hcaulfield57

iTrader: (1)

I apologize if this has been covered before, but it's something I've been questioning for awhile now.

Secretly, I find vintage Saabs very interesting, especially the two-stroke variety. Maybe it's the quirkiness, the Swedish-ness or simply the fact that Saab two-stroke engines sound similar to rotaries. I've been reading about the Saab 96 in particular, which included a freewheel on the transmission. For those that aren't familiar, a freewheel disconnects the engine from the transmission when the transmission speed exceeds the engine speed. Meaning these transmissions have no engine braking. The reason why Saab included a freewheel was to prevent high-rpm, low-throttle usage on their two-stroke engines during engine braking which would destroy the engine from oil-starvation.

My question: is prolonged engine braking dangerous for Wankel-style rotary engines? As we all know, the engine oil is used to lubricate the outer surface of the rotors and the various seals on the rotor. Do the engines get less oil when the throttle is closed, but the engine is at a high rpm, for instance coasting downhill? I've wondered about this for awhile, and can't answer the question myself. To my knowledge, the Saab 96 did not include any sort of OMP, and gasoline at the time could be found premixed from the station. What am I missing?

Thanks for reading!

misterstyx69

iTrader: (142)

My thought would be that on the S4 the omp is mechanical so as long as the engine is running it is getting oil.
S5 is electrical and If it is not working then the engine goes into limp mode so it must to a degree inject oil anyways.
Coasting and off throttle are sparatic and would not really hurt the overall injection of oil to internals and the Time that the engine doesn't see any lube(if at all) should not hurt the internals since the time is so minimal that the oil injected already should still be lubricating the internals until they get another shot of oil injected when you go back on throttle.
FD?..dunno.,.,can't afford one,so I don't care..hahhahhaha!

peejay

This is a LARGE reason why racers who premix will set their idles far higher than required and tune the idle circuits to be far richer than required. Bridge ports don't need to idle at 2500rpm but if the minimum throttle position is cracked open that far, the engine won't "oill starve" at high RPM off throttle.

With EFI you can just throw all the fuel in the world down the gullet when at closed throttle. This also cuts down immensely on backfiring, makes exhaust systems last a lot longer!

j9fd3s

iTrader: (3)

here are the oil pump "maps" for the mechanical S4 and the electronic S5. these are from an SAE paper, happily these fun little engines are actually very well documented.

hcaulfield57

iTrader: (1)

Okay, so it looks like the OMP is the difference here. So the amount of oil distributed is based on engine speed, and not just on air/fuel intake?

So would prolonged high-rpm / low-throttle be a real problem on an engine with the OMP removed / disconnected and oil premixed into the gasoline?