Sleeve Porting: What does what?

[jaxracer]

Just looking for a general run down of the general consensus of what does what regarding sleeve porting. I have a general idea of what I want to do but I was looking for additional information and opinions on how to do it.

Bypass ports in the piston? Booster exhaust ports and how to cut and integrate them effectively in a sleeve that doesn't already have a booster exhaust system? Widening ports? Adding ports below the chamber opening? Port shape? Proper way to flow ports? How much is too much? Etc. etc.

Also, what might be an easier question to answer is what should you NOT do when modifying a sleeve.

Any help from you engine gurus would be very much appreciated.

Thanks,

-Mitch

 

[RonShaw]

Jr,

Marty Davis is "your man" on these discussions for sure. There seems to be a lot of people that swear by his software to help achieve the correct timing numbers BEFORE you start cutting. Steve Woods, Joe W, Stu Barr, Mark Bullard, Aussie Aaron Alberico, and others hopefully will chime in and give their thoughts. NovaRossi seems to me the "master" of directional porting as some of their competition sleeves look like they were shot with a shotgun....hahaha. There is a delicate balance as the intake (crank, rotor, disc) opening and duration timings will likely need to be made as well to match what you are doing with the boost and exhaust ports.

Good luck. I will be following this one as well.........

 

[Jim Allen]

Modifying an existing sleeve would at first appear to be the easiest thing to do. One question to ask yourself is; how would an engine manufacturer change any port geometry, timing, area, shape, etc.? Does any one think that a Dremel tool or a degree wheel would be used to do this type of work? As is the case with all small size 2 stroke engines, 40 cc down to 5 cc, great accuracy in cutting & knowing the exact "number" becomes absolutely necessary when doing any modifications.

When studying examples of modern day, highly successful, high performance 2 stroke engines such as the Metkemeyer .40 cu in speed engine; the Aprillia 125 cc motor cycle racing engine; etc., it can be easily seen that the transfer shapes & window geometries used are not remotely similar to what is used in "modern", present day, minature two cycle engines that we use. Also, the tuned pipe technology & the materials used to construct tuned pipes are very different.

When an engine builder or modifier begines to effectively apply already existing technologies, such as; ceramic hybrid bearings; steel roller rods with a cage; radiused transfers; increasing transfer port time area numbers; increasing blowdown time area numbers; toroidal type heads; radiused port edges to increase the mass flow through the engine by eliminating turbulence & loss of pressure in the flow streams; applying the correct piston & liner taper amounts according to the stroke of the engine; etc.; will engine HP amounts & RPM's be greatly increased.

Jim Allen

 

[shoboat]

Fellas,

You can do all the cutting in the world to our engines, but you still need

to match the propeller load to the engine and tuned pipe combination.

Enjoy Your Testing Program,

Mark Sholund

 

[RonShaw]

Fellas,

You can do all the cutting in the world to our engines, but you still need

to match the propeller load to the engine and tuned pipe combination.

Enjoy Your Testing Program,

Mark Sholund

Yes Mark,

This step is probably more important than engine porting. Proper pipe tuning and prop selection is the easiest and largest power and speed gain any boater can achieve. Inside the motor is the icing on the cake and was why I'm sure Jr. started this thread and what he wanted to find out!!!!!!!........

 

[Charles Perdue]

Probably one of the areas for the largest increase in HP and durability, is the fit and finish of the piston and sleeve assembly. This in conjunction with the proper care, maintainence procedures, and breakin procedure to maintain this fit. If you do not have this, then nothing else really matters.

Charles

 

[lohring]

Read the posts here:

http://www.intlwaters.com/index.php?showtopic=49555

Lohring Miller

 

[David Bryant]

You can do all the cutting in the world to our engines, but you still need
to match the propeller load to the engine and tuned pipe combination.

Enjoy Your Testing Program

yep, you're correct. And being able to drive clean & efficient.

 

[Joe Warren]

Mitch, Depending on what you are trying to achive? Some alter the intake and exhaust timing. Most modern day engines come with head bowl volumes that use low nitro & must be changed for your high nitro use... Many engine today incorporate Piston LOOP porting. One of the 1st guys that I bought a engine from and watched him tune a boat & race was Stan Simpson Sr. Stan made this LOOP PORT mod before he even cranked the engine, Later he was one of the first to cut the T porting into the liner to increase time for the fuel to be blown up towards the top of the piston.. It enhances fuel flow thru the engine at high RPM, Frank Orlic uses (Upside down) piston/liner porting. As the piston travels down the Postive pressure pushes the fuel flow up with direction. This mod today it extremely efficient & I`am surprised the engine mfgers have not pick up on this modification. We call it the Poor Mans Super Charger Effect!!! The best advise is to understand the theory of a 2 stroke before you start to cut on it to mod the existing numbers & find the limits of changing the existing numbers.... Where / What the pressure is and when it changes is important... Altering the port timing does efffect Pressure changes. You can enhance the stk numbers and sometimes the engine mfger is trying to limit the Total RPM of there engine or it could be just theory... ( it is time to close the port to start to make postive pressure) After you altered the engine and the Engine Rpm is Rasied. You must remember to load the engine with more prop. Or contact a engine tuner to improve the performance of the engine.

 

[moparbarn]

proper load is huge! i've had 2 different .21 cmb engines ( 1 TT & 1 evo2 LS) that were modded by 2 different well known engine builders. both were VERY picky about prop load. they ran ok, but when i INCREASED the load, they both woke up. kinda like a chain saw clearing out in the heart of a tree - more power, more rpm (even with increased load), & a "happy song". both were EXCELLENT engines, but not until i found the proper load.

 

[Joe Warren]

Load = heat!!!!

 

[moparbarn]

& heat = better burn

 

[jaxracer]

Mitch, Depending on what you are trying to achive? Some alter the intake and exhaust timing. Most modern day engines come with head bowl volumes that use low nitro & must be changed for your high nitro use... Many engine today incorporate Piston LOOP porting. One of the 1st guys that I bought a engine from and watched him tune a boat & race was Stan Simpson Sr. Stan made this LOOP PORT mod before he even cranked the engine, Later he was one of the first to cut the T porting into the liner to increase time for the fuel to be blown up towards the top of the piston.. It enhances fuel flow thru the engine at high RPM, Frank Orlic uses (Upside down) piston/liner porting. As the piston travels down the Postive pressure pushes the fuel flow up with direction. This mod today it extremely efficient & I`am surprised the engine mfgers have not pick up on this modification. We call it the Poor Mans Super Charger Effect!!! The best advise is to understand the theory of a 2 stroke before you start to cut on it to mod the existing numbers & find the limits of changing the existing numbers.... Where / What the pressure is and when it changes is important... Altering the port timing does efffect Pressure changes. You can enhance the stk numbers and sometimes the engine mfger is trying to limit the Total RPM of there engine or it could be just theory... ( it is time to close the port to start to make postive pressure) After you altered the engine and the Engine Rpm is Rasied. You must remember to load the engine with more prop. Or contact a engine tuner to improve the performance of the engine.

Awesome info here guys. Joe you brought up using "T" ports. I've seen these ports in several engines and some older engines from Stan from a while back. I believe Marty also touches on these style ports in some of his technical papers. My question though is, when you create this "T" port, doesn't that lower the timing numbers of the side transfers and overall affect the engine? How exactly does that work and how would you effectively use a "T" port without really messing up the timing numbers? For this fuel blow down you were describing, wouldn't it be safer and less likely to mess up the timing numbers if you were to leave the main side transfer ports alone and just create an additional long retangular port underneath it below the piston's BDC so as to not affect the timing while still achieving the same goal?

Also, do you have any kind of pictures regarding Orlic's upside down piston porting? I'm not familiar with this type of porting at all and don't quite grasp the concept. You sure do make it sound good though. Haha.

Charles, you mentioned fit and proper breaking in of the piston and sleeve. That brings the question of, What would you consider a proper break in procedure and how much difference have you noticed doing it that way versus a way that you may have done it in the past? I'm asking because I've heard numerous "Correct" methods for breaking in engines from running a couple gallons of fuel through the engine with it blubbering fat to let the piston work it's way in the sleeve before wrenching down on the needle, to leaving the needle fat but bench running the engine without water in order to get the engine temp over 200 degrees farenheit to allow the piston and sleeve to expand properly. So as long as I've been running r/c boats (over 10 years) I'm still not sure what is "right" and what will gain the biggest increases in horsepower while maintaining the lifespan of the engine.

Jim you brought up toroidial heads? What is so different from those types of heads versus a normal stock head button say found in a CMB? Do you have a link that could explain those a little more clearly? Also, you talked about increasing blowdown numbers. What would you consider the "sweet spot" for blowdown time area numbers and what limit is there to increasing blowdown?

Aside from timing numbers, one of the most important things that I see to be a recurring mention is flow within the engine and how to maximize that. How can that be achieved because across engine builders I've seen different things from "T" ports, to piston bypass ports, to finger like lines dragging from ports, to some engines cutting out a square section of sleeve behind the main intake port (like in the CMB TT), and even different finishes (rough, smooth, brushed, etc). What actually works?

Thanks a lot for the info gentlemen, this is becoming a tremendous help. Definitely getting the wheels spinning. h34r:

-Mitch

 

[Charles Perdue]

Everyone has an opinion and a procedure, this is mine.

On breaking in an engine it basicly comes down to load, heat and plenty of oil. No point in running the engine in without a load. Put a smaller prop on the boat, take off the water line, keep it rich without being slobbering and run it. Let off the throttle for a few seconds to let the engine breath and the internal temps neutralize. Let the extra fuel cool it. Do not even start the engine the first time without preheating the engine. It can be damaged almost instantly. Once the fit is damaged then it is all down hill from there. Add extra oil to the breakin fuel, up to 5% and gradually decrease the amount until the engine is broken in. It can be raced using these conditions. Run it, run it and run it.

It will thank you.

Charles

 

[Jim Allen]

"Jim you brought up toroidial heads? What is so different from those types of heads versus a normal stock head button say found in a CMB? Do you have a link that could explain those a little more clearly? Also, you talked about increasing blowdown numbers. What would you consider the "sweet spot" for blowdown time area numbers and what limit is there to increasing blowdown?"

The sites that describe in detail how toroidal heads work are proprietary, even though these type heads have been in existence since 1973. When considering, by dyno & lake testing, the difference between any hemi style head & torodial head types, two things become apparent. Toroidal heads run at much higher compression ratios without any detonation. A much richer needle setting can be used, even when port geometries are not ideal. Typical deck clearances are; "reduce the deck clearance until the piston just begins to touch at the engines maxium RPM point." In my .90 cu in nitro engine this number is .001" & in my 26 cc gas engine it is .002". "The flat electrode of the spark plug in my gas engine is .016" away from the piston crown ATDC."

The "toroid" shape produces very high MSV ( maxium squish velocity) numbers at the intersection of the bowl's outside wall & the very sharp corner of the squish band. Squish band areas are held at 50% of the bores area. Moving the ignition point to the center of the chamber speeds up the entire combustion process, raising the peak combustion pressure higher, "much sooner", The flame propagation is downward & outward from the center. It rapidly accelerates away from the center in all directions. Because the toroid can burn much more fuel in less time, more power can be generated from the same fuel. Evidence that a toroidal head design is working will be a much richer needle setting & increased HP across the entire RPM range.

The "sweet spot" for any blow down time area, for any bore stroke combination, can only be determined by testing. Without the use of CFD ( computational fluid dynamics) simulation, I believe already established engine technologies show the following. An exhaust width of 90% to 120% of the bores diameter is best; a flat top exhaust always gives a greater blowdown time area number than any oval or round top exhaust window of the same width; a triple windowed exhaust port is best, with transfers placed beneth the outer triangle shaped exhaust windows; "T" top shaped exhausts also give large blow down time areas & can be designed with 2 angles to reduce initial window opening flow turbulence.

Jim Allen

 

[Joe Warren]

Mitch I really dont know what size engine you are thinking of But... anything you can do to increase fuel flow and enhance the original numbers is a good starting point. however i will tell you that unlesss you are going for Max Effort, Boat set up, Pipe length, Prop Pitch & High Nitro Content, Stk enhancements are sometimes very good....Example, a awesome boat can make a Stk engine look Very Good!! There is no doubt there are some friends of yours that can pick your speed up with just a pipe change or a pipe length change, the next friend can help with more speed from a different prop or a different prop Mod, and the next guy could help with boat set up....... if you see a boat run exceptionally well. Someone is rubbing on all parts of that boat..... Point is the engine dont have to do all of the work, it just needs to be right & in good health.....Sometimes a Good Combo of parts make for a awesome running boat!!!! the Marty Davis tech help .. helps anyone understand all theories and the mechanical aspect of what needs to happen to get a boat to perform at its Best!!!!! It may or may not cover all of the Finger Porting on intakes and transfers, Winged Ex Porting, sub Ex porting,Piston Porting designs,

 

[Charles Perdue]

YEP!!!

 

[lohring]

We just finished some interesting dyno testing on a SAW engine I built. I increased the timing for over rev power and was surprised to find the peak power off considerably from another engine that had the same over rev power. Both engines were running the same carb and pipe. A quick look at the torque curves of both engines showed that the mid range torque on my engine dropped giving a constant, low power from 14,000 to 18,000 rpm. The other engine's torque held constant giving a nice power peak.

I attribute this to poor scavenging due to poor rear transfer aiming on my engine. Past the power peak the similar large port areas keep the flow going. The engine still could be a usable SAW engine, though since the part of the power curve that would be used is the part after the peak. It would just be harder to prop to and launch. I wouldn't try to heat race it. The low power would hurt acceleration off the turns.

Lohring Miller

 

[Mark Poole ModVP]

You will find the same thing happens in a large (lifesize) two stroke. When we raced OPC outboards raising the exhaust ports for more top end speed would flatten the bottom end power. If we were racing on a short course with single pin turns, someone with an unported motor and the right set up would eat your lunch. Your top end engine did not have time to catch back up on a short straightaway.

 

[dwilfong]

I have found and was led in this direction that keeping the ex timing as low as possible to achieve 30% blow down works the best. On most new 3 port eng gust flattening off the top of the transfer and adjusting the ex if needed to achieve 30% difference from ex to transfer timing will give the best over all performance. Most new CMB eng are there already. Also the amount of ex area open before the transfers open is something to look at. Would like to get some input on intake to ex timing area % from those that have experience on the subject. Timed area means a lot to the whole equation. David