Common mis-conceptions about compression/head design and fuel requirements as it relates to a 2 stroke internal combustion engine
First off: This is NOT to be considered a “Covering EVERY Scenario” or “Lesson in Science” type article. It will, most likely, have some “holes” in it that could be seen as incorrect under certain scenarios.
This article is being written to touch on certain misconceptions regarding this area. It will be “Generalized” and NOT all encompassing.
This will, most likely, be an ongoing discussion as more data and topics surface. It is difficult to recall everything on the spot.
It will be based on Theory, Reality, Direct Experience, Automated Testing, and Common Sense. All topics and references will have been “realized” using one of the above at some time. NONE will have been “fabricated”.
If you do not agree with any of it, please ask yourself if you have DIRECT EXPERIENCE, by “Direct”, it is meant-> 100% direct as the example you disagree with, NOT 99% and not lumping , components (like cylinder head design or other) into one general “bag”.
NOTE: ALL references to Compression Ratio will be full stroke, uncorrected
OK.. let’s get started….
2 Stroke Cylinder Head Misconceptions:
1) Cranking compression via compression gauge will tell you what octane your engine requires in order to run safely… 100% FALSE!
The cranking compression will not tell you much of anything about the required octane. Cranking compression is a good tool used to compare a previous, known, value to a current value in order to tell if anything has changed. This comparison is good for a “health check” of an engine. Again, not real useful in terms of determining the “required” octane for any engine.
2) ALL 10:1 UCCR compression ratio heads (or any other compression ratio) will function the equally on the same engine. 100% FALSE!
This could be one of the largest mis-conceptions out there. Let’s break it down: 10:1 is a ratio of the volume trapped at TDC as it relates to the volume of the cylinder and head together. For example, if you have a 100cc engine, a 10:1 compression ratio head would be 11.117cc-> 100cc+11.117cc (full stroke cylinder volume) / 11.117cc (head volume at TDC).
As you can see 10:1 will always be the SAME volume given the same engine. What will NOT be the same as how that volume is geometrically accomplished.
There are infinite geometric designs that can arrive at 11.117cc volume.
This is where the fun begins! The same VOLUME head will yield the same compression ratio but can also yield VERY different results in terms of how it performs when installed on the engine.
The geometric design of the head is critical as to how it performs. A simple .001” change in a certain area can have a huge influence on its “effectiveness”.
Back to the misconception… Brand “A” 10:1 head can, and usually will, perform VERY different from Brand “B” head.
Think of fast food hamburgers. If you have a double cheeseburger from one fast food chain, it will/can taste totally different than a double cheeseburger from a different fast food chain even though they have basically, the same ingredients. SAME with Head design.
3) If you raise the compression on an engine it will ALWAYS require more fuel to run safely… 100% FALSE!
This is a loaded subject. It also relates, heavily, to #2 above. It is also going to be difficult to explain. Let’s give it a go anyway.
2 Stroke head design is a huge player (as is exhaust, ignition timing, piston, reeds, and porting etc.) in the tuning and performance of any 2 stroke engine. They all work together.
Changing ANY of these variables can have a pronounced effect on performance (HP, Torque, Over-Rev, Timing, Heat etc.) and fuel requirements (octane and volume etc).
Suffice to say, they are all “Shaking Hands” or “Punching Each Other in the Face” depending on the change made.
This article will be limited to Head Design but wanted to mention that there are other “players”, directly, involved.
Fast combustion is what is always desired. The faster we can complete the combustion process, the better. The head design has large influence on how fast this process completes and what ignition timing is optimum. Advanced ignition timing is not desired. The later we can start the ignition process and still have a good rod angle ATDC, the better. Again, the head design is has a large influence in this. This area can become very detailed discussion. We will stop here for now.
Head Efficiency or Combustion Efficiency is the measure of the head’s ability to convert the supplied Air/Fuel into useful energy. Obviously, we want the highest efficiency we can. Of course, there are exceptions to this as well where we do NOT want a highly efficient head ie. A tuned exhaust system that requires more energy to function better… but that is discussion for another time.
For the purpose of this article, we want the most efficient head design possible.
This, directly, relates to how much fuel/air (F/A) is “needed” to be supplied to the head.
When the head is more efficient, it is converting more F/A mix to useable energy. Does this require MORE Fuel to accomplish? Not always. Anything that is more efficient usually requires less to get the same or better result. This is the definition of efficiency. But, with head design it is not always that simple.
Whether or not your engine requires more or less fuel when adding a head with a higher combustion efficiency directly relates to how good or poor the previous head design was and how the fueling was set up.
For example.. 2014 and newer KTM 250 and 300 Enduro or SX OEM Head.
This head design is so inefficient that it is plagued with a high frequency of misfires. These misfires manifest themselves as a rich running condition when, in fact, the F/A supplied is close to correct with stock jetting.
The misfires are so prominent that most will lean the jetting to lessen this rich condition (caused by the head’s inability to combust). It stands to reason, if you have a head that is struggling to combust the given F/A mix, you will have residual (non-combusted) F/A mix “lingering” in the engine and exhaust that will be combined with the new F/A charge and push it to a F/A mix that is too rich. Of course, this does NOT occur every stroke, but is frequent.
Leaning the carb mix via jetting alterations will provide less Fuel and, in turn, lessen (not eliminate) the frequency of the head misfires. Of course, those times (frequent) when the head is NOT misfiring, allow for a lean condition. This lean condition will create added heat and will lessen power output. If left too long it can damage your engine.
Point being.. You are treating the “symptoms” of the problem vs. addressing the “source” (head design). You end up with a “compromise” with less power BUT ,possibly, a “cleaner” running engine. So, you feel you have fixed your issue.
If you address the source of the misfires (head design not rich jetting) you get rid of all the symptoms as well. This is the better solution. It is like having a cold. You can treat the runny nose (symptoms) and feel better OR you can get rid of the cold (source) and the runny nose goes away with it.
Now, how does this relate to installing a highly efficient head in terms of fueling?
In the case of the KTM 250 and 300, like mentioned, the head was the real culprit of the rich condition and the leaner jetting was a compromise to lessen the misfires. The engine required the larger jetting spec, but the poor head design limited the engine’s ability to utilize the required fuel.
When you run in a leaner state, you, generally, will make less power even if the engine is running cleaner. The engine requires sufficient amount of F/A in order to produce the maximum power.
They can run fine lean, they are just down on power and you would not realize this unless you compared to one that was not running lean. You don’t know what you don’t know!
When you install an efficient head, like the RK Tek Head, you do not have this frequent misfiring issue because the design of the head helps to prevent it. With the higher efficient head design, the engine can benefit from the larger F/A volume and produce more Torque and HP.
How about fuel injection? With fuel injection, you are only as good as your Fuel Mapping, Injector Firing, and Fuel Pump Pressure. If any of these are “out” you can have a poor running engine. It can be “lean poor” or “rich poor”.
What happens when you add a more efficient head to a fuel injected 2 stroke? Well… There are many scenarios. Suffice to state that the head designer better have some good knowledge of how to accommodate the inner-workings of 2 Stroke FI. With this knowledge, nice gains can be had with no fuel alterations or controller required.
HOW? you ask?--> It all reverts back to how the exhaust, head, ignition timing, and reeds “hand shake”.
Knowing how these interact with each allows the head designer to “compensate” in the design to allow for more power without upsetting the “balance”. This is a very complicated topic.
It is often the case, that the design that works best for a carbureted induction engine will not be optimum for a FI engine.
Testing is required to find which design can keep all the other players “happy”.
4) Air Fuel Ratio Pre-Combustion can be measured, and is the same as AFR measured Post-Combustion.
There is a huge mis-conception that Air/Fuel Ratio O2 sensor readings (in the pipe AFTER combustion) have a direct (one to one) relationship with the Air/Fuel Ratio reading Pre-Combustion (Carb to Head Path).
O2 or Lamba sensors measure the amount of Oxygen present in an exhaust sample and relate/compare this reading to a known reference oxygen level (Usually the ambient air).
While these readings can provide valuable information about POST Combustion efficiency and ratio, they do NOT tell you about the F/A ratio PRE-Combustion.
It relates back to #3 above. How efficient is the head? If you have a head design that is very efficient, you will have a more complete combustion process resulting is a “better” AFR shown on the exhaust sensor.
What this sensor reading does NOT tell you is what the head had to work with to create this output. It also does not tell you how “optimum” you are because you have not pushed the head to its limits (ie. Adding/Subtracting more fuel or air) to determine what it can efficiently combust. This is controversial. You can have a 13:1 AFR measured.. add some fuel or air (or both), and STILL have a 13:1 measured AFR. This will largely depend on the head’s design and how it works with the other primary engine components. It is like stressing a frayed rope., you really do not know when then rope is going to break until it does.
Point being, there are many variables in play here, including the limitations and design of the AFR measuring device, itself. Suffice to say, that measured AFR is NOT the “End All” and can lead you astray if not careful.
With any carb system, unless the head is increasing air-flow (possible), fuel flow into the engine will remain near constant for a given RPM, heat, and load EVEN if the AFR reading changes. What, really, has changed the AFR reading is the head’s ability to combust a higher or lower percentage of what it was given.
If the head is very efficient, usually, LESS F/A is required for the same output. Again, this is all relative and not always the case.
For example, on the 2000-2012 Ski Doo 800 engine. We were able to increase the compression, significantly, and also reduce the main jet 5 sizes. This resulted in a large power increase and better fuel economy. This was due to the OEM head design being very inefficient and hot. The OEM design needed extra fuel to keep combustion temperatures in a safe range. Without this added fuel the OEM head would run too hot and detonate. It was, essentially, cooling temps with fuel. The RK Tek Head design focused on increased combustion efficiency and minimizing hot spots within the chamber. This allowed for a much better and safer running engine.
5) Is Higher Compression required to extract more power? In short NO!
One can easily create more power using the SAME compression ratio as before but using a better design. How much more power depends on how much better the design.
Increasing compression (leaving all else the same), is always good for increased performance but it can come at a cost unless you optimize the design and “hand shaking” that is happening with the other primary engine components.
IF you optimize these relationships you can, successfully, increase the compression ratio without any compromises (gains across the board).
It is, usually, never as simple as a head “shave”. However, while this can be effective, it, usually, is not and comes at a cost. Robbing Peter to pay Paul type scenario.
It ALL reverts to the HUGE complexity of the 2 stroke engine and how ALL primary components interact.
‘Nuff for now.. Already way too long!!
2 STROKE ENGINE AIR/FUEL RATIO: What it means and how is it determined?
Air/Fuel Ratio (AFR) seems to be widely mis-understood as to what it actually represents and how a non “ideal” AFR effects the running of the engine.
Let’s try and break it down into VERY simple terms and ,hopefully, gain a better understanding of it and other related areas where it has an effect.
OK, found this definition on the internet and it is fairly accurate so, let’s use it for now. “Air–fuel ratio (AFR) is the mass ratio of air to fuel present in a combustion process such as in an internal combustion engine or industrial furnace. ... If exactly enough air is provided to completely burn all of the fuel, the ratio is known as the stoichiometric mixture, often abbreviated to stoich.”
In simple terms, it is the ratio of Air to Fuel in a combusted charge.
Think of mixing your oil in your 5 gallon fuel container. If you mix at 50:1 that is 50 parts fuel to 1 part oil.
KEY NOTE: AFR is a RATIO and is not referencing a VOLUME. There are an infinite number of possibilities of Air-Fuel Volumes that can have the SAME Air-Fuel Ratio. Just like mixing your fuel and oil. If you mix 10 gallons at 40:1 it is much more fuel than mixing 1 gallon at 40:1 BUT the 40:1 RATIO remains the same.
AFR for a 2 stroke engine can vary greatly and the engine can still run well. There are MANY variables that determine what the “best” AFR is for a particular engine and its set up. What is ideal (AFR) for one engine may be problematic for another, Application and Power output play a part in this, as well as, many other variables. The purpose of this article is not to “dive in” to all those variables (maybe later) but to simply gain a more comprehensive understanding of AFR and how it relates in an engine.
What is the AFR range for a good running engine? As stated, above, it varies. Generally, this range will be from 12:1 to 15:1 for Gasoline Engines. Again, at 12:1 AFR that is 12 parts Air to 1 part Fuel.
For this article, we will focus on a Naturally Aspirated Engine equipped with a slide valve carburetor and an air-box that is exposed to the atmosphere. Typical motorcycle set-up. We will also assume that the fuel octane requirement is adequate for the engine’s design.
How is the Air and Fuel supplied? Air is supplied via the air-box and inlet track. Fuel is supplied via the carburetor circuitry.
Air passes through the carb body causing a venturi effect which, in turn, pulls raw fuel into the incoming air stream creating a stream of Air and Fuel Mixture (AFM).
This AFM enters the engine when the pressure on the engine’s intake track is less than the atmospheric pressure found at the carb outlet. This pressure differential (Delta P) is mandatory if any AFM is to enter the engine.
This AFM is atomized before it enters the engine and becomes even more highly atomized once inside the engine.
This, highly atomized, AFM is directed towards the combustion chamber (head) where it will, hopefully, ignite and combust. Remember, this AFM has an Air-Fuel Ratio (AFR) associated with it.
This AFR will determine how completely it will combust and how much energy will be delivered during the combustion process. Yes, there are other “players” involved besides just the AFR, but we are keeping it simple for this article.
The combusted charge is expelled and the whole process repeats.
Now, that the process has been defined (in the most simplistic manner). We can talk about what occurs when the AFR of the AFM is not ideal or close to ideal.
RICH Air-Fuel Ratio: This would represent more parts fuel vs. air than is needed.
With a Rich AFR, the AFM may not completely combust. Incomplete combustion means that you have not extracted the max amount of energy that was available for a given AFM. While this is not desired, it is not always a bad thing. Incomplete combustion, a result of a rich AFM, does have some “perks”.
One perk would be that any un-combusted fuel can act as a cooling agent to lower internal engine temps which can help keep the charge density higher.
Another perk is that it can lower the exhaust temperature which will cool the pipe. With a 2 stroke pipe, a cooler pipe will alter its effective “tuned” RPM and this can greatly aid performance when operating at a lower RPM than the pipe was designed.
There are some other “perks” but we will stop for now and move on.
Rich AFM can manifest itself in a few different manners:
1)A very common example would be to have a stuttering or hesitation in the engine’s running. NOTE: This is NOT just a “NOISE” but a REAL runability issue. Do NOT chase NOISES!
2) Massive mis-fires and spark plug fouling.
3) Extreme jetting sensitivity. Engine can be overly sensitive to temperature and elevation changes.
LEAN Air-Fuel Ratio: This would represent more parts air vs. fuel than is needed.
With a Lean AFR, the AFM may also not completely combust.
Lean AFM will produce more internal heat. This added heat can be un-harmful for short periods. If you allow this lean AFM to continue, the heat will build/grow onto the engine’s surrounding components and it WILL cause problems including severe engine failure!
Lean AFM can manifest itself in a many different manners. Here are a few:
1) Narrow Power Band: The effective power-band can be shortened causing abrupt power delivery. This also lessens the lower RPM power output. If your engine comes into it power-band very abruptly, with little power before (ie narrow power-band, big hit), it could be due to a lean AFM.
2) Engine over-heating: Like stated above, lean AFM raises internal engine temps. When your engine is hotter, everything else is hotter. It is not uncommon for water cooled engines to over-heat as a result of a lean AFM.
3) RPM run-on: The lean AFM’s added heat input can cause a higher RPM that is slow to return to its correct RPM. This is sometimes ref erred to as a “Hanging RPM”
4) Detonation: Please see the article here: https://www.2strokeheads.com/index.php/site-map/articles/80-technical/91-exposing-the-myths-of-high-octane-fuel-and-the-definition-of-detonation
5) Pre-Ignition: Not really a direct result of the lean AFM, but the lean AFM can certainly be a contributor to pre-ignition. Pre-ignition occurs whe becomes so hot that it becomes a source of ignition and causes the fuel to ignite before the spark plug fires. This, in turn, may contribute to or cause a detonation problem. Pre-ignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbon deposits within the combustion chamber that have been heated to incandescence by previous engine combustion events.
The phenomenon is also referred to as 'after-run', or 'run-on' or sometimes dieseling, when it causes the engine to carry on running after the ignition is shut off.
Excessive carbon build up or any sharp object present during the compression stroke can onset pre-ignition. This is much more common a 4-Stroke Engines vs. the 2-Stroke Engine.
POINTS of INTEREST:
1) All AFM is supplied via the intake track into the lower end of the 2 stroke engine. If there is any residual AFM within the engine from the previous combustion event, it can richen the AFR of the AFM. It can also dilute the new AFM charge lowering its potential energy.
2) Detonation, most always, requires a load in order to occur. Meaning… if you think you are hearing detonation under a “no-load” running condition (i.e. idle), you are probably mistaken.
3) Air Leaks: Added air via a “leak” is common in creating a lean AFR condition. These leaks can come from a few areas. Some of the more common areas are: Cylinder Base Gasket, Reed Gasket, Reed Boot, Air Filter Seal, Air Filter Boot and even a cracked exhaust or cracked cylinder. These are just a few examples.
4) Air Leak “Weight”: This is an important concept. Given you have an air-leak, the effect that leak will have will be directly related to the volume of AFM. Let’s break it down further: Given a 0.5mm size air leak hole, how much “added” air that can be introduced via that 0.5mm hole is relative to its size, the pressure surrounding it, and RPM. This is also relative to the AFR and volume of the incoming AFM. For example: During idle there is a VERY small volume of AFM entering the engine. A 0.5mm air leak hole, can have a large effect on the AFR of the AFM because the volume is so small. That same 0.5mm air leak hole would have much less effect on the AFR of a larger volume of AFM like you would have at high load and high RPM engine running. So, air leaks will have a greater effect when the engine is under low load and low RPM (i.e. Idle, Low Throttle Operation).
5) Once the AFR of the AFM has been set (pre combustion phase) it is set. Meaning, the combustion chamber is going to try and ignite and combust WHATEVER AFM is trapped in it. It does not care!! It will do its best to complete the process regardless of the results. The combustion chamber design will not cause a supplied AFM to go lean or rich. The combustion chamber does not alter the AFR. If it is supplied a rich AFM, the engine will have a rich AFM combustion event, if it is supplied a LEAN AFM the engine will have a lean AFM combustion event.
Side Note: having a more complete and energetic combustion process can increase air-flow within the engine. This is where it gets a bit complicated. When everything is working better you can have a higher delivery ratio and the pipe can deliver more charge as well. In short... when all internals and externals are "jiving", it can require more fuel via the carburetor.
6) AFR’s are generally, leaner at low load RPMs and richer at the higher loads and higher RPMs.
What is the real function of the ring?
OK, RINGS?? What are the functions of the piston rings? The most common answer is " To create a seal for compression." OK, the sealing off of the gases for the compression portion of the stroke is a major function of the piston ring, BUT this is not all the ring has to accomplish. Let's look at at what else is going on with the rings.
We'll start from Bottom Dead Center (BDC). At BDC, the crankcase is highly pressurized, the tuned pipe is sucking its hardest ,and the cylinder is filling with the fresh charge via the transfer tunnels. The ring has, hopefully, collected a bit of oil from the cylinder wall and is still transferring heat to the cylinder wall. The piston now begins its race towards Top Dead Center (TDC), the ring's radial tension is keeping it as tight against the cylinder wall as it can. The ring is collecting oil from the cylinder wall and getting ready for the compression portion of the stroke. Once the exhaust port has been closed, (controlled by the piston crown edge, or in the case of pistons fitted with a Dykes ring, the ring itself controls port timing), the ring is retaining oil to help with the compression seal, as well as lubrication. The gas pressures from the compressing gases keep the ring tightly sealed against the cylinder wall.
- As the piston approaches TDC, cylinder pressures are building rapidly, the piston crown is getting very hot, and the ring is doing its best not to allow any of the pressures to blow past it. Then combustion occurs (hopefully at about 11-14 degrees ATDC). The ring now takes on its role as a heat transfer. The crown temps are very high and rising and if these temps do not get reduced the aluminum piston will surely melt. The ring will try and absorb as much of this heat as it can and transfer it to the cylinder walls where it can be dissipated . Ridding the piston of these high temperatures is a very important function of the piston ring.
The style of ring, number of rings, and its location on the piston is very important in assuring that this heat dissipation successfully takes place.
Now, the piston is back at BDC and it all starts over again.
The piston is subject to more abuse then any other part of the 2 stroke engine. It is constantly being pushed on, sucked on, fired on, squeezed on.... well, you get my point.
It is the weakest link in the engine.
Over the last decade or so, advances have been made in piston technology. It has been found that adding Silicon to the Aluminum will reduce piston expansion caused by the extreme heat that is present within an engine. This reduction in thermal expansion reduced piston seizures. Silicone also adds strength to the aluminum and reduces wear.
Pistons are often though of as being a perfectly round cylinder. In actuality, pistons are tapered from the top to the bottom. Why?... Well, different parts of the piston are subject to different levels of heat and since heat tends to expand metals, then it stands to reason, that the areas which are subjected to more heat will expand more then the areas that are subjected to less heat. The top of the piston is obviously subjected to the most amount of heat, as well as pressure, and therefore; will expand more.
Pistons are not only tapered, but oval ground at the skirt. Once again, this is to accommodate the different temperatures that are present on different parts of the piston.
So, when measuring a piston for wear, one needs to measure on the skirt faces at the widest point which is always below the wrist pin. Measuring anywhere, but the widest point will give an inaccurate measurement
RK Tek SKI-DOO Custom Pistons for 800R, 800 ETEC,600 ETEC 600HO,600SDI, and 600RS Engines
QUALITY Made Pistons Specifically Designed for Snowmobile Engines
We, at RK Tek, have spent years developing a VERY HIGH QUALITY line of Dual Ring Pistons.
These pistons have be PROVEN to aid with power fade and reliability issues associated with the stock single ring pistons.
These are NOT a Chinese or Taiwanese piston made from our old cars and
These ARE a
HIGH quality combination of materials and
ALL pistons are designed from a blank sheet of paper and made 100% to our spec.
They Have been thoroughly tested and proven to work.
NOTE: These pistons require no special treatment for using!!
You treat them as if they are the OEM piston!!
ALL pistons are $370/PAIR..
The "KEY" is to design a forged piston that is CORRECT for the high load snowmobile engine.. That is exactly what we have done with our piston line..
Our pistons are not smaller than stock and they require ZERO "extra" warm up over the stock cast piston..
So, in short, it is ALL about the piston design..
A Little History....
RK Tek was the 1st company to recognize the short-comings of the OEM BRP pistons. In 2000, the Ski Doo 700 Twin was introduced with its single ring piston design and it Moly impregnated cast piston rings. We, quickly, discovered that the rings were flaking on any pro-longed pull lasting over 45 seconds. Upon further inspection, we determined that the rings were being overloaded with heat and this would cause the ring faces to "chip" or "flake" and performance would suffer because of this.
After countless efforts to remedy this situation (including, Cryro-Genic treatments, different ring materials. etc..) we came to the realization that the single ring was simply inadequate to transfer the heat from the piston to the cooling system. At this point, we decided to find a better suited piston that was equipped with 2 rings vs. 1.
This kit is our now, famous, "DROP IN" piston and head kit (over 5,000 sold) where , not only, did we fit the engine with 2 ring pistons, we also gave the engine a VERY nice porting change via the piston geometry. So, the engine would now be fitted with a much better piston and also have a better port timing design than stock. HORSE-POWER was WAY up! This kit has proven the test of time (over 10 years and running) and has put smiles on 1,000's of people faces!! We could not be happier.
It took Ski Doo until 2004 to fully realize the issues that plagued their engines (remember RK Tek discovered this problem in 2000).
Ski doo only realized half of the issues and decided to keep the single ring design BUT change the ring design to a better design that would not suffer from "ring flake". So, now, we had a better ring but the same old single ring piston. You can read more about the benefits of a dual ring piston and why BRP might have opted for this design in the Tek-Nikal Section of this website.
Since the RK Tek designed pistons are so successful, We decided to expand our piston design line to include many other pistons that are specifically designed for snowmobile engine applications!
Our pistons have a geometric design that is specifically for the rigorous use that a snowmobile engine subjects the piston to... We also use a different alloy that better suits the snowmobile engine..
ALL if our pistons are tested for at least ONE FULL SEASON BEFORE offering them to the public. Using this method, we can rest assured that they will handle the task without issues.
We have went the extra mile and developed our own piston using a custom forging, cam grind , and taper.. basically a snowmobile, high LOAD. design that allows for sustained , heavy, running without failure...
There is no doubt that after 5 years of development on this piston design and manufacturing, that it works and there is no piston that will handle the loads and deliver the performance of this design,. It really is a new evolution in piston design.
Using pistons made in Taiwan or China with absurd claims of added silicone etc. and such are simply gimmicks. Try and call China direct and tell them you need only a 1000 pistons and to bump up the silicone a tad for ya!! (ya know change their WHOLE manufacturing and chemical processes for your 1000 pistons) See where ya get with that .. Yes, you can get a different design with some added holes, bore, markings and what not... but you will never get a different chemical composition of the material itself. Never!
These Manufacturers build 100,000 pistons or more every year.. try getting a small number modified.. Not to mention do you speak Chinese??
OR better yet..
Go order a new truck from Chevy, Ford or Dodge and ASK for a different seat pattern or gauge cluster etc. etc. (simple enough eh?) for your truck.. See if you get it??? Not happening.. and that is in the USA to boot!! Give it a shot.. they will be totally unresponsive..
Long story short.. all pistons are NOT created equal.. there are many differences in chemical composition, machining processes, metal alloy, and of course, design criteria.. You will never see top fuel dragster engines running an "off the shelf" or Chinese piston for that 4-8 seconds. They run very special "Dragster, Nitro," specific pistons to get the job done and done without failure and with max performance..
Why should the snowmobile engine not have the same opportunity?? Now it does!!
Another added "BONUS":
The stock Ski Doo 800R piston with pin and ring weighs in at a whopping 567 grams.
The RK Tek Direct Replacement 800R Piston with pin and rings weighs 484 grams.
So, the piston is 83 grams LIGHTER than the stock piston! This will translate into
more power and LESS stress on your crank. The engine will rev quicker and last longer!
See below for more weight comparisions All weights include pins and rings:
800R Stock(2007-2011): 567 grams RKT Direct Replacement: 484 grams
800R Stock(2007-2011): 567 grams RKT Drop In Piston: 471 grams
800HO Stock(2001-2007): 513 grams RKT Drop In Piston: 493 grams
Here is a list of what RK Tek has to offer to make your snowmobile engine much "happier"
800HO and Non-HO (Series III) Engine: "Drop In" Dual Ring Piston and Head Kit
800R Engine: 800R "Drop In" Dual Ring Piston and Head Kit
800R and 800 ETEC Engine: 800R Direct Replacement Dual Ring Pistons
600HO, 600 SDI, 600RS Engine: Direct Replacement Dual Ring Pistons
Nov. 2006 RKT 827 Dyno Run at Dyno Tech Research in New York
2004 Rev 827 MXZ
Independent CUSTOMER'S Run--> NOT RK Tek's Personal Engine
Below you will find the dyno results of one of our CUSTOMER'S 2004 827 engine builds. This engine was tested with the 3 different pipes.
1) Stock pipe and Can
2) BikeMan Pipe and Stock Can
3)Decker/Straightline Performance Pipe and Stock Can
This engine was run on 91 octane for 3 repeated 20+ second pulls with each test. You can view the results for yourself.
It is worth noting that an engine that is capable of producing this kind of power will benefit from increased air-flow from the air-box..
The 2004 MXZ 800 is at 138HP in its stock configuration. The RKT 827 is adding 33HP and TONS of Torque to this engine. That is a 23.9% increase in power!! It is all being done on 91 octane pump gas and with the stock pipe and can.
One should also note the VERY broad power-band width of this engine build. With a broad power band, clutching becomes a breeze!!