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Discussion Starter · #1 ·
Apologies if I am being thick here, I have realised that I do not know how the engine brake works on the AT. Many engine brakes I have come across have a means of varying the valve timing to turn the engine into a compressor or a mechanical exhaust brake, admittedly most of these arrangements are diesel engines. As far as I can see the AT has relatively simple camshaft drive and valve gear arrangement so I can't see how the retardation has three variations according to the selected mode or what the mode selector actually does.

I would be grateful is one of the experts out there could enlighten me please?
 

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Apologies if I am being thick here, I have realised that I do not know how the engine brake works on the AT. Many engine brakes I have come across have a means of varying the valve timing to turn the engine into a compressor or a mechanical exhaust brake, admittedly most of these arrangements are diesel engines. As far as I can see the AT has relatively simple camshaft drive and valve gear arrangement so I can't see how the retardation has three variations according to the selected mode or what the mode selector actually does.

I would be grateful is one of the experts out there could enlighten me please?
I’m no expert but was told by someone who also was not an expert that to decrease the engine braking Honda ‘hold open the butterflies’. Does this make sense? I test rode the bike with engine braking last week and found the difference between the levels very subtle but I also now believe that all 3 of them provide less engine braking than on my 2017 bike. But this is entirely subjective and probably wrong
Mike
 

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I've been told the same thing - tickover is effectively increased slightly in higher 2 settings. I assume some electronic jiggery pokery too! (Hmmm....what will our transatlantic cousins make of that phrase!). Pretty sure this has come up before on this forum. Only changed mine coming down a steep and barely surfaced track in snowdonia recently....not sure if it made a difference but I did try descending with out using brake, as per off-road course I did a coupla years ago.
 

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Not sure about the tickover being altered. This is my understanding.
Engine braking is caused by the work required to pull the piston down against a vacuum. This occurs on the induction stroke with the inlet butterflies closed. So if you have 3 settings it means the butterflies have 3 positions when shut - or nearly shut . So for least engine braking they will be open slightly to create less vacuum,The work done is drawing air (no fuel) past the almost closed butterflies.

Get a cycle pump and put your finger over the end and pull it open - the resistance you feel is what we are talking about.
 

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Throttle by wire gone amok! On the 17 the throttle butterflies are directly connected to the twist grip so engine braking closed throttle is fixed.
With electronics the servo motor can open the butterflies with no fuel injection and thus vary the perceived amount of engine braking.
What's the point? I don't see the necessity.
Why do Engineers do stupid sh!te like this? a) because marketing asked for it. b) because it's possible.
 

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Throttle by wire gone amok! On the 17 the throttle butterflies are directly connected to the twist grip so engine braking closed throttle is fixed.
With electronics the servo motor can open the butterflies with no fuel injection and thus vary the perceived amount of engine braking.
What's the point? I don't see the necessity.
Why do Engineers do stupid sh!te like this? a) because marketing asked for it. b) because it's possible.
Well I am used to driving vehicles with no engine braking (my auto car and my Triumph Rocket3), and I much prefer it - I wish they had provided another couple of levels of adjustment on the Africa Twin.
Mike
 

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The absolute best technique for stopping a motorcycle the quickest is clutch in & apply both brakes hard, & if your motorcycle has ABS even better.
 

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The absolute best technique for stopping a motorcycle the quickest is clutch in & apply both brakes hard, & if your motorcycle has ABS even better.
Unless you are on gravel - then ABS on the rear needs to be off or you will skip-hop along for a long way...
 

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Well I am used to driving vehicles with no engine braking (my auto car and my Triumph Rocket3), and I much prefer it - I wish they had provided another couple of levels of adjustment on the Africa Twin.
Mike
When I wrote the 2017 AT (standard) had fixed engine braking because throttle butterflies are cabled to the twist grip - I should have said it is excellent engine braking. Little need for braking in city riding or on trails to slow down unless you need to scrub speed quickly.
Simple is better.
 

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When I wrote the 2017 AT (standard) had fixed engine braking because throttle butterflies are cabled to the twist grip - I should have said it is excellent engine braking. Little need for braking in city riding or on trails to slow down unless you need to scrub speed quickly.
Simple is better.
Depends whether you want comfort or speed. If you like driving hard then having high engine braking is probably a good idea, but for me the constant slamming backwards and forwards is just tiring. So surely it's better for us to be able to choose how much engine braking we want?
Mike
 

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Depends whether you want comfort or speed. If you like driving hard then having high engine braking is probably a good idea, but for me the constant slamming backwards and forwards is just tiring. So surely it's better for us to be able to choose how much engine braking we want?
Mike
That's what the throttle is for - feather it for light engine braking, close it for more. I do understand people like the ability to tune a bike to their needs and throttle by wire allows for a lot of electronic wizardry. I just wish Honda would spend a few bucks on the suspension instead of electronic stuff.
 

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Depends whether you want comfort or speed. If you like driving hard then having high engine braking is probably a good idea, but for me the constant slamming backwards and forwards is just tiring. So surely it's better for us to be able to choose how much engine braking we want?
Mike
That's what the throttle is for - feather it for light engine braking, close it for more. I do understand people like the ability to tune a bike to their needs and throttle by wire allows for a lot of electronic wizardry. I just wish Honda would spend a few bucks on the suspension instead of electronic stuff.
I’ve heard of feathering the clutch but never before heard of feathering the throttle. It’s so sensitive at the bottom end, I doubt I’d be able to control engine braking via the throttle. And wow - it just shows how difficult it is for Honda to cater to all tastes because the reason I’m buying another Africa Twin is mainly because I think the suspension is just brilliant.
Mike
 

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Discussion Starter · #13 ·
I wasn't questioning the benefit of engine braking, I only asked out of curiosity as to what was actually going on in the engine. As we know, trucks fitted with the old type exhaust brakes worked by the compression of the exhaust being released to the inlet on valve overlap at the end of the exhaust stroke. The compression stroke had no effect as after TDC the resultant cylinder pressure acts pushing the piston down. Other variants (ie Jacobs brakes etc) change the valve timing, effectively turning the engine into compressor. If the AT only works by closing the inlet butterfly, I could be wrong, but if this is the case, it seems little more than a token gesture.

I am sure there is a Honda technician out there that will answer my curiosity.
 

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I was under the impression that exhaust brakes on trucks are only fitted to those with diesel engines, which are not throttled (no carburetor blades, no intake vacuum). The closure of the exhaust path increases the backpressure, which has the same effect as closing the intake blades. But I could be mistaken.
The Honda variable engine braking feature can only work by keeping the throttle blades open a small amount, which would reduce the braking effect. It would appear that this may be beneficial in repeated very low-speed, small-throttle-movement circumstances, to smooth out the jerkiness.
 

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I was under the impression that exhaust brakes on trucks are only fitted to those with diesel engines, which are not throttled (no carburetor blades, no intake vacuum). The closure of the exhaust path increases the backpressure, which has the same effect as closing the intake blades. But I could be mistaken.
The Honda variable engine braking feature can only work by keeping the throttle blades open a small amount, which would reduce the braking effect. It would appear that this may be beneficial in repeated very low-speed, small-throttle-movement circumstances, to smooth out the jerkiness.
Presumably if this is what Honda are doing they could only open the butterflies when the throttle was fully closed (otherwise they knock their Euro emissions figures for 6 even though there would be modes where they would still be compliant)?
Mike
 
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