what do think on porting

In the first photo the red arrow is the transfer port on a modified Super Tigre 51 that a friend sent out to have it modified. In the second and third photo's the red arrow is the transfer port and the blue arrow is the exhast port as you can see the transfer port is 1-2 drgees higher than the exhaust port. In the forth photo look at large off center hole a round the spray bar. How do you think it will run?

The engine is the C/L version the boost port is unchanged. I checked a differant G51 that the same modified and it had 6 degrees of blow down so I think this one is messed up.

It looks to me that he attempted to grind the ports at a 45 degree angle. There are some who think this is a sacred number and don't even bother to see how it affects the timing or whether or not one port opens before the other. If you do this on an FP, for instance, the 35 FP will end up with a lot higher porting than the 40 and the 20 a lot higher than the 25 simply because they have thicker sleeves. This particular engine also has a thick sleeve resulting in a higher porting as you have discovered.

I once had a discussion with a modeler who posted in his club's newsletter the "proper" way to modify the FP engine, and his recommendation was just such a "suggestion"--angle the port up by 45 degrees. I told him this would result in the intake port opening before the exhaust and would ruin the engine. DO NOT PUBLISH THAT! He insisted he was correct and went ahead and did so.

The sad thing is when we start messing with Dremels and angles, we get very inaccurate results. One engine may work. The next may be a horrible disaster. This particular engine may run, but if you compare its results with a stock sleeve, the stock engine will outperform it by far.

As to the needle, the location of the spraybar is not critical. It does not need to be centered in the venturi. But one must make sure there is no leakage around the needle. If the needle does not seal, you are in for more troubles.

Mike Starret raised a little the ports of his .25VF's, but he used a drill press.

If you put the Dremel on one of those presses, use the right bits and do the right math it's not so hard to acomplish.

If you have those routers it becomes easier.

The hard part is not doing it, is KNOWING WHAT TO DO...

I don't know much about engines to be able to tell if the supertiger is gonna work or not, but it didn't have to look so bad.

In France they'd call it a "travaill d'arabe"...

Ion (Allah is great, but Jesus is greater) Muniz

>The engine is the C/L version the boost port is unchanged. I
>checked a differant G51 that the same modified and it had 6
>degrees of blow down so I think this one is messed up.

Carl,
My eyesight is not what it used to be. However, it appears that the first 2 pictures show a sleeve where material was ground away from the OUTSIDE of the sleeve at the transfer ports. The next 3 pictures show a sleeve where material was ground away from the INSIDE of the sleeve at the transfer ports. Are these picture of two different sleeves or the same sleeve? Sorry to be so nosey but inquiring minds want to know. Thanks.
DennisV

Dennis,
I know all the pics.are of the same cylinder.
Gordy

Gordon,
Thanks for the clarification. I think I got disoriented because the pictures were taken from different views (i.e. side vs bottom/top view). I believe the attached drawing shows what the modification was supposed to look like.
DennisV

Would filling in the top of the port with JB Weld before profiling it work? That way, you leave the metal untouched but cut the JB Weld and don't change the timing of the port. Would the JB Weld stay?

>Would filling in the top of the port with JB Weld before
>profiling it work? That way, you leave the metal untouched
>but cut the JB Weld and don't change the timing of the port.
>Would the JB Weld stay?

Are you suggesting putting JB Weld at the top of the port in the sleeve? I don't think the JB Weld would stay at all if you tried to use it to fill in a square cut. With the angled cut it "might" stay, but there would still be the little problem of getting a proper fit between it and the piston plus the heating/expansion problem. It probably would not follow the expansion of the liner very well adding to the problems in its use for this purposes. The wear characteristics on the JB weld would also not be good.

Using it to fill a port in the case, however, is beyond reproach. There is no wear factor here, and we are not concerned about heating/expansion affecting the piston fit.

Ron B.
F4Fguy

I don't know who did it,but keep him away from any of my hardware.Not only has it got negative blowdown,it's got badly mismatched port shapes.It also appears to have been done by hand with a Dremel or a die grinder,not too bad in the hands of a craftsman,but in this case, disastrous.I'd be surprised if it runs at all,and if it does it will run poorly.If it was intended to be like this,then it must have been an experiment gone horribly bad.If you're going to experiment,you shouldn't do it on a customer's engine.Ruin your own.

Ron B.

PS:You may be able to save it by raising the exhaust to give About 5-7 degrees of blowdown then removing the same amount from the bottom of the flange.Be sure to measure first,the flange may get too thin.Obviously you then have play with shims to get the deck clearance right.

.It also appears to have been
>done by hand with a Dremel or a die grinder,
Dremel??

It looks more to me as done by some stone age tool...

>PS:You may be able to save it by raising the exhaust to give
>About 5-7 degrees of blowdown then removing the same amount
>from the bottom of the flange.Be sure to measure first,the
>flange may get too thin.Obviously you then have play with
>shims to get the deck clearance right.

I'd bye me a new piston and sleeve.

BTW, it beats me why people mess with ST 51',s they are great engines stock! Just plug and play, except for the muffler.

Ion

Just for the heck of it, I'll go against the marjority and will say this engine will run okay, maybe even good for what the tune-up was intended (CL Stunt flying, racing, or whatever?). Has anyone ever looked at the first K&B .15 schneurle ported engines, the ones aimed at the Q-Midget Racing modelers way back. If you look you will see very similar timimg as you see here .... the by-passes were / are actually higher than the exhaust port! Those particular K&B .15 engines were the engine of choice in their day I think?

As for the off size venturi spraybar hole, it won't matter IF the venturi is good snug fit into the case and IF the spraybar is good snug fit in the venturi itself? I'll be anxious now to hear the test run results on this engine modification ..... please DO run it exactly as it is before you toss or change it?! I wonder if the engine tuner did anything to the crankshaft timing too?

>Has anyone ever looked at the first K&B .15
>schneurle ported engines, the ones aimed at the Q-Midget
>Racing modelers way back. If you look you will see very
>similar timimg as you see here .... the by-passes were / are
>actually higher than the exhaust port! Those particular K&B
>.15 engines were the engine of choice in their day I think?
Hey, you're right about the K&B, I just had a look at mine and that's something I'd never noticed before. Both my ST G20/15 and G15 are the same as well. Maybe that G51 could be a screamer

the work in the photos does seem to be a little ham-handed. Hard to see why anyone would make such radical changes to the ST 51 when most everybody seems to think it runs very well as is(CL version).

As far as the ports all opening at once, Super Tigre did that on a number of engines in the 60's and 70's. The G21-35 and C35 ran just fine with flat-topped pistons and bypass ports timed to open at the same time as the exhaust. Similar to the G.15. They did like to backfire hard though. But they ran well. Not stunt type runs though.

>Just for the heck of it, I'll go against the marjority and
>will say this engine will run okay, maybe even good for what
>the tune-up was intended (CL Stunt flying, racing, or
>whatever?).

OK, lets bet on this!

I'll be the bookie.

So far, I'm laying 3 to 1 that it ain't gonna run, 2 to 1 that it'll run but'll stink, and 5 to 1 that it'll be a great stunt engine!

Place your bets!

Ion (smokin' a cigar) Muniz

The guy was either 1)having a bad day or 2)he does not know the basics of two stroke engine theory, looking at the further pictures you have posted I think that 2) is the more likly.
Maybe he had too much to drink as the port work is very second rate, I am not too sure that I would even put the glow clip on this one, gentle disscussion with the tuner to find out his theory with the disscussion heading towards him supplying a fresh piston/sleeve to at least get back to stock setup.

I know it will run,but it will run poorly.If I had done this I would have given you a new liner and piston.The workman ship is very poor.Must of been up all night.As far as ST15 goes I use to mod.these little engines and raise the exhaust ports to 165Degrees and some other trick stuff and they would run 101mph on my FAI Combat planes.
But that was along time ago.I think it was when I was young.It`s getting harder to remember because I`m getting too many holes in my memory.HA;)

Say, didn't GMA discourage customers from taking apart engines which

he had set up? This doesn't look anything like GMA's work, however.

It would be interesting to see how well or how poorly it runs with

this set up. There is a chance, small that it be, that it might work.

Not sure what the story is here but I can tell you that had I made such a botch of your port work I'd buy you a new piston and liner. Fortunately its not me.

I have seen boost ports lead the exhaust, but I've never seen anything like this. I would like to know how it runs and what the tune was supposed to be. Was this supposed to be for stunt?

PLEASE let us know how it goes. Our tame engine guru John Dixon theorises that the fashionable vertical fence some people instal in a Fox 35 bypass is a means of de-tuning it a bit, i.e. reducing transfer area. I would guess these ports might have the same effect, it sure should de-tune it a bit. Who knows, you may get a great 2-4 out of it? The work does look a little "hand-made", give it a try and do let us know.

>PLEASE let us know how it goes. Our tame engine guru John
>Dixon theorises that the fashionable vertical fence some
>people instal in a Fox 35 bypass is a means of de-tuning it
>a bit, i.e. reducing transfer area. I would guess these
>ports might have the same effect, it sure should de-tune it
>a bit. Who knows, you may get a great 2-4 out of it? The
>work does look a little "hand-made", give it a try and do
>let us know.

Actually that vertical fence, as you call it, in the Fox doesn't de-tune it at all. It just increased the pressure in the case making the fuel flow more efficient and keeps it from slopping so much when the engine goes from upright to inverted.

On this particular engine, the question is not if it will run, but how well it will run, and, in particular, in comparison to a stock engine or properly tuned one. That is always the test. Has the modification that you just did improved the engine or not? If raising the porting just slightly helps, then you can raise them just slightly more until it hurts. This has gotta hurt--bad. I remember in working with the FP that raising the ports just ten thousandths beyond where I set them made the difference between turning a 12 inch prop and an 11 inch prop. It still ran great, but had begun to lose power. You don't just eyeball these things and say, "That looks about right." Compared to what? That is the question.

Leonard and Brett, (20 & 21) - Note your comments. I think John's thinking is that over the years as engines have developed more and more power, a contributory factor has been that transfers (intakes) have got bigger and bigger. Making it smaller is a retrograde step in the power department. Personally I agree that if you reduce transfer area you will certainly speed up the gases, but nevertheless racing engines do go for larger (slower?) transfer passages. Is this something to do with "a larger mass moving slower is more efficient than a smaller mass moving quicker"?
I do note that in "power" engines there is usually a large exhaust lead, and the GMA stunt tuning incorporating reduced lead gives the nice 4/2 run and reduced power.
It does seem there are a lot of variables here, and to say which one/s are dominant needs a lot of very well controlled experiments. Or accurate theory, beyond me!
I have recently heard technical terms which are quite new to me, like "tumble", in some corres with Randy Ryan.
I'll draw John D's attention to this corres and see what he thinks. He may not thank me for this!
Meanwhile - has the engine been run yet? I'm still interested to know.

>Leonard and Brett, (20 & 21) - Note your comments. I think
>John's thinking is that over the years as engines have
>developed more and more power, a contributory factor has
>been that transfers (intakes) have got bigger and bigger.
>Making it smaller is a retrograde step in the power
>department. Personally I agree that if you reduce transfer
>area you will certainly speed up the gases, but nevertheless
>racing engines do go for larger (slower?) transfer passages.
>Is this something to do with "a larger mass moving slower is
>more efficient than a smaller mass moving quicker"?

Oh, no argument at all here, at least on the principle. If the bypass was the "bottleneck" on the pumping efficiency, there's no doubt that making it smaller would incur a power hit. I merely maintain that the bypass is not the limiting factor on the Fox, something else is, and therefore making it smaller will have no effect - until of course it gets so small that is becomes the bottleneck.

Both subjective experience (i.e. just flying it and seeing, hearing, and feeling how much power it seems to have) and Frank's objective dyno test bear this out. Even a drastic reduction in the bypass area on the Fox (with no other changes and in stunt trim) seems to have negligible effect on the power. I would guess I have, at most, 1/3 the cross-sectional area of the original bypass, and it seems at least as strong as ever, if not slightly stronger.

But, it can now run through hard outside turns on a profile with no "burp" or quitting entirely, which it did regularly before. I can't tell you how many needle valves I ran through in my youth, from the engine quitting in the first corner of the outside square. Dozens for sure. This fixed it completely, as it has for many others.

Intriguing. I really must point this at John D. and we'll see what he makes of it. This is the sort of conundrum that could interest him.

I did forward this to John Dixon, and now I have to forward his comment! He says he never did say a fence in the Fox 35 transfer has a detuning effect. He said it speeds up gasflow and as long as the port area is not the limiting factor, it will have little or no effect on power. All this is as documented in SN and propounded by Brett. In my defence I have to say he did say it, but truly he was in jocular mood, has a great sense of humour, and I am quite willing to believe it was said in jest! Whatever.

> Oh, no argument at all here, at least on the principle.
>If the bypass was the "bottleneck" on the pumping
>efficiency, there's no doubt that making it smaller would
>incur a power hit. I merely maintain that the bypass is not
>the limiting factor on the Fox, something else is, and
>therefore making it smaller will have no effect - until of
>course it gets so small that is becomes the bottleneck.
>
> Both subjective experience (i.e. just flying it and
>seeing, hearing, and feeling how much power it seems to
>have) and Frank's objective dyno test bear this out. Even a
>drastic reduction in the bypass area on the Fox (with no
>other changes and in stunt trim) seems to have negligible
>effect on the power. I would guess I have, at most, 1/3 the
>cross-sectional area of the original bypass, and it seems at
>least as strong as ever, if not slightly stronger.
>
> But, it can now run through hard outside turns on a
>profile with no "burp" or quitting entirely, which it did
>regularly before. I can't tell you how many needle valves I
>ran through in my youth, from the engine quitting in the
>first corner of the outside square. Dozens for sure. This
>fixed it completely, as it has for many others.
>
> Brett
>

Yes, and bearing this out, take a look at the by-pass area in a Fox 40 engine. These are very narrow compared to a lot of engines, but they still put out bunches of power. Those ports don't need to be as wide as they are on a lot of engines, and, in fact, you get better pumping action if they aren't so wide--especially at the slower rpms where we run our engines.

There is no way to know until you run it. It could be a crankin' motor or a POS. It's like firearms; the proof is in the shooting (or running in this case).

My guess is it'll run but very sick. Same as installing a Fox.35 sleeve in 180 deg.off

Was this a CL version or an R~C? I just looked in the exhaust ports of two of my 3 G.51's, one a Tom Lay rework, the other NIB. Neither resembles that (DUH!). I'm thinking that it may have been an R/C sleeve, and radical rework was needed...and it wasn't very well done.

I think it will run poorly, but better than a Fox .35 with the sleeve 180 deg. out (because I don't think that Fox will do more than belch). I'll send you a dollar if you'll private message me the name of the tuner. I promise I won't repeat that info on this forum. I'd be upset, if it was mine, and I paid good money to have that done.

How about adding a pic of the boost port and either transfer port? Was the boost port left stock or raised to match the transfers?
Steve

HOLY SHEET!!!!!!!!

Ion (in bewildered awe) Muniz

This is ALL great info!! But its strange that DUKE was not cognisant of the 35 stunt BURP!! I mean really, what a cheap skate!! Yeah Yeah, I know-- PROFILE GUYS!! WHAAAA!! Paul

Sorry guys, What i meant to say was that i dont think duke really cared about how the 35 stunt worked on a profile plane -- Peace-- Paul

>Sorry guys, What i meant to say was that i dont think duke
>really cared about how the 35 stunt worked on a profile
>plane -- Peace-- Paul

Maybe, maybe not. Given the number of people who still deny it ever burps in the first place (but then offer numerous "solutions" to it), I wouldn't make any assumptions. TO be honest with you, I had tried to figure out how to fix it for years, and I know others had too. I just didn't have the right idea. Until someone understood the root cause of the burp, it probably *couldn't* have been solved.

When I saw Frank's article, I slapped myself on the forehead and said "D'OH!" for not having thought of it myself.

Brett, I think Your posts are great!! I learn something new from you everytime. And thats no joke!! Thanks Bud, Paul

Bret,
I've looked at hp curves for several engines with and without bypass plugs. Like you say, the reduced bypass is just a tad more hp, but not enough to write home about. The main thing is that it does kill the burp in the Fox. I did one for the Fox guy (can't remember his name now) but he agreeded that it worked for the profile. I've never taken he time to try to optimize the shape or volume of the bypass.
Frank

>
>>I'll send you a dollar if you'll
>>private message me the name of the tuner.
>
>
> I don't think that you would need more than two guesses.
>I've seen this sort of work before...
>
> Brett

Got it right the first try, actually. It confirms some stories I've heard. My contract says I can say who it was NOT, so if anybody "gots to know", I can give a "good list". Steve

I am rather conflicted on this issue, a whack job of porting on some unfortunate soul's ST 51.

First, why a person would send good money to another for engine rework and then promptly disassemble the engine is completely beyond me. Okay, in this case it seems to have uncovered some really intriguing details. In general it's still a real bad idea.

For what it's worth, and this may not apply to all engines, certainly not to all customers to the tuners of the world, if one buys something like a custom-built Fox 35 and then takes it apart, a good bit of the basic cost/benefit ratio was compromised.

I notice the actual customer has not been identified. Why not?

Seems a little strange to me that the tuner has not been identified either, although I will be very surprised if my first guess proves incorrect in that he is the same fellow who would like to see Stunt News contest coverage expanded beyond mere names and scores.

We seem to be so open as to the results obtained from Foster, Woolard, Len, Tom Lay and so on. What is the reverse image and why is it so feared?

Another perspective: As made clear in opening post, this was a custom deal. By simply laying it out there without attribution, are all the tuners supposed to each take a small part of the hit? Or should this be laid directly on a specific doorstep?

I would have handled this much, much differently. Beginning with actual running tests, a trip back to the tuner if not happy. Only after the guy who modified this engine either produced the expected goods, gave up or dug in his heels would I have taken it apart.

And then, if I chose to display the internals on this site all would know that I was the customer, here's what happened, I've got all appropriate documentation, this is the guy who did the work. Buyer beware.

>First, why a person would send good money to another for
>engine rework and then promptly disassemble the engine is
>completely beyond me. Okay, in this case it seems to have
>uncovered some really intriguing details. In general it's
>still a real bad idea.
>
>For what it's worth, and this may not apply to all engines,
>certainly not to all customers to the tuners of the world,
>if one buys something like a custom-built Fox 35 and then
>takes it apart, a good bit of the basic cost/benefit ratio
>was compromised.
>

I certainly agree. While I find this level of work disturbing, to say the least, I'm not entirely convinced it won't run as intended (given that even what was "intended" may not be a very good or helpful compared to a stocker). I can't imagine that doing this with a hand-held Dremel will be repeatable from one engine to the next, either. But if you buy something, you probably ought to run it as recommended before sending it back or diassembling it.

In this case, I know from previous experience that this particular practitioner is not as circumspect as possible about cleaning out the engine before putting it back together, and therefore opening it up to at least get rid of the grit, etc, that would otherwise would destroy it is a good idea. But even then, I would at least try to run it instead of just assuming it won't work. There's a lot more to this topic that a set of "magic numbers" and I would at least like to have evidence before getting into it with the reworker.

>I would have handled this much, much differently. Beginning
>with actual running tests, a trip back to the tuner if not
>happy. Only after the guy who modified this engine either
>produced the expected goods, gave up or dug in his heels
>would I have taken it apart.
>
>And then, if I chose to display the internals on this site
>all would know that I was the customer, here's what
>happened, I've got all appropriate documentation, this is
>the guy who did the work. Buyer beware.
>

Well put.

>We seem to be so open as to the results obtained from
>Foster, Woolard, Len, Tom Lay and so on. What is the reverse
>image and why is it so feared?
>

>Dan

Dan, you forgot to mention Randy Smith, but he's an engine reworker above any suspicion, after all he baame a kind of "standard" of good craftsmanship.

Well, anyow, nowadays he's more into makingg the whole darn engine than reworking engines so they become "stuntable"...

Dan

Very well said, thanks for bringing into perspective hard won good reputations.

>Dan
>
>Very well said, thanks for bringing into perspective hard
>won good reputations.
>
>Bazzer

You are welcome, but it is easily done, as I have a hard-won *bad* reputation, so it is easy to see things from behind the looking glass.