I am new to rc boat and 2 stroke engine
I am learning about engine porting

reduce squish will create more torque
enlarge exhaust timing will give us more RPM but reduce torque
what is intake and transfer timing for? and what is the effect ?

Man, your the first conversation starter here in weeks. I have gotten more PM's over the last 3 weeks, than conversation here in the engine section---and that never happened before. Thanks for sparking conversation.

People often confuse torque with lower RPM power, but if you want higher RPM power, you have to increase torque at higher RPM also. To me, if you want to enhance the power at any given rpm range (lower rpm or higher rpm), you have to increase the torque at that rpm range. The formula is ("torque" times "rpm") divided by "5252" = HP at the rpm plugged into the formula. If you plug in 16,000 rpm as your peak power rpm desired, it is only the torque that you have to raise to increase power at 16,000rpm. As a result of increased torque, you will get increased HP at any RPM. If your engine work increases torque at higher RPM, your engine should also rev further, because it has added torque to do so. Porting is only one factor of the engines performance also, and what pipe you use is probably a bigger factor. The proper way to build a engine is design the porting for your application, and then design a pipe to match that porting, but if you don't make your own pipes, you are at the mercy of the pipes on the market. I don't build my own pipes, so I choose what I think is the best pipe on the market to work with, so I choose the QD hot pipes for the boat racing applications.

You say-
"reduce squish will create more torque" But that usually requires lowering the cylinder with thinner base gaskets or no gasket at all. A tighter squish will force more of the fuel/air charge into the combustion chamber, closer to the plug for a more complete burn, but the lower RPM torque is more due to the ports being lowered (exhaust port mainly) and a slightly higher compression ratio.

"enlarge exhaust timing will give us more RPM but reduce torque" This tends to produce less torque at lower RPM's, but increase torque at higher RPM's. Also, port time is only one factor of the ports capability at any given RPM (but probably the biggest factor). It is "port time area" that gives the whole picture of how the port will function at any given rpm. "Port time area" is a function of the area of the port, and the location (time) of the port together. QD cylinders with a bridged exhaust port is a excellent example of this. The 34mm bore cylinders I worked with have a bridge down the middle of the port, and that allows QD to make a very wide exhaust port, but still make outstanding power at 16,000rpm with port duration under 180 degrees. The rule of thumb is go wide, before you go up (exhaust) or down (intake), and you should be able to get the power you want with out making the power curve (rpm range of useable power) too narrow. Boat racing is one of the few applications that can tolerate a narrow power curve, but you have to stay in that narrow curve to be effective. Make a mistake that causes you to fall out of that power curve, and the boat can lose big time trying to get back into the power. Even though a powerful but narrow curve can give tough to beat lap times for boat racing, more driver skill and luck will be needed to make it work lap after lap in racing conditions IMO.


"what is intake and transfer timing for? and what is the effect ?" For boat racing, people are usually looking for more top end power/torque. As rpm rises, all of the ports are open for less time, but the cylinder volume remains the same. Think of port time area size and location as having enough time/area open to fill and evacuate the cylinder at the higher rpm, and your torque should go up at those higher rpm's---given you don't use a pipe that hinders your ports performance targets.

On this site, a couple of books are offered for reading. Most of us have read those older books. Study those books more than once, and you should start to gain the understanding pretty well. Then it will be time to practice what you have learned, but be careful not to jump to false conclusions of why you may not be getting the results you thought you would get. It is easy to jump to false conclusions, and move your work in the wrong direction, because just about all the factors overlap each other. For example--simply tightening your squish by lowering the cylinder is actually effecting at least 5 factors that overlap, and that can make it hard to come up with the correct conclusions if you don't understand the contributions of each factor---and sometimes even if you do. The trick is to find what factors are involved, find the factors that contribute the most (to fix first), and controlling the factors as well as you can. That is the basic plan of most every engineering testing.

Also---remember this quote of a man I worked with at my very first machine shop 30 years ago. "The day you think you know it all, is probably the day you have a lot to learn."

Have fun

Doug @ ESP

Doug thank you very much for your kind explanation
but I still have a question if you don't mind

Transfer duration is measured from where to where?
with longer transfer duration, it will give more power/torque?

about intake timing duration, some said it is better 155, other said it should be 158. why it is difference?
that 158 will give more torque/power?

Doug
May be first conversation in weeks to you -- but more to boats than just porting. When you actually run them. Nice to see you have pm's -- that's good thing. But lately here what I see is tons of bench talk - but not from people who run the boats.

I see lots names in record books - CC Butch Insane -- how about ESP what records lately?? Just curious - not slamming

Cheers

We don't have any Marine records worth bragging about yet that I know of in the states, but in heat racing and off shore racing, we have won races against stiff competition. Now, If I had 50 racers using my engines at each race like I have seen with CC racing for example, instead of one racer who can only hit a few races and have to find a driver for each, our chances to win a lot more would be exponentially higher. So I would say you are ignoring a very important factor of sheer numbers of my competitions engines against one to three of mine. I just recently picked up a top racer named Dave Horsley in Dist 3 Florida (may be the toughest District in the states), and we hope to shut people like you up, who do not understand "probability" due to numbers. I build engines for go-peds, have won a lot of races and championships but I do not race Peds. I don't race Formula 1 racing cars either, but we won Formula 1 racing in Europe, National championships and won a world championship in 2009 (beating all of socialist Europe on our first try), and currently leading the points race this year (all with one sponsored racer and 2 championships in our first seasons with a lesser known racer--now well known). I build engines for the rc buggies (who I sponsor none) and have no idea how many races they have won (to the best of my knowledge, there really isn't a good series built yet in the USA, but some cool weekend races). So when people see my less expensive engines do well (You bought a $800.00 piston port engine---really?), it won't matter how much a cheer leader bashes newer competition on line. Already I find it easier to win races on the water with one or two good racers working with me, than it is to win on the internet with people like you around.

Your not curious, you know who has won the boat records. Your a trouble maker who does not like new competition.
People like you, and your crony friends---is why this forum is dead. People like you are also the reason why TS may not bother making PUM reed cases anymore either--so feel proud you shut down a great product you can't beat. None of my racers want to say a word here, only to run into trouble like you. I am just a glutton for punishment, and that is why I am still here having discussion---when your really a waste of my time.

500 views---3 replies, is typical here today. And you earned it by slamming people you know nothing about. Heck, this place does not even want new sponsors, because it seems to be a conflict of interest to them. The racing is alive---this place is dead. It is not my fault or problem that 497 people out of 500 don't want to talk here. It is yours IMO.

Same old Doug ............

Trouble maker ?? You might want to actually read some of my posts.......... Lol

Same old

Now look what you have done, Randy!
You have awakened The Troll!

Cheers!
Woody.