Engine Braking without OMP
 

I've gone down the rabbit hole of engine braking with rotaries and it seems to somewhat of a solved issue: I've gathered that it's not really anything to worry about if you have kept the OMP. However, there's not really much advice or information on how exactly you're supposed to drive if you AREN'T running one.

I should start by saying I'm new to these cars and it's also the first manual transmission vehicle I've owned, but I have driven a few manual cars with piston engines. I was taught (and most seem in agreement) that you should keep the car in gear for as long as possible; then of course I run into the whole discourse surrounding engine braking with rotaries, and of course I'm not running an OMP. Naturally this raises some concern for me so I'm trying to get some deeper answers here. I know it's fine to coast in gear while coming to a stop, but at what point does it become harmful? What happens if I'm driving more aggressively and coast at 4k rpm? 5k? 6k? Do the track guys just deal with the increased wear, or do they have some trick up their sleeves to continue oil/gas flow while at 0% throttle? If so, is that something any Joe Shmoe can do, or does it require some insane custom modification?

I tried searching for existing threads on this topic, but most lacked the info I was looking for. Please let me know if there is any existing threads or info on this, as well as any advice or answers. Thanks

When you coast or slow down, the engine/fuel doesn't shut off, so if premix,
the engine is still being supplied with lubrication.

^That behavior depends entirely on what kind of engine management unit you're running, and how it's setup/tuned if it's an aftermarket unit. The OEM S5 FC and later FD/RX8 ECUs will cut fuel on deceleration from high RPMs under low load/high vacuum situations when the throttle is closed. Those OEM ECUs support the electronic OMP, which will still be delivering some oil during those situations, based on load (MAP) and RPMs.

My car is an 86/S4 running the stock ECU.

In that case, your OMP is mechanically controlled by the throttle. There's a linkage between the throttle and the OMP, so throttle closed = minimum (but non-zero) oil delivery; wide open throttle = maximum oil delivery. If you haven't deleted/blocked off the OMP, you won't have to worry about engine braking, as the engine will still be getting oil during decel conditions.

My OMP is blocked off though, which is my concern.

He's not running an OMP.

Put the OMP back on the car. You can still run premix with an OMP

Okay but in the hypothetical scenario where that's not possible then what would you do? Do you just not ever decelerate and instantly go into neutral every single time you slow down? Or do you just deal with the wear?

As stated early on, just premix.

I do, but on decel with 0% throttle there's no gas right? Hence no premix? I'm asking if that's something I should worry about for hard driving.

I read that thread already. One guy saying it's completely fine with nothing to worry about, as there is plenty of lubrication left over that isn't burned away when you aren't on gas. Another guy saying you should totally worry about it because all the lubrication will be forced out with no new oil coming in. Is this really just something that NOBODY knows for sure?

I wouldn't know, I run an OMP in the S5 TII and no problems for 35 years.
It's there for a reason.

I don't think there's going to be any useful information (as in, clear objective scientific data) on whether the wear incurred from decel fuel cut-off without an OMP is significant. Like most of these issues you're going to have people claiming it's no problem and other people claiming it killed their engine. Look at all the fuel pulsation damper threads; it's a similar situation.

My take on the situation is that the wear incurred during decel may or may not be significant, but it absolutely IS avoidable. Either retain a working OMP or deactivate DFCO in your ECUs settings. The problem in your situation as far as I can see is that you're on the stock ECU and have no option to deactivate the DFCO. So other than upgrading to a standalone that leaves you with two options: 1. Restore the OMP and don't worry about this ever again, or 2. Decide to be okay with the possibility of increased wear. To me option 1 seems to be the most logical, especially since OMPs aren't particularly hard to find or expensive. Even if you need new lines, they're only about $100.

I think this is the most coherent and actually somewhat helpful answer I'm gonna get. I'm planning on upgrading to a new ECU eventually anyway, so I'll keep that in mind.

How much engine braking are we talking about here? Simple downshifts to hit an apex of a corner? Coasting downhill of a mountain for 10 mins with the throttle closed?

-M

Unblock and restore your OMP system, problem solved.

^That would definitely make a difference - the latter situation is much worse than the former! If you ever do any driving in the mountains coasting downhill in gear is unavoidable fact of life. I'd hate to think of what my housings would look like after driving the downhill part of the Cherahola Skyway without a functional OMP system - about 20+ minutes of that drive on the downhill side is coasting in gear.

As much as you would have for track driving/racing applications. Not coasting downhill

That's not what I'm asking, obviously plenty of people remove or block off the OMP for some reason so I wanted to know if you should drive differently without it.

Why do people even remove the OMP in the first place if it's that bad?