Everyone who races in any RC hobby has had this discussion with his buddies (“Bench Racing”): What is the perfect timing for the RC engine? I must admit that I have participated in more than one such session!

What then IS the perfect timing for a 2 cycle engine?

First we must analyze several things which will materially affect the answer to this question:

1. What pipe are we using?
   

2. What is the size of the engine?
   

3. What is the maximum RPM we want to operate the engine ?
   

4. What is the load? (Prop, gearing, etc.)
   

5. What percentage nitro are we going to use?
   

6. What compression ratio are we using?
   

7. What is our driving style ?(Tight inside, Fast outside, Middle of the Road)
   

8. What type timing are we talking about? (Exhaust, Boost, Transfers, Rotor or Crank Assembly)
   

Lets analyze these things in reverse order.

TIMING TYPE

Most often, Exhaust Timing is thought of as the magic number responsible for the big part of performance. This is really not

the case. All of the components are about equal in the total equation. First let me state my PERSONAL opinion about what the perfect timing is, for those items that I believe are the same for ANY engine.

INTAKE TIMING

I believe that the Intakes (Boost and Transfers) operate most efficiently with a total open duration of 124 to 126 degrees. The Very First thing I do to my engines is to set the intakes to this range. I usually do this by cutting the UNDERSIDE of the liner and dropping the liner until I get 124-126 degrees of duration. An important note here is that you MUST be very sure that if you drop the liner you DON’T allow the bottom of the piston skirt, at TDC, to be above the bottom of the exhaust port thus allowing the engine to have “Sub-Piston Induction”. Why do I think that this is the magic number for the intakes. I have done considerable testing both at the pond and on the dyno during all times of the year, at all temperatures. Most of you will verify that as the temperature gets really hot in the summer over 90 degrees, your engine looses a lot of power. This can be almost totally eliminated, by using lower intake duration’s. After you have dropped the liner to the 124-126 degrees you can start to think about the exhaust.

EXHAUST TIMING

Exhaust timing is like a tuned pipe, the higher you make it the higher the RPM band. If you want to use an engine in the higher RPM ranges you will want to use a higher total exhaust duration. This will be at the expense of some loss in torque. If you want to use the engine to LUG a high pitch prop or tall gear, you will want to use lower exhaust timing. I personally think that the way to heat race most effectively is to use the higher RPM area of the engine. It seems to have a much broader range of power. The people who use the LUGGER concept have great success at the timed events since they are relying on a very narrow HP band and can control it for use in the timed event. If you accept my opinion, that it is better to use the higher RPM area of the engines capability for heat racing, I think that an ideal exhaust open duration can be defined with some degree of accuracy. I believe that the smaller the engine, the lower the total Exhaust duration

http://rcboat.com/timing.htm 1/19/2011

Page 2 of 3

you should use. As an example, I use 183 degrees of exhaust duration on my own heat racing .21 size engines, 185 degrees for my .45 engines, 188 degrees for my .67 engines, and 192 degrees for my .80/.90 engines. I usually run a smaller area propeller, with high pitch in order to utilize the RPM area of the engines capability.

ROTOR/CRANK TIMING

Rotor or crank timing is one of the easier areas to deal with. Since this is the “MAIN VALVE” of this air pump (rc engine) it is very important that it seals closed VERY WELL. You have no doubt had an engine that performed well and would launch almost any propeller and pull very strong off the turns. After running the engine for a few months, it lost most of its power and launchability. This can be traced “in almost every example” to a poor sealing rotor assembly or crank assembly. This unit should be surfaced to insure a perfect seal at least 2 time per season for a rotary valve engine. JFA Custom (317-241-4724) can do this for you at a VERY reasonable price if you don’t feel confident in doing it. On the front induction engine (Crank Induction) you should change the bearings AT LEAST 2 times per year (Once before the season and once in the middle of the season) with the best bearings you can buy (Boca). As for the timing of the rotor/crank assembly, I believe that the rotor/crank should close 65 degrees after top dead center. I think that the total open duration should be 215 degrees, thus automatically making the intake open at 210 degrees after top dead center. I believe that this is the most efficient rotor/crank timing for all size, high RPM 2 cycle engines, using high nitro.

What effect does compression ratio have on the timing you use?

COMPRESSION RATIO’S EFFECT ON TIMING

The higher the compression ratio you use, the more horsepower you are going to generate! This will have a huge effect on the durability of your engine parts, and the heat the engine generates. You should use the highest compression ratio you can and still allow the engine to be reliable. It depends to a large degree on the nitro content that you use as to how high a compression ratio you can run. The higher the nitro content the more heat which is generated, thus a somewhat lower required compression ratio. If you try to fool the engine into thinking that it is being cooled very well, you can get away with a higher compression ratio. I started running a special head which cools the glow plug with water, and am able to run 1 to 2 point higher compression ratio, thus making maybe 10% more horsepower. These heads are now available for most engines in my home page through Lakeside Racing Products. You will have to adjust your compression ratio to suite your application(Nitro, boat-car-plane weight, driving style, etc.) You will want to experiment to find out what “works for you and then use this ratio on all your models”.

NITRO’S EFFECT ON TIMING & PERFORMANCE

By this time you already know that the higher the nitro content the higher the heat level you will generate, but also the higher the horsepower! I use high nitro fuel in ALL my boats! Why do I do this? Simple, I can “throttle down” and effectively have low nitro. BUT, when I need the extra power, it is always ready to serve me with my throttle. You don’t have to use high throttle all the time you are racing, but as you NEED it! I suggest you set your model up initially to use high nitro and use the throttle to lower the nitro. What is high nitro? I use 65% in my .21 engines, 60% in my .45 engines, and 55% in my .67 engines, 50% in my .80/.90 engines.

THE LOAD - WEIGHT OF THE MODEL

A large consideration in the application of all the data presented here is the basic concept of Physics that a LIGHTER object is much easier to push than a HEAVIER object! In constructing your model, I believe that the lighter you can make it the better! Look for boats, cars, planes that are constructed with integrity, yet are very light. Most of the “HIGH END” competition models will advertise lightness. These people KNOW the importance of lightness.

THE RPM BAND WE WANT TO OPERATE THE ENGINE IN

After numerous tests on the dynamometer, I have a very good feel for the RPM range which allows the engine to operate in its most efficient mode. I believe that a .21 engine with a fairly “square” bore stroke ratio (the bore is almost exactly the same as the stroke measurement) should be run in the 26500 to 30000 RPM range, a .45 24500-28000, a .67 22000-25000, a .80/.90 20000-24500. You will find that the engines which have a larger bore than stroke will operate in a higher RPM range by about 1000 to 1500 RPM.

WHAT TUNED PIPE ARE WE USING

The tuned pipe is a tremendously important item to the total equation. I will spend a complete technical

http://rcboat.com/timing.htm 1/19/2011 Page 3 of 3

paper on this subject sometime in the future. The pipe MUST be integrated into the total equation by testing on the water, in the air, or on the track unless you have a dynamometer at your disposal. I have a dynamometer in combination with John Ackerman at JFA custom. We test year round on many items. One of the first items we tested was tuned pipes. Why, because the largest gain by bolting on a component is the tuned pipe! In a typical test we would see a variance of 5000+ RPM under load on a typical engine. This translates to more than you can gain by engine modification! You must get the proper pipe for your model before starting to modify the engine. What is the best pipe? I won’t state that in this paper, but you can call or E-Mail myself or John Ackerman and we will tell you our opinion. Marty Davis E-Mail (mdavis76@tampabay.rr.com), John Ackerman’s Phone Number (317-241-4724)

SUMMARY

As you can see, the timing of an engine takes into account MANY items of importance. There are a few items which are almost cut and dried, but MOST require some variation, dependent upon model & operator variables. Your analysis of the items discussed above are what directed me to develop my Engine Analysis Program. I found the mathematics and analysis cumbersome to the point of making me dread working on engines. I don’t dread it any longer since I have a tool I use constantly to analyze data. I might state also, that I found a tool anyone working on engines MUST HAVE. It is a depth measuring gauge developed and made by Bill McGraw owner of Rossi Sales of America (901-396-7485) This tool will ACCURATELY measure head clearance and piston depth.

Until Next time......................

A special Thanks to Many that Contributed to the constant quest for information and answers over the many years, especially including: Dr. Brian Callahan, Tom Grannis, Norris Sparks, John Ackerman, Joe Kramer, Bobby Coleman, Tom van den Brink, Norm Doerr, Rod Hendricks, Joe Wiebelhaus, Hank Schneider and many others.

]]> http://rc-engine-analysis-software.com/rc-nitro-engine-timing-suggestions/feed 0 http://rc-engine-analysis-software.com/how-rc-nitro-engine-tuned-pipes-work http://rc-engine-analysis-software.com/how-rc-nitro-engine-tuned-pipes-work#comments Thu, 29 Sep 2011 01:55:51 +0000 Marty Davis http://rc-engine-analysis-software.com/?p=166

Page 1 of 3

Tuned Pipes & How They Work

Engine Analysis Program

May 1, 1996

As you have discovered, changing the tuned pipe on your RC Car, Boat, Airplane can make a drastic difference in performance. Why is this?

In order to answer this question, a general discussion of the characteristics of the tuned exhaust is necessary. A historical discussion will allow an easy understanding of each component of the tuned exhaust.

In the 1950's an engineer named Walter Kaaden was consulted by motorcycle racers asking him to help them "Go Faster". He discovered that by putting different length "Straight"pipes on a 2 cycle engine it changed the characteristics and performance. By adding a Divergent Cone (Figure 1) there was an even greater change in performance characteristics. You should view the 2 cycle engine as a "Sound Generator". Each time the piston uncovers the exhaust port the pulse of exhaust gases rush out the port can create a positive pressure wave. This wave radiates out of the exhaust port. The sound will be the same frequency as the RPM the engine is running. If the engine is turning 25000 RPM the exhaust will be generated at 25000 RPMs or 415 cycles per second. The length of the tuned exhaust is determined by the RPM the engine will reach and NOT the size(displacement) of the engine.

The original straight pipe attached to the exhaust port used the "negative pressure wave" created by the opening and closing of the exhaust port to suck out the charge in the cylinder. Since the sound waves that start at the end of the pipe travel to the other end of the pipe "at the speed of sound", there was only a small RPM range where the negative waves return to the exhaust opening at a useful time. At too low an RPM range, the wave would return too soon, bouncing back out the port. At too high an RPM the , the piston would have closed the exhaust port, doing no good.

This early pipe was easy to tune. You started with a long pipe and cut it off until it worked at the RPM range you wanted.

The next progression was to add a Divergent Cone on the end of the straight pipe. This intensified the sound wave and and in fact lengthened the returning wave, thus broadening the power band. The wave was not as strong as the straight pipe, but returned the wave over a LONGER TIME FRAME (Figure 2), thus making the chance that it would find the exhaust port open greater. The exhaust gasses could be sucked out if the exhaust port was found open by this returning wave. The divergent cone shape or angle was found to be important, since the steeper the angel the more intense the negative wave returned, but also the shorter the duration. The gradual divergent cone returned a less intense wave over a longer time. It was found that this negative wave was strong enough to suck the exhaust out and at the same time pull fresh mixture up through the intake ports into the combustion chamber. The addition of the divergent cone to the straight pipe produced great tuning advantages, but it had severe limitations. The broader negative wave from a "Megaphone" can arrive to early and pull fresh mixture out of the cylinder. How could we put this extra mixture back into the engine?

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Wave" reflect back into the open exhaust. These positive waved would follow the negative waves back into the open exhaust port and if properly timed would "Stuff" the fresh mixture into the combustion chamber through the exhaust opening just as the exhaust port was closing. This in effect supercharged the engine with no moving parts - only that addition off the tuned exhaust.

In addition to the straight Head Pipe, the Divergent Cone, the Convergent Cone. there are two other components of the tuned pipe. The middle section connecting the Convergent and Divergent cones, or the Belly of the pipe is the section of the tuned pipe which is changed in length to adjust the RPM Band which you want the pipe to operate. There is also the Stinger Section of the pipe which serves as a "Bleed Valve" to allow exhaust to escape.

The Belly section of the pipe determines the relative timing of the Negative and Positive waves. The timing of the waves is determined by the length of the straight pipe. If the belly section is too short, positive waves have a shorter distance to travel, and return to the exhaust port sooner. This can be good if the engine is to be operated at High RPM's only, but very bad if you want to have a broad RPM range to operate in. The diameter of the belly section is not important except to allow fit to the model.

The Stinger Section of the pipe is a pressure bleed valve to allow the exhaust gasses to eventually leave the pipe. Back pressure in the pipe, caused by a smaller or larger or longer or shorter stinger helps the wave action of the pipe, and can increase the performance of the tune pipe. This is due to the higher pressure created by the smaller stinger making the charge a denser medium. Sound waves will travel better in a denser medium. However, the more you restrict the stinger, the higher the heat retained. This can be a very detrimental characteristic of a two stroke engine, but the gains from a higher density medium can yield considerable performance increases.

As the two stroke tuned pipe has evolved, it has been found that if you have a gently divergent "Head Pipe" it will keep the gas velocity high near the exhaust opening, then a second medium divergent cone and a third high taper divergent cone attached to the belly section.

The design and tuning of expansion chambers is a relatively easy process if you can define the criteria needed in this design. You must know the RPM range you want to operate in, the top rpm, the

temperature and thus the speed at which the gasses travel (dependent upon fuel used and temperature inside the pipe)

Built into "The Engine Analysis Program" is a pipe design module to design a single stage tuned pipe. There is the capability to adjust the wave speed constant, to adjust for temperature due to atmosphere and nitro content.

A special Thanks to Many that Contributed to the constant quest for information and answers over the many years, especially including: Dr. Brian Callahan, Tom Grannis, Norris Sparks, John Ackerman, Joe Kramer, Bobby Coleman, Tom van den Brink, Norm Doerr, Rod Hendricks, Joe Wiebelhaus, Hank Schneider and many others.

]]> http://rc-engine-analysis-software.com/how-rc-nitro-engine-tuned-pipes-work/feed 0 http://rc-engine-analysis-software.com/rc-nitro-engine-combustion-chamber-squish-band-discussion http://rc-engine-analysis-software.com/rc-nitro-engine-combustion-chamber-squish-band-discussion#comments Thu, 29 Sep 2011 01:55:00 +0000 Marty Davis http://rc-engine-analysis-software.com/?p=164

Technical Notes - Head Design Page 1 of 2

Monthly Technical Notes

A Supplement to "The Engine Analysis Software"

Combustion Chamber (Cylinder Heads): The Squish Band

I have long known that the Two Cycle Engine's combustion chamber is one of the most important items contributing to outstanding performance. One of my close friends, Steve O'Donnell and his father Jack have been competing at the highest level in individual RC Sports, e.g., Tether Race Cars, Straight-away RC Boats, etc. They spend a lot of time in finding the correct head design to maximize performance. I am not telling you here what they do, because I don't know. I do know some of the basic principles they use to make their engines a "cut above" the typical RC Modeler.

I recently had the opportunity to spend a couple of days talking engines, props and boats with John and Andy Brown, of Mongoose, Eagle, SG fame. Andy really lives two cycle engines and he found a book laying on my reading table which he asked about. I told him that I had a friend tell me about a recent book done by some researchers in Belfast Northern Ireland. They had just published this book in conjunction with the Society of Automotive Engineers and I had a copy. The also came up with some VERY SOPHISTICATED simulation software which would be available later. This book can be purchased from SAE (Click Here to Go to Order Page of SAE). If you would like to go to the SAE Home Page and look at what they have -Click Here!

Enough about the books, let's talk about general head design for High Performance two cycle RC Engines.

Squish Band:

One of the most important items in the design of a good combustion chamber is the squish band. I believe that a flat squish band produces much more power than an angled squish band. The flat squish band head has a flat area (squish band) around the perimeter of the head which comes in close proximity to the piston at top dead center. This squish band is designed to keep the layer of combustion mist very thin, in order to let heat travel quickly from a hot piston to a cooler combustion chamber (head). The thinner this layer (the closer the head clearance), the better this heat transfer is accomplished. If your head has its squish band to far away from the piston at TDC and the compression ratio is high, you will get pre-detonation (knock). You can tell if this is happening by looking at the squish band. If it looks like it has been lightly sand blasted, it is pre-detonating. Most people when they see this pre-detonation automatically raise their squish band piston clearance. That is the WRONG WAY!

Is the flat or angled squish band better? If you can run your engine with a flat squish band, you will make more power. With anything which produces more power there is a downside.

http://rcboat.com/heads.htm 1/19/2011

Technical Notes - Head Design Page 2 of 2

With the flat squish band it is in the form of a "shaking effect" The engine will seem to run roughly and wont transition smoothly on the tuned pipe. It will act as if someone turned on a switch and more power came on abruptly. If this doesn't seem to hurt your application, I would stick with the flat squish band. If not you should put a 3 degree angle on the squish band starting in .100" or so from the outer edge of the squish band and proceeding inward to the combustion chamber. Be sure to slightly round the edges at this point.

Next time I will talk about the shape and proportion of the combustion chamber………….

>




A special Thanks to Many that Contributed to the constant quest for information and answers over the many years, especially including: Dr. Brian Callahan, Tom Grannis, Norris Sparks, John Ackerman, Joe Kramer, Bobby Coleman, Tom van den Brink, Norm Doerr, Rod Hendricks, Joe Wiebelhaus, Hank Schneider and many others.

]]> http://rc-engine-analysis-software.com/rc-nitro-engine-combustion-chamber-squish-band-discussion/feed 0 http://rc-engine-analysis-software.com/rc-nitro-engine-combustion-chamber-shapes http://rc-engine-analysis-software.com/rc-nitro-engine-combustion-chamber-shapes#comments Thu, 29 Sep 2011 01:54:02 +0000 Marty Davis http://rc-engine-analysis-software.com/?p=162

Untitled Page 1 of 3

November 1996 Technical Notes

Supplement to " The Engine Analysis Program" "Order "The Engine Analysis Program"

Last month we started an initial discussion of Part One - Combustion Chamber (Cylinder Heads): The Squish Band.

This month a discussion of some different Combustion Chamber designs and the reasoning behind them. This is a major research program for me this off-season and I will write about my findings in the Spring.

"OFFSET CHAMBER COMBUSTION CHAMBER"

This chamber is the work of John Ackerman and Bobby Coleman. This past month Bobby, who works at Navistar International, told John Ackerman he had seen something at work which was brought in by a large customer which might have application to our models. After a discussion, John and Bobby came up with an oblong chamber combustion chamber. After I saw it I thought of how we might apply it to our use. I immediately saw the possibility of more than one glow plug (maybe even 3 for .90 engines) with installation of these plugs made easy by their 90 degree relationship to the squish band. No more angle of the glow plug, a decidedly difficult task. You would have the benefit of the wide squish band talked about on the offset chamber as well as multiple plug configurations. We have only run the head on Ackerman's .90 OS Max engine on the water. We don't have ANY dynamometer runs or data to tell us what we saw. It appeared to me that this head produced very good power and we will study this configuration in detail this Winter. How good was the performance? The wider squish band produced enough power that it lifted the top of the case off of the bottom of the case. This is the first time we have produced this much power. Looks REALLY promising!

http://rcboat.com/chambers.htm 1/19/2011 Untitled Page 2 of 3

"Double and Triple (Bubble) Combustion Chamber"

We have been using double and triple bubble combustion chamber designs for the past 3 or 4 years. This configuration makes it simple to adjust the volume of the chamber without changing the width or proportion of the squish band. This is the head design which I would recommend to the serious 2 cycle tuner who doesn't have a dynamometer or very sophisticated machining capability. You can make VERY FINE ADJUSTMENT to the chamber volume easily. You start out with a much smaller ball mill

than you would use for a Hemispherical head chamber and draw it out away from the center. You can shallow the next draw and thus you form the multiple bubble chamber.

You can get into as much detail as you can stand by reading the SAE Book by Dr. Blair & his Research Team-Click Here! (Cost about $180 for the Book and Software or $80 for the software alone) I will very soon have the software that is talked about in the book, which will allow computer simulation of some of these very interesting theories. Also, if you want the data upon which to base building a dynomometer, here is a technical paper prepared by Dr. Kee & Dr. Blair. He outlines how to build an inertial dynomometer. If this is important to you Click Here! This is a VERY detailed publication, and is not for everyone. It will be very confusing if you are not highly engineering oriented. Will let you know how this all works out. Some early plans to produce an inertial dyno so everyone has access to this important tool. Keep your eye on this site for information. Won't be available until at least middle of 1997!

One of my Close Boating Friends - Bob Bonahoorn - This months Feature Article Author of Boat Modeler Magazine - wrote me an E-Mail to add to the discussion of what is at play in the combustion chamber. His comment is as follows:

'I just read your tech tip on squish bands. I have a different understanding on why a thin squish band reduces auto-ignition, (Pre-ignition is a different thing. in spark engines it is caused by hot spots on the spark plug, etc. We can get pre-ignition if we use too hot a plug with high nitro). Auto ignition is what is referred to as knock ". It is caused by the rapidly increasing pressure from the expanding burning gasses acting on the unburned fuel/air that is farthest away from the glow plug. That fuel mixture Is called "end gas". it is heated by the steadily Increasing pressure from the wavefront until it detonates. Normal nitro flamefronts move at about 200-300 meters per second. A detonation moves at more that 2000 meters per second and it can put pits and holes in things like the blast from a high explosive. (Nitro methane is actually a high explosive under certain extreme conditions!) If our squish band is thin, then the end gas will be closer to cooler metal, (head and piston) and it will be very difficult to heat enough to detonate. My fuel experiments were an attempt to find a blend that inhibited auto-ignition, The theory was that the end gases were less likely to auto-ignite, but no one knows what the theory is that causes the improvements. I have been putting a 3 degree cut on all of my buttons. I have been doing it all the way across. After reading your article I am going to try a straight cut. It makes sense that it would help you use higher compression ratios without auto-ignition. By the way, the reason 21 engines like nitro so much is that the chamber is too small to have much auto-ignition because the end gases are closer to the plug and don't have time to heat up to detonation temperatures. Multiple plug heads should help with auto-ignition in big engines. I've never used them. Do you know if they help?"

An important note about the software by Dr. Blair. This program will analyze squish velocity, and other important criterial dealing with the combustion chamber.

If you have technical input on any of these subjects please let me know your thoughts.

Until Next Month………….

A special Thanks to Many that Contributed to the constant quest for information and answers over the many years, especially including: Dr. Brian Callahan, Tom Grannis, Norris Sparks, John Ackerman, Joe Kramer, Bobby Coleman, Tom van den Brink, Norm Doerr, Rod Hendricks, Joe Wiebelhaus, Hank Schneider and many others.

]]> http://rc-engine-analysis-software.com/rc-nitro-engine-combustion-chamber-shapes/feed 0 http://rc-engine-analysis-software.com/rc-nitro-engine-fitting-discussion http://rc-engine-analysis-software.com/rc-nitro-engine-fitting-discussion#comments Thu, 29 Sep 2011 01:53:03 +0000 Marty Davis http://rc-engine-analysis-software.com/?p=160

Engine Blueprinting Page 1 of 3

"Engine Blueprinting"

using

The Engine Analysis Program

Part 1

"The Engine Analysis Software is on sale While the Technical Articles are being written on Engine Blueprinting........Regularly $99.95 save $19.95 now only $80.00..... You MUST use Order Code EAPTECH to get this discount!......"

Initial Documentation:

Using the Head clearance gauge that is available from Rossi Sales of America (901)396-7485, carefully measure the stroke of the engine. Also the head clearance of the engine as it comes. Write down this clearance in thousandths. Using a depth micrometer or a good set of calipers (MSC has good digital calipers cheap) ($80.00) (800-645-7270), measure the depth of the head from the flange on the head to the bottom of the squish band (the depth the head protrudes into the liner). Measure WITH the head shims in place. Add the previous two measurements together to get the measurement of "top of the liner to top of piston". This is a primary input item for the program. Using the head clearance gauge

Disassemble the Engine:

Completely disassemble the engine and inspect all parts for machining flaws. Measure the diameter (bore) of the liner with a good set of calipers.

Measurement of the exhaust and intake ports:

Holding the liner in your hand insert the piston and rod into the liner and using a very high intensity light, find the place where the

http://rcboat.com/eng1.htm 1/19/2011 Engine Blueprinting Page 2 of 3

piston closes EACH port. Measure the depth from the top of the liner to the top of the piston at each of these closing points. It will be easy to see when the light goes out, looking through the port and moving the piston up. It is very helpful to have an extra set of hands helping you here, as these measurements are VERY important (ACCURACY!). The exhaust port is usually slopped, so it is necessary to use the light method. Input these numbers into your program and the timing of the engine as it came stock is shown. Remember that the boost port is the intake port(s) opposite the exhaust and the side intakes are the transfers. After you have this documentation it is time to decide what kind of timing you want for your engine. I can tell you my personal preferences. But in the end, you will have to decide what works best for you. There are MANY considerations. How heavy is your model, what is your driving style, etc. My models are always light weight and I like to drive VERY close to the buoys. I use intake ports with timing of 126 to 128 degrees on ALL my engines of all sizes. I use exhaust timing on my .21 engines (183-185), .45 engines (185 -188), .67 engines (183-188), .80/.90 engines (187-192). If your model is heavier, you will want to preserve a larger part of the "low end power" of the engine, thus LOWER the exhaust timing..

On your spreadsheet, set up a line (under the line which you have documented the engine in stock form) to show the engine in modified form. The intake ports will have to be set initially. I input exactly the same measurements on the line below the stock measurements and start changing the top of liner to top of piston measurement, until I get the INTAKE timing I want. The amount I have changed the top of liner to top of piston measurement, is the amount I will have to turn off the UNDERSIDE of the liner flange to lower it to get the intakes where you want them. Note: Be careful that you don't lower the liner enough that you let the bottom skirt of the piston be higher than the bottom of the exhaust port at TDC(Sub Piston Induction). You DO NOT want this condition as it takes away from low end power. In some rare instances, you will have to make a liner shim to raise the liner to get the intake timing where you want it. VERY RARE that you have to raise the liner. This takes care of setting the intake ports....... Next the Exhaust Port Timing and the Shape of the Exhaust Port.

Another FINE source for any serious 2 cycle engine builder is a book authored by
Dr. Gordon Blair, a researcher and one of the foremost 2 cycle experts in the world.
This is the ultimate technical guide available.
The Blair book & software can be purchased from SAE.

A special Thanks to Many that Contributed to the constant quest for information and answers over the many years, especially including: Dr. Brian Callahan, Tom Grannis, Norris Sparks, John Ackerman, Joe Kramer, Bobby Coleman, Tom van den Brink, Norm Doerr, Rod Hendricks, Joe Wiebelhaus, Hank Schneider and many others.

]]> http://rc-engine-analysis-software.com/rc-nitro-engine-fitting-discussion/feed 0 http://rc-engine-analysis-software.com/rc-nitro-engine-exhaust-port-shapes http://rc-engine-analysis-software.com/rc-nitro-engine-exhaust-port-shapes#comments Thu, 29 Sep 2011 01:52:20 +0000 Marty Davis http://rc-engine-analysis-software.com/?p=158

Engine Blueprinting Page 1 of 3

"Engine Blueprinting"

using

The Engine Analysis Program

Part 2

" The Engine Analysis Software is on sale While the Technical Articles are being written on Engine Blueprinting........Regularly $99.95 save $19.95 now only $80.00..... You MUST use Order Code EAPTECH to get this discount!......"

Exhaust Port Shape & Timing:

After you have set the intake timing to figures which are within the range we talked about last month, it now time to start on the Exhaust port. It is here that you will determine, to a large extent, the RPM range that your engine will run within. What do I mean by this? It is VERY IMPORTANT at this stage to think about how you will use your power plant. Are you setting up an engine to power a heavy model? Is you racing model VERY LIGHT? These are primary questions you MUST answer at this point. If the model is very heavy, you will want to preserve power in the LOWER RPM RANGES. If this is the case, the exhaust timing should stay near the stock configuration. If you don't raise the exhaust port and thus the duration of it's open time remains relatively short, the engine will operate VERY well with a heavy model in the lower RPM ranges. A good example of this is for most 1/8 scale hydros. These boats range in weight from a very light 1/8 scale boat of 10 lbs to a heavy 1/8 scale boat of 18lbs and over. Most 1/8 scale boats are somewhere in between. What then is the IDEAL exhaust duration for the heavy model. I would say that you should look at 175 to 178 degrees. If your model is very light you should look at exhaust open durations of 180 to 190 degrees. The higher the exhaust timing (more the duration of open time) the higher you shift the RPM band. I could talk about the relationship between the engine timing, the prop, the pipe, the fuel, etc at this point, but first lets get the engine "blueprinted" and as optimized as possible. What is the best shape for the exhaust port? How do I cut the exhaust port higher, thus increasing the open time of the exhaust port? I can tell you what has worked for me, and you can probably get as many DIFFERENT answers to this question as you want. So I will share what has worked for me. After reading as many different books as I could get my hands on, I early on figured that we must make it easy for the piston to stay in the liner. What do I mean? The LARGER the exhaust port, the more the piston tries to climb out the port! If you make the cut along the top of the port full width, it gives the piston an easier chance to climb out the port and ruin the piston. I cut only a notch approximately 1/3 the width of the port so as to minimize this characteristic. I believe that it also preserves a larger part of the low end power of the engine, by only cutting 1/3 of the width. The following sketch shows how I do this.

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Using The Engine Analysis Software, it is easy to determine the amount to raise the exhaust port as illustrated above. You have at this point decided the duration that you want, based on the weight of the model, and now using The Engine Analysis Software you can measure from the top of the liner to the top of the exhaust port to get EXACTLY the timing you want. Note: Be sure to deburr around the areas of the port where you have cut. I use a small round stone to break the edge and deburr the port. What is the best way to cut the raised port? If you have access to a milling machine, use a carbide cutter spinning as fast as the mill will run. If you don't have access to a milling machine, use a Dremel Tool with a carbide cutter. I can't tell you how many engines I have done with nothing more than a Dremel Tool! BE VERY PATIENT AND ACCURATE! You can scribe a line where you want the top of the exhaust port to be using a set of Vernier Calipers. They will scratch a very fine line at the point indicated by The Engine Analysis Software.

Here are some inexpensive digital calipers available from MSC which I found recently. Also shown is a depth micrometer, which is very helpful for measuring the depth from top of liner to top of

We will move to the rotor assembly next time.......... Be sure to get your copy of The Engine Analysis Software while it is on sale. You will have trouble following these tech tips without the software. This WILL be the best engine tool you will EVER buy!

Another FINE source for any serious 2 cycle engine builder is a book authored by Dr. Gordon Blair, a researcher and one of the foremost 2 cycle experts in the world. This

A special Thanks to Many that Contributed to the constant quest for information and answers over the many years, especially including: Dr. Brian Callahan, Tom Grannis, Norris Sparks, John Ackerman, Joe Kramer, Bobby Coleman, Tom van den Brink, Norm Doerr, Rod Hendricks, Joe Wiebelhaus, Hank Schneider and many others.

]]> http://rc-engine-analysis-software.com/rc-nitro-engine-exhaust-port-shapes/feed 0 http://rc-engine-analysis-software.com/rc-nitro-engine-rotor-or-crank-fitting http://rc-engine-analysis-software.com/rc-nitro-engine-rotor-or-crank-fitting#comments Thu, 29 Sep 2011 01:51:35 +0000 Marty Davis http://rc-engine-analysis-software.com/?p=156

Engine Blueprinting Page 1 of 2

using

The Engine Analysis Program

Part 3

" The Engine Analysis Software is on sale While the Technical Articles are being written on Engine Blueprinting........Regularly $99.95 save $19.95 now only $80.00..... You MUST use Order Code EAPTECH to get this discount!......"

"The Rotor or Crank Induction Assembly"

The rotor or crank induction assembly is the heart of the engines low end power! How is this so? Consider that the engine is "A PUMP". The efficiency the engine shows in this role as a pump is dependent upon a GREAT seal of the rotor disk to the backplate or the crank to the front end. When your engine comes to you from the factory, it has adequate clearance between the crank and the front housing or the rotor disk and the backplate (For the sake of this tech note I will use the crank induction and the crank fit to the front housing in a parallel with the rotor and its fit with the back plate, that way I won't have to repeat this every time I use an illustration for one or the other). If you were manufacturing an engine, you would make the interchangeability of parts easy and the fit within a range to accommodate the widest range of machining tolerances. We can make the fit better with the rotor assembly! The flatness of the rotor disk and the back plate assembly can be made MUCH better. How can you do this? By lapping the back plate assembly on a VERY flat surface. I use a ground plate available from MSC for about $25. Some people say they use a piece of glass (it is really not very flat and I wouldn't suggest that you use glass). I then apply a small amount of "Non-Imbedding Garnet" or special aluminum lapping compound available from the Helical Lap Company. If you want to buy a very small amount of the lapping compound, I would suggest that you buy it from John Ackerman at jfa@rcboat.com. This is the same compound that I use and it works VERY well and does not imbed in aluminum. Be VERY careful that you don't use diamond or some other compound that will imbed in the aluminum, as you will continue to get lapping of all the internal components of your engine. How then do you lap the back plate assembly? Applying a small amount of the lapping compound on the ground plate you pull the back plate assembly toward you in a continuous stroke. Rotate the assembly 90 degrees and move it forward, rotate another 90 degrees and move it toward you, etc. This will prevent lapping in one area only, and you will get a perfectly smooth and FLAT back plate assembly. How about the rotor disk? If you have access to a lathe, you will want to use a piece of bronze and face the surface flat and drill a hole the same size as the flange on the rotor disk. Apply a small amount of the lapping compound and start lapping, holding firm pressure against the disk. If you don't have the capability to lap the disk, lap only the back plate! If you lap the back plate only it will be 100% better than it came.

Wash up the components using soap and water with a toothbrush, being sure to get ALL the lapping compound removed.

You are now ready to fit the back plate and rotor disk. Using a .0015 to .002 feeler gauge, place it between the disk and back plate on ONE SIDE ONLY. Secure the rotor pin and loctite using #242 blue loctite. This will give you about .0005 +/-clearance. Spin the disk and make sure it spins freely with no

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evident high spots. The assembly is now ready to put back onto the engine. Check the fit and re-lap at least 3 or 4 times per season and you will be VERY pleased with the launchability and power of your engine. This is the reason, when your boat stops launching easily. The rotor fit has gone away and it needs to be re-lapped. What about the crank induction engine. Sorry, you can't re-lap it, you must get a new case and crank assembly. To keep the fit perfect in the front induction (crank) engine CHANGE THE BEARINGS BEFORE THEY FAIL!!!!!! I change my bearings during the Winter and once before the Nationals as preventive maintenance. I have been using a 3.5 Nova Rossi for 4 seasons and it keeps getting better and better with no loss of seal between the crank and housing (CHANGE YOUR BEARINGS REGULARLY!!!)

For those of you who like to have an expert do your engine work, I suggest that you send an E-Mail message to John Ackerman owner of JFA Custom. He is the best engine builder around and has all the tools to make the job easy for him. By the way, John and I along with Norris Sparks, Brian Callahan and Joe Kramer, are building an inertial dyno from the SAE paper written by Dr. Kee. Here is a picture of it and a picture of the virtual instrumentation we use to generate charts and all the readouts.

Until NEXT MONT Rotor Timing

Be sure to get your copy of

The Engine Analysis Software while it is on sale. You will have trouble following these tech tips without the software. This WILL be the best engine tool you will EVER buy!

A special Thanks to Many that Contributed to the constant quest for information and answers over the many years, especially including: Dr. Brian Callahan, Tom Grannis, Norris Sparks, John Ackerman, Joe Kramer, Bobby Coleman, Tom van den Brink, Norm Doerr, Rod Hendricks, Joe Wiebelhaus, Hank Schneider and many others.

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