Buuuuuuuut...running the engine on a de-rated profile will curb the heat output somewhat to normal 360 levels (may be slightly higher due to the small decrease in usable cooling area/air flow), but should still be very managable without a whole lot of undue stress on the pilot. I plan to use a Sam James cowl regardless of what engine I use, and the plenum options with that cowl should work pretty well for the bigger bore motor.
Spike, the 320 is far from a lowly engine in my book. There's probably no better engine out there from a reliability and fuel efficiency standpoint. Plus, your putting in the biggest engine recommended by Vans, and there ain't nothin' wrong wit dat!
And to Rivetbangers Max!! Please do hang around, and don't be shy!
Thanks Maxwell007!!! ...and welcome to Rivetbangers!!!
I appreciate the explanation of compression and what these builders really mean when they talk about 8.7:1 and 10:1!
So in your opinion more displacement in a lower compression environment is the right way to increase HP without sacrificing longevity? ...which if I understand it correctly seems to be the thought of CJ, Chad, WS and the rest of the group.
What is the downside of more displacement and lower compression to get higher HP? Not able to achieve as much performance? More fuel burn? ANYONE?!?
- Peter
Peter Fruehling
RV-7 Wings -> QB Fuse in the shop!
North Oaks, MN -> Home Base (KMIC)
Well, more displacement is always going to cause an increase in fuel burn. Bigger engines produce more heat, and are tighter fitting (under the hood, so to speak), so there is an issue with removing that heat in a timely manner from a smaller space. Performance with a big bore engine, even with a small increase in weight, will be nothing short of awesome. The higher power output will offset the weight, and the engine can be turned slower to get the same speeds. So in that case, fuel burn should be equal to or lower than an engine/airplane running similar speeds (of course there is much more to it than that with things like airframe drag, cooling drag, differences in prop efficiencies, and so on, but in comparing RV to RV, this should work). With all the talk of high horsepower numbers, it's been said, I've been told, yada yada yada, that it's all about torque. If you want a fast airplane, you gotta have a high torque output. 390's and 400's will be huge in that department. A torque monster as CJ put it!
One of my hangar neighbors has a Giles 202 powered by a IO-360 built by Lycon. He says it produces 245 HP. It flies when ever he wants to fly it. I don't see him working on it much. The airplane really performs, and the engine doesn't sound like other 0-360s in the neighborhood. The engine turns a three blade MT Propeller.
Since this thread opened I have been reading it with some interest. I also began putting a few thoughts of my own down to post but find that most of what I would be saying is just rehashing those things already written. All of them good thoughts. A few interesting (to me at least) points could be brought into the fold though. Producing power from an internal combustion engine isn't only dependent on how tightly you can squeeze a given volume of fuel and air. Where you ignite it is along the piston stroke is equally important. Since a given volume of fuel produces X amount (and that's an absolute) of energy it becomes our endeavor to optimize the energy that spins our prop. In order to utilize fuel efficiently we have to contain the burning fuel (whatever it's volume) long enough for it's energy to be transferred to the spinny bits of the engine. So here are some numbers I came across while settling on my engine configuration. The electronic ignition of choice in general raises the CHT 50 degrees while lowering the EGT 150 degrees. I'll leave those numbers for you to interpret for yourselves however my next thought may help out with you're interpretation. There is the reason for the FAA to be so set on certifying mags as they are designed as opposed to an ignition with some kind of spark advance system electronic or otherwise. Some of us already know (I was surprised to find this out) that mags have a setting of 0 degrees TDC for starting and, depending upon the engine, an advance of 20 to 25 degrees BTC for all other RPM settings above about 600 RPM. That means that an engine with standard mags has one throttle setting that is it's most efficient, any other setting and you may be throwing burning fuel out the stack in some cases and raw gas overboard in others. What limiting the advance setting does (the FAA's choice) is make it almost if not entirely impossible for the engine to experience the killer of engines, Detonation. So whatever you're choice is there is a little more info for you to use. Hope it's interesting and helpful for ya'll.
Last edited by jim_geo on Wed May 10, 2006 9:23 pm, edited 1 time in total.
Spike, I wouldn't worry about getting someplace 10 minutes after the others. The group I fly to breakfast on Saturdays fly abut 100 miles out most trips. Our 9A guy has a 160 hp lyc and a fixed sensenich prop and last Saturday he got off the ground about 3 minutes before me and when we got to the destination airport he was still about 3 miles ahead of me and was traveling about 170 kts! So the 9 is rather fast with the lyc 160 and a fixed prop.
Dan
We don’t recommend experimental engines with compression ratios above 8.5:1 or that have electronic ignition to use Mogas. Many do use it under those circumstances successfully, but here at Mattituck we don’t approve it.
The IO-390 is essentially the same engine as the 200 HP IO-360-A1B6 with a larger cylinder bore to give it more displacement from 360 to 390. The stroke is the same between the two. The 390 also relocates the prop governor drive from the rear of the engine as on the IO-360-A1B6 to the front left crankcase section. Other then these two changes the engines are identical inside and outside. The A1B6 delivers 200 stock horsepower and the IO-390 delivers 210 stock horsepower.
The weight difference between the two, similarly equipped, is what I would consider negligible.
Roller tappets have not shown any difference in power output as compared to standard tappets in our test cell.
Precision balancing as compared to our standard balance package has not shown any significant power differences in our test cell.
Increasing the compression ratio above 8.9:1, will increase power output, but will also strain certain of the engine components more. It will also lessen the detonation margin of the engine, on the same fuel with the same temps, as compared to the same engine with less compression ratio. Significant increases in displacement, weather from increased stroke or bore, will tend to increase the wear and tear on the engine but will increase power output of the engine. Significant power output increases from a package that was designed for less power output, will generally shorten the expected durability of that package.
Significant modification to cylinder ports, to significantly increase flow characteristics, may tend to weaken the cylinder and possibly shorten its life. Significant increase in power output, from minor porting to equalize flow between cylinders, has not been seen in our test cell.
Hope this helps….
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at you own risk."
No, I didn't mean to infer that at all. If you do lots of mods to the stock package to increase horsepower, then yes I am saying that those mods can cause wear and tear that a non modified engine would not experience under the same operating conditions and yes I am saying that those mods could shorten the expected TBO of the so modified engine.
I am very comfortable with a stock IO-390 going to full TBO without major issues..... Now, will an IO-390 that is making 260 horsepower, go as far as one that is making a stock 210 horsepower? I don't know for sure but I don't think so. Would I feel comfortable telling one of my customers that an engine, we modified to produce 20 to 30 percent more horsepower then it was originally designed for, would run to TBO the same way and with the same expected durability, as one that wasn't modified. No I wouldn't.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at you own risk."
N200PF.....What I am saying is that modifying the engine by increasing the compression ratio will generally increase horsepower (though there are circumstances where it will not) but by doing so, you run the risk of placing more stress on the engine's internals and reducing your "fudge factor" regarding timing and mixture control.
Building horsepower by increasing displacement is the least stressful on the engine components (assuming RPMs are kept at reasonable limits) and makes for the least tempermental package.
Understand that this is a theoretical discussion. As was already posted, there are many examples of modified engines running just fine. It boils down to the degree of modification and how much you are willing to trade off. More compression builds more heat/power to a point. That point is different on each engine and each circumstance. While limiting spark advance helps to control detonation, leaning of the mixture also becomes more important with increased cylinder pressure.
As for trade offs....increasing bore and stroke size will cause the engine to ingest more fuel which generally translates into more power. But, the increased stroke also places more strain on the crankshaft, rods, etc. The further the weight of the rods, bearings, and rod journals are from the crank centerline, the more stress is placed on the crank at a given RPM, but moving the rod away from the centerline (increasing stroke) gives the rod more leverage on the crank, increasing torque. Everything is a trade-off and everything works in combinations. That is why engine builders are always tweeking things. What works in one application is all wrong in another. I have built dozens of car engines in my shop and each one was different. Some ran like a scalded dog and others wouldn't pull the skin off a pudding. But, each one was a learning experience. Me......I'm going with a stock engine in my airplane.
I think you've answered your question! I think this thread helped ME a lot as well!
Angle valve and parallel valve engines are beyond me to explain, but I do know that the angle valve is typically the 200hp engine, and the parallel valve is 180hp. Parallel is lighter...
The Parallel valve engines are lighter because the heads are smaller. You can tell one from the other by the shape of the valve covers. The symmetrical ones are Para engines.
These are lighter and typically (all things being equal) less powerful than their comparative Angled counterpart.
The Angle engines are so because ( and I may stand to be corrected here) the valves are larger and/or better positioned to allow for better flow. The better flow means more hosses.
CJ
RV-7
Garmin G3X with VP-X & a TMX-IO-360 with G3i
It's all over but the flying! 800+ hours in only 3 years!
Good read... Any Hp above 210 is wasted.. The 7A does have a Vne of 200 kts.
With 210 hp @ 8000 ft you will be over Vne. Remember Vne is TRUE AIRSPEED... not indicated.
Our planed engine is Aerosport (same as what's in Van's RV7A) IO 360 paralle valve... with dual light speeds.. 8.5 to 1 comp... Bart tells us this combo is between 200 and 205.. Vne power!
Unless 2500 ft per minute climb is not fast enough for you, or <500 take off run is to long... we like the 200-210 Hp size.
Mike, yes... agreed. True airspeed is what Vne is based on.
Buuuut, riddle me this...
If the pitot sees X pressure (indicated and measurably lower than true) why isn't the airframe comparable fooled?
Molecularly, the pitot measures the air and as altitude is increased less crammage happens. As we gain altitude this exaggerates and descending, the opposite happens. This I dig.
Sooooo, my question is (and I know I should know the answer) why then is Vne based on true and not indicated? I remember and know that you are right. I just don't know why.
Anyone???
CJ
RV-7
Garmin G3X with VP-X & a TMX-IO-360 with G3i
It's all over but the flying! 800+ hours in only 3 years!
What I'm looking for is an honest look at 180kts cruise at a reasonable power setting. It seems so far that it will take 200+ HP, a Sam James Cowl and fresh wax to get there.
I don't plan to play anywhere near Vne. I wrote earlier ->
N200PF wrote:Vne just plain scares me in anything I fly. I leave the playground above 200 Kts to the dare-devils out there.
Van's says that 200hp brings about a 217mph top end. It just doesn't seem that an extra 10 to 15 HP could bring you up to 230.156mph. (200kts)
- Peter
Last edited by N200PF on Sun May 14, 2006 10:57 pm, edited 2 times in total.
Peter Fruehling
RV-7 Wings -> QB Fuse in the shop!
North Oaks, MN -> Home Base (KMIC)
John, At an indicated airspeed of 200 MPH at say 8,000 ft. your airframe is feeling the wind resistance of 200 MPH. But if you then calibrate your speed for air density your actual speed will (should) be higher. So if you were to be flying on a perfectly calm day your ground speed would (should) be something higher than 200 MPH.
Jim, yes... and ground speed has nothing to do with this.
I understand that the airspeed will be higher but, like I said:
If the pitot sees X pressure (indicated and measurably lower than true) why isn't the airframe comparable fooled?
Molecularly, the pitot measures the air and as altitude is increased less crammage happens. As we gain altitude this exaggerates and descending, the opposite happens. This I dig.
Do you understand what I mean?
CJ
RV-7
Garmin G3X with VP-X & a TMX-IO-360 with G3i
It's all over but the flying! 800+ hours in only 3 years!
to Rivetbangers Max!! 
Please do hang around, and don't be shy!
CJ
CJ
CJ