two stroke glow engine design&tuning forum
 

Hi I'm not a engine expert by any means but back when i was into 100cc karts i read a few books on this topic so Ive started this thread for every one to discuss this topic

1st Do you class these engines as so sort of rotary valve type

2nd The scollop's i see in the crankshafts whats the theory behind these Ive seen people grind these all over the place does anyone grind these in relation to engine timing

3rd with kart engines we yous to raise the barrel to increase exhaust port duration has anyone raised the liner in the case to increase the port duration you could re pinch the liner at a lower point and drop the the head button to retain compression

4th does any that mods these motors change the port timing or is it all grinding the liner and case to aid in air fuel flow

Id like to know your thoughts on these subjects thanks

Re: two stroke glow engine design&tuning forum
 

Hey, Jasen. You brought up very interesting points and will be very interesting to dicause it.
Yes Nitro engines qualifyed by induction-front or rear. Front type of induction is mostly the same on all brands. If we are talking about tipical design it is mostly the same from brand to brand. There are couple of high end engines ( not mass production) that have port offset to right or left from center line. There are couple of reason to do so (use centrfugal forces, easier balancing etc)
Rear type of induction is much more developed and it has at list 5-6 different types-rotating barrels, Zimerman, rotating disc, diaphragm type etc. All of them has it's own +/-. Depend of aplication to use-racer choose more suitable design. In RC cars front induction is most suitable type then everything else due to the space limitation.
The Scollop you are talking about also called "turbo scoop"-it is done to improve uninterupted flow from cranckshaft to crancase ( nothing else). It has certain timing and in most cases it is one of top secrets of design. Most of the guys are just copying famose designers without even knowning how important it is. Cutting scoop is improving the flow, but in the mean time increasing csae volume (which can realy kill performance). So if you do scoop, you have to see if benefits of it will be greater then the rest bad part of it. There is also funnel type chamfer made on some engines and it is working realy good as well.
About raising timing, not neccessary raise liner-you can cut ports to desired ###.
Not to many people are changing timings on liner and mostly it is done during the manufacturing process.
In case talking about my self-it is only me (as I know) in the world is making my own piston/liner sets and I make that timing which I want to. I am not major engine manufacturer, but I do make my own engines, parts for existing brands and also servicing some manufacturers as well.
Anything else if you have to ask, I will be glad to answer. There is some clasified info-i can't disclose, but the rest I do open any info.
Edward
Defenetly all above is my own words based on my own knowlodge and expirience-It means some other peole can have different opinoin and and can be disagree with me. I don't disreguard it.

Top Gun 777 thanks for your info

talking about crankcase volume have you seen anyone make any changes here my understanding is if you decrease the volume increasing crankcase compression in makes for a peaky power band Ive also noticed that these engines don't have a squish band in the combustion chamber like a conventional two stroke it may have something to do with the glow ignition

You are very welcome.
I did seen one guy did it, more then that he did his own engines , spares for existing brands and made a lot of experiments with that. It was me! LOL
Nobody here in RC cars make any of this kind of experiments, nobody makes own Piston/Liner sets-everybody just massaging and carving existing brands.
Yes decreasing crancse volume ( increasing internal pressure) will increase velocity on transfer and in many cases it does help, but you got to be very carefull with that-decrease a lot of volume will make engine realy flat on very top RPM. Ther is reasonable ### and we need to stay within that limits.
Our engine does use squish band, but again because nobody makes parts for engines-so in many cases squish band clearance out of range and no power additions come.
Edward

Top Gun 777: I have novarossi NS15S5 and it comes with 0.30mm and 0.10mm gasket.

I'm thinking to remove 0.10mm gasket. Is it safe if I increase compression ? From your experience the fun vs. damage factor ?

Top Gun 777 so they do have a squish band I must of drank to much bear before posting the other night I wounder if there could be any improvements made here changing angle or width etc I might go and buy some engine simulating software and have a play around will the chrome on these liners hold up to port timing changes (without flaking)

I have never work with NS15S5, but any decreasing head volume will bring torq up, but in the mean time it can bring to detonation and this thing is dangerouse-cheapest will be just sand blasted piston and head botton and worse-you can loose whole thing. To determinate if it is to high compression ratio-run car with normal tunning for 2 laps and if temperature increase tramedosly-it is detonating.
If you have chance to mesure combustion chamber volume it should be somewhere in 0.19-0.20 cc
Edward

I am not sure if simulationg software will realy help you with that.
There is numbers for squish band which was determinated over the years of expirience and they are working pretty good.
Yes chrome will stays and will not come uot on ABC and BRB, but on AAC will not-it will chip out.
Edward

Is there a thread that mentions the importance of the exhaust configration and how it effects power? To me this is the most important aspect of the engine.

Cheers

I haven't seen any thread like this.
It is not most important aspect, there are many more important aspects, but again our engine is chain of events and interuptions, so changing one will affect others and always need to be taken to concideration benefits and loses of any aspects.
Ports sizes, configuration, angles are very important things in our engines and I am sure nobody will ever disclose any numbers or ideas behind the numbers. I am not going to do it as well, specialy in public forum. Sorry! I always say: be my gest and copy it if yuo can. :D :D :D
Edward

http://www.maxxtraxxusa.com/Page.cfm?InfoID=3608

I found this and it verifies what I had thought. the exhaust can have a dramatic effect on engine performance

Cheers

In generaly speaking exhaust timing is regulate balance between torque and top RPM. It is not just simple, but yes exhaust timng impact tramendosly engine performance-will it be torque or top RPM unit. But again, our engines are unit with chain of events and one small change can be as a benefit or interuption. Everything must to be balanced. Increasing exhaust timing should increase top RPM, but without altering induction ( where? on opening or closing?) and transfer will not add a lot. One more thing which is realy important when we are talking about engine performance is tapering on sleeve and piston material-if everything is done even right and taper and piston are not able to run fast-not much will happened-it will be great interuption which can't even visible be recognized.
Edward
Edward