Engine Modifications Needed
10-07-2014, 10:33 AM
#1
Thread Starter
Engine Modifications Needed
Trying to find out who does engine mods or just some ball park numbers for a 46. Just playing around and not looking to race but I know these engines do more than 18,000.
Exhaust timing, head clearance and nitro % are about all I'm looking for.
Thanks! in advance
Exhaust timing, head clearance and nitro % are about all I'm looking for.
Thanks! in advance
10-07-2014, 12:50 PM
#2
I took a Webra .50 that was already a very strong performer and turned it into a fairly high speed engine.
The key is to start with a very free but "tight" lower end. I used the best Swiss made bearings rated for this application. The crank should be a snug fit into the inner races and of course the case needs to be heated to 350 degrees or so for the bearings to drop in place.
The exhaust port [open] timing is increased to 180 degrees, the closing edge of the crank's intake is moved back to about 60 degrees, the crank's "tunnel" is increased by patient sanding drum work until it is as big as you dare take it to increase air handling capability.
I made a 10 or 11 mm venturi and placed the carburetor in storage.
The crankcase is tapped to supply pressure to the fuel system.
The engine uses a very short Mac's header and tuned pipe.
This combo is tuned for 7.5 x 8 props and it will pull a Diamond Dust or Screamin' Demon delta in the 170 mph range without getting hot. on 15% nitro.
I've taken APC 8 x 8s and chopped them down for cheap props to break.
Once you increase the timing to 180, that liner will only be useful for small speed props, so you are making a commitment when you decide to modify an engine to this degree.
The key is to start with a very free but "tight" lower end. I used the best Swiss made bearings rated for this application. The crank should be a snug fit into the inner races and of course the case needs to be heated to 350 degrees or so for the bearings to drop in place.
The exhaust port [open] timing is increased to 180 degrees, the closing edge of the crank's intake is moved back to about 60 degrees, the crank's "tunnel" is increased by patient sanding drum work until it is as big as you dare take it to increase air handling capability.
I made a 10 or 11 mm venturi and placed the carburetor in storage.
The crankcase is tapped to supply pressure to the fuel system.
The engine uses a very short Mac's header and tuned pipe.
This combo is tuned for 7.5 x 8 props and it will pull a Diamond Dust or Screamin' Demon delta in the 170 mph range without getting hot. on 15% nitro.
I've taken APC 8 x 8s and chopped them down for cheap props to break.
Once you increase the timing to 180, that liner will only be useful for small speed props, so you are making a commitment when you decide to modify an engine to this degree.
10-07-2014, 05:34 PM
#4
Be careful here, CP of course knows his stuff when it comes to pumping up an engine. However that engine needs to be mounted in the correct airplane that has a low enough drag profile to take advantage of the small high rpm prop. Example, both these airplanes are .40-.46 size but put a screaming .46 with an 8x8 into the P-51 and you would be lucky to hit 80mph, put the same setup into the Miss Ashley and your good for 160 mph. Put a race designed .40 in it and your good for 180 mph.
10-07-2014, 06:17 PM
#5
Thread Starter
I really apreciate all the advice. And the cautions! I was racing boats and I know exactly what you mean about sacrificing torque for rpm and the considerations of the airframe. We will be just playing. I don't plan on going full mod. I just wanted a ball park so I could stop short. You should have seen their faces when I showed them 4,000 rpm from a MACS pipe!
So, another question. We would run 40-60% nitro in the boats. Now these boats ran between 70-100 mph depending on the hull and engine size. Record speeds in some classes. Why don't plane guys run higher nitro?
So, another question. We would run 40-60% nitro in the boats. Now these boats ran between 70-100 mph depending on the hull and engine size. Record speeds in some classes. Why don't plane guys run higher nitro?
10-07-2014, 07:11 PM
#6
You can get incredible performance from low [even zero %] nitro if the combustion chamber is made for it.
What's really cool, is to get a real screaming run from whatever your hot set up is and having the engine just warm right after the model touches down.
The color of the exhaust residue should never be real dark. Medium brown is about right. I've never used the inflight temp gauge or knock sensor because of limited space [and funds] on a .40 sized project. If you are experimenting with nitro %, it's good to always begin under propped and under compressed, then inspect the head button and the plug for stress, plus look at the exhaust residue.
180 degrees of exhaust is the "Magic Number" if you want to see one of these little 2 strokes really hit the pipe hard.
Tiny differences in prop load will greatly affect whether or not the engine can hit resonance or not. I imagine if you have boat experience [I don't] you know this already. This is why the Speed Hobby really becomes the Prop Hobby, because with "off the shelf" props you might find "off the shelf" results, even though APC has just about got all the bases covered for the small to medium sized engines. Once you get to .60 sized, then it's just about mandatory to go carbon fiber props if you plan on exceeding APC's red line of 190,000 divided by prop diameter.
One nice thing to know is if you have a high timed engine that doesn't work in a conventional plane, you can always whip out a simple delta and get some pretty thrilling performance that way.
Moving up in nitro % really makes things expensive for me, so I usually run no more than 10-15% in most any sport engine and spend my time with airframe work and prop work to see results. Some great fun has been from seeing how fast I could make a few $30 ASP .12 powered plane designs go, or even with just .049 engines on 12 ounce sheet balsa racers..
What's really cool, is to get a real screaming run from whatever your hot set up is and having the engine just warm right after the model touches down.
The color of the exhaust residue should never be real dark. Medium brown is about right. I've never used the inflight temp gauge or knock sensor because of limited space [and funds] on a .40 sized project. If you are experimenting with nitro %, it's good to always begin under propped and under compressed, then inspect the head button and the plug for stress, plus look at the exhaust residue.
180 degrees of exhaust is the "Magic Number" if you want to see one of these little 2 strokes really hit the pipe hard.
Tiny differences in prop load will greatly affect whether or not the engine can hit resonance or not. I imagine if you have boat experience [I don't] you know this already. This is why the Speed Hobby really becomes the Prop Hobby, because with "off the shelf" props you might find "off the shelf" results, even though APC has just about got all the bases covered for the small to medium sized engines. Once you get to .60 sized, then it's just about mandatory to go carbon fiber props if you plan on exceeding APC's red line of 190,000 divided by prop diameter.
One nice thing to know is if you have a high timed engine that doesn't work in a conventional plane, you can always whip out a simple delta and get some pretty thrilling performance that way.
Moving up in nitro % really makes things expensive for me, so I usually run no more than 10-15% in most any sport engine and spend my time with airframe work and prop work to see results. Some great fun has been from seeing how fast I could make a few $30 ASP .12 powered plane designs go, or even with just .049 engines on 12 ounce sheet balsa racers..
Last edited by combatpigg; 10-07-2014 at 07:34 PM.
10-07-2014, 07:55 PM
#7
It's funny how with 2 strokes most guys want to up the nitro when in fact when correctly set up an engine can make just as much power with low nitro if the engine is designed for it. I remember when the ultimate pylon racers were F1. 60% nitro and a plug per run were the norm. The rest of the globe were going just as fast with zero nitro. Makes me feel,a little silly to admit that the racing I currently do is based on YS 4 strokes running up to 60% nitro. Last weekend I ended up straying from my formula of running a max of 30% and pumped in some 55% nitro. Any idea how much an engine shakes with only half a 14x13.5 at 10K. Got it on the ground but still need to toss the airframe. If you care to see the video do a web search for Unlimited race at SCCMAS on Oct 4.
10-08-2014, 04:15 AM
#9
Yes and no. the YS 115 WS ( Warbird Special ) is simply just the evolution of the .91 FZ but has the compression reduced for high nitro use and has been balanced to run in the 10K range. It kind of funny to be needling the engine at full throttle and see the vibration reduction as you bring it into the correct rpm range. Even without those two relatively small changes the YS engines come closer then any other 4 stroke with their unique supercharging and close to mechanical fuel injection. It takes a great deal of power to spin a 14x13.5 at 10K. I tried for years to keep up with the YS guys with hopped up 2 strokes and finally gave up.
10-08-2014, 05:49 AM
#10
What I'm getting at is a true "full race" engine would be too much of a product support headache for these companies and the money just isn't there for the competitors. They could provide valve timing, spring pressures, etc. that require frequent valve spring changes, lifter wear, rocker arm damage, etc. IOW, engines that require full internal inspection and routine parts replacement between rounds.
Engines that are purposefully set on KILL for a type of flying [straight line speed runs] that hardly exists. If there was big interest in seeing what these engines could do in a German Speed Cup format, then there would be aftermarket tinkerers selling specialty upgrades like what you see in full scale auto sports.
Engines that are purposefully set on KILL for a type of flying [straight line speed runs] that hardly exists. If there was big interest in seeing what these engines could do in a German Speed Cup format, then there would be aftermarket tinkerers selling specialty upgrades like what you see in full scale auto sports.
10-08-2014, 07:19 AM
#11
Yes, that would be pretty cool. I can see a tool box with different head and cam sets. The cam and head swaps would only take 15 min. One would really be able to dial in airframe, prop, nitro, cam, head to the conditions of the day. There is some real potential there but as you said, the days of tinkering like that are pretty much gone. You and I are are cut from similar cloth. We grew up in an era where if you wanted something really above and beyond we knew we were going to have to build it and there would be no part untouched. Today it's buy and play. The true sport aspect is all but gone.
10-08-2014, 12:20 PM
#12
My Feedback: (10)
Just buy a jett or nelson engine and take a look inside. Its fun to play making your own but they will reliably make some great power. I had a diamond dust with a jett 50 that would run away and hide from quarter midget racers that were running 175-180 mph.
10-08-2014, 01:35 PM
#13
Yes, that would be pretty cool. I can see a tool box with different head and cam sets. The cam and head swaps would only take 15 min. One would really be able to dial in airframe, prop, nitro, cam, head to the conditions of the day. There is some real potential there but as you said, the days of tinkering like that are pretty much gone. You and I are are cut from similar cloth. We grew up in an era where if you wanted something really above and beyond we knew we were going to have to build it and there would be no part untouched. Today it's buy and play. The true sport aspect is all but gone.
10-09-2014, 06:03 AM
#14
My Feedback: (1)
I'll still take a 65% nitro engine with open exhaust over a piped engine on FAI fuel. Better torque, wider rpm range, better fumes during start, and a much better song in the air. When guys were racing the same airframe with both nitro engines and piped engines, nitro was always faster.
Engines make power based on a lot of factors, and one of those factor is the mass of the air/fuel mix. Nitro weighs more than methanol, and runs a much wetter mix. Where you might run an oz. a minute with low nitro/no nitro fuel in a 40, with 65% nitro you will flow at 3 oz. a minute.
Of course now with plugs costing 10 to 20 times the 50 cents we used to pay...........that one flight per plug would certainly hurt. But if you stay with mild sport fuel (40% and lower) you might not kill the plug if the head is not screwed down too tight..
Engines make power based on a lot of factors, and one of those factor is the mass of the air/fuel mix. Nitro weighs more than methanol, and runs a much wetter mix. Where you might run an oz. a minute with low nitro/no nitro fuel in a 40, with 65% nitro you will flow at 3 oz. a minute.
Of course now with plugs costing 10 to 20 times the 50 cents we used to pay...........that one flight per plug would certainly hurt. But if you stay with mild sport fuel (40% and lower) you might not kill the plug if the head is not screwed down too tight..
10-09-2014, 09:56 AM
#15
Thread Starter
I have a Jett 40. It only turns 18,000.
10-09-2014, 11:19 AM
#16
I'll still take a 65% nitro engine with open exhaust over a piped engine on FAI fuel. Better torque, wider rpm range, better fumes during start, and a much better song in the air. When guys were racing the same airframe with both nitro engines and piped engines, nitro was always faster.
Engines make power based on a lot of factors, and one of those factor is the mass of the air/fuel mix. Nitro weighs more than methanol, and runs a much wetter mix. Where you might run an oz. a minute with low nitro/no nitro fuel in a 40, with 65% nitro you will flow at 3 oz. a minute.
Of course now with plugs costing 10 to 20 times the 50 cents we used to pay...........that one flight per plug would certainly hurt. But if you stay with mild sport fuel (40% and lower) you might not kill the plug if the head is not screwed down too tight..
Engines make power based on a lot of factors, and one of those factor is the mass of the air/fuel mix. Nitro weighs more than methanol, and runs a much wetter mix. Where you might run an oz. a minute with low nitro/no nitro fuel in a 40, with 65% nitro you will flow at 3 oz. a minute.
Of course now with plugs costing 10 to 20 times the 50 cents we used to pay...........that one flight per plug would certainly hurt. But if you stay with mild sport fuel (40% and lower) you might not kill the plug if the head is not screwed down too tight..
Bob, you should hear 4 YS 115 come to tune running 55% nitro. Our warbirds are approaching speeds very close to current Q500. I'm typically getting through 14 oz of fuel in 4 min. Thankfully even running my typical mix of 30% nitro I can race all weekend on a single F plug.
Last edited by speedracerntrixie; 10-09-2014 at 11:25 AM.
10-30-2014, 03:52 PM
#18
Thread Starter
Ok. A littlle update. Keep in mind this is all in fun for me and my friends. So I took a $25 super tiger 45 and cut in the 180 and 60 timings. Not much change on the bench. (My mistake there.....maybe). So I went with what I knew and shoved the pipe down to 10 from plug to end of divergent cone, .010 clearance, and cut out thew low end needle and the spray bar back to the center of the carb. Mounted the engine to a Viper 500 and OH Yeh!!!!!! It's what I call third stage! I went a little higher on the timinng and you have to barely pinch the fuel line on the ground to get it on pipe. I think I can lengthen the pipe or go to a hotter plug to get it to turn on quicker. I would be interested in transfer timings and overall duration of crank and exhaust.
Again, thanks so much for the help and it was cool to finally hear one of these things rip.
Again, thanks so much for the help and it was cool to finally hear one of these things rip.
10-30-2014, 05:57 PM
#19
What size is the "MAGIC PROP"...?
With your current engine set up, I've had good results with a 7.5 x 8 prop on a .40 sized delta. If your plane has more drag than that, then you would trade away some pitch in favor of diameter to provide more thrust. All the engine cares about is maintaining the same load that it can spin up to the magical, invisible point where the pipe can sing. With your very similar engine set up [to one of my engines], I basically kept seeing gains until I ran out of header to take cuts from. At this point I took a cut or two from the pipe until there was no further gain.
It really is great to hear that you had good results from "HOT RODDING" an engine yourself..!
On my first attempt at this the results on the bench were disappointing until I whittled the prop down, scraped enough thickness off the blades...basically removed just enough load from the engine to allow it to hit resonance. You also want to use the least amount of compression that will do the job. Too much compression will make the exhaust black and this invites rapid engine wear and crappy, over heated, inconsistent runs. What you want is a root beer brown color, or lighter.
With your current engine set up, I've had good results with a 7.5 x 8 prop on a .40 sized delta. If your plane has more drag than that, then you would trade away some pitch in favor of diameter to provide more thrust. All the engine cares about is maintaining the same load that it can spin up to the magical, invisible point where the pipe can sing. With your very similar engine set up [to one of my engines], I basically kept seeing gains until I ran out of header to take cuts from. At this point I took a cut or two from the pipe until there was no further gain.
It really is great to hear that you had good results from "HOT RODDING" an engine yourself..!
On my first attempt at this the results on the bench were disappointing until I whittled the prop down, scraped enough thickness off the blades...basically removed just enough load from the engine to allow it to hit resonance. You also want to use the least amount of compression that will do the job. Too much compression will make the exhaust black and this invites rapid engine wear and crappy, over heated, inconsistent runs. What you want is a root beer brown color, or lighter.
10-31-2014, 07:45 AM
#20
Thread Starter
I had a few of the smaller pylon props. I can't remember the numbers but the biggest was an APC 8.75 x 9 or similar. I had the narrow, normal, and wide versions. The bench RPMs were no more than that of a standard APC 10x6. The Viper had too much drag for the narrow style props so I put the 10x6 on and that's what sung the best. I need to order some other props around that size and play a little. I'll also look at the exhaust......don't want black. I'll also lower the compression and see what happens.
I was hesitant to tell what I actually did with the pipe as many will tell me I'm crazy. But yes! There is almost enough straight section on the header for the coupler to be comfortable and the pipe is just taper! You should have seen the reactions as I made 1" cuts to the MACs pre-tuned length. There are a few more believers now. LOL!
I was hesitant to tell what I actually did with the pipe as many will tell me I'm crazy. But yes! There is almost enough straight section on the header for the coupler to be comfortable and the pipe is just taper! You should have seen the reactions as I made 1" cuts to the MACs pre-tuned length. There are a few more believers now. LOL!
10-31-2014, 01:14 PM
#21
You really need to have a feasible "target" prop selected for your bench runs before you hack into the exhaust system. I think the 9 pitch prop you mentioned would be too much, even if it was cut down to 7 inches. With a 6 pitch prop there isn't much speed potential.
For your bench runs a 8 x 6 or 8 x 7 is about the right load and I think it helps to have a fan blowing right into the engine..or else keep the runs as short as possible.
APC used to carry a 7.2 x 8.6 that worked pretty well with high timed .45-.50 powered deltas, but probably not enough thrust for a Q-500. I can't say for sure. I mention this prop to give you a ball park idea of what a max load would be.
Rule of thumb for prop load puts a 10 x 6 next to a 9 x 7 or a 8 x 8 prop, but with a high timed engine it takes very little variation in load to miss your mark and force the engine to turn more load than it can do comfortably without producing too much heat. Being reckless with load, compression, pipe system size, nitro % can spoil the fun before you know it.
Learning how to handle a model diesel engine [and experiencing their failures] is good training for having a calculated, carefull approach with a pipe timed, high revving glow engine.
For your bench runs a 8 x 6 or 8 x 7 is about the right load and I think it helps to have a fan blowing right into the engine..or else keep the runs as short as possible.
APC used to carry a 7.2 x 8.6 that worked pretty well with high timed .45-.50 powered deltas, but probably not enough thrust for a Q-500. I can't say for sure. I mention this prop to give you a ball park idea of what a max load would be.
Rule of thumb for prop load puts a 10 x 6 next to a 9 x 7 or a 8 x 8 prop, but with a high timed engine it takes very little variation in load to miss your mark and force the engine to turn more load than it can do comfortably without producing too much heat. Being reckless with load, compression, pipe system size, nitro % can spoil the fun before you know it.
Learning how to handle a model diesel engine [and experiencing their failures] is good training for having a calculated, carefull approach with a pipe timed, high revving glow engine.
Last edited by combatpigg; 10-31-2014 at 01:17 PM.
11-05-2014, 08:31 AM
#23
