HT engine True MAX RPM

[210061741]

If you can get even 6000 / 7000 rpm with a shift kit that would be more than enough.

Check out my other thread that has the calculations figured at 6000 rpm.
You could be pushing 70 MPH.

Now that is much faster than i would ever want my bike to go.

DiyMark

How about sharing some info on your porting.
Like how exactly did you modify it.
Width / Height / Shape ?

I know porting can make a great diff.
But it can also ruin your engine if not correct.

I would actually file .5mm or about .020 inches off the top of the piston crown on the exhaust side at a time until you have the power band you want.

Once you have gone too far it would be easy to put in a new piston and modify the exhaust port to the proper Duration.

On the intake side I believe the bottom of the piston can be machined away to increase the duration there.

Now if you have gone too far with your porting then your fresh intake charge could be going right out the exhaust.

One trick ive seen is to add a couple of boost ports to the cylinder about 1 mm above the intake ports as deep as the cylinder lining.

Then drill 2 holes in the piston to feed the ports.
This is a good thing cause it causes more flow through the piston and past the small end bearing providing more lubrication.

Also the increased flow at the piston will keep it cooler.



Now lets talk about you piston.

You mentioned optimized timing.
My guess is you created severe detonation to blow that hole in your piston.
What you really did was cause the engine to fire wile the piston is actually still moving upward to TDC. Very Very BAD.
Also that would explain the no power you are experiencing.
You engine is fighting itself. You loose alot of power when the explosion in the combustion chamber is rocketing down on the piston before it hits TDC.

With the CDI ignition package the timing should not really need modified.

You managed to get the max engine rpm up which is good but that all gets ruined if things are taken too far.

IE porting + Timing

 

[DIYMark]

The detonation was a result of the motor leaning out and thus heating up. On the piston face you can see a molten pool of aluminum at the edge near the exhaust port and the piston face is all deformed - the temperature rose up high enough to melt the piston and then once the aluminum was softend it didn't take much to punch a hole in it.

The timing is in fact firing 2.5 mm (~24 degrees) before TDC which is about average for a rev happy motor. Advanced ignition is good (well not overly advanced) and is required for full power output.

The lack of performance my engine has now is due to the fact there is no piston! What I was trying to say before is that anyone can make revs, its just how much power you have at those revs that matters (as I found out it has plenty - my m8 said he had to keep the front end down at full speed because the front wheel was all over the place).

Ill try and explain the porting.

*Goes and grabs cylinder and ruler*

First - either leave your piston be at the exhaust port or file it to match the port floor - whatever you do, make up your mind now. The exhaust port height measurement is now from piston edge at the exhaust port during BDC, upwards.

Second - file the piston skirt so that at TDC it is flush with the intake port roof.

Now - my exhaust port is 27.5mm across the chord, it has an oval shape, it is blended into the stock exhaust flange (plus about 0.5mm bigger for flow) and is 15mm tall. Don't forget the 0.5mm tall 0.25mm deep chamfer on all ports. Polish the exhaust port.

Next - the intake is 13.5mm tall and 24mm across the chord. Port is oval on cylinder end and blending into stock intake flange (plus about 0.5mm bigger for flow). Hone this port with 180 grit emery paper to create intake tract turbulence.

My transfers have been cleaned up (remove flash and blend) with a engineers scraper and the transition from cylinder liner to transfer port is filed/sanded to blend it and reduce air resistance (see photo).

If you have a mill do what I did with a 12mm end mill and cut out these boost ports till inline with the transfers (see photo) then using a scraper form the boost port roof to a 45 degree angle.

Do this and your cylinder should be about spot on - all that is left is crank truing/balance, cylinder head, expansion chamber, ignition timing tune and then you should be set for 10K rpm. Even if you just do this porting you should have an engine that will have a smooth power band with a good average torque (not like no power until 6000 then starts to come on until the vibration kills the engine) with this porting you get good all round power which is what is needed for a single speed set up.

The boost ports are optional (for now) as I haven't tried the cylinder with out them and thus I have no control to base my results off. However, it seems to have no negative effects.

All this porting assumes a 47mm bore and 38mm stoke - if your engine differs DON'T USE THIS MEASUREMENTS - the port durations will be different!

http://img405.imageshack.us/img405/3448/cylinder.jpg

 

[DIYMark]

Now lets talk about you piston.

You mentioned optimized timing.
My guess is you created severe detonation to blow that hole in your piston.
What you really did was cause the engine to fire wile the piston is actually still moving upward to TDC. Very Very BAD.
Also that would explain the no power you are experiencing.
You engine is fighting itself. You loose alot of power when the explosion in the combustion chamber is rocketing down on the piston before it hits TDC.

With the CDI ignition package the timing should not really need modified.

You managed to get the max engine rpm up which is good but that all gets ruined if things are taken too far.

IE porting + Timing

The stock Ignition is **** and NEEDS to be tuned so that it fires at the right time in order to get into the realm of high revs - this is why everyone is such a non believer about 10k RPM. They go out and buy a 200 buck kit, slap it on, do a pathetic mod like file the intake/cut out a baffle or something pathetic like that and then stand back and go hey it doesn't pop wheel stands like it ought to or rev past 6200rpm. Then they are astounded that the bottom end gave in after 500Km.

Well bottom line is as soon as my engine landed on my doorstep it was pulled apart to the crank in less than 30mins and then I started building it up as a good engine should be - also assembling it clean unlike in the factory (new engines ALWAYS have aluminum shaving in the crank case/cylinder. Thats why your stock bearings gave up people and mine still work at 10K RPM.

Secondly I'm well aware of ignition timing requirements, fuel/air, detonation and the like - thats why my engine does 10K rpm and other peoples dont.

Everyone has to treat these engines like they are castings that have been roughly machined - then work up form there. Not as if its a darn german built, engineering masterpiece of an engine and just take it for granted and install on a bike - do that and you have no performance and typically the engine gives out quickly.

Lastly, if your engine fires exactly at or just after TDC it will be gutless and retard the ignition anymore and your exhaust header will probably glow red. I can not stress it enough that even a stock low performance engine will need ignition advance of about 1.7mm

 

[210061741]

Well now DIYMark i must say is surly sounds like you know what your doing.
Do you have the actual duration of the port timings.
The degrees when open and closed.
Where are you feeding the boost ports from?
Have you replaced the bearings with better ones?

The boost porting i'm not so sure about.
It looks like yours starts at the bottom of the Jug.
I haven't seen it done that way.

Boost porting could give some extra power but from what i understand....
You want to cut boost ports and feed them by drilling holes in the piston.
The benifit is that you increase flow past the small end bearing and keep the piston much cooler.

How is it that the boost ports you have cut don't really impact your transfer timing in a negative way.

I guess i just don't understand where your feeding them.

Do you know what the BMEP for this engine is?

What i would like to see is a new thread created by us for the Barrel and Porting Design.

I would like to go through all the Calculations to determine the BEST port timing and expected engine power.

Obviously that can take some time but if several of us joined up as a team we could get things done much easier.

Or at least have a good way of double checking our own work.

Have you Mapped The porting?

Have you done the calculations?

Have you used a degree wheel to check them?

I have alot of plans but right now i don't have an engine to mess with.
The one on my bike is in use and my main transportation.
I ride it everywhere in all weather.

Soon as the Grubee GT4 parts come out I'm gonna buy them and build the engine.
You can't buy the engine cause it dosen't meet EPA requirment in US.

After the trial and error with the Ported / stock GT4 Barrel I would actually like to Design a High Performance Barrel and get it machined Billet Style.

That would rock.

 

[DIYMark]

The bearings are stock.

I did at one time have all the durations worked out then I simplified them into lengths using the stroke/con rod length and somewhere along the line Ive thrown out all my calculations after porting the cylinder.

SOME boost ports are fed from a hole in the piston, through the liner, into the cylinder. Others are fed from the crankcase through a port, into the cylinder. Mine is the latter.

Simply put a boost port is an axillary port that is opposite the exhaust port (typically with a roof angle of 45*). So my ports achieve what boost port should minus the cooling/oiling effect of fuel/air over the little end. Id like to make them like that (fuel air flows through the piston) but I don't have a T slot cutter with a long shank for my mill.

My boost ports don't effect transfer timing as they open at the same time as the transfers.

I cannot calculate BMEP as I don't have a Dyno - hence no torque measurement.

As far as determining the "best" port timing you need to work out what you will do with your MB - either have gears or have single speed. This is because with gears you can mod your exhaust port and increase blow down time for higher revs and more power - at the expense of a narrow power band (not an issue with gears) However if you want a single speed setup you have to have a port map that delivers power across the board (wider power band).

Simply put, the bike with the highest average power will win the races.

Having said this, my porting with a 38mm stroke engine seems to be good as it has good average torque and allows the motor to rev high which is ideal for both single speed and geared bikes. However, if you have gears I suppose you could increase intake and exhaust duration and enlarge the transfers more then you could have a "race" setup which would then require a 9 speed (34t - 11t) cassette (depending on how far you take the porting).

At the end of the day - I like my fixed gear setup. Its already stupid fast (70Km/h) and can take me up hills. Isn't that we ever wanted from these engines? Speed and hill climbing ability. Adding gears is a recipe for death (Ive crashed at 50Km/h on gravel roads and that's no fun - imagine 70km/h on a tarmac road!)

Besides, now that I got my license I want to get the HT engine equivalent in car form...a KE30 corolla lol - that and also now that Ive maxed out my MB theres not much room for improvement/gains as I see reaching 10K RPM and 70Km/h on a 44T sprocket the pinnacle of performance...before you have to turbo the **** thing.

 

[210061741]

Actually i'm thinking that i don't want to run 10000 rpm.
Sure you get up to 45mph but how long dose it take you to get there.
My engine is fairly modified and i'm sure i can get up to 35 /40 mph.
Without porting and a I have a single speed 36T.

I ride to work and back every day through down town.
Lots of Traffic lights.

Now i can't get up to speed fast enough and at top speed i pretty much keep up.
But by the time i hit top speed it is time to stop at the next light.

I'm looking to run a well designed shift Kit.
Have the ability to take off and get to at least 25 mph very quickly.
Then shift gears and have the power to get up to 40 MPH quickly without revving my engine to death.

So in all reality.
We need and engine with extreme torque at low speed.
And high torque at high speed.
Capable of traveling much faster than we ever would.
Capable of revving much higher than we need it to.
Rather than pushing to the limits.
Stay within sound well thought out limits and see the performance desired wile never getting close to Max anything.


The problems i'v run into are Lack of Sound Information.

IE:
Engineered by brainstorming and backed up by all the math.
Then tested and prooved to be effective.

The main reason many of my threads are so technically intensive.

#1 when i'm all done or i get side tracked and start working on a new project
I can go back to my threads and the data is there.

#2 The data is also available to other members and if they choose to understand it they can adapt it to there situation.

The biggest setback i have run into is the data available for the HT engines.
We need the Factory Specifications to Blueprint the motor and then improve it to the max.

 

[DIYMark]

A factory specification is somewhat useless as each different supplier uses a different manufacturer and thus each engine is a little different - like not all 66cc piston are the same height (making it harder for me to locate a spare).

With a 44T sprocket Im getting 70Km/h and because Im not using a 36T sprocket my bike accelerates great. In about 50 meters I'll be at 50Km/h and in about 100 meters Ill be at top speed - this is all on flat ground.

 

[Fabian]

DIYMark

Your engine mods sound well researched and executed.
The hi-res pic of your cylinder and boost ports are proof of this.

By any chance do you have hi-res photos of your crankshaft after it was balanced.
I'm curious as to what size holes were drilled in the crankshaft and where they were placed.
What was your balance factor and how many grams did you remove from the crank webs.

I am having huge difficulty finding someone competent in my area who is knowledgeable about balancing and truing a two stroke crankshaft.
Today i had a discussion with an engineer about how he was to balance my crank, rod and piston assembly.
Not too long after chatting, he made a statement that the work "idiot" applied to.

-:- Asking him about balance factor: he didn't even know what it was.
-:- Asking him about why he was not going to factor in a percentage weight of the piston and connecting rod: answer was that the rod and piston go up and down and not round and round so it doesn't need to be considered in the balance. My god, this idiot is an engineer and he charges $120 per hour for his work.
He said it would take between 4 - 5 hours including machining the bearing recievers so the crank bearings easily slipped in and out of the reciever without an interference fit.

The word "moron" comes to mind, stronger language as well.
He was simply going to put the big end bearing on the crank pin and balance the crankshaft on a set of knife edged bearings.
I was put onto him by the local motorbike shop - heaven help the poor souls who have had machining work done by this idiot.

The guy got all upset when i calmly picked up my stuff and walked out of the shop, deliberately slambing the door behind me.


That said, i would be grateful if you could post some pics of your balanced crankshaft.


Cheers Fabian

 

[DIYMark]

Hmm now that you mention it - I was at uni studying engineering and from day 1 I hated it and it never got better so I left. Like I had good marks (Credit or higher) and all that, but what really got me were the people there. Such as you experienced these "engineers" wouldn't know sh!t; and this is still shown in the drawing I have to make some parts from!. So that I way I work as a fitter/machinist now.

The design balanced percentage I opted for is a rather high ~57% as I intended the engine to rev pretty high. For "normal" use I'd suggest 55%.

I do not have a pic of the crankshaft as It is currently installed in the bike after a total tear down to clean out the crankcase (properly!) after my piston incident lol.

I concluded that my engine was in fact balanced (more or less) from stock BUT the counterweights that balance the engine were NOT machined concentric at all. So what I did was remachine them to make then true, then I machined the crank to turn true. Then once assembled I trued the crank and took care to install it without force so it remained true.

So in essence I did balance it - but not by removing metal unevenly (ie from one side) but instead by making the balance weights spin true - which in effect is balancing the engine.

Once done I put my counter balance weight on the little end for 57.5% and the crank was balanced - this is why I used to stock balance holes.

Given the time and material (few chunks for bright shaft or even better - duplex) I would like to make my own crank from scratch that is true to within 0.005mm (considerably easy) and at the same time still balance the engine yet use less metal - hence less mass. Then fill in the space with bolted on plastic "displacement washers" to reduce crankcase volume. Then while I'm at it I should make up some patterns and cast my own cylinder/crankcase at home and build my own engine from the ground up! Then Ill get 13K revs and more power! Oh yea, liquid cooled of course with reed valves and dont forget the exhaust powervalves!!!

 

[Fabian]

DIYMark

Is your crankshaft a 3 piece or a 5 piece unit.

Mine is just 2 crank halves and a crank pin; no removable flywheel weights.

Fabian