More power more RPM?

It all started because I wanted to try a new technology prop instead of that old aluminum club.
A new prop built to Lonie Prinz specs turned out out be a little coarse for my O320. Only 2150 rpm on takeoff, a little low.
I had always wanted more power (who doesn't) so rather than have the prop repitched I bought a freshly overhauled O360.
A couple of Pmags and an injection carb from Rotec and all I have succeded in doing was raise my fuel flow from 40 to 49 liter/hr and not one more RPM.
Straight and level, flat out 2320 rpm, 27in map, same as before.

Did I unecessarily replace a real good O320?

Am I missing something here?

Any suggestions would be appreciated.

From a hot rodders point of view horsepower is created in two ways. RPM and displacement. That is, increasing horsepower can be achieved by turning the motor faster or increasing the displacement of the engine. Therefore, you should be developing more power at the same RPM (horsepower / torque) with the larger displacement motor upgrade.

Disclaimer: I know a little about this subject and my knowledge comes from the car hobby, not via an engineering degree or aviation engine expertese. Others on this board know a whole lot more on this subject and hopefully will provide their input. I am eager to see the responses to your inquiry.

You have too much pitch in your prop. Time to get another prop that will allow the engine to turn 2700 rpm, which the engine should do at full power, level flight, at or near sea level.

It is quite true that more rpm makes more power. You are restricting the power output of your engine by not allowing it to make full rpm. The only solution, assuming your engine is running well, is to repitch or replace your prop. I have nothing against the Prince prop, but it is clearly not adjustable. You will need to replace it with one with less pitch.

Unfortunately, replacing your prop is something you should have done when you still had the O-320, but it is a little late for that now.

If you want a metal prop call Sensenich. They can help you select the right pitch and diamater for your plane. If you want a fixed composite prop I recommend Catto Props in CA. Sensenich also makes a ground adjustable composite prop for the O-320, but I don't think they have the O-360 version ready to sell yet. You could ask, though. Whirlwind makes a ground adjustable composite prop, but it it pretty pricy.

These are just some of your options. Good luck with your new prop.

Dave Prizio

Did you redrill the O320 prop to fit the O360 or did you buy a new prop with the same pitch? Tell us more.

Quote:

---

Originally Posted by raytoews

It all started because I wanted to try a new technology prop instead of that old aluminum club.
A new prop built to Lonie Prinz specs turned out out be a little coarse for my O320. Only 2150 rpm on takeoff, a little low.
I had always wanted more power (who doesn't) so rather than have the prop repitched I bought a freshly overhauled O360.
A couple of Pmags and an injection carb from Rotec and all I have succeded in doing was raise my fuel flow from 40 to 49 liter/hr and not one more RPM.
Straight and level, flat out 2320 rpm, 27in map, same as before.

Did I unecessarily replace a real good O320?

Am I missing something here?

Any suggestions would be appreciated.

---

I used the same prop.
I used a different spacer, bolted the spacer with the large bolts to the engine and then used the same bolts to install prop to spacer.
I am an experimenter but not enough of one to redrill the bolt holes on a prop.
The prop I am using has a 6 inch hub and in talking to Prinz I should be using the 7 inch.
Lonnie admitted they have never had a failure with the 6 inch on an o360 but I will change props if I find a solution.
I didn't use the original Marvelous Schebler because it wouldn't fit in the cowling.
Paul Chernekeeff at Rotec has been helpful in giving advice even sending me a new spray bar and modifying it but that doesn't seem to be the problem.
I was thinking I wasn't getting enough fuel but EGT's and Map are good, I am using a Van's airbox. I assume that has been worked out so I am a little stumped as to why I can't turn the same prop a little faster?
Right now I want to get more power out of the existing engine and if I don't come up with a solution soon I will reinstall my O320, get the prop repitched or buy the adjustable one from Sensenich, and write it off to experience.

I have a whole year of work and half a dozen test flights into it.

And a pretty big bag of money!

Ray

If you can only make 2320 rpm in level flight your prop has too much pitch for the engine. Whether or not your engine is otherwise operating correctly is another question. Even though you have a freshly overhauled engine it would be worthwhile to do a differential compression test and double check the ignition timing. These things are probably OK, but you should rule out engine problems before you spend any more money.

Assuming your engine checks out, you will need to get a different prop, which apparently you will need to do even if you go back to your old O-320. Maybe Prince will give you a break on a new prop, since the first one didn't work out. If not there are good prop people out there who can help you. This shouldn't be that big of a problem to solve.

Dave Prizio

Man, EAA guys sure love to tinker, sometimes more than flying.
It is good procedure to change only one item at a time so you can see what the result is attributeable to that item. You changed about 6 things.

Here is my guess:
1. Prop has too much pitch, just too big for engine to pull.

2 You had a good Lyc engine, with the accesories designed to work with it. Then you started using an off brand of carb and mags. I think it is also likely that they are not right, epecially the mags may not be timed correctly. How do you even know what the timing should be on an engine that the mags were not designed for? Were they ever tested on the Lyc engine?
doubt if bad compession is your problem unless the overhaul was not a good one, but you can always check it.

3. The different prop mounting may have some efffect, but 400 rpm seems unlikely.

What is the spray bar that you memtion?

if it is any comfort, a friend was racing his Wright engined Fury at Reno; doing pretty well speeds around 420 or so. Someone told him about a new genius prop designer. So for just another $25 K or so, he got the latest high tech, computer designed, smarter than anyone, fancy new prop. It even looked great, only problem that his plane was immediataly 15 mph slowert than before.

4. Sometimes a new oh engine is tight and needs some run in to acheive full rpm. Again I think this is unlilkley to be your 400 rpm defeicit.

And I have to give you credit for admitting that there is a problem after your changes. It is human nature to claim whatever new thing we spend money on is the greatest.

Yeah, I probably fit into that category, like fixin more than flyin.I agree to many mods at once but circumstances sometime dictate.As I said I wanted more power.When I installed the engine and first started it one of the mags was dead. I don't know how the overhaul people got the test cell data but they did and it was dead.So do I buy a new mag for $1200.00 or go with new technology Pmags and if so what I had read was they did better together rather than one mag and one Pmag. They are "dead" simple to time and they work.Then the carb for an O360 is considerably longer than the one for the O320, dimensionally the engines are the same except the O360 is one inch wider. The carb wouldn't fit in the cowling. The only options were EFI or an Ellison or Rotec. EFI was too tricky, Ellison gets some bad revues and Rotec has the answer, a pressure regulator.Exhaust is the same as many people use on RV's.It is frustrating when it doesn't work out the way it should.30 more hp should turn the prop faster, period. Apparently not.RayApparently not.

If you get a new glass panel for the cockpit at perhaps $20, 000 and a new I pad for $700 with all the latest aviation apps on it, you may be so happy you'll not even notice if your power, rpm, and speed are down.

Hey, the business of the U S is business and in this recession we need all the consumers we can get, especially in the aviation field.

And again what is the "spray bar" that you mentioned? The only ones I know are for cooling.

And you say that the new mags are "dead simple" to time. Maybe so, but how do you know what spec to time them to? Is it 10* btdc or what? Is it the same as the setting for the stock mags? Or does whoever makes the P mag give their own spec, and is it tested for the Lycoming engine? A retarded ignition setting of 15* or so can take away a lot of power, though I suspect your prop is more likely the cause rather than the engine. Maybe the prop maker, Prinz, has a money back return or exchange policy. You don't say who did the overhaul or if they ran the engine on a test stand. But it would raise some big doubt for me if I got an engine that was sold as a fresh overhaul and a mag was "dead". I am pretty sure a good shop would put on overhauled or new mags. So it seems like the quality of the new engine is another of your unknowns.

I am not familar with Pmags or Rotec pressure regulators, me being pretty old fashioned, and not up on many of the latest gimmicks. I never heard of Lonie Prinz, and Google doesn't seem to know him either. I do recall Freddie Prince, but don't think he made props. I looked up Pmags on Google and it says it holds ammo, nothing about aviation or ignition.

I do know of the Rotac mags on a Merlin and it's pressure carburetor. With this outdated old technolgy, Strega limps around the course at Reno and can only get about 520 mph on the straights. Man, just think what they could do if they got some of that new genius stuff.