Boast vs Transfer

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dr gary turner

Well-Known Member
Joined
Dec 25, 2004
Messages
2,737
What is more important Boast or Transfer ports and WHY?

Is it possible to increase port volume to the point of having to little velocity?

What are the symptoms of not enough velocity?
 
Gary:

It is all a total package in a two stroke engine with the time/area of the exhaust port needing to be close to the same time as the combination of the side and boost transfers. It is thought that the boost port should open a little earlier to start the loop of the the charge upward to the head and then looping over the top, fired, and then exhausted. I can't say that this is correct or not, but it makes sense. The sizing of the ports and the time they are open is really the most important consideration. With the new Beta Version of my software, you can calculate this time/area relationship. It is an area that I think has not been explored very much by our boaters. Brian Callahan had me reduce the size of the exhaust opening some time ago to get the time/area balance more even between the exhaust and intake ports and it seemed to make quite a difference. The time area of the intake tract is the 3rd part of the equation and also is important to balance with the other ports.

As far a velocity, that is controlled probably more by case volume and pipe reflection.

Many people polish their port runners to a high shine and also very smooth. I have found that with our flow patterns, there is enough velocity to make the polishing not very important. You can ask Stan Simpson about flow patterns in our engines, as HE IS the cutting edge of this technology in our hobby.

I can tell you that a balance between open durations of the ports, the open and close of the intake tract and the size of the carb opening and intake tract being balanced is SUPER IMPORTANT and an area where I am working a lot now. Conversations with some people that I greatly respect have pointed me in this direction.

Probably more than you asked, but it triggered a response
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Thanks. So more flow to either boost or transfer is not critical but the timing of port opening is the critical factor?
 
Thanks. So more flow to either boost or transfer is not critical but the timing of port opening is the critical factor?
I think that is part of it (helps control the time/area) but the time/area balance between the three components is probably most important.
 
I don't think you can make the ports in the "case" to big running "HIGH" nitro.

You need room to flow all that fuel.......................................

Ports in the sleeve will do no good if bigger than the cross section of the case ports.

Transfers will flow more than the boost. Boost is just for top side scavenging and swirl mixing.

Just how I see it.................

Have hogged the crap out of the transfer ports in my RS1.01 case and it loves it.

Get the right pipe and you will suck the guts right out of it all the way to the carb.

The right pipe will create the velocity when you are up on it.
 
just open the boost first. once it starts to move it will tend to stay in motion.

Newton has some kid off law against it changing......
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Stan no need to communicate in sifter's the CIA could care less about your toy boat affiliation...............
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Stan,

That was an easy one.

ABC-Propellers

TRD-Truex Racing Designs

SS-Stan Simpson Engines

Jim Schaefer, Martin Truex Jr., Dad.
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Hope those "Game Changers" are working well in that FLA humidity?

Have Fun Testing,

David,

I may have a small project for you?

It involves Boost and Transfers.
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Thanks,

Mark Sholund
 
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On the dyno and in boat/car while doing R&D i have pretty much always seen pwr gains from opening the boost earlier or at a minimum of at the same time as the transfers.... Marty made some good points as to why this is the result.
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Some information that will be helpful to you....

Adam Blevins is one of the best engine tuners in the RC Nitro Car Racing World and when he speaks, you should listen. He has a dyno, uses it all the time and really knows the why's of engine tuning. I have been working with him for a while and respect his knowledge a LOT. Ask questions of him, he knows.....
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We also welcome him to our RC Boating World as he has gotten his feet wet in our hobby.
 
Thanks Marty for the kind words they are much appreciated especially coming from you! I value your knowledge as well so believe me when i say the respect is mutual! Ive been using your software for years
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Now I am fairly new to the boats compared to you guys that have been racing these units for 30+ years... and i wont claim to know it all in the slightest... but i have been working with these small engines for many years mostly for the cars and buggies. Although i think i have a decent grasp on them "at least enough to get me in trouble lol" I believe we are ALWAYS learning and when we think we have stopped learning or know it all and have no need for others help or input THATS when we start going backwards. I personally don't like going backwards! SO im glad to share things i know and not in the slightest bit am i ashamed or afraid to ask a question. Sharing and working with others is something i enjoy doing. I believe it is one of the best things you can do in this hobby, and life in general as it helps everyone to work together and not against each other. As smart as we all think we are sometimes there is always someone else out there somewhere that's put the time in to figure something out that maybe we ourselves couldn't or simply just didn't.

I'm also not one to speak to high and mighty or get to technical with big words etc.. I'm a simple guy. I just believe hard work, A LOT of R&D and some OCD will take you a long way to your goals
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To make it easier for all to understand, please identify which are the sleeve ports - boost, transfer, etc. Some are new at this hobby and are not up with the lingo. Picture will be most helpful.
 
Actually all the intake ports are really transfer ports. We started calling the port opposite the Exhaust the Boost Port because it boosted the charge upward to create the loop. Our engines use this loop to efficiently charge the cylinder and then empty the cylinder after the burn out the exhaust port. The side transfers are mass input ports to supply a LOT of charge. Opening the boost port a few degrees earlier starts the loop in a really straight line and CATCH the charge that the side transfers supply a few degrees after the boost starts supplying. Just a boost port wouldn't be enough to charge the cylinder totally so we need the area supplied by the side transfers.

I haven't worked a lot with grinding the channel that the side transfers use to charge the combustion chamber, but I suspect that it would make some difference in where the charge ends up to help it by some redirection. Of all the people that modify engines and work in that area, Stan, Jr and his Dad are probably at the leading edge of that technology. Jack and Steve O'Donnell probably know a substantial amount in this area as Jack has Teather Cars running over 200 mph and turning amazing rpm's.

Most of us RC boaters are more of the "Hacker Type". I am one of those
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If you have ever seen one of Stan's liners, you would be amazed at the Jewelry Quality channels, etc that he puts in his parts.

There are some others on this Forum that are the real craftsmen in this area, but we seldom hear from them. Jeff Lutz is also one of them, as is Andy Brown. Would be nice to hear from them.

Since I started running the Nova Rossi 21DD I have not has to do a lot of modification. The engines are so well engineered that the pipe selection and carb selection makes it a dominant engine. I have found only a mod to the head button, a larger carb and some other very minor mods are all that are necessary. In fact I have run the engine stok (still can't spell that) most of time I have had mine. I now am starting to experiment in some more mods and each time it seems to give me more performance. Unless you have your boat/prop combination optimized, I wouldn't suggest that you do much. Once you do, then it does makes sense.
 
This could turn out to be a very good thread..........................

Would like to here some input from Andy also. He has a wealth of info packed away in his head.

Case in point..............(get it case)................MAC engs.

I keep referring to "HIGH" nitro for a reason.

When you get to 60% nitro the fuel suspended in the air stream is huge............

The flow characteristic change to more of a liquid flow.

Lots of small ports cut in the liner I feel just hinder the flow.

Port entry angles and slight manipulation of the flow at the port entrance can accomplish just as much as multiple entry ports with out the reduction of time area.

You either go horizontally to gain timed area with out a rotational timing change or you have to go vertically to gain time area.

So when you talk time area what do you refer to? Bigger horizontal ports or higher timing?

Thy both change timed area. That is the total amount of time port area is open in one revolution.

My feeling is the sleeve port has to not be bigger than the cross section of the casting in the case.

So looking at it this way you can see what size sleeve port you want to end up with.

This kind of determines the timing unless you jack the sleeve up and the piston is below the port at BDC.

Look at the case it will tell you what you can or can not do as far as port size and shape in the sleeve.

IT IS ALL IN THE CASE PORTS..................................
 
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