suganuma

Brian, the guys up top are correct. The problem with detonation is the speed in which the combustion of the fuel is taking place. It IS much quicker and uncontrolled and when the "true" spark comes into play, then you have the problem of the 2 flame fronts (shockwaves) hitting each other. btw, all of this is disclaimed by an IIRC clause



Obviously in a turbo motor, these pressures will always be greater, but i dont see how it will really be much different than in a piston motor - s reading there should be relevant to however you want to carry out any further research. I mean, gas burns like gas no matter if piston or rotary.

Travis R

OK I looked up the graph in the book. It didn't give any numbers but the picture said enough... the explanation from a professor with a doctorate in M.E. helped too.

Like j9fd3s said it is the pressure waves that causes the problems. In a normal burn there is no localized pressure from the fuel-air mixture. When a knock occurs the pressure wave bounces back and forth in the chamber causing the mixture to localize and creates much higher than normal pressure.

In some conditions the wave will burn so much hotter that it will change the properties of the material. That's how you burn a hole through a piston.

Here's my ghetto MSpaint version of the graph.

BDC

Ah, a thread back from the dead...

j9fd3s

i remember it!

GMON

Nope, its 30k psi pushing the side of the housing away from the rotor. Since the dowel sitting in crappy cast iorn is the only thing holding it in place it pushes untill it hits the bolts.



Also, the front has the threads for the bolts where the back has about an 1/8" of play. Mind you the bolt is tight but if you want to see just how tight take a punch and a good sized hammer on a junk engine and hit the bolt squarely. Youll be supprised how far it will move.





And to make this all crystal clear try this one, put 500lbs on a 4X4 settin on your garage floor. Get a hammer and hit the block of wood. You will be supprised at how easy it is to move.



Same priciple in the housings. Only thing stoping them is the dowels and thats why they break there.



I have never seen or heard of one breaking on the exhast side. Why? Becuse its not the compression side.

Its a pretty mellow place compared to the other side of the engine.





I think the reason maza kept moving the engine mounts back was to move the weight of the engine more to the center of the car. Instead of moving the engine back they just moved the mount.

j9fd3s

the stated reason for moving it from the front (pre fc) to the FC spot was to cure a resonance at 3000rpms? rpms, i have heard it, but its really not that noticeable, and the fc has one thats worse around 3200rpms.



could be just as easily to fit the steering rack too.



i dont know about the fd mounts, i dont recall seeing it mentioned anywhere.



but it also seems that the hp goes up the mounts move further back, maybe its not a big deal

PDF

A week ago I managed to crack a s4 rear plate, Stock engine/turbo on 10psi. The secondary injectors failed and it went lean. I believe this problem is definately knock related and does not need to be a high hp engine.

heretic

The FD mounts were most likely moved back in order to balance the engine/transmission assembly on the motor mounts, since the PPF holds the pitch angle motion in check.



If the FD had the front or middle motor mounts, the engine would have a strong tendency to pitch backwards, putting a downwards beaming load on the PPF.



Then, under acceleration, the diff would put an upwards beaming load on the PPF.



Cyclical reversal of forces is EXACTLY how you break things. It's much gentler to have a force in one direction that gets weaker and stronger, versus a force that changes direction.