Can you still use your shifters?

[FurryOnTheInside]

The question you have to ask yourself is if the act of creating that extra 10% power cancels itself out in other ways. Bear in mind a couple of things. We know that adding small ammounts of power has diminishing returns because aerodynamic drag increases in a nasty way. The increase in drag from say, 15mph to 20 mph is more than it was from 10 to 15, and so on.

Now remember we suffer this effect much more than we're used to thinking about, because a bike with a rider is just about the least aerodynamic thing. A brick with rounded edges would do better.

Now start pedaling fast, and suddenly that extremely unaerodynamic object has gotten even worse. It won't even stay the same shape, so the drag goes crazy. If you ever watch cycling on TV when they're going down a mountain, you'll notice they stop pedaling and put their feet level at 9 and 3 on the crank. Their speed is entirely within their gear range, but they stop anyway, because the aerodynamics mean powering themselves would be slower than just tucking in and letting gravity do the work.

The top speed of a decent ported out motor with the vibration taken care of is what, 40mph according to your own figures? That's well in the speed range where trying to assist the engine is just pointless behavior.

As for chains dropping on a 1x, I have to say that yeah sometimes they drop, and sometimes wheels fall off too. I don't have special wheel-holder oners though because I know that'd be an exceptional situation. Tighten your wheelnuts, make sure your chainring isn't bent and stop worrying.

I almost wish I hadn't mentioned that I pedal along with my engine because it's a bit off topic. The OP only said that he wants to be able to make use of his gears when his engine is not running. It just so happens that I can (and do) do both.

On smooth paved flat ground the aerodynamic drag increases to the square of the speed, but the power required to overcome aerodynamic drag increases to the cube of the speed.
On flat ground 10% extra power from engine mods is not going to yield a huge difference to the top speed..

(bikecalculator.com)
254lb rider, 66lb motorised mountain bike, 0% gradient,
2000W = ~40.88mph
2200W= ~42.36mph
That's 3.62% faster.

However if you are accelerating or climbing, the extra power will be far more noticeable. An extra 10% power can yield close to a 10% increase in the climbing speed of the bike if the gradient is steep enough (>20% gradient).
Accelerating is similar to climbing.

(bikecalculator.com)
A 254lb rider, on a 66lb motorised mountain bike, on a 20% gradient,
2000W= ~13.66mph.
2200W= ~14.93mph.
That's 9.29% faster.

But I just pedal along with my engine because it feels natural and I enjoy it, and it's less embarrassing for me as a fat guy (I'd hate to look lazy as well as fat!).
It does also accelerate and climb faster and it keeps me warm.

40mph isn't my top speed. I have not found my top speed yet. I have been up to 8000rpm (around 37mph).
I might have a go at finding my top speed after I change the rear sprocket because I don't particularly want to go above 8000rpm.
I can only pedal until around 36-37mph anyway so I cannot test whether my top speed is increased by pedalling.

 

[KCvale]

And nah a bike doesn't need anything there to stop it from dropping a chain.

Actualy the SB shift kid comes with a Jump Stop, if adusted right and no chain drooping issues, and I at least don't have have any that way.

 

[FurryOnTheInside]

Actualy the SB shift kid comes with a Jump Stop, if adusted right and no chain drooping issues, and I at least don't have have any that way.

The OP has a 3x7 speed mountain bike so probably front sprockets of 22T 32T 44T. The RD won't be able to keep the full tension on the chain when using the 32T because of the extra chain length that is needed for the 44T and the way the old clutchless RDs work (where the spring that tensions the chain is the only thing keeping the tension).
Not to mention that there is no 32T SBP sprocket, and all the sprockets will have to be replaced if he wants to make a 7 speed shifter that keeps the triple chainset for when he uses it without any motor power. But he never mentioned a shift kit and I don't think he wants one.

 

[KCvale]

But he never mentioned a shift kit and I don't think he wants one.

Well, if he's going single speed direct drive the pedal system he has will still work.

 

[LewieBike]

Why would you continue to look for derailleur parts when an internal 5 -speed hub shifter is so much better with JS power?

You can pedal fine with engine off and help it when it's running, once you hit ~30mph or so your legs don't help much.

First off multi geared engine powered though transmissions are illegal on a engine assisted bike per Oregon's laws, so that rules out running it through a shift kit, also because the law states an assisted bike can have no bigger than a 35 cc engine, and has to be autoclutched. and not more than 25 MPH top speed.

Secondly, I don't feel comfortable riding a powered bike that can maintain a 30 mph cruise, that's too fast for the brakes and frame integrity of a unsuspended 1980's MTB with 14 gauge spokes in the wheels.

Thirdly I'm keeping all of my installations as 'assist engines' which means I'm focusing on small displacement and light weight, if the whole power system weighs more than 25# it's a no go with me. I want to be able to ride the bike with the assist engine off as light as possible because we have coastal winds and lots of short steep hills.