Engine selection based on chassis dynamics
Engine selection based on chassis dynamics
(OP)
I'm stuck in a hard place. Both the 13B Renesis (Mazda rotary) and EJ25 (Subaru boxer) are accredited with lightweight and low center of gravity. The weight differences (based on what I've found) are marginal from each other, both roughly 260LBs but I think the long block of the EJ would have a lower center of gravity but since the easier packaging of the 13B you could mount the turbo low down and make custom brackets to hold the accessories lower as well would would probably make it have the same CG of the the EJ (this is all theory in my head).
Then I started thinking about moment of inertia, since the EJ spreads further out towards the sides then it would help the car resist the temptation to roll while the compact 13B in the center of the chassis would have a lower MOI so it wouldn't help resist roll at all. This might be a deciding factor, but it could also be a marginal effect not worth considering. Based on a 2100LB car with 50/50 L/R and 40/60 F/R, what would you think about this MOI theory?
Can you think of any other considerations besides torque/horsepower differences?
Then I started thinking about moment of inertia, since the EJ spreads further out towards the sides then it would help the car resist the temptation to roll while the compact 13B in the center of the chassis would have a lower MOI so it wouldn't help resist roll at all. This might be a deciding factor, but it could also be a marginal effect not worth considering. Based on a 2100LB car with 50/50 L/R and 40/60 F/R, what would you think about this MOI theory?
Can you think of any other considerations besides torque/horsepower differences?





RE: Engine selection based on chassis dynamics
then cgz
then cgx
roll MoI ranks about equal with color IM()O
Cheers
Greg Locock
I rarely exceed 1.79 x 10^12 furlongs per fortnight
RE: Engine selection based on chassis dynamics
RE: Engine selection based on chassis dynamics
RE: Engine selection based on chassis dynamics
The rotary engines are not particularly easy to package, either, since they are practically as wide as a boxer engine. Inline engines, and to a lesser extent V engines, can carry their manifolding up high to clear framerails and steering mechanism. Rotaries do not have that option.
RE: Engine selection based on chassis dynamics
Regards
Pat
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RE: Engine selection based on chassis dynamics
RE: Engine selection based on chassis dynamics
Norm
RE: Engine selection based on chassis dynamics
It still seems like noise.
Norm
RE: Engine selection based on chassis dynamics
In a motorcycle, that initiates a turn by first pivoting in large-magnitude roll along a longitudinal axis before actually starting to turn, it's a different story and a narrow, compact engine with its mass concentrated closely around the center of gravity (think Ducati across-the-frame V-twin) ought to have some advantage over an engine with its mass sticking way out past the bike (think BMW flat-twin or Honda Gold Wing flat-six with cylinder heads projecting way out into the breeze).
In a car ... it just isn't going to matter much.
RE: Engine selection based on chassis dynamics
For a different example, on a VW Golf-chassis vehicle, the crank centerline isn't much different in height from the diff (the oil pan is pretty low to the ground, which has its own set of disadvantages) and I know the engine is leaning significantly backward, which gets the weight of the cylinder head back towards the firewall and not as far ahead of the front wheel axis.
RE: Engine selection based on chassis dynamics
MoI car ~1000*1^2 =1000
MoI engine ~150*.4^2=24
MoI engine that is 25% more compact 150*.3^2=13.5
difference in response frequency of car =1-sqrt(oldMoI/NewMoi)= 1/2%
So, if the weight transfer took 100 ms with the fat engine, and 99.5 ms with the thin one, who (a) cares and (b) even knows which is better?
Cheers
Greg Locock
I rarely exceed 1.79 x 10^12 furlongs per fortnight
RE: Engine selection based on chassis dynamics
RE: Engine selection based on chassis dynamics
Subaru places their steering beneath the drivetrain, so by necessity the drivetrain has to sit rather high. This may be why they don't seem to concerned about having a shallow sump or close-fitting exhaust - the engine has to sit that high anyway, so why not take advantage of it? Audis, on the other hand, have the steering mounted high, and the drivetrain is slung beneath it.
Interesting that the two-cylinder-long engine in my ex-Subarus held 4.5 quarts of oil, while the five-cylinder-long engine in my Audi product holds one quart less.