Spaceclam

i own a pumped .91 four stroke, and i need every last drop of performance out of it. the one condition i have is that it will help at least one aspect of the motors performance, but not in any way hurt another. i don't take tradeoffs that way. i am already using that nitro blast stuff, and i am running 20% nitro. i will not go higher.

xlr82v2

My Feedback: (1)

The Muffler may help...

But if you need more power, you have to buy more cubic inches...

And, there are always tradeoffs. It's unavoidable. You can't have your cake and eat it too.

Billy Hell

My Feedback: (2)

What kind of prop are you turning and what is your goal? Speed or thrust?

Shortman

My Feedback: (21)

Answer to your solution... YS 91

Spaceclam

i am going for thrust, running a 14x6 prop. that prop is apparently the ideal prop for that engine. i have had 3 hobby shop owners say that, two senior members at my field, and my personal experiance but i am looking for all aspects of improving performance. i will not change engines becase i am only 13 and i am doing everything off of allowance. therefore, after spending 350 dollars on an engine, i want to know what i can do to make it better. by tradeoffs, i mean, for instance, increasing the top end, but decreasing the low end.

ChuckAuger

My Feedback: (12)

There's just not a lot you can do..try different makes of props is about it. If you are set with your nitro content, you can't do a whole lot more.

My suggestion would be optimizing the airframe you put it on. Every ounce you can take off is an ounce of thrust you have gained. Add up a few ounces and you are getting somewhere.

To the best of my knowledge there is no magic pill you can give a 4 stroke and get a great increase in power.

hroachen

There is no such thing as "the ideal prop for that engine", but there is an ideal prop for a particular engine/plane combination for a specific task.

If maximum thrust is your goal, I'd look a lot harder at the prop than the exhaust. You say you're running a 14*6 prop, can you specify which brand and model if they make more than one 14*6? I don't think that would be my first choice for thrust on a .91, I run an APC 16*4W or a Menz-S 16*6 on my YS91, I've never had anything smaller than a 15*8 Menz on it. The 15*8 Menz had a bit less thrust than the 16" props, but flew the plane a bit faster.

If you're running a YS, then you're definitely under-propped, if you're running an OS, you still need a bigger prop. I'd try the 16*4W APC for sure, you may need to trim the tips a bit, but you should be in the ballpark.

IF you're looking to hover, bigger diameter and lower pitch is the key. Don't go entirely by what the shop owner and the senior guys at the field say, hovering and 3D require thinking in different ways than the long held standards. Most of the guys at my club are surprised at the props I'm running, but most of them just tool around the sky at high speed and have never tried hovering or 3D.

I'd bet money that you're going to get much more benefit by finding the right prop for your situation than by a different exhaust. 4 stroke engines can benefit some from exhaust tuning, but not to the extent that 2-strokes do. At least not for the kinds of prices the average person is willing to pay.

Another thing you might do is double check your valve clearance, if they're out of spec there's probably several hundred RPM of free power waiting for you there.

Good luck,
David

Billy Hell

My Feedback: (2)

The difference you can feel between a Zinger and an APC is surprising. It would make you think you had added a pipe on the engine (APC being the good one).

Spaceclam

i forgot to mentnion, that i am running master airscrew, but the reason being, that i have tried a multitude of props, but this one worked the best. becasue of the wind at our field, and the extremely high stall speed of my plane, i can't really go lower than a x6, as a mattter offact, i tried a x5, and it could not combat the wind at our field. it is always windy there. i have been told that for four strokes, the master airscrew props are better becasue of the fat-blade, and because it is not necessary to have really thick props, they are not. i could understand for a two stroke, but for four strokes, i hafgve ben told many times, to stick with the master airscrew.

majesticmonkey

How about some clarrification? What's the plane and what kind of performance are you looking for? ie. speed, thrust, etc.

Spaceclam

I have found the ideal prop for my style of rlying, and for my plane. i am not going to change that if that is why you are asking, buti am flying a cap 232, and i am very aerobatic. everybody asks if i will change props, although i think it states in the first post that i am really fixed on this one. if not, it comes later. i have uped the nitro to 20%, and this was not a cheap engine, so that is as far as i will go.

majesticmonkey

no offense - but why are you asking if you're not willing to experiment?

Like others have said trying different props can really change things. I still don't know what you mean by performance and aerobatic. What kind of flying do you do? Is it speed, 3D, general sport flying???

A 14x6 prop is sort of an inbetween prop -- for sport flying (some do use them for 3D). If 3D is what you're going for then maybe a 15x4w would work best. For speed you obviously want more pitch (like a 13X8).

ChuckAuger

My Feedback: (12)

If you are flying an OS .91, won't try another prop, won't try different fuel, then just exactly what are you looking for??

What if I told you I had a high-lift cam for the OS .91?? Would you try that?? No, because it costs more than a prop or a gallon of fuel and it would stress your engine more than upping the nitro.

Pipe?? Lots of bucks, not much gain.

High speed servo?? That ain't gonna do jack to improve your engine's performance!

You are 13, with no money. Fly what you have. There IS NO MAGIC POWER INCREASE FOR YOUR ENGINE.

Read it, learn it, live it.

Oh yeah..there IS one thing..there is a Thread Here that has some info you MIGHT be able to use..

YNOT

I got it.

Xacto knife.

Start cutting out some wood out of that plane. Make the plane lighter.

I find MA props terrible for any type of aerobatics.

hroachen

Spaceclam,

There's no magic to be had, I wish there was. I don't understand why you're so unwilling to try and follow some good advice. Just buy one APC 16x4W prop and bolt it on. I'm guessing that the shop where you go doesn't keep them in stock, and rather than go to the small bother of ordering it, he just tells you that what he does keep in stock is "the ideal prop for you". There are plenty of shops like that around. The way they've been doing it for years is the only way, and they're not about to learn anything new. Don't believe everything they tell you.

I'll make you a deal... I have a few extra APC 16x4W's here. I'll send you one, no charge, completely free. Just try it. Hold your plane on the ground with your prop and have someone run the throttle to full while you feel the pull. Then try it with the APC. I think the difference will surprise the heck out of you.

As soon as you apply the power to takeoff you'll know while you're rolling if the prop will get you safely airborne with enough airspeed. If you don't think it'll do the job, then throttle back instead of pulling up. Taxi back to the pits, throw the prop in the trashcan, and call me an idiot.

But at least give it a shot. You have nothing to lose.

David

dhooks

My Feedback: (24)

Lets see we want help but we dont want to try anything? For 3d with the os .91 try a 15x4w. And yes your plane will still go fast enough to take off with out stalling.Also like was mentioned check your valve clearances.

Spaceclam

Would you guys believe me if i told you that when i tried a x5 prop, i had trouble keeping it in the air? imy cap is 9 lbs, and i am as advised, cshaving down weight, but i dcan't do too much, just becasue of the way the plane is made. a x6 prop is about the lowest i can go and kep it safe. about the ma props, i was recomended to stay with them when you have a four stroke because of their wide, thick blades, trhey provide a lot of thrust at lower rpm's while apc's have less vibration, with less thrust at lower rpm's, but are mor efficient faster. about the nitro thing, i am already 5% above my manufacturer's maximum recomendation, and once again, because i am 13 with no money, when that engine wears out, $350 is a lot of money to come up with. basically, i want to know if you guys know of any little tricks with four strokes. the reason i am asking somebody is because all of the obvious things are done, besides increasing the nirto further.

ChuckAuger

My Feedback: (12)

While I don't advise against good natured advise in general, this is some advise that I think is leading you astray. You say you have tried a X5..I bet it was a MA X5, no?? APC props work just dandy at 4-Stroke RPMs.

Why not, just for the heck of it, try using some of the advise given here and try an APC?? You might be very surprised and would be a local hero if the advise you got here actually worked!

BTW..I have a 9lb biplane with an OS 91 Surpass and have at times run a MA 14X6..It had incredible performance, so much more whan a "scale" effect it was scary. If your 9lb plane is a dog with a 14X6 MA and os91, something else is wrong.

Spaceclam

i have had some 14x6's on backorder for around a week now, but master airscrew does not make a 14x5. the only 14x5 i could find was a zinger. (wood) by the way, the lane is not a dog. infact, it is shooting strait up at a good 15 mph solid, but i want to be able to pull out of a hover, not necessarily aggressively. my goal is to be able to do that around 10-20 feet above the runway, and then pull out with enough power that i do not loose much altitude when i kick it over to level flight again. i am sorry if i gave you the wrong impression. however, if you know of a line of props specifically designed for four strokes, i would appreciate it, because i am still llooking for a better prop, i have all kinds of props in m;y bag. i have as high as a 15x8 which it swings without trouble, to my favorite so far, the 14x6, and as high a pitch as a 13x9. all seem to work, but my goal is to pull out of a hover. it is possible that the reason it performed so poorley was simpley because it was a wood prop, which i have not heard any legendary stories about, but nobody else makes a 14x5.. also, keep in mind, my plane will stall at really high speeds, 9 lb and 625 square inches of wing area. i did check the valve clearences, they were as recomended (between .04 and .1. i did not mean to ignor4e all of you guys, if i did i appologise.

hroachen

Spaceclam,

The 14x5 Zinger is not much of a prop, I'm not surprised you didn't like it.

Believe me when I tell you the 16x4W APC will do the job. The only thing you might need to do is trim jsut a bit off the tips, but try it first as it comes. I promis you the thrust and speed will be far better with this prop thanthe 14x5 Zinger, and noticeably better than the 14x6 MA.

I don't know why it's so hard to believe when for a couple of bucks you can find out and be certain. And if no one around your way has one in stock, my offer to mail you one absolutely free still stands.

Spaceclam

thanks. your advice is enough, i will order one. i just got the zinger because it ws the only 14x5 i knew of.