My current bike is a 2014 Breakout. My last bike was a Honda VTX 1800. I've noticed a MAJOR difference in engine braking on the two engines, and wonder why.

For anyone not familiar with the terminology, "engine braking" is the "braking" that occurs when you shut the throttle while the bike is in motion, and you leave the clutch in its "drive" versus "disengaged" position.

What happens when you do that is the engine, instead of being a "power source", becomes a "braking pump", as the piston movement on the intake stroke with a closed throttle acts as a vacuum pump trying hard to suck 1695/2 cubic centimeters of air past the closed throttle valve, and getting slowed down in the process. Since the engine is still connected to the rear wheel, it naturally slows down or "brakes" the bike.

On my VTX 1800, engine braking was VERY strong. Basically, I didn't need to use the brakes to slow down and stop for a traffic light - I just needed to close the throttle, and then disengage the clutch just before the bike came to a stop (so it wouldn't stall).

On the Breakout, engine braking is very, very mild. More like a coastdown with only mild drag on the bike.

I'm wondering why the huge difference, as both bike are similar in displacement (1695 versus 1800cc), and both are V-twins.

One difference that I'm sure accounts for a portion of the difference is that the gearing on the VTX is notably numerically higher - 1st gear is only good to 40 mph on the VTX. But, the difference in engine braking is far larger in magnitude than the gearing alone could explain.

I am wondering: is it the internal balancing system? That system, whose objective is to make the engine smooth enough, despite its huge V-twin size, to enable rigid versus rubber engine mounting. I understand from a few postings on this forum that the system includes a sprocket on the flywheel, a balance shaft with sprocket, the chain that connects the flywheel sprocket to the balancer sprocket, and the balance weight.

I know from at least 2 expert HD tuners that Softail balanced engines normally deliver several percent less power on a Dynojet dyno than the unbalanced engines do, so their inertia is apparently quite significant. Is the balancer system acting as an additional flywheel during engine braking events, and thus limiting the engine braking so notably?

Can someone knowledgeable on Harley engines in total, and on Softail engines specifically, shed some light on why the engine braking is so modest?

Jim G

 

Could it be the mods you've done to your engine? My Rocker has slightly less engine than my previous bike (Honda shadow 750), but I still use downshifting to slow down until the last 50-100' or so when brakes are needed. I also never downshift below 2nd for engine braking.

And when you say 1st gear was only good until 40 mph on the VTX at what point are you shifting to 2nd on the breakout?

 

It's the extra reciprocating weight of the counter balancer in the TC B motor that causes less engine braking. Once mass has been accelerated it wants to stay in motion.

 

On my Breakout, the rev limit before the Stage 4 mods that raised it was 5500 rpm = 45 mph. With the new 6200 rev limit, 1st gear is now good to 51 mph. Like you, I never engine brake below 2nd gear, but I was making the point that the entire drivetrain on the Honda VTX was numerically higher in ratio than on the Harley, so presumably 2nd and 3rd gear engine braking would have less "leverage" on the Harley than on the VTX.

You raise a good point worth exploring: I had not considered the effect that the Stage 4 mods could be having. The 259E cams in the Stage 4 kit have much longer durations for both intake and exhaust than the stock cams. While they succeed in moving a lot more air through the engine at high engine rpm / open throttle blade conditions, we know that they do an inferior job of pumping air accurately at low rpm / closed throttle conditions - the loping idle is proof of that.

One simple illustration: The intake valve in my Stage 4 engine opens a lot sooner and closes a lot later than it does with a stock cam. By opening early, at low rpm, with a closed throttle, where there is no column of incoming air with high rpm momentum rushing through the intake tract, I can see the open intake valve instead exhausting the remains of the exhaust stroke air into the intake tract, and then pulling it back into the cylinder after TDC, thus achieving little in terms of actually pumping any air past the almost closed throttle valve blade. Hopefully someone smarter on engines than I am can bring this into better focus.

Jim G

 

does it have a tuner of some kind????
IMO the only reason I'd say it doesn't do it is because the engine is not tuned correctly.

When I had my cams done and they redid the dyno it did the same thing, (very little engine braking).. After some tweaking by the tuner all was back to normal.

 

I know what you mean, I had a Kawasaki Mean Streak and it did the same thing. I prefer the Harley way more though because its so smooth on and off the throttle. My Kawi was "jerky" on and off and it bugged the hell out of me.

 

Thoughtful questions and theories, JimGritecki.

The balance shaft engine definitely has slightly more rotational intertia, but I haven't noticed a difference on decel between it and my non-balance-shaft Harley. Perhaps I just wasn't paying close enough attention?

There may be other factors to consider, like at what point the ECM totally shuts off the injectors on various bikes under decel.

 

Just to clarify my purpose in asking: I am finding that with my Breakout I am using the brakes a LOT more than I had to when riding the VTX - enough difference that I am sure the brakes will need new pads FAR sooner than they did on the VTX.

On the other hand, one "advantage" I can see to the less dramatic engine braking is that on slippery surfaces, it is far easier to regulate the braking force on the wheel via regulating the pressure on the brake pedal than via trying to regulate the amount of engine braking via throttle control. On a really slippery road, this could be a big advantage.

Jim G

 

I dunno, but my fatboy slows the heck down as soon as I get off of the throttle.

 

Huh. Had quite a few bikes over the years and as a rider (not mechanic) understood the diff. A high compression large displacement engine gives more engine braking in general. A high revving power band spools up (and down) with little engine braking.

Gotta say my engine braking on 07 softail feels bout right for what it is. If you are higher in the RPM powerband when you let off the throttle it will be less engine braking than when lower in the powerband. Or at least it will seem like less.