Technical Q. What forces affect engine braking?

[OreoGaborio]

A thread on another forum was talking about the "Euro ECU" for the 00-02 zx6r (carbureted) and one rider who had the mod said he thought he noticed it reduced engine braking.... & that kinda surprised me so I started thinking about it... how could an ECU on a carbureted bike reduce engine braking?

As far as I can see, engine braking is affected by 3 main things... internal friction, linear inertia (big pistons moving up & down, changing direction 180 degrees) and to an extent, compression.... 4 if you include a high idle setting.

So... that's the question... what other forces affect engine braking & how could an ECU on a carbureted engine reduce engine braking?

[Wishbone]

exhaust back pressure. if the kawi has some sort of electric exhaust valve

[Paul_E_D]

I think it can cut power to two cylinders and/or somehow dump the compression effectively halving the engine braking. I belive some bikes come from the factories this way. Ducati 620s come to mind, and Ive heard of race teams using ECU controlled engine braking systems. Not sure if the kids info is BS or not...

[TheIglu]

If it changes the timing of the engine to an earlier spark you could see a reduced engine braking if my mind is telling me correctly......

The engine is still running during deceleration, if the engine is being forced to spin faster than the combustion cycles dictate then the firing of the idle mixture would dictate how much of the engine's non-running braking action is slowing the bike. While the power cycles are not enough to make the bike accelerate, it still will make more power (less engine braking) than a bike that has later spark. Think about it, they advance the spark to get a more powerful and complete burn when accelerating, why wouldn't that take place during deceleration? RPM's are still there, ECU doesn't know if you are on the throttle or not.....I'm better it's because it is a more advanced ignition curve.

[TheIglu]

To sum up what I said:

If the Euro ECU has a different spark timing (ignition) curve, I'm willing to bet that is what is causing the change.

[zx1012r]

It could still be spraying fuel at 0 throttle opening.

My 2000 ZX12 was jerky between off-on throttle. The stock ECM turns the fuel off at 0 throttle above 2,000 rpm. The fix with a PCIII was to either move the throttle position sensor, or up the idle slightly so the ecm never sees 0 throttle.

That definately affected engine braking.

Mark Dages

[Wishbone]

that would make sense. i just advanced my timing over the winter and it seems to have more engine braking, i thought i was imagining it because i didn't ride my bike for a few months

[TheIglu]

It could still be spraying fuel at 0 throttle opening.

My 2000 ZX12 was jerky between off-on throttle. The stock ECM turns the fuel off at 0 throttle above 2,000 rpm. The fix with a PCIII was to either move the throttle position sensor, or up the idle slightly so the ecm never sees 0 throttle.

That definately affected engine braking.

Mark Dages

Being that it's a carburetor, I'm thinking not.

I'm willing to bet that the cylinder timing being advanced is reducing the amount of cavitation post-combustion, hence making the braking force less than it normally would be.

[zx1012r]

Didn't you know I only read half of any post? I'm married and it's like listening to the wife ;-)

Maybe they increased the rear ride height and now it is going down hill more.

[TheIglu]

Didn't you know I only read half of any post? I'm married and it's like listening to the wife ;-)

Maybe they increased the rear ride height and now it is going down hill more.

I bet you think your racebike has EFI and that's why you are so fast

[OreoGaborio]

you guys crack me up.

btw, yes, this euro ECU does in fact supposedly advance the timing... interestingly enough though, the timing can also be advanced with these kinda things... didn't think the ECU could advance the timing as well

On a side note, some kid on the same forum has both the euro ECU and a regular timing advance kit... a dyno showed a REDUCTION in power w/ both installed.

[Paul_E_D]

You would need less advance to decrease engine braking...

[TheIglu]

didn't think the ECU could advance the timing as well

So what exactly did you think the ECU did on a non-fuel injection bike? Sit there and look pretty?

Timing is the ONLY thing it does Pete

[Degsy]

You would need less advance to decrease engine braking...

Yes, it would need to be retarded...somewhat like this thread.

[TLRMan]

A thread on another forum was talking about the "Euro ECU" for the 00-02 zx6r (carbureted) and one rider who had the mod said he thought he noticed it reduced engine braking.... & that kinda surprised me so I started thinking about it... how could an ECU on a carbureted bike reduce engine braking?

As far as I can see, engine braking is affected by 3 main things... internal friction, linear inertia (big pistons moving up & down, changing direction 180 degrees) and to an extent, compression.... 4 if you include a high idle setting.

So... that's the question... what other forces affect engine braking & how could an ECU on a carbureted engine reduce engine braking?

Dude...it isn't braking due to compression, it's braking due to vacuum....
Chances are there is a valve that gets opened that bleeds more air into the system....Check out the new FI bikes. I think the New Honda 600 has it.

[RandyO]

plain & simple, engine braking is cause by trying to pull air thru closed throttle plates

easiest way to reduce engine braking is too turn the idle up, it opens the throttle plate slightly

[TLRMan]

Didn't I just say that?....

Oh! Do I have my invisible button on again?

[SVRACER01]

Dude...it isn't braking due to compression, it's braking due to vacuum....
Chances are there is a valve that gets opened that bleeds more air into the system....Check out the new FI bikes. I think the New Honda 600 has it.

that makes sense since when you do a negative HP test on the Dyno the throttle has to WFO with the kill switch "off".

[Paul_E_D]

OK, vacuum. Why does a twin engine brake so much more than a four? Or for that matter, what about a 2 stroke? There's still a closed throttle on those...

[13]

OK, vacuum. Why does a twin engine brake so much more than a four?

Good question, but does it really? Maybe it just feels like it? My 1000rr feels to engine brake just as much as my old superhawk, at least I think...

[RandyO]

Didn't I just say that?....

Oh! Do I have my invisible button on again?

I'm getting blind, I only saw the part about a valve that introduces air


isn't a jake brake just the opposite, a valve that closes/restricts the exaust

[TLRMan]

OK, vacuum. Why does a twin engine brake so much more than a four? Or for that matter, what about a 2 stroke? There's still a closed throttle on those...

Twins = 2 big holes , I4 = 4 smaller holes, internally now days, they punch holes between the cylinders to reduce pumping losses, which even decreases it more.


2 cycles...
You got a one helluva exhaust port that's exposed every time the piston decends....so it doesn't matter what the carb is doing....

Are we being tested here???

[highsider]

Boys have a penis, girls have a vagina.

Oh, wait a minute....

[TLRMan]

Boys have a penis, girls have a vagina.

Oh, wait a minute....

You perv!

[rolker]

A jake brake on a sport bike... would probably make it sound like a HD!