RCKen

My Feedback: (9)

Ok guys, I've had to step in and clean up this thread so you may notice a lot of posts missing here.

Let me first clear up a misconception. Asking technical questions to the OP and not agreeing with them DOES NOT constitute a presonal attack, so please do not create report tickets on this. Asking technical questions is prefectly acceptable in a thread such as this. As is disagreeing and discussing the issue.

Second, there is nothing wrong with disagreeing with somebody's opinions. But what IS WRONG is insulting or attacking a person that you don't agree with. If I see any more of that here in this thread I'll assure you that the person doing it will spent some time in time out. If you can't discuss these issues without resorting to attacking or insulting those you don't agree with then I would highly suggest that you stay out of the conversation, because if you can't discuss it civilally you're not going to like the outcome.

For those trying to discuss these issues I apologize that I had to take these actions.

Ken

SManMTB

Thank you!


US Open Live stream at: [link=http://www.usopen.org/en_US/interactive/video/live.html]Click me![/link]

SLAYERDUDE

I have a K5.9 and was wondering what your take on the design as an RTR engine if it's a good design or just crap?
Regardless of the materials is this a well designed RTR engine compared to most comparable RTR MT engines...
MGT 8.0, LST, LST2.
I have had a very good experience with this engine that gets alot of hatin here at RCU.
I'm on gallon #7 and I know it's time for a new rod (some play at tdc) but the pinch is good and it runs strong as ever.
And is IMHO a very capable engine for the Savage XL platform.

Here's some pics of my K5.9 and I would appreciate some input as far as the design of this RTR engine performancewise.

Pinch after 6 gallons-




Internals-




















Pinch at about 4 gallons








The majority of the pics were taken with a $10 cam so please excuse the clarity.

I just wonder if this engine was well thought out as is my opinion, or a slapped together like many here say...
Compared to other RTR Monster Truck engines.

savagecommander

dont listen to people who say rtr engines are garbage- not all of them are. i had the stock .25 in my savage last for more gallons than i could count.

on another note- maybe its just the pics, but it looks like youre getting a little better flow on one side of the transfers than the other- maybe a little buzz of the dremel is in your future?


SmanMTB- that was a decent answer, but its just a tad bit more complicated than just length. maybe total length was all you were getting at, and i hope thats the case. and id also like to mention Mr. Jennings book- its good reading, but ive read far more literature that touches on areas he didnt, so dont take it as law.

PowerHouse RC Performance

My Feedback: (1)

I have been looking at doing some case volume changes on some engines to see how they react. The one thing I do want to change if anything is the entrance angle at the port window. Alot of engine's cases make the the mixture turn a pretty sharp corner and then they enter at an up ward angle so I will be back filling the transfers to change the entrance angle but also increase velocity right at port entrance. Hopefully this will not only increase throttle response but also increase overall efficiency. The trick is getting a material that doesn't break down under heat and pressure. The oils in the fuel may cause the filler to detach but I have a couple ideas that I will be trying in the future. For the bigger engines, I was using Z-spar which is a two part epoxy used to repair boat hulls. It works very well as it cures very hard, is easy to grind on and doesn't break down with the fuels and oils used in most engines. The only thing it won't withstand is direct exhaust heat but that is pretty understandable considering it's chemical makeup. The trick is getting it to anchor and I usually did it one of two ways: 1.) Drill, tap and insert a screw in the casing for the epoxy to bite into or 2.) grind a few indentations into the material you want it to adheare to in a fashion that when dry, it can't pull away from or move in any direction. This will work good in areas such as transfers, boosters etc.

As far as the K5.9, I think they are are pretty well thought out design. They may not be made out of the absolute best materials in the world but they do run good stock, last awhile and with a race port, they wake up and haul the mail. Every engine has room for improvement and as long as you start out with a decent layout, you will get good end results.

savagecommander

ever try devcon?

lez1troubles

Hello peeps, I would like to try doing some moding to a Kyosho GX 21 just because most people doent like them, I have 3 of them but doent really know where to start, any ideas. Mr Mark? I am a mechanic from profesion but only from actual hands on work and not from a mechanics school. I have never really had any problems with my RC motors but would just like to expand my mind a tad. By the way, I do revisions on some of the biggest ship engines on the planet such as Ling Hyundi, ABC(Anglo Belgica Corp), some of the engines that I have to work on are bigger than houses so I really get to see how they work especially when I got to crawl through them.:-) I England they call us grease monkeys.

daveschutt

i personally know mark and i race with him. I can tell you right now there not backyard mods!! This guy knows what hes doing. The motors he modofies are insane.

SManMTB

It was a different way of explaining the equation for tuned length. For static conditions it's actually pure physics so it is a 'law', ie law of physics.
The question was intentionally asked in a strange 'backwards' way to illustrate this. With increased exhaust timing the peak rpm will move up in the rpm band meaning (in real life) that if you increase timing (and correct the compression and retune the engine) and keep the pipe length the same you will see your car/boat/plane go faster (the engine can pull more rpm).

Of course there are more parameters that influence the end result and the primary parameter is exhaust gas temperature which changes the speed of the sound wave in the pipe which is a direct parameter in the equation.

Good to see you found the link to Jennings book I posted earlier. Good read but somewhat dated. The book by Blair is 'better' or more up to date but also way more complicated.

willclark77

My Feedback: (2)

Very cool link. I never knew how it was done. Thanks. I have lots of machining stuff but nothing to accomplish that on a consistent, repeatable basis. I actually put two sleeves in my lathe and slowly turned it while applying pressure with a smoothe roller tool (looks like a knurlin tool with no flutes) and I'm not even sure what it's actually called, until they mic'd .0002 tighter. I haven't tried them out since I already had new sleeves, and I'm not real confident on the accuracey of my inside mics. Kinda hard to get em positioned.

savagecommander

i introduced myself to Mr Jennings back in '07... and i find that an increase in port area, not duration, yields a significant increase in power without having to "re adjust" trapped comp ratio- its been my practice the increase in duration correlated with the slight drop in CR makes the low end not so.... soggy.

PowerHouse RC Performance

My Feedback: (1)

you are on the right track.

dittch

Just wanted to jump in and say this is an awesome discussion. I have been watching it from the beginning. Lots of good information here.

SManMTB

Yes absolutely, widening the ports also increases the time area. I've tried it, it works but only up to a certain point. The ports can't be made infinitely wide because the piston can 'tip' slightly and catch the edge of the port. After this you have to raise the timing.
On top of that you can only widen the exhaust so much until it will start to 'short circuit' the fresh charge from the transfer ports.

The C6BB uses a variant of this technique. Look at the exhaust port(s).
The center port has a vey low timing. Don't remember exactly what I measured the timing to be but I believe it was 155 to the low 160. At the same time the two sattelite ports are very small but with a much higher timing. I think it was 180 or so.
This gives great low end with some addition to the top end provided by the two small ports. At the same time the bridge between the ports provides stability for the piston.
The on-road version of the C6 looks similar but the big main ports has almost the same or the same timing as the small sattelite ports (It could clearly be seen on the RB website. They changed models now and I haven't checked the latest but it might be the same now).
That should give massive top end power.

savagecommander

im sorry, are you speaking of the motor in the pictures?

SManMTB

You saw I was talking about the C6BB in the later part of the post.
The first part was general comments.

Back to the pipe length question. You said there are more parameters... which ones did you have in mind and how would they change the tuned length? It was never explained by you.

SManMTB

The transfer ports should be fairly flat (10-15 deg) compared to the boost port (50-60 deg). How would changing the transfer angles increase throttle response an efficiency?

PowerHouse RC Performance

My Feedback: (1)

That is correct about the improved performance to a certain point with widening the exhaust port. Rule of thumb is the exhaust port shouldn't go beyond 70% of the piston diameter. This pertains more to ringed engines but you also need to have a nice rounded corner with a slight taper on the top of the port to give the ring a chance to tuck in before the port closes otherwise the ring could catch the top of the port and break. The flatter the port, the more aggressive start the the blowdown timing which results in more "pop" on the bottom and the opposite for a more tapered port ceiling. As far as the short circuiting is concerned, there are ways around that if the ports are border line say if the exhaust boosters hang over the front transfer port too far. It's called backporting the window which will redirect and create a surge of charge that act as a wall to keep the fresh charge and expelling charge from mixing too much during blowdown. A little bit a charge will always exit the cylinder but depending how well the pipe is scavaging will determine how much will return to the chamber to ignite on the next cycle.

savagecommander

is the CB66 the one in slayers pics? if so, which ports are the "center"....

yes. much much more perameters- however, before any further discussion takes place, i have had limited exp in modding small nitro motors. ihave only done one, but that motor was incredible after i finished. im gassers now, so that changes a few things, but the theory is constant. as far as perameters are concerned, i touch on EVERY aspect of the motor and pipe.

"The transfer ports should be fairly flat (10-15 deg) compared to the boost port (50-60 deg). How would changing the transfer angles increase throttle response an efficiency? " lower angles promote higher peak HP values, but higher angles support the powerband under the peak, so an adjustment there could yield better cyl filling at lower RPM's, and thus having noticeably better responce-

PowerHouse RC Performance

My Feedback: (1)

Most of the time transfers do come fairly flat but since the engine loop scavages, depending on port layout, angle of entry etc. sometimes you can increase the angle of the transfers to change the entry angle to assist in the loop scavaging process but again, it will depend on a few things. Some will like it and some won't. Alot of the time, you can can eyeball it and visualize what the engine will do during the complete cycle and get an idea of where you want to go with it and some engines have responded well to it and some haven't but that is part of the R&D. Nothing is built perfectly and never will and sonetimes you just have to throw some hail mary's and see what happens.

PowerHouse RC Performance

My Feedback: (1)

As far as the throttle response that I mentioned, I was talking about tightning up the case volume with some putty in the transfers. That would accelerate the charge at port entry and help with increased cylinder pack for increased performance. It isn't a guaranteed thing but it has worked in alot of engines and depending what the case volume is when you start will depend on the percentage of gain.

SManMTB

HPI_Savage_RC

Mocking someone is not a good idea when they are using established physical laws to support their point. Everything SMan stated is simple logic, not the outputs of a computer simulation. Funny how people will always take the word of someone who claims experience as law, without actually making an attempt to understand the subject sufficiently to have an independent opinion on the matter.

I believe supertib has told you numerous times that it is a poor design. Very low intake port durations and overall port area, small exhaust port, poor port placement, etc. These are all characteristics of RTR engines. They are all the same mediocre junk. Perhaps one day you will actually try a real race grade engine, and you will look back wonder why you wasted so much time running and defending the 5.9 RTR turd.

As far as PowerhouseRC, he seems to be legit, but I would be wary about sending an engine his way after reading this entire thread, and seeing his attempts to back-peddle and revise his statements after being called out on technical issues. Most of what he states shows that he does have experience in this field, but I'm not entirely convinced. Mark, why should I or anyone else send you an engine to modify when there are other businesses around who provide dyno and video proof of the value of their work?

PowerHouse RC Performance

My Feedback: (1)

I hear where you are coming from about the videos and dyno results. To me the best way to do that is too have a third party do a comparison. There is a video on youtube under "nitro engine modification" or something close to that that has a gentleman from Cali who did a back to back on a GRP based Ninja .21 with my turbo crank package. As far as me doing my own videos,I might but one thing people always wonder about dyno numbers is "Are the perameters inputted correctly?" You make a dyno read high orlow depending on the setup so unless you have a program that is locked and you use that setup time after time, you can atleast compare percentages with that particular dyno. When Iwas building engines for Polaris, our dyno was hard on numbersmeaningwe alwaysmade lower numbers than most with the same engine for a couple reasons. First,some people would go to a neutral dyno session to compare numbers and get a second opinion to see if we doctoredup the results any so when itran higher numbers on someone else's unbiased dyno, the customer was happy. Too many times wehad people buy from a competitor and come to us fora dyno session after getting beat by an engine thatwas thought to have 30 less HP andthe 217HP claim to fame turned into a 170HP turdand when our 190HP motor would beat them, it would make them furious. I have seen people gear stuffdown to make it look better than it was andit went flat way too early because it ran outof legs. So I guess what I am saying is I haven't spent the money on a dyno because I figured that people would question the results anyway. Videos are touchy as well. I have seen alot of videos with engines that are way bigger than the original and when you plug a modded .28 into a .18 size application and you say "look at it go!" what is that really saying???I have also seen people gear their truggy down a few teeth to make their .21 seemlike a monster but ran out of legs in 50'so again, what is that saying? A customer is going to run it theway he wants to andif itdoesn't do whatit did in the video becausethe video was misleading, that makes the engine guy look bad and word of mouth is huge.

As far as people being leary of modified engines, and who to get them from, who wouldn't be??? All I can say is I have enough exposure around theinternet and the world andmore and more people are inquirying all the time and as I send them out and they run them, they spread the word. I'm sure at some point some of you will see some of myengines run and if the people setting them up are decent, youwill form your own opinion. You will always have your faithful so I don't expect to earn everyone's business, just want to have a nice piece of that competative pie is all.

HPI_Savage_RC

By video evidence I meant short clips showing acceleration and a GPS/Radar gun reading of top speed, similar to what supertib has done to showcase his modded engines. He has a video of a 12lb Savage XL with a modified Picco 28 accelerating to over 50mph in less than 5 seconds. When you see something like that, you know the engine is a beast and a huge improvement over stock.

As for dyno results, I was referring largely to what Adam (AB mods) has done to show the performance gains his engines achieve. He overlaps torque VS RPM graphs of stock and modded engines, so you can see the gains in all areas of the powerband with no uncertainty arising from differing dyno setups.