Don't use O.S. plugs in a Novarossi! I've been told by reliable sources that O.S. and Novarossi have different thread taper, and that's it a sure way to damage the thread in the head button.

Kindest regards,
Lars.

Not quite. ALL turbo plugs use the EXACT SAME threads so no damage will be done to the threads. However, the tapered seat is a bit different. Nova plugs in an OS motor WILL leak. OS plugs in a Nova usually don't leak but the fit isn't great and there are plenty of other plugs out there that work better in Novas (Nova, RB, GRP, Sirio, Werks, Picco, OD, etc.)

I ran 4 tanks of fuel though it today on the stand, and all went well. Its a little slugish due too the rich settings, after breakin I'll do a lean drop on it, it should be a little more crispy. I think that this engine will be a "wild bullet" for us. :sneaky:
Bob

Correct, the taper is exactly the same, it just has less contact area, it works perfectly if you don't tight it to break it.

Will mod a old .18 SH engine and see how it goes,will just see how much timing on crank needed to gain more rpm and mod sleeve.How about crank hole diameter,my SH .18 has a wider hole than my SH .12 but uses the same case and bearings so how it afects performance?Thanks!

Hi all.The modding went great,just beveled ports,shaped teardrops,enlarged upper corners in exhaust port and cut a tiny amount on the crankshaft on the closing side.Engine felt way better.could't test at track yet.THANK YOU ALL!

retard timing
 

which is a better way to retard timing?
1. use a colder plug than stock, keeping head volume same
2. use stock plug but increase head shim by 0.1mm.

lastly, is it the same or any better if: example...
stock using #7 plug with 0.7mm head shims but now use #6 with 0.8mm shims...or #8 with 0.6mm shims. :)

Im not 100% sure on how to retard timing, but I am pretty sure the plug temperature does make a bit of a difference, but more in the engine temperature sense - Say you are running a #6 and it's nice at 105 degrees. You switch to a #7, it should take your temperature down because the plug is "extracting" heat from your engine headbutton faster than the #6. But I believe it will also delay the firing time as well.

Changing your head gap will change timing also but I would only run on the recommended stock settings or larger up to a 0.2mm limit.
I've heard that a few people ran their engine on stock shimming, then increased it by 0.1mm and there was a better and noticeable difference in power and fuel consumption, but that may have just been the "track factor" because having a larger gap should give better performance on the top end.

Im sure more of the engine guru's here will chip in and correct me if I'm wrong - I'm not completely sure, but that is what I understand.

Experience dictates that just by lowering the head (more compression) you gain more power especially in lower rpm range, idle quality can suffer, but the engine also runs cooler . Also, that a higher head (less compression) will increase top rpm speed on bigger tracks.

A decrease in head shims (an increase in compression ratio) will increase torque because as the compression ratio goes higher, the actual ignition timing occurs sooner. However there is a point of diminishing returns where detonation occurs or engine temps can soar, and if this happens a colder plug can help.

A colder plug will also increase torque, except in the instance of a colder plug the ignition is slowed until a greater point of compression build occurs.
When you increase head shims (a decrease in compression), top end is enhanced as the ignition timing is retarded and occurs later. Generally a hotter plug is needed to advance the ignition cycle so that timing does not occur to late in the cycle, but at this point you end up over leaning the engine to get it to rev properly and the engine life will suffer dramatically.

On a .12 engine we would only advise going 0.10mm over or under 0.46mm, so that is 0.36mm or 0.56mm of total head clearance at sea level.
Generally on a .12 engine 0.10mm will change the compression ratio about 3/4 to 1 point..

We should also state that the comments with regards to plugs and head shimming are when both are used together. Used alone a hotter plug will rev harder and a colder plug will make more torque.

AFM

That's ignition timing, the previous conversation has been referring to the engines crank-timing.

Raising the compression will raise power across the performance curve, low and high rpm, since HP is a proportional to compression. You have to correct the plug temperature (timing) for it to be fully effective, if your plug setup is out of range, the full potential will not be achieved.

Any highly tuned/modified engine will require a finer tune or setup. That's why low performance engines operate flawlessly no matter what plug, fuel, you use, and throughout a huge temp range. When you try to extract all the power an engine is capable of producing, the engine "gets" VERY intolerant to miss tune/setup.

I agree 100% :nod:

To tune an engine is not always needed to change the timings .

There is always a lot of work to do in the crankcase . You have to asure that the flow is going fast without stucking .

To change the timing you will need to know the actual timings of your engine .Compare it with tuned engines on the market . Most of them are very closed to the limit of timing .

Pay attention on the closingtime of the crank . This can be bad for fuel consumption .

Polishing is not so good .Better rawing up with a fine sandpaper . This will encrease flowingspeed .
What I go to polish is only the intake of the crank. You can work the valve without changing timings . You can encrease the intakevalve extracting material and sharpening the edges. Than harmonize it with the crancase .

Lightenen the moving parts like piston and conrod will give you better accellerations and rpm. But there is a limit on all .
Do only lidle steps . One change after the other .

The pumping effect of your crancase is a very good tuning solution .
Try to reduce the volume . When you be able to do this you will begin to smile ;)


And how reloaf said ......there is a very good book you can download as PDF .

You have to learn first how an engine works , than you understand what you can do .

Very interesting; a couple of matters that I would like to learn more about:

1. Which areas should be roughened up with sandpaper for better flowspeed?
2. What is pumping effect of the crankcase?
3. Do you have a download link to the book that reloaf has recommended?

Any advice of would be greatly appreciated.

Kindest regards,
Lars.

on the bottom of a novarossi sleeve exhust side there are 2 little round holes next to each other some sleeve are drilled out and some not what do they do and what happens when u drill them? thanks

The drilled holes are there for lubrication and cooling down the piston from that side. It is the hottest side of the piston and does need some fresh fuel for that. There are channels in the crankcase for them.

The sleeves without the 2 holes but only some dots are markings, maybe to center the milling machine or to give some info about the size or tolerances becaust I have seen 2 up to even 8 dots and you can find the same markings on the buttonhead.
Drill them through will not work because normally there is no channel in the crankcase.