I'm doing some engine mods to my 180 hp Superior XP O 360. I think the 4 place Tundra at 2550 max take off wt. with this engine is a little short of breath for mountain ops. A turbo is not an option. I am doing a port and polish for about 5hp/cylinder for an estimated 20 hp. In addition I was recommended to go to 10:1 pistons for another 30hp. Since this engine has roller lifters they also can change the cam for more lift. Gain? Not sure on that one but it breathes better. Anyway expectations are 235-240hp. Engine shop is Ly-Con out of Visalia, California. Their resume includes 13 of 15 Red Bull Racers and the shop of choice for porting and polishing new Scouts from the factory before they go to their new owners.

I found this formula to work with since elevation and density altitude have the same effect:

Hp loss = elevation x 0.03 x hp @ sea level/1000

So at my home base of 1400'
Hp loss = 1400' x 0.03hp x 180hp/1000
Hp loss= 7.56 180 - 7.55 hp loss = 172.44

At 5000' Hp loss becomes 27 leaving 153 Hp
At 10,000 Hp loss doubles to become 54 leaving only 126 Hp !!!


So the modified engine with 240 hp at home base of 1400'
Hp loss = 1400 x 0.03 x 240 hp/1000
Hp loss = 10.08 240 - 10.08 = 229.92


At 5000' Hp loss becomes 36 leaving 204
At 10000' Hp loss doubles to become 72 leaving 168

This engine is commonly pushed to 200 hp with fuel injection and so I expect to be able to go balls to the wall at 5000' or 5000' density altitude without additional burden to the engine. Below that altitude I will watch manifold pressures. The shop is telling me I will see a gallon/hr in fuel savings by being able to throttle back at cruise over what I can do now. I was also told I can still burn auto gas by limiting the manifold pressures to avoid detonation. I usually burn 100LL.

Any one know of something I missed? Comments welcome.

I was never any good at math at the chalk board in front of the class.

To figure it out on the chalk board is good. but nothing replaces taking off from a high DA airstrip and finding out what your aircraft will act like. Last summer I took off from Warren, ID. at noon in Aug. with four in my original 182. Warren elevation is 5902 ft above sea level. I was glad that I didn't have full fuel. I was also glad that it is down canyon out of Warren. Start out light and work up to see what it will do. Don't just rely on the numbers.

I really like this information. Port and polish on the next rebuild is on my "must list".

skybobb wrote:To figure it out on the chalk board is good. but nothing replaces taking off from a high DA airstrip and finding out what your aircraft will act like. Last summer I took off from Warren, ID. at noon in Aug. with four in my original 182. Warren elevation is 5902 ft above sea level. I was glad that I didn't have full fuel. I was also glad that it is down canyon out of Warren. Start out light and work up to see what it will do. Don't just rely on the numbers.

Totally agree. My decision to upgrade doesn't come from the math. I looked up the math to understand my actual experience and to decide how much to compensate for the hp loss in my engine. In an attempt in the spring of 2010 to make the Caveman Ranch fly-in, I hooked up with Hicountry and the FBO out of Sidney, Neb. The winds were against us crossing from the east in to Utah but those two did their best to get me some mountain flying in spite of the sometimes 25 to 30 plus winds. It may have been about 60 degrees when we were climbing out after take off from Steamboat Springs, 6876' and my 180 ponies were panting hard so I tried to give them a break by leveling off once in the climb but dropping the nose to level off and cutting the throttle any to do so resulted in loss of altitude. Both the American Champ Explorer and Adventurer were 180 hp two place planes with one person aboard while I was in my four place 180 hp with two people on board. I felt like we handled all the wind pretty well that day through Cheyenne to Steamboat and Saratoga (6978') but the performance at high altitude was something I knew I wanted to improve. I hate having to call for the brown pants

TomKatz wrote:I really like this information. Port and polish on the next rebuild is on my "must list".

One note on the port and polish. This is as much an art as it is just mechanical enlargement and generally reserved for parallel valved engines. Angle valved heads are not as much a restriction since the air does not make as sharp a corner to get in and therefore do not see the same gains.
Also some shops can enlarge the port but getting the ponies doesn't happen. This shop has a lot of experience in doing the P/P and the normal gain is 4 or 5 per cylinder. They also have a slightly more expensive option where it is not done by hand but is a CNC operation but gets a more consistent 6 hp/cylinder.

dirtstrip

I found this formula to work with since elevation and density altitude have the same effect:

Hp loss = elevation x 0.03 x hp @ sea level/1000

To get a better approximation of Hp loss, use density alt in place of elevation.

At 6700 ft and up in all directions that is why I have a TO-360-F1A6D!

In my topic I did say Density Altitude vs HP but then used the word "elevation" in the formula. If only the "msl" elevation changes the formula should hold as is. If humidity and temperature are different, then those effects should be included in the value used for elevation in the formula. (Humidity and temperature effects I will not do at the chalk board in front of the class.)

Suffice it to say that with elevation "Honey I shrunk the engine".

Are you running a constant speed prop?

dirtstrip wrote:I found this formula to work with since elevation and density altitude have the same effect:

Hp loss = elevation x 0.03 x hp @ sea level/1000

That's a pretty lame formula. HP is torque x RPM (divided by a constant). And, because the formula ignores RPM, it is wildly inaccurate for those with fixed pitch props.

My 172 POH gives a table of actual hp numbers at various altitudes and RPMs for the O-300 (145 hp).

For instance, at 10,000 ft, the formula predicts 101.5 HP.
The manual gives these numbers: RPM/HP 2600/91, 2500/81, 2400/73, 2300/64, etc.

However, the only way I can hit the higher RPMs at the higher altitudes is to put it into a dive. For example, when I'm at 10000 ft, I can't get it above 2400 RPMs in level flight. So, the formula is predicting 39% more HP that I actually have.

stewartb wrote:Are you running a constant speed prop?

I am now but in 2010, in the story I related above, I was running a fixed pitch. No doubt I could have done better with a constant speed to maintain rpm's, which as Kevbert points out above, adds another variable to the simplistic formula of the post. It would be interesting though to know the hp loss on Kevbert's chart for the 172 at 2400 rpm at 10,000 feet compared to the hp produced at the same rpm at sea level, just to see if the formula is close.

dirtstrip wrote:It would be interesting though to know the hp loss on Kevbert's chart for the 172 at 2400 rpm at 10,000 feet compared to the hp produced at the same rpm at sea level, just to see if the formula is close.

My manual doesn't give the numbers for sea level, but I think the engine is rated for 145 HP at 2700 RPM at sea level, so one can interpolate. 2400RPM/2700RPM*145HP = 128.9 HP. (This isn't exactly correct, because the torque curve isn't flat across all RPM's, but it should be pretty close).

Using 128.9 HP and 10,000 ft in the formula yields a predicted 90.2 HP, which is better, but still quite wrong, as it's 24% higher than the actual 73 HP.

I'm very envious of going to 230 hp from a 180 hp O-360. Bridgeport, Ca in July and Nevada, Idaho, and Montana in August made me viscerally appreciate density altitude and hunger for more horsepower. I've got a certificated plane and constrained budget so my options are not wide open.

I am hoping a tuned exhaust for my MX7-180C will happen before I need to replace the exhaust but nothing seems to be getting through for Maule these last years.

Aren't you going to be putting out more heat and is that a concern? A fair amount of the year, I get very nervous when my JPI is reporting cylinder temperatures of 395/400 during climb out.
-rjb

TomKatz wrote:I really like this information. Port and polish on the next rebuild is on my "must list".

My bad for slight thread drift ( on me. )

Who can do Port and Polish? Is it STC'd, FAA approval, done only by a certified engine shop, etc, etc???

The reason I ask, when it comes time to replace all my cylinders, I thought about having them port and polished by our engine builders at our race shop. The guys in the engine room said they would do it as long as they legally can.

Any comments about this? Thanks

Actually the high comp pistons and porting often makes the heads run cooler. As i understand it higher compression makes it burn faster and more completly and the porting is designed even out the temp difference between the intake and exhaust sides of the head.

Of course at full power more power=more heat but not as bad as you might think.

58Skylane wrote:
My bad for slight thread drift ( on me. )

Who can do Port and Polish? Is it STC'd, FAA approval, done only by a certified engine shop, etc, etc???

The reason I ask, when it comes time to replace all my cylinders, I thought about having them port and polished by our engine builders at our race shop. The guys in the engine room said they would do it as long as they legally can.

Any comments about this? Thanks

When I questioned the Ly-Con shop at Visalia, Calif. for a customer reference I was told to contact a shop in Idaho who takes down the engines on new Scouts and sends them to the Visalia Ly-Con shop for the port and polish. These are new from the factory and it is done at customer request. I think Husky's also. I tried to look back in my notes to find the name of the shop but could not come up with a number but if I remember correctly the shop was Performance Air out of Caldwell, Idaho. Certified shop. Skip the race shop job, this is an aquired art form on a Lycoming big bore. Additionally this work was tried at the factory but they did not get the consistent gains that this shop got. They decided to go with proven experience. After being port and polished, the heads will go to a flow bench and each will be flow balanced to the other. I am told by the customer that the 0-360 will then run as smooth as a six. The equalized firing pulses take the shake out of the big bore four. He also told me most people think their prop needs balancing but actually it is that big bore cylinder that differs in how much each cylinder/piston pushes at firing.
About $250 per cylinder for port/polish/flow matching. Per hp, the 10:1 piston swap is actually a cheaper power gain but that alone doesn't do it for me and it would sure be a bonus to have a smoothed out O-360.

ccurrie, I was also told that the O 360 will cool better with the high compression pistons for the same reasons you stated and a more complete burn to the fuel that takes place while the valves are both still closed instead of late burning fuel from the lower compression pistons exiting the cylinder as the exhaust valve begins to open. Better cooling because there is less waste heat created and more converted to push the piston down making better economy. Hence about a gallon better at cruise.

dirtstrip wrote:

58Skylane wrote:
My bad for slight thread drift ( on me. )

Who can do Port and Polish? Is it STC'd, FAA approval, done only by a certified engine shop, etc, etc???

The reason I ask, when it comes time to replace all my cylinders, I thought about having them port and polished by our engine builders at our race shop. The guys in the engine room said they would do it as long as they legally can.

Any comments about this? Thanks

When I questioned the Ly-Con shop at Visalia, Calif. for a customer reference I was told to contact a shop in Idaho who takes down the engines on new Scouts and sends them to the Visalia Ly-Con shop for the port and polish. These are new from the factory and it is done at customer request. I think Husky's also. I tried to look back in my notes to find the name of the shop but could not come up with a number but if I remember correctly the shop was Performance Air out of Caldwell, Idaho. Certified shop. Skip the race shop job, this is an aquired art form on a Lycoming big bore. Additionally this work was tried at the factory but they did not get the consistent gains that this shop got. They decided to go with proven experience. After being port and polished, the heads will go to a flow bench and each will be flow balanced to the other. I am told by the customer that the 0-360 will then run as smooth as a six. The equalized firing pulses take the shake out of the big bore four. He also told me most people think their prop needs balancing but actually it is that big bore cylinder that differs in how much each cylinder/piston pushes at firing.
About $250 per cylinder for port/polish/flow matching. Per hp, the 10:1 piston swap is actually a cheaper power gain but that alone doesn't do it for me and it would sure be a bonus to have a smoothed out O-360.

ccurrie, I was also told that the O 360 will cool better with the high compression pistons for the same reasons you stated and a more complete burn to the fuel that takes place while the valves are both still closed instead of late burning fuel from the lower compression pistons exiting the cylinder as the exhaust valve begins to open. Better cooling because there is less waste heat created and more converted to push the piston down making better economy. Hence about a gallon better at cruise.

You are correct that it's Peformance Air in Caldwell.

It seems to me that the total performance of any airplane diminishes in thin air. Improving thrust makes some sense. Increasing HP, or at least increasing HP alone, may not be the best way to achieve it. Prop improvements and wing improvements need to be considered. At face value I'd think a CS prop would do more for improving performance than adding HP behind a fixed pitch can. The real magic of most engine upgrades is attributed to the better prop that could only be utilized with the new engine. It's interesting to think about, though.

Polishing ports smoothes out casting irregularities and allows improved air flow. Flow matching should be done to balance all the cylinder's potential as well. If improving air flow potential inside the engine is to work that engine must have induction and exhaust flow potential to spare. Otherwise cylinder flow improvements can't be realized. I recently replaced an almost brand new Cub muffler with a Hot Rod muffler. From the benefits I saw after the change it's apparent that my stock muffler was holding my 160hp 0-320 back. I know lots of guys using the identical muffler on 180hp Cubs. Some with tuned cylinders and higher compression pistons. They'd have been better off accommodating increased flow than just spending the money on cylinder mods for cylinder mods' sake. The point is that there's more to total engine performance than cylinders.

dirtstrip wrote:I was also told that the O 360 will cool better with the high compression pistons for the same reasons you stated and a more complete burn to the fuel that takes place while the valves are both still closed instead of late burning fuel from the lower compression pistons exiting the cylinder as the exhaust valve begins to open. Better cooling because there is less waste heat created and more converted to push the piston down making better economy. Hence about a gallon better at cruise.

The efficiency gain really the increased thermodynamic efficiency of the higher compression ratio. A 10:1 ratio can theoretically be 15% more efficient thermodynamically than a 7:1 ratio.

http://alternativefuels2.tpub.com/2834/28340011.htm
http://en.wikipedia.org/wiki/Thermal_efficiency

The charge also gets hotter, not cooler, although the final exit temperature (EGT) will be about the same.

I wonder if the few extra HP is worth the trade in engine life though.

stewartb wrote:It seems to me that the total performance of any airplane diminishes in thin air. Improving thrust makes some sense. Increasing HP, or at least increasing HP alone, may not be the best way to achieve it. Prop improvements and wing improvements need to be considered. At face value I'd think a CS prop would do more for improving performance than adding HP behind a fixed pitch can. It's interesting to think about, though.

Polishing ports smoothes out casting irregularities and allows improved air flow. Flow matching should be done to balance all the cylinder's potential as well. If improving air flow potential inside the engine is to work that engine must have induction and exhaust flow potential to spare. Otherwise cylinder flow improvements can't be realized. I recently replaced an almost brand new Cub muffler with a Hot Rod muffler. From the benefits I saw after the change it's apparent that my stock muffler was holding my 160hp 0-320 back. I know lots of guys using the identical muffler on 180hp Cubs. Some with tuned cylinders and higher compression pistons. They'd have been better off accommodating increased flow than just spending the money on cylinder mods for cylinder mods' sake. The point is that there's more to total engine performance than cylinders.

Agreed. I had already done the easier performance gains. My O 360 is rated 180 hp at 2700 rpm. That is without a set of mufflers that happen to best fit within a particular cowling designed or to make cabin heat with restrictive baffling. It is 180 hp without additional muffler restrictions. Got restrictive exhaust? Subtract more hp yet.

I had sent money to a company called Aircraft Exhaust Inc. out of St. Paul Minn. They did work similar to Power Flow in Florida, providing low restriction exhaust for aircraft, only this company had half the price because they specialized in experimental aircraft. They got my down payment and went belly up. After licking my wounds on that I found Vetterman Exhaust, nearly in my back yard at Hot Springs, SD. He has become the standard in performance exhaust systems for Van's Aircraft and his systems are sold through Aircraft Spruce. Once he knew I had a two into one exhaust system on each side he had me look inside the mufflers. I saw an inverted cone baffle inside, which he said is one of the more restrictive designs and was made primarily to hold back exhaust for the purpose of heating the muff for cabin heat. Moving from that design to his cross flow exhaust he guaranteed a minimum of 15 hp advantage on my 180 hp over the present exhaust. That doesn't mean I would get 15 over the 180, that means I would get back the 15 that it was shorted by the present system, and possibly 20 hp. So I really never actually had 180 hp with this system in the first place. Vetterman built me a cross over system for my Tundra after I sent the measurements to the firewall from rear exhaust port of a O 360 and the distance down to the cowling ramp point of exit. The cross over system pipes exhaust from cylinder no.1 to the other side of the engine and joins with cylinder 2 in a common pipe and then 3 and 4 are piped together in a second one, so two separate pipes exhaust. The one I got uses no mufflers. I wanted to try that first before deciding to add mufflers. What I found is that the outlets were too close to the cabin floor and loud and I had to use a turn down on each to quiet them. Not bad then and the Bose headsets finished it off.

The heat muffs are mounted on each pipe where there is sufficient straight tubing soon after the joining Y, where the two pipes come together. He said cabin heat would not suffer with the long pipes of the big Tundra cowling and I would not need to add studs to the pipes, so I got by cheap. Turned out the measurements were nearly the same as he had designed previously for the Glass Star. 800 bucks and shipping and I had it in a week.

It was after I made the changes to my exhaust system and added the constant speed MT prop that I went back to the hp well. I will eventually have a mountain performer. The whole story takes a book.

The question about altitude vs HP is really one of 'excess' or 'climb' HP. If you subtract the minimum HP required to maintain level flight from the rated HP, you get a starting point. This can either be done by simply looking up rated HP at the service ceiling in the POH (not commonly available), or determining the value during minimum power flight (found near Vy, naturally). There are a few more accurate ways to do this from the cruise values in any POH, but they do require a bit of math effort.

In any case, available excess HP is roughly:

[(density altitude)/(service ceiling)]*[(max rated HP)-(min level flight HP)]

The value is a bit conservative since the atmosphere density is logarithmic, not linear, and since the absolute ceiling is often a few thousand feet higher than 'service ceiling' for most light piston aircraft.

This technique also shows up more or less in Kershner's multiengine text as well. This technique is fun to show high school physics students how to predict climb and cruise performance for a small plane (C-150, usually) and for a large passenger jet flying at slow speed (<~180mph). The numbers generally agree within a few percent for "clean" configurations, and they suddenly feel like they might have a crack at being an aeronautical engineer someday....

Thrust propels an airplane, not HP. That's what I was driving at before. If high altitude performance is the objective and a fixed pitch prop is being used the prop would need to be optimized for that specific condition. Outside of that condition the performance will be a compromise.

For you book smart engineer types. If a guy like dirtstrip improves his engine's power by increasing the volumetric efficiency of a fixed volume (as opposed to increasing cylinder volume), does the HP increase as reported at sea level remain a linear/constant percentage improvement at higher altitudes where manifold pressures are reduced? Is there a curve? How does the improved volumetric efficiency model compare to increasing displacement to increase HP?