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Engine braking?

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Old 07-20-10, 07:24 PM
  #26  
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Originally Posted by Vell
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.
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.
Old 07-20-10, 07:50 PM
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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.
Old 07-20-10, 08:07 PM
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Originally Posted by Sgtblue
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.
Old 07-20-10, 08:19 PM
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"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.
Old 07-20-10, 08:31 PM
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Originally Posted by Sgtblue
"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.
Old 07-21-10, 07:11 AM
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Originally Posted by Rotors R Cool
Well, I can't see how the two engines are different.
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.
Originally Posted by Rotors R Cool
I'm pretty sure the omp runs based on rpm not inj duty or throttle input.
It's rpm and load based.
Old 07-21-10, 10:28 AM
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I think all has been said ...
Old 07-21-10, 10:54 AM
  #33  
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Referring to the OMP:

Originally Posted by Sgtblue
It's rpm and load based.


That's data on a Series 5 FC (which has an airflow meter), but it's the same basic concept
Attached Thumbnails Engine braking?-s5_omp_logic2.jpg  
Old 07-21-10, 11:24 AM
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Slow your roll...

Originally Posted by Vell
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.
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.
Old 07-21-10, 11:27 AM
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Originally Posted by arghx
Referring to the OMP:
That's data on a Series 5 FC (which has an airflow meter), but it's the same basic concept
I was referencing this on the S6 Denso, but maybe I'm missing something......
https://www.rx7club.com/showthread.p...&highlight=omp
Old 07-21-10, 01:34 PM
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Originally Posted by Sgtblue
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.
Old 07-21-10, 04:01 PM
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Originally Posted by Rotors R Cool
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.
this
Old 07-21-10, 04:15 PM
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Originally Posted by Sgtblue
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.
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.
Old 07-22-10, 05:51 AM
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Originally Posted by Rotors R Cool
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.
Old 07-22-10, 06:10 AM
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It's a rotary, you'll be rebuilding it soon anyway
Old 07-23-10, 10:37 AM
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Originally Posted by juicyjosh
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.

You've just forget the first words of my post : "About racing ..."
Old 07-23-10, 08:53 PM
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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?
Old 07-24-10, 10:26 AM
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Don't over analyze. Engine braking is part of engine operation...
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