bonesonpoint

Does anyone know of any other setup, including the turbo plugs, that will yield more rpm's than a stock Norvel 074 head and plug? I get right at 17,000 with a 7x3 APC and Byron's 15% nitro, 20% oil. I just wondered if the turbo plug setup would yield a little more than the stock plug.

Also, other than the Cox 7x3.5 gray prop which I have found to be the best on the little extra and norvel 074 combo, which prop, size and pitch, have you found that yields the most speed for this setup. I broke my last Cox prop. I'm not interested as much in power, just speed. Which brand and size.

Last thing, I get more rpm's from the 15% Byrons, 20% oil than I do from 25% Sig fuel w/20% oil. This is on a stock Norvel plug with one shim. It seems backwards and I wondered if anyone knows why this is.

I'm sure this has all been hashed out through the years but I can't find this specific info. I am looking for the best prop/fuel/plug combination that anyone has come up with.

Thanks

mtntopgeo

My Feedback: (12)

17K with a APC 7x3 sounds right. The old style (pre-GF3) MAS 7x3 will get you a few hundred more RPMs, but I've not noticed much (if any) difference in the air. Even though most guys seem to use the 7x3 prop on their .074 Norvels, the little engine really can't get into it's "happy" zone with that large a prop. (I know, with a large plane like the Lil Extra, you can't go to a smaller prop) I like to run a MAS 6x4, or 5.5x4 with that engine. With these smaller props, it keeps responding to more & more nitro. I generally use 35 % nitro (SIG) with enough castor added to get 25% lube. This drops the nitro to about 33%. I always use the stock Norvel head/plug.
...................... George K.

ffkiwi

The Cox 7x 3.5 and APC 7x3 represent quite a load for this engine which may limit its ability to rev in its power band. That being said-your quoted revs for this prop is good. Another reply from George K (mtntopgeo) mentioned the Master 7x3-which is a lighter load than the two props above. [also FWIW a very good prop for 0.5-0.8 diesels when you want peak performance!]Master airscrew have just come out with a 6.5x3 prop which would definitely be worth following up, as would the APC 6.5x 2.9 I don'tthink the turbo heads thus far are proving to have any more performance than the standard Norvel insert-but that being said-I doubt people are doing much experimenting either. To get more go you might have to try half a dozen brands of turbo plugs-and perhaps three heat ranges-thats a lot of expense time and effort for possibly no significant (if any) advantage. As for getting more out of your Norvel-the only realistic (ie proven) option would be to get a Nelson head made up for it-and as far as I am aware no one is doing this commercially. Doug Galbreath (who is the main supplier of the 049 Nelson head) could perhaps be approached-but he would need a confirmed market before tooling up.

ChrisM
'ffkiwi'

bonesonpoint

Thanks guys. Very helpful info.

George, your comment on more nitro getting more performance is logical and I bought the Sig 25% just for the Norvels, but for some reason I just can't tune the Sig 25% to get as many rpm's as the Byron 15%. Doesn't make sense but I can't adjust it to get an increase. The 17,000 is coming from the 15%. I have never been able to get more rpm's from this Sig fuel on any of my Norverls over what I get on the 15% Byrons. It's just an interesting oddity I guess. I'll just use the 15%. You both are saying that the 7x3 is a little too much load. I didn't know that.

Where is the happy zone on the .074? Would you go to the 6x4 on this plane? It does seem like the engine at 17,000 wants to rev faster, just from the way it sounds. It's fairly new and I've been running three shims in it until last week. I started pulling them out and didn't get up to the 17,000 until I got down to one shim. It still idles, transitions and runs great. Three shims were giving me around 16,400 rpm. I have some 6x4 MAS props but never thought of trying them on the .074.

Chris, I am very interested in the new props you mentioned. I checked Tower and I can't find them. I'll keep looking. That MAS 6.5x3 sounds definitely worth trying. I just want this plane to go as fast as the Norvel will take it. I'm not as interested in the power. I have several of the Norvel .074's and I love running them and want to use them. I know I could go up to a bigger engine but I just like using the Norvels so I am trying to squeeze as much as I can out of them. That death dive at full power is down right exciting. I think I have some cracks in the radio from squeezing it while pulling out right above the ground. The fans don't cheer if you pull up too soon!

I have plenty of the Norvel plugs and actually I have never burned one out so I'll just stick with them and look for those new props. I want to get in the happy zone. What would you say would be too many rpm's for this engine?

Entropy

My Feedback: (2)

So when you say that no performance gains have been seen from using Turbo heads, does that include Jon Valentine's Turbo head for the .074?

Mr Cox

Regarding props, there's an APC 6.3x4 that I like for these engine sizes.

mtntopgeo

My Feedback: (12)

I've always considered 2-stroke engine tech. to be some sort of black magic, so don't have an answer for your getting better performance with the lower nitro fuel. Just a WAG, (wild ass guess) but I'm wondering if the big 7x3 prop has something to do with hi nitro performance thing. Hopefully some other member, more in the know, will comment on this. Although I have not tried it, I kinda doubt that a 6x4 is the right way to go with the Lil Extra. I have a Enya .11 swinging a MAS, pre GF3, 7x4 on mine, & am thinking of changing the engine to something that can swing an 8x4 prop with some authority. .................... Norvel rates the .074 HP at 22,000RPMs, so I like to have the engine running in the 19 to20 K range on the bench. Again, others here might comment where this engine likes to be. Good luck, even with things like they are, sounds like you're having a ball ................. George K.

ffkiwi

Try Hobby Club for the new Master prop. I saw them on their website. The APC 6.5x 2.9 goes like stink on the MP Jet 061 diesels (17,000+) so on a Norvel 074 should turn quite a bit faster. The Cox 7x3.5 has a lot of blade area-and that's why I consider it a bit much load (even on the Cox TD 09 it was designed for its a bit much load)-in contrast the Master 7x3 has quite thin blades-and is a better match-but the blades are a bit thick. I didn't mean to imply that a 7x3 per se was too much load for the Norvel-but there is a very limited range of options internationally in the 7x3 size-only the Cox, Master, APC and Graupner. If you want to fly fast, then as an earlier reply of George's you have to go up in pitch (and obviously down in diameter!) George users a 5x4-but you might experiment with a 6x5. Graupner does some nice narrow blade CAM props that we used very succesfully in 1.5cc diesel speed in NZ back in the 90's-I think there are 6x5,6x6 and 6x7 options-and there's nothing to say you can't trim them.......
Equally some of the APC and other C/L combat props-which are around 6x4 nominal (and intended for F2D .15s turning 30,000 odd) might also serve your purpose on the Norvel.
The short answer is there is no substitute for experiment and test. The prop your Norvel turns at 22,000 MAY not be the one that flies your model the fastest......................
As for heads, (in answer to 'Entropy')so far there doesn't seem any body of evidence suggesting that the turbo heads are any better than the OEM one-and that includes the Jon Valentine one. What we do know is that both Graham C and I had problems with the plug to head fit of the Valentine one. If the QC doesn't improve....... [or worse still if there are variations from brand to brand of turbo plug]
What the world still waits for is a Norvel 074 Nelson plug head adapter.

ChrisM
'ffkiwi'

bonesonpoint

Oh yeah, it's fun just the way it is but it just seems like the engine wants to hum a higher tune, like it's trying too hard and wants to be set free. Thanks for all the good suggestions. I have a couple of these sizes but I had them for the .061's. I've never tried them on the .074. It just never occurred to me. I am going to spend a little money and experiment, like you said. I found the 6.5x2.9, 6.3x4 and 5.5x4. I'll get a couple of each of those. I already have the 6x4's and 5.7x3's but I didn't know you could run those on the .074. It will be interesting to see how it turns out. I'll keep playing with the nitro, too, and I'll just stick with the stock Norvel plugs. I appreciate all the ideas. It should keep me busy for a while.

combatpigg

My Feedback: (3)

I've tried going down in diameter and using a 4 pitch prop with the .074, but the "in the air" results just aren't there. The engines respond OK, but the weight and drag of a .074 powered plane seems to be what is holding things back. I've run them with over-sized venturis, open exhaust and high fuel pressure bladders. Maybe someone with a fresh approach can do better? I'll estimate my best effort at around 80 mph or so.

There is a big difference in thrust between 7 inch and 6 inch props that the .074 can't make up for with rpm. Norvel never offered a hot version of this engine, now wouldn't be a very good time to experiment with internal mods until a good working plug adapter is available.

17,000 with a 7x3 is pretty decent power for some of those classic 1/2A designs that come out weighing over a pound.

eroc144

My Feedback: (1)

I have a love/hate relationship with Norvel .074s. Well, maybe not hate - perhaps disappointment? I've got several .074s and they all chug an APC 7x3 at around 17k, but I've never been able to get them to unwind the way my Norvel .061s do.

I built a .074 Pacer last year specifically to give the .074 a low weight, low drag airframe. AUW was 18oz but it was still kind of pokey with limited vertical using 7x3, 6x4 and 6x3 props. MT George suggested I try MAS props, and the one flight I got in on my HOB P-47 before my ankle surgery was better, but not great. I'll continue the experiments in a few weeks when I'm off the blinking crutches.

EG

bonesonpoint

Well guys, you may be right about the 7x3 being the one. I've tried the other recommended props that I had in the box and the other sizes came in yesterday. It does wind up with the 6x4 and I thought I was in business, but like combatpigg said, it didn't translate to more speed in the air. A lot of it may have to do with this fat winged Little Extra but if EG couldn't squeeze any more out of it on an 18 oz. plane then I don't know what.

I had two dead calm days to play with it. That is rare around here where the wind come sweeping down the plains. I think part of the problem is perception. I am also flying the Herr T6-Texan with a hot Norvel .061 on it and it is a bullet and a blast to fly. Then I fire up the Extra and it just doesn't compare. Obviously, apples and oranges but the Texan is more exciting.

On a side note, I was in one of those high vertical (down) death dives with the .074 on the Extra and it was wound up pretty good on the 7x3 APC. About halfway down I heard a distinct reduction in rpm's and the sound/pitch of the engine. It had three shims in it at that time. When I got it back down I had to richen the needle for the next flight, a lot, and never could get back up to the 17,000 after that until I finally went to one shim. Now I have no shims after trying these other props. Can't get back to the 17,000 on the same APC 7x3. Nothing is loose, I can't spot anything externally, I wonder what went wrong? Something changed. I guess if I can't get it back up to speed on the next trip I will take it apart and see if anything obvious jumps out.

I'll try these other props that came in and see how it goes.

Larry Driskill

I would first make sure the carb is still fully opening and that I had no fuel line problems or leaks.

Then check that the cylinder bolts did not loosen.

Then I might pull the plug and run the piston down as low as it would go and inspect the cylinder walls for marks or scratches (especially on the front and rear walls where the wrist pin runs - use a flashlight).

Also 'feel' the shaft fit/drag with the head still off.

Fourth, pull the engine, remove the rear cover and see if the rod looks bent.

And finally, if nothing has shown up, a full tear down.

mtntopgeo

My Feedback: (12)

I think that what most replies, to this thread, alluded to was that you won't be able to get this engine into it's "happy zone" & still get the performance (that you desire) from the plane. IMO, if you have a plane that is heavy/dirty/big enough so that it needs a 7 inch prop, then it (the plane) probably needs a .09, or a light .15. The best "big" plane/.074 Norvel combo that I've come up with is a profile with a MSS wing. Fairly clean, < than 15 OZs (dry), & a rather thin wing. A real fun (fast) plane. !!!!!! Just located another Tiger 400. The last one I had weighed 18+ OZs (dry) with a heavy Enya .09 for power. I think that this plane is more clean than my profile, & with the Norvel & a baloon tank, I should loose another 2.5 OZs. Expecting some good performance out of this one. Think Rog had one (Tiger 400) with a Norvel .074 on it, but don't know what he used for a prop. Just think that you need a cleaner, lighter, smaller plane for that .074, considering the performance you desire. Get a light .15 for the Lil Extra. ................... Hope you get the Norvel running right again. ........................ George K.

bonesonpoint

Well Larry, I wouldn't have believed it and wouldn't have checked it if you hadn't suggested it. Everything you listed checked out ok until I got to item #4. I took the engine off the plane and took the back plate off. There it was, the bent con rod. I don't know how long it would have taken me to look that far trying to find out the problem because I can't imagine how that could happen. Engine running wide open in a full on vertical dive and the rod bends? Could it not turn that APC 7x3 that fast or will I find something else that caused it. I don't know but you nailed the problem and it looks easy enough to fix. Before I left I took a couple of pictures of it and when I get back I will take the engine all the way down to see if I can figure out what caused it. It still runs great but it's just 1,500 rpm's slower than it was before the rod bent. I will try to post a picture of it at the bottom.

George, I know you are right. I may try a .15 on another Little Extra that is on standby and waiting for an engine. I posted on the other current Extra thread asking what people would consider the best .15 to put on it. I thought it would be one of the OS engines but I don't know. I've never owned .15. This plane is not really built for speed, like you said. I want to use these .074 engines so I will be looking for something faster like you suggested.

Hopefully, here is the picture of the bent rod. It will either show up twice or not at all since I can't tell in the preview if it uploaded.

bonesonpoint

I'll try again.

combatpigg

My Feedback: (3)

bop, that's the first major .074 failure I've ever seen, have a cigar! [8D]. Most death dives I've seen that cause less power afterwards are because the glow plug unscrewed or the element got used up [chalky white].
Never hurts to check the liner screws, I had a McCoy .35 powered plane land with just a naked piston flopping around, the cylinder and head were nowhere to be found.

Larry Driskill

Bonesonpoint, Good morning from Texas,

I'm not sure how the rod was bent, but we have seen rods 'stretch' on high performance engines. On F2D (.15 sized CL Combat) engines with very tight head clearance a runaway engine may see the piston hit the head.

Or some foreign bit may have entered the picture.

I suspect that rod can be straightened. And may work pretty well and get your 1,500 back. While it will probably not be like new, new may be hard to find.

Rods are not the most difficult engine part to make and several guys on this forum have made them for other engines.

bonesonpoint

I have taken it all the way down now and inspected it closely. I don't see any scratches anywhere. The plug looks good and the engine was running good, just slow so I think the plug is good. The head screws were tight and I don't believe they had ever been removed. They had that pop that you get the first time you bust one loose. Piston, cylinder crank, everything looks good. The idea that some foreign partical of some sort got in there must be what happened if this is the first time you guys have seen a .074 do this. I don't know how many rpm's it was doing but it was about halfway down at full throttle when everything changed so it was turning pretty fast with that heavy APC 7x3 on there.

It looks easy enough to fix with my little brass head hammer. I have other wrist pins if this one were to not work out. I got some of those piston/cylinder sets from the heli engines a while back, and also have some of the complete heli engines minus the throttle so I have a wristpin if I need a new one. One of my .074's runs with one of those heli sets in there and runs good. The only problem I have with taking the pin out is staking it back in. This one is staked on four sides. I'll have to look at it when I get back home.

So Larry, you know what I mean about the wind sweeping down the plains. I am getting ready to go big again with a new war bird so I can fly in the wind. I am tired of flying that Goldberg Cub and if the wind is blowing that's my only option right now. I'm going with a Saito 115 so that will also put my Raven and Waco back in action at some point. I'm having so much fun with the little Herr Texan that I am going to get a big Texan to go with it and put the Saito on it. But I will always throw the little guys in the back seat just in case the wind dies down.

DeviousDave

nevermind, read the tread!

bonesonpoint

Just so as to not look more ignorant than necessary, all those times I mentioned wrist pin in that last post, I was talking about the rod. Just wanted to clear that up.

Have you guys had success removing the wrist pin and rod and then staking the new or repaired pin/rod back in? I can't wait to get my 1,500 rpm's back but I won't get to work on it until Monday.

Larry Driskill

I have not removed an .074 pin, but here is how I do .049s & .061s:

Use an Exacto with a #11 blade to cut away just enough of the crimp on the back wrist pin hole of the piston to allow you to remove the wrist pin.

Use a small drill bit to press the wrist pin out by hand.

Use the drum sander on your Dremel to make a shallow 'cradle' in a scrap piece of pine that the piston can sit in.

Clean everything up and re-assemble the piston, pin, and rod.

Put the assembly in your cradle and stake the pin by rapping the smooth end of a small drill bit (1/16'" or smaller) with your lightest weight hammer.

The piston material is fairly easy to crimp.

Be gentle and don't distort the piston.

Reassemble putting a bit of light oil on the rod, wrist pin, and in the piston.

Test run.

Marvel at your cleverness and go fly while the masses watch TV and vegetate.

bonesonpoint

That should work great. The drill bit idea is really good. On the other pistons I have looked at they just had the pin staked in at two places. This one is staked in at four and on some of the other close-up pictures I can see that the hole is actually almost square.

I took some pictures of this piston. Just holding it in your hand looking at it you would think that it is as smooth as can be. It's not very old and had great compression before the rod bent. It is amazing how the piston looks in the photos. If I didn't know it is nearly new and that it runs great I would think it was junk just looking at these pictures. I'll post them just because I thought it was interesting. Thanks for the tips on fixing the rod.

Larry Driskill

Bones,

Looking at that rod makes me think "Aren't 2-cycles great"?

Neat that it was still running at all, much less only 1500 RPM off pace.

Imagine a full scale single engine, single seat plane and how comforting it would be the think the engine might well bring you home even with damage like that.

As for the picture of the piston. Were that a good lookin' 40 year old woman, she would not let you put that much light on her and then shoot a photo as every
wrinkle and flaw would jump off the paper at you.

(Unless, of course, she was that 28 year old that Toad is claiming to be 50.)

Toad

LOL, my wife says "thanks Larry"