Jspeed

I've been told that you can adjust engine timing on nitro engines.

Can anyone explaine how its done and what the gains are?

Roelof

Ignition timing is done by headshims and glowplug.
Lower compression will give a later ignition
colder plug will give a later ignition.
(by the way: less nitro will give a later ignition as well)
later = more rpm but less power
sooner = more power but les rpm and a hotter engine....
Colder plug with higher compression will keep the timing the same but the higher compression will give more power, the colder plug can give an unstable engine....

Porttiming can be changed mechanical.
Higher ports by grinding the ports out
Higher ports can also be made by adding a modified headshim under the edge of the sleeve
lower ports can only be made by taking off some material from under the edge of the sleeve.
Higher exhaust will give more rpm but lower power, lower exhaust will give more power but les rpm. Widening the exhaust will give more rpm without affecting the power.

Take care with positioning of the sleeve that you change the headshims as well.

Changing crankshaft timing can do a lot to get more power or more rpm, it can only be done by grinding,

Dave_x8

great post, but way too advanced for me to even try these things

Roelof

I can tell you that only 1 tiny change to the crankshaft timing has more result than all those fancy porting and polishing.

JetMD

iTrader: (1)

I did a little experimenting with this and what I found on my os tz .12 was that when I cut the small grooves in the head button, that gave me a decent increase in bottom end and didn't affect mileage. I tore the motor apart again and did some grinding on the crank opening and lowered the ports on the sleeve. I didn't feel any difference in power and it litterally killed my mileage. I went from about 5.5 min. to about 4.75 min. to a tank. I wasn't too happy about that. So, I put a stock sleeve in it and now it's my back-up motor.

Jspeed

Very interesting stuff.

I asked because we're racing the Kyosho Inferno GT cars in a Spec class and wanted to gain some knowledge about the subject.

Some people have been talking about timing mods to the stock .28 IGT engine. I feel they cars rules shouldn't allow these types of mods because it is intended to be an entry level and level playing field for all.

Thanks for the educational info

Jspeed

Grooves in the head, must help with a scavenging effect.

I've been racing my IGT car running 16% Werks Racing fuel. I did take out 1 of the 2 factory shims and the car seems to be faster on the lower percentage with a McCoy 9 plug.

I think the Spec class rules for the IGT class should be cool with that since the lower nitro would be easier on the engine.

Roelof

Sing-grooves, I have tested is and I am amazed...
http://www.somender-singh.com/

My JP Eagle.



It is shown that the combustion is more spread on the piston and did give a better performance. The question is what is legal to modify....

As I told here before the cranktiming can do a lot, but if it is not alowed to modifi the crankshaft and they do inspections you can always alter the cranktiming by modifying the crankcase in the hole under the carburator, they will never inspect that

ck960

iTrader: (11)

this is good stuffs thanks for the info...
changing crankshaft timing... what is the effect when grinding the opening and closing and how much to grind??

Roelof

This is what I normally do with some engines I like to run a bit faster:



On the closing side just removing some tenths of a mm to close it later and sharpening from the inside so it cuts the flow nicely. This will make the engine better in accelerating and will run a few more rpm's. If you go to far the engine will be very tricky to adjust om the low speed needle and can not have a rich setting. Going to far means you have to take away more than 1 or 2mm on a already fast motor

Also very nice information about 2-stroke, some people say this is the 2-stroke bible.
http://edj.net/2stroke/jennings/

Xr Turbo

iTrader: (10)

I'll have to give it a go on one of my old motors.

ck960

iTrader: (11)

thanks for the info, great stuff
i'll try it out on my old ZX21... will see how it goes

TomB

iTrader: (10)

Roelof, how, and in what directions do you do these grooves? are the 3 small groves towards the exhaust port? and are the other two just placed arbitrarily on the other sides in a uniform manner, or should they be placed at a certain angle/degree after the 3 exhaust port cuts on the button?

cheers

stefan

Hi Roelof,

I think the info you are giving here is a bit too general and could lead people to mess up their engines.

First of all, you have to find out the timing of a crank, before you can decide how to modify it.

For example: a Picco .12 based crank opens very late at 40° ABDC and closes at 60° ATDC. On this kind of engine, you'll see much better results to make it open 5-10 degrees earlier, i.e. take material off the other side than in your graph.

Oh, and stay within 220° of total induction, other wise it will be hard to tune and fuel consumption will go throught the roof.

Roelof

The advise of Mr. Singh was 3 grooves with one above the exhaust port.
This was my first attempt and was to quick with the dremel so I started with a small groove out of line. To make it good I made the right groove and another small one, This part is indeed above the exhaust port.

This is how it is supposed to be:


Using 2 smaller grooves is done more:
http://somender-singh.com/component/...d,384/catid,2/

Just make a few, to many will effect the working of the squishband and does need to compromise the compression.

Oh yes, you are right, thats why only some tenths of a mm, that room is always there in a non-modified engine and does make noticeable changes in the performance.

By the way this is another interesting site:
http://www.first-racing.eu/html/steuerzeiten.html