HT engine True MAX RPM

[DIYMark]

You're all full of it lol.

My HT is some what modded but the big/little/crank bearings are STOCK and my engine is just fine even though it revs up to 10,000RPM (and thats with load - who knows how high with out load).

You see my mates followed the bike and at WOT on a flat we hit 70Km/h with a 44 tooth sprocket and a 26" wheel - that equates to ~10,100RPM.

In fact my mate held it flat out for 3Km of country roads (hills aplenty) and the bike never fell behind 50Km/h (only once it was a 50, 90% of the time is was at 60 to 70Km/h).

Problem is...the muffler tip fell off and that changed the fuel air - you guessed it! 100m later bike stopped and upon inspection the piston melted! Oh well new piston and rings and it will be all good (I have split the cases and cleaned out the whole motor from aluminum). I still have to make a new muffler tip - the other one fell out at 70K's and sparked on the road and we lost it.

I should make a video some day.

PS - I'm making a phosphor bronze bush for the little end as I fear the stock bearing is about to explode at 10K Revs lol

 

[wildemere]

Piston didn't melt, It scuffed itself to death.

Also, pics or it didn't happen (10,000rpm)

 

[Fabian]

DIYMark

10,000 rpm - prove it!

 

[210061741]

This is exactly why i started this thread.
Everone has diff ideas of haw fast the motor rpm is.

My guess is at least 6000 rpm.

Now at 4500 RPM there saying max HP and Torque.
But if you look at most torque curves the RPM keeps going up but you loose torque. But at such higher RPM you don't need as much torque.

So how about everyone posts there gear setups and engine types.
And thosse who have an accurate way of knowing MPH post there speeds.

Then i can do some math and come up with the average RPM we get from these motors.

 

[210061741]

specs from Flying Horse HT Engines
Seem to be closer to what i guess

 

[210061741]

http://www.zm-bicycleengine.com/product2.asp

a link the screenshot didnt come out good

 

[210061741]

Key Factor for MAX Engine RPM

Exhaust Porting and Expansion chambers = RPM

The exhaust open period determines to some extent
what the maximum hp will be
and at what engine speed it will be produced.

The expansion chamber, on the other hand, 'adjusts' the power characteristics of the engine
at speeds above and below maximum hp revs.

expansion chamber design is far more
critical than exhaust port duration.

 

[DIYMark]

Scuffed? No way it was in mint condition (the sides anyway - I use Castrol Power TTS) However there was a 10cent coin sized hole blown into the top of it lol.

Anyone can get 10,000RPM - just raise the exhaust port/lower intake - problem is that you have like no torque hence no power. But my bike made it over hills at over 50Km/h so it has revs + torque = power.

Ill try and get a video once its put back together (may be a while because Im moving house and my engine supplier doesn't want to talk to me now that I mentioned a spare part - amazing how he wouldn't shut up when I asked to buy the engine lol)

Until then you have to trust me on the 10,000RPM.

My wheel has a circumference of 2.11meters.

The speed It reached was a touch over 70Km/h (actually 73ish) lets call it 70 then.

70,000 meters per hour (70Km/h) is 1167 meters per minute (70,000/60).

1167 meters per minute is 556 wheel revolutions per minute (1167/2.11)

Gearing is stock - so internally its 4.1:1 and externally its 4.4:1.

Therefore my engine is doing 4.1 * 4.4 * 556 RPM = 10,030RPM

As for the engine its is modded as follows...

CNC made cylinder head with 50/50 squish band
NGK B8HS plug
Transfers/Intake/Exhaust matched
Gaskets matched
Intake Lowered + porting
Exhaust Raised + porting
Transfers ported
Piston Machined on intake side
Rings honed
Crank Balanced
Crank Trued
Timing optimized (make an offset wood ruff key to tune timing)
Carburetor Bored/Honed
Custom straight Intake
Polished head
Polished Exhaust port
Honed Intake Tract
Output sprocket profile corrected
Custom built Expansion Chamber exhaust ("tapered" header)

Don't forget all the simple things like correct fuel/air, good oil and fuel (bike needs 98 octane), correct chain alignment and tension, correct sprocket alignment, correct engine alignment, trued wheels, etc.

I just realized then lol that this is on a STOCK carburetor! All along I thought to my self man I need a new carb - but if the stock one will get you to 10,000RPM...why buy a new one? If anything a larger one will give me less bottom end but more top end - however, I like my power curve the way it is.

Finally I don't see whats to "unbelievable" - go get a ~70cc moped and go flat out on it. How fast did you get 70/80km/h ish? Now get a HT and do the mods that I did to it (so that it is kind of the same quality you'd get as if the engine came off a moped) then go flat out on that. How fast you get? Again 70/80ish.

My point is any half decent 70cc engine will get you to 80Km/h (50MPH), its just that a HT engine is not half decent - its ****. Once you bring it into the ball park of a small motorbike/moped engine in terms of "engineering quality" (ie correct dimensions/design) then it will perform the same - only difference is that the HT engine is not a high mileage/durable engine (once brought up to the same power level that is).

So sure my engine can do 10,000RPM so what? How long will it last - I give it 500Km (the way I ride it) before I need to get new bearings for it (Chinese bearings are rubbish).

PS - Id like to try a 30T sprocket on my bike - I'd reach like 100Km/h haha! Even better would be a shift kit with a wide range cassette (11-34) then my MB would literally be a 70cc motorbike.

 

[Fabian]

h these two factors set correctly - Crank Balanced and Crank Trued, 10,000 rpm is possible.

What manufacturer and specification of big end bearing are you using.

Fabian

 

[DIYMark]

All bearings are stock.

I will be making my own bushed little end bearing (from phosphor bronze) because I trust that more than the stock needle roller. However the stock crankshaft and big end bearings I fear aren't even rated for 10k revs so I'm seriously thinking of upgrading them.

And yes the crank is one of the main mods that lets my rev that high. However being a single cylinder engine it will always vibrate. But the compromise Ive chosen for is that at around 10,000 rpm the engine vibrate a fair bit but then at cruising rpms (~7K) the engine is smooth.