake sizes, power figures and whatnots. all of this means that there is an optimum size for things that you can use which in turn means that there is a minimum weight you can aim for
i.e if you don't need a bigger heavier turbo, then use the smaller lighter one.

in the case of road cars, there are no such regulations so the packaging can be different and there is not the need for extra lightness.

looking at the R390 model, i can see that the engine of the 390 actually sits on/in the bottom half of the semi-monocoque. as far as i can remember, the engine on the F50 is bolted onto the back of the F50s.
this difference goes to explain why both cars use members at different locations; to prevent twist in certain directions.

NewyorkKopter · 06-15-2006, 09:12 AM

oh true. Doesn't the R390's engine sit on the underbody? Because with the Sauber C9, the Engine sat on the underbody, and the area which it sat on was covered in aluminum.

drunken monkey · 06-15-2006, 02:38 PM

underbody=the bottom half of the semi-monocoque

look for details of the ferrari 365 GT boxer or miura and see how that was made.
essentially, it is a shell type structure that is also rigid and acts as both body and chassis.

NewyorkKopter · 06-16-2006, 08:39 AM

oh, so once the underbody is bolted to the chassis, they both act as one piece?

drunken monkey · 06-16-2006, 10:43 AM

not quite but yes the underbody IS part of the chassis.
it's basically a shell that is structurally rigid.

technically, a monocoque is a strutural shell (simplified description); think egg where there are no other structural elements apart from the shell itself.
a semi-monocoque is a shell that has secondary structural elements such as ribs along the inside or a strut across the top.
(so yes, it is the underbody attached to the frame - but really, they are both designed as one so it's not just an arbitary attaching of shell to a frame)

NewyorkKopter · 06-16-2006, 03:23 PM

true. But even though the underbody/semi-monoque and chassis/monoque are designed as one piece, they come as two peices which have to be put together to function as one piece right? Also can you use a stressed powertrain layout with a tubular chassis?

UncleBob · 06-16-2006, 04:18 PM

most race cars are tube frames that the drive train is hard mounted.

drunken monkey · 06-16-2006, 10:17 PM

not quite.
the monocoque will start life as more than one piece, yes
but it isn't like a structural frame attached to an underbody.
the secondary elements are designed to make the part-shell rigid.
without the shell there, these elements might not actually do anything.

like i said, it is a single thing that is designed at once.
it isn't simply putting a shell/underbody onto a tubular frame, although the end results usually looks like it is.

**chasing them typos**

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