Q: Are there any practical, appropriate and compliant modifications that can be made to a 150-hp, narrow-deck O-320? For example, can the compression ratio be tweaked a bit, or are there aftermarket exhaust systems with less back pressure, or is there any porting/polishing possible to effect a tad more power to the propeller?
Gordie
A: Gordie, I wish you had provided me with a specific engine model so that I could offer more specific information in response to your question.
There is a possibility that certain models of the O-320-series engines may be converted to a higher compression ratio piston. Generally speaking, most O-320 series 150-horsepower engines, except the O-320-E series, may be converted to a higher compression.
This conversion would increase the compression ratio from 7.00:1 to 8.50:1. Any conversion of this type should be completed in accordance with an approved FAA STC.
As you mentioned, there are aftermarket exhaust systems that claim to increase engine horsepower, but I have no experience with these products, so I hesitate to comment.
There is no doubt that any improvement in helping the engine breathe better will result in an increase in horsepower, however it may be very difficult to actually document or detect any increase in power during normal operation.
From my experience, I’ve been told that if you take a 2,000-hour engine and put it through a factory overhaul or a good field overhaul using the engine manufacturer’s new limits on all components, the result when flying the aircraft is like the engine has gained horsepower.
It stands to reason that any high-time engine may be a bit down on power, so anything new will appear to be a more powerful engine. This certainly makes sense to me.
There is one thing that you must keep in mind. Your O-320 series engine, if installed in a certified aircraft, has an FAA Type Certificate stating what horsepower the engine is rated at for that particular airframe engine combination. Therefore, if the TC states the engine is rated for 150 horsepower, you must keep the engine at that specific rating.
If any modification you make allows the engine horsepower to exceed that rating, then the aircraft would not be in compliance with the FAA Type Certificate.
My suggestion is for you to do some additional research focusing on specific engine modifications for your specific aircraft. Please don’t be misled by all the hangar talk or information provided by aftermarket product suppliers.
Check it out for yourself before spending any money. I guarantee you’ll be a lot better off and have peace of mind that you did it right.
We installed the Power Flow exhaust on an O-320-E2D and noticed a couple of improvements. First, the takeoff RPM increased from 2500 to 2700, which generated more thrust and more noise complaints from the airpark residents. This was the older Power Flow with the motor cycle looking pipe, which prompted us to dub the plane the Skyhog.
The second improvement was in fuel consumption. A typical cross country before Power Flow ran around 7.7 GPH with the RPM and mixture set for 75% power. After Power Flow, I regularly saw 6.7 at the same TAS.
Exhaust parts plus installation ran about $3100 in 2004. Make sure your A&P re-does the W&B.
Without spending gobs of money, the best bang for the buck is to have impeccable sealing on baffles. RTC the corners of your baffles, and seal off areas where pressure can leak out. The goal is to maximize that area of high pressure over the cylinders so as to displace the greatest amount of laminar air from the cylinders which keeps cylinders cooler and enhances horsepower without extra fuel burn.
Simply explained, take two identical aircraft, one with impeccable baffles and the other ‘standard’ baffles. The one with the better baffles will keep about one inch of additional manifold pressure at same altitudes as the other, giving improved climb and thrust.
Interesting comments.
To keep “squeaky-clean” and within certification (as mentioned by Paul), ensure your engine is in tip-top condition and is producing the power it should.
Obviously, cylinder differential pressure test results are normally all in the upper seventies with Lycomings, even high time. This, however, only proves the cylinder at top-dead-center; the barrels could be worn further down the stroke (sometimes indicated by black oil, high oil consumption, excessive residual oil out of the engine breather).
Another problem we see at our FBO is worn camshaft lobes on low-usage Lycoming non-roller tappet engines, which may be immobile for months between flights. Even if the LW16702 oil additive has been used the camshaft may be “running dry” for a while after starting the engine. If the camshaft hardened surface has been damaged or worn, the camshaft can wear quickly. This is a cumulative process which worsens with time, and might not really noticed by the pilot. Theoretically this should (or could) be picked up during thorough inspections of the oil filter.
On suspect engines (or new customers with low-usage engines) we always measure the “valve lift” of the intake and exhaust valves, as an indication of camshaft wear – in fact, we have one such new customer right now, who was completely unaware that the intake lobes of his camshaft were worn to 7mm of valve-lift; the values we normally see are 11-12mm (unofficial figures).
I wonder how much power he was losing.
Colin
The single easiest thing you can do to boost horse power is to install an electronic ignition in place of the right mag. A friend of mine did that to his Citabria and had to have his prop re pitched to keep from exceeding red line rpm.
+1 on this. I was about to say this before I saw that Neil beat me to it. I installed an Electroair EIS 41000 on my PA28-180. It has made a noticeable difference. What’s even better is the fact that I can get 75% power performance at a 65% power setting so I am saving fuel.
For the O-320, you also consider the powerflow exhaust mod. The idea behind the powerflow exhaust is that the original factory exhaust was so inefficient that it was robbing your engine of power. So this exhaust mod does not “increase” HP, it simply restores HP that was stolen by the original exhaust design.
I imagine after adding electronic ignition and powerflow exhaust you may see an effective increase of 10 to 15 HP.
+1 on installing a PowerFlow exhaust. Be aware that the ‘short stack’ version is a little less efficient than the ‘classic’ (aka “rat tail”) version. The ICAW takes about an hour extra at each annual because the muffler must be leak checked. Plus an important part of the ICAW is periodic balancing of the prop… both of which are very good ideas anyhow. Depending upon what you hang a PowerFlow onto your increase in airspeed may not be all that much, but you WILL see a big boost in climb performance.