lsurber

It is not exactly an egr but works similarly. It is an internal port!

Anthoop

Yes i see where your coming from and good luck to you.
Have you tried advancing spark timing as you would with an egr system.

lsurber

I will be working when I have time to develop, photograph, and document the procedure. Once I can measure, confirm, and repeat results it may be something I wish to patent.

lsurber

That is what head shims are for! Ignition is a product of critical temperature and pressure!

Anthoop

Oops yes sorry,talking 4 strokes then.
I take it then that's a yes.

lsurber

By the way, I went home at lunch and ran 12 min. and still had a 1/3 tank left. This is on an engine which I am still breaking in.....so it is a little rich.

hpi apollo

i have modded a few engines before, i havent reached double fuel economy but well over a 50% difference, the way i did it was just general sleeve porting, knife edging the rod, cutting a little bit off of the piston skirt, and grinding a groove in the head button directing fuel over the glow plug for a better burn, i did alter the crank timing a bit in both ways too but thats just because my crank allowed me to

bikeracer

Sounds like sub piston induction to me,thats where the piston skirt uncovers the bottom of exhaust port.If it is, it's nothing new.


Allan

lsurber

Well, since it's nothing new,,,, you nailed it! I have never worked on or built any kind of engines other than 4 stroke race engines so this stuff was all new to me! When I had to mod my cheapo engine I saw that notching the skirt on the exhaust side would increase efficiency and decided to try it! I am used to having original ideas so I had to guard it a little until I did some research! Thanks for the info and good engineering detective work on your part bikeracer!

Lee

lsurber

I still have a few tricks left up my sleeve though! LOL!

downunder

Sub piston induction was used on many engines long ago but the only ones that actually had a slight benefit from it were the piston ported types like the Mills diesels where the inlet of air through the venturi was so inefficient that any extra bit of air helped. With open exhaust engines, before mufflers, the sub piston induction didn't affect them much because the exhaust port was virtually free of gasses and it was only open for a few degrees around TDC anyway. When mufflers came into vogue the exhaust gas was trapped and this would then contaminate the fresh mixture and power suffered.

lsurber, don't get discouraged from trying out ideas just because this one has bombed but you have to remember that even though our 2 strokes are extremely simple they're also extremely well developed. It's only in detail refinements that any extra power can be squeezed out of them and most of this is already done with the more expensive or specialised engines. I know of one for instance that force feeds the lower rod bush with oil instead of relying on splash lubrication from the fuel/oil mist inside the crankcase.

bikeracer

No detective work involved,I've had engines with sub piston induction,a Mills .75cc over fifty years ago and such as Oliver Tigers and PAW diesels after that. Webra used to use it on their long stroke .60 aero engine about twenty odd years ago.I've not seen it used for a while though.

If it works,there's no reason not to use it especially if your getting more mileage from your fuel.More power to anyone experimenting I say, certainly makes a change from the "Why won't my engine start/what's the most powerful engine" type questions.


Allan

lsurber

I have noticed a very good bottom end, an unwillingness to stall, and significant mileage increase. The idle dropped a little low even with the set screw all the way in. I can fix that with a little slide work though! It idles so low you would swear it was gonna stall out but never does. I have also noticed that you don't see the typical increased idle when leaning it and decrease when richening. It just has a very nice 4 stroke idle all the time even after full throttle hard runs. When I got home I filled the tank and ran it hard for about 15 min. then let it idle to cool down and burn the remaining fuel out! I don't know how long it ran but I had enough time to smoke a camel and drink a beer before the tank ran low enough to start leaning out where I shut it down! Overall it's a keeper with plenty enough power to roast em down low and into mid range!

2916jr

so all your doing is running a tube from the pipe to the crankcase(tube as in fuel line or something)

lsurber

No, it involves cutting the piston skirt on the exhaust side!

RBMike

I think Honda called it active recubustion when they did it 10- 15 years ago. If I rememeber correctly it cost them power but improved emmisions & milage.

lsurber

I really don't see a performance hit against a modestly flowed engine with no timing changes even though I haven't leaned it yet. I have never had power issues since carb tuning and gear selection can overcome most of that unless your are on really high bite surfaces such as asphalt or clay. From what I have experience thus far after the mod I would highly recommend it! What really impresses me the most with this mod is how consistent the thing idles! Normally after a hard run when you pull off and come to idle the rpm's will drop off after about 30 sec. if properly tuned. I get none of that! It idles at very low rpm also (well below normal clutch stall) and sounds very rough but just won't stall AT ALL! It is amazing! I am still running very rich because the engine is still breaking in but experience none of the common load-up issues. It is now on day 4 and keeps getting stronger and running longer! LOL! AND I haven't even touched the needles one time after first tank break-in. Normally as break-in continues you must lean out or you will be so rich it will load-up! This is not happening! Also, it is common to lose the glow plug during break-in....... this has not happened! It is totally blowing my mind how this thing is reacting! I haven't had a run under 16 min so far with a 125 cc tank and .26 ci Go-Tech engine. At lunch today I ran it the hardest yet as if I were racing on an oval. I timed the hard run at 13 min. then putted around for another 1 min. then drove it onto the patio for cool down idle. It idled until timer hit 16:48 at which time I killed it myself with enough fuel left in the tank to run maybe another 30-40 seconds.

j_blaze

lsurber, isn't that the main reason 21s are used for racing? fuel mileage? What if you do this to a ported 28 and run it on a smaller tank for shorter races then the bigger tank for the longer mains, it would be almost unfair. I'm gonna definitely try this soon, I'm expecting my replacement engine from VTX this week so the 21 will be expendable. Double the mileage will be great on saving gas too, $25 bucks a gallon, whoo.

lsurber

I think the main reason 21's are used is because they were the only practical size for the 1/8th scale class at the time and are still very practical for buggy applications. They provide great power and high rpm's! BUT, along comes the monsters like the LST and big power becomes widely sought after! Fuel mileage is always a concern for me coming from real race cars. I set up my short track cars with maximum air up front to cool radiator and a higher than normal dif ratio. This allows me to use smaller jetting in the carb and increases the fuel economy.

RBMike

.21's are used because that is the spec for 1/8th scale class buggies. 125CC fuel tanks are used because that is also a class rule. Many .21's are faster that the .28s anyway because the engine manufacturers focus most of their R&D on .21's due to the class rules (and higher sales of .21 displacement motors). Also most .21's will spin at higher RPM tha .28's because of enternal mass of the parts (pistion, rod crank etc.) is lighter.

RBMike

How about a picture of this induction port?

lsurber

[link]http://www.rcuniverse.com/forum/m_5200537/mpage_18/tm.htm[/link]
I didn't take pictures do to laziness of the mod but here is the link to a thread that does have a picture. Scroll down to j blazes photos and that is the sub-piston port as viewed through the exhaust outlet.

savagecommander

EGR on 2 stroke nitro, whats next, smog tests on my savage? there could be a few things going on here. the port in piston(pip) is allowing a small amount of exh gas into the case, thus warming the mix, and allowing better combustion due to better fuel atomization.
or.... the pip allows the exh gas to reduce the flame front during combustion(which is proven in 1:1 engines) which also allows a slower but rougher idle speed. there also may be less heat loss to engine parts and cyl wall due to introduction of exh gas, which= more effective combustion. this may also only occur at low rpm, due to the piston being near tdc when the pip opens, and the escaping exh gas does not have enough time to be "sucked" into the case before the piston is on its way down. these are only thoughts i have.

Anthoop

I believe the throttle will always have a wider opening for a given rpm with any form of EGR system.
The combustion process is slower and more efficient as there is less oxygen in the combustion chamber.
Regarding 1/1 cars egr systems have a valve to shut off at low and high rpms

lsurber

I have the engine down now for inspection and will take pictures. Another member J Blaze is trying this also but is having troubles which I have not had! My engine was brand new and his is spanked hard with no compression at all.............probably where his troubles are!

So far I am liking the mod alot! No noticable loss of power and really takes a tune well and likes to be run hard! Lots of smoke due to extra oil coming back in! No load-up stall on full throttle from idle normal to a rich running engine! Very low idle and needs a ton of priming to get it going.......but, once it's lit it won't quit!

I really need to get the degree wheel on it to look at the timing! Very interested in knowing the results! If I had to guess I would say open from TDC through 40-60! If I remember from measuring last night my radius cut on piston skirt is 14.48mm from center line of crank at BDC!