Engine has stressed member

Hey.

Can anyone explain to me what makes an engine become a stressed member in a car´s chassis, any special design feature, casting, or can a motor stiff enough be used as part of the structure with no modifications?

Im a bit of a noob so any help woulbe good :)

Thanks

this is typically done in all top level single seaters, and some LeMans sports prototype cars, but only some of the latter.

The critical features are ensuring the head to block interface is solidly clamped, this is taken care of by the many head studs.

the second most critical feature is the sump to block interface, as well as the 10 studs on a 4cyl or V8......Top line IRL and F1 engines use what I would term laid-down dowels, about 10mm OD, 20mm long, the faces of the sump and face of the block have a valley cut to a depth of about 5mm using, a ball nose cutter, by the whole width of the main bearing journal, and the dowel is sized as a very close fit, the dowel is then laid in the valley, on its side, and the block and sump are bolted up.

once both of the above are done, the engine is considered very rigid, but careful attention needs to be paid how the chassis bending and torsional loads are fed into the engine into the sump and the cam covers, the cam covers need special care when designing too.......the chassis bending/bump loads are particularly bad

all F3 engines are fully stressed, and so are Infiniti pro-series V8's......they for me are interesting, as they are production derived blocks!

so to conclude

fully-stressed is when the engine is the only link to the rear of the car

semi-stressed is when a-frames are used, one either side, this is how the majority of LeMans cars do it

In many cases in a mid engined car with the engine acting as a stressed member the suspension loads are fed first into the gearbox and then through the engine into the chassis.

I believe I read that besides the things mentioned previously, the block itself has to be stiff enough to cope with these suspension loads being fed into it via the gearbox end and it into the chassis at the other, otherwise bore distortion can occur. I have also read that production blocks are rarely designed to be suitable for use as a stressed member.

Thanks that pretty much explained me what I wanted to know ;)

In many cases in a mid engined car with the engine acting as a stressed member the suspension loads are fed first into the gearbox and then through the engine into the chassis.

I believe I read that besides the things mentioned previously, the block itself has to be stiff enough to cope with these suspension loads being fed into it via the gearbox end and it into the chassis at the other, otherwise bore distortion can occur. I have also read that production blocks are rarely designed to be suitable for use as a stressed member.

Pheonix is correct, this is why the Infiniti and F3 engines are most interesting.......bore distortion occurs in an engine due to a number of reasons anyway, cylinder pressures, head stud torques, clamp loads etc......F3 engines are very clever as the cam covers and sumps are literally beams that are bolted to the engine......the sumps are the same width as the chassis.......and the cam covers are very tall near the front.......all in order to better link the gearbox to the chassis and reduce bending and twisting forces.......as well as suspension loads.......bump loads are the killer, I'm told 7g is a typical figure that you must be robust against

Just remembered........AER did it with the Nissan world series engine too......an alloy 3.5L V6 in the back of a Dallara........and Renault / Mechachrome / Heini-Mader did it with the BMW V8 alloy block in the back of the GP2 single seater.......using production blocks does work, just carefully.:cool:

I believe the F3 engines are only semi stressed with very basic subframes either side of the block and structural cam covers and sumps.
I always though that you need a v-form or 180 deg V (eg ferrari flat 12) to achieve a stiff structure without causing all sots of internal engine problems due to flexing

Did you blokes see the diagram of the Audi R10 chassis (including engine/box) stiffness in the latest RCE?

Didn't Renault have to use A-frames with their 110 degree V10 a few years ago? I think it would be near impossible for a flat engine to be fully stressed. The Mercedes C291 flat-12 also used subframes no? (the V-engined 3.5 liter protos it competed against all had stressed engines). Was the "Willman"-IES 120 degree V6 stressed?

I don't think Porsche ever made a stressed flat engine...

If you look carefully at this picture of my Huron (1971) in F II trim (Atlantic) using the first Twin Cam engine, the engine was indeed a pretty much stressed component.

The tub finished in a thick Dural bulkhead plate behind the roll bar and apart from the Upper and Lower trailing arms, all loads between the Dural Bulkhead and the transaxle, including the rear subframe assembly which carried the suspension (i.e. wishbones and coil spring/dampers) were taken out through the engine.

Some load was taken out - from memory - by side members, attached to the usual Ford engine mounting points and back to the bulkhead.


http://i74.photobucket.com/albums/i278/Michaeleff/HuronBrands72.jpg