Engine braking?
 

so i was talking to my buddy cam and he said that using your transmission to slow a third gen down instead of the brakes was bad for the motor?.. what do you guys think?

your friend is an idiot. downshifting isn't bad for the motor. if you go from 5th to 2nd while doing a 100km/hr. then yes that would be bad for it.

If downshifting is bad, then I am in trouble! lol

Are you sure you understood him correctly? It does put some additional wear on the clutch

I think he's referring to engine braking, which can be done in any manual transmission vehicle. It could decrease the life on your engine/transmission/clutch.

I always brake with my brakes, they're a lot cheaper to replace than the above.

I always use brakes too.

It takes too much effort to downshift before every corner, stop light, stop sign etc.

If i see a red light ahead and im cruising in 3rd @ like 30mph, ill drop to neutral and stop from 30 mph in neutral.

I rather change brakes than a clutch. Plus its much easier to just put to neutral and stop like an automatic. Granted i dont have to stop in a hurry.

Just thinking out-loud.........
Engine braking means that if your pre-mixing, the fuel is stopped and no lubrication for hard seals either. Even with a working OMP, I think oil injection is reduced. A little short term engine breaking and residual lubrication should still be available since it's not being burned away by a combustion event. But all things in moderation.

It's a gazoline driving style, with the big engine braking available ...

Now, never forget that a big turbo blabla setup can't make more Gs in accel than the brakes in decel. So, why using the engine to brake if it's that non-efficient ?

:scratch:
I am confused by this statement....

fuel never stops.... even if your at idle it is always being injected into the motor so lubrication is always there.

Please clarify as I maybe missing something in translation...:blush:

When I decel quickly, my commander says zero for inj. duty cycle. Doesn't last long, but there would be a brief time where rpm is still relatively high, but fuel (and lubrication) isn't being injected. Probably inconsequential, because that will also happen in between each shift. Except with engine braking, it typically lasts longer.

for more info, search for the "saving the whales, save your motor" thread, howard discusses how the omp and injectors work in that thread

My point had little to do with the OMP and I'm too tired right now to search his posts about fuel injectors.

Fuel is cut on deceleration until the rpms drop down near idle speed. Lubrication requirements are low though.

lol.. no i didnt understand him wrong he was talking out of his ass and he was blabbing on about the motor would be come unbalanced.. lol.. i definatley wasnt listening to him cause well.. thats garbage. the third gens have a counterweight attached to the flywheel to keep it balanced.. like a fluid damper for a older big block :P but.. in any case brake pads are cheaper then a tripple plate clutch from os giken :P so i use my brakes lol..

you will get better fuel mileage by engine braking. im not sure about the omp but since no fuel is being burned i would think there would be plenty of residual oil for the seals

I would love to see empirical evidence (e.g., a peer reviewed study) that compression braking causes meaningful wear to transmissions in cars. I would guess that any wear would be so far below the noise floor of normal wear that it would not be measurable. (And pads and rotors for many modern cars are not all that cheap, either.)

I absolute hate driving with someone who pops the car out of a higher gear when approaching a stop. It is sloppy driving. Good luck getting it back into the right gear again if you need to accelerate quickly for emergency reasons. In parts of the world with real driving tests, 2nd is the last gear you should be using before coming to a stop.

Engine braking for the win.

If you aren't using it you're a girl....and you should be driving a fuschia coloured Prius.

I never seen anyone who drives a manual not use the engine along with the brakes for deceleration. They certainly don't when racing. I think the slightly increased trans / clutch wear might be significantly out expensed by increased brakes wear.

There is absolutely nothing wrong with engine braking. It doesn't really wear down the clutch as much as people think and will nearly double the life of your front brakes. I find myself always down shifting when slowing down. Sure brakes are cheap but for me it's really about protecting the rotors. The less hot they get, the less they warp (especially in stop and go traffic).

well.. excuse my ignorance.. but dont race car drivers use both the transmission and the brakes when slowing down?.. hence the upgrades to the brakes and the driveline :P..

I'm gonna go ahead and say the downshifting race drivers use is mainly to be in the proper gear, thus, the proper powerband, for the next corner. But, of course, the engine braking does stop you a little faster.

nothing wrong with downshifting or engine braking. and its a hair bit better on gas mileage (downshifting causes an increase in vacuum and a decrease in INJ-D cycle) i suppose over a long span (say 100k miles) it would decrease the life of your trans. its also VERY good to do it if you need to stop fast. the addition of downshifting to braking will aid you in stopping faster if you need to avoid slamming into some asshole in daytime traffic.

I could see a little more wear & tear on the syncros, but that all depends on the skill of the driver. If you give them time and don't push them I don't think there would be any issue. The clutch gets a lot more action at takeoff than it will ever get downshifting. In the whole scheme of things, driven with some care I think it's a non-issue.

About racing ...

Your brakes are able (if not 90% worn ^^) to block your 4 wheels at high speeds. So the brake system is well designed to do his job : braking.

Why the hell would you interfere this precise braking with something more unpredictable like engine braking ? You just shift down when it's necessary. Engine braking is just a consequence, not something you try to use.

No offense to anyone here, but this is probably the most useless topic on here.

Simple driving rule:
Keep the car in gear as often as you can.

Explanations:
If you come up to a light and you keep it in gear as long as possible without changing down, you save fuel and brake wear. You're also cooling the motor internally. Think about it, you're cycling cold air without the heat of combustion. (Although this is minor)

If you downshift without rev matching, you're needlessly wearing out your clutch. (And making me sick)

If you downshift and blip the throttle, you're wasting gas. (But you're doing it the correct and fun way)
--------------------------
I personally heel-toe every downshift every time. It keeps me on top of my game and I stay familiar with my car.

Word of caution and advise. Part of the reason I heel-toe at all times(use the brake pedal while slowing) is because we live in a world of morons. If your car slows down but your brake lights don't light up, people behind you will enter stupid-mode like a miss-firing Honda enters limp-mode.

I also tap my brakes (like a racecar driver resets the line pressure) right before I start to brake. The only reason for this is to flash the brakes so people behind me wake up.

Just to add, on some corners the front end might require more grip while the car doesn't really need to slow down. In this case, sudden engine braking caused by a sudden lift off the accelerator would cause the weight to shift to the front without really slowing the car. This is most true on a lot of kinks.

Useless topic = long winded post ?

I just used the question to think about what happens to the engine internally during engine braking. Especially since I recently returned from some mountain driving and did it....alot. For that I didn't think it was useless.

Wasn't really long winded. Didn't take too long to post and got most if not all of everything related to engine braking covered.

Just wanted to get the point across that engine braking is so inconsequential to engine life that you shouldn't think about it.

In other words, don't worry about it, it's safe.

"Worry"? No. Inconsequential? Probably. But I think the rotary is different in this regard from a piston engine. I was hoping some of the experienced engine builders, Ihor, Chris/Banzai would chime in on the subject and confirm.

Well, I can't see how the two engines are different. I mean we're not talking about anything crazy or outside the normal for an engine. We are talking about an engine, just spinning, without combustion occurring. As far as the omp goes, I'm pretty sure the omp runs based on rpm not inj duty or throttle input.

Now if we are talking about a car running premix without an omp, then I would say extended engine braking may be more harmful than in other situations. I'm a big advocate of the omp. I think the only problem with the omp design is the substance that it injects into the motor. Engine oil is probably the worst thing, besides sand, that you could inject into any combustion chamber.

No four-cycle piston engines that I know of inject oil into the combustion chambers to lubricate rings and cylinder walls. No four-cycle piston engines that I'm aware of require pre-mixing oil into the fuel to take the place of removed injectors for that purpose.
It's rpm and load based.

I think all has been said ... :)

Referring to the OMP:

https://www.rx7club.com/attachment.p...1&d=1279727602

That's data on a Series 5 FC (which has an airflow meter), but it's the same basic concept

Slow your roll...
 

Wait a sec... "the hell" .. "precise braking" .. "unpredictable engine braking" .. "consequence" ??

Yeah... none of that makes sense.

It's downhill from my brother's house to the first stop sign. The car wouldn't have very "precise braking" after holding the brakes going down a mountain for a third of a mile.

The hill is why "the hell."

There's also plenty of other very steep streets in the Bay Area. In fact this planet's covered with hills. No, really, check. ;)

I was referencing this on the S6 Denso, but maybe I'm missing something......
https://www.rx7club.com/showthread.p...&highlight=omp

It's the same basic idea. I was just throwing that out there to showing some information directly from Mazda.

this

Well then in that case the issue I see is with cars that have had the omp removed.

I mean since the omp is apparently rpm and load based, then as long as it works I wouldn't figure any damage or irregular wear would occur.

Not necessarily.

It's a rotary, you'll be rebuilding it soon anyway :)

You've just forget the first words of my post : "About racing ..." :rolleyes:

lol so the only issue with engine braking is when your omp is removed.. so im curious to know if there are any studys done stating that it does put more wear on you motor when its removed... anyone?

Don't over analyze. Engine braking is part of engine operation...