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I have a silly little idea for a car involving moving the engine to the back (FF or FR, into a RR). I know it sounds silly, but silly ideas are just how I seem to run. I simply don't see the fun in placing a v8 in something or chasing milliseconds of time like my dad.

However, my main concern is affecting the crumple zones of the car (in placing the engine in the rear, low down for centre-of-gravity as well as a few other reasons, the spare tyre/fuel tank area will be partially cut out. I am also concerned that some cars may design the crumple zone with the intention of there being a solid engine, and thus maybe crumpling TOO much when it's removed?)

So, how do you know what's the strong zone and what's the crumple zone? Especially given that every model of car will be different... I know parts that are meant to be strong can be reinforced to compensate (especially given it'll be a small engine and I'll likely only be removing the spare tyre hole?) but anything that is specifically designed to be a precise weakness is something I don't wanna touch with a 10 metre pole!

To recap:

Engine removed from front of car

Spare tyre well cut out, and maybe some cutting where the fuel tank was for the differential?

I wish to retain factory-like safety. Exact car unknown as of yet but will be late 90s-early 00s

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2 Answers 2

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The crumple zones are designed to accommodate how the engine/gearbox move towards or deflect around the passenger volume.

If you change the position of the engine/gearbox then you will need to consider how that will happen in the "new" configuration. How will the chassis rails, or equivalent, behave when supporting the mass they were not originally designed for? If you strengthen them, then were and how much strengthening will be required? How will those strengthened areas "crumple"?

Similar things have been done in the past, an example was a RangeRover chassis had the front axle placed where the rear axle was ie front/rear swap so the "Rangie" was now rear engined. Then a TR7 (iirc) body was mounted on top. Looked great and the "real" chassis provided the strength.

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You airbags are triggered by accelerometers. The signal these see may be affected by the removal of the engine, although given anecdotes of hooligans setting them off with baseball bats perhaps that is me being over-careful.

The engine itself forms part of the crash load path, in some cases it is designed to slide down and then elegantly under the floor, in other cases it crashes back into the firewall. I can't see a huge downside in removing the engine from that path, as more crumple distance is a good thing, but you are venturing into the unknown.

With rear impacts you have 'shorted out' much of the crumple zone but added a fairly significant mass, things will be worse I think, unless you can arrange the elegant sliding arrangement.

I'm not a crash guy but have done a bit of it now and again.

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