intakes and cams
Mr.zav6a
There certainly are"small" ways to help the 320, but you must first look closely at the beast. GA aircraft engine in comparison to the rest of the internal combustion engine world are poor examples of engine designs. This can be proven by their reliability records as well as the constant "reminders" AD notices, that come up on a regular basis.
Porting, flow paterns are somewhere between poor and mediocre. Most Briggs and Strattons found in lawn mowers are far more sopisticated. The fact that they spin so slow is a hindrence in producing power. Looking at a horsepower formula will tell you that HP is a result of engine speed. Increasing engine speeds has it's drawbacks not the least of which is reducing the efficiency of the "screw". In addition, look closely at a crankshaft, crancase and overall construction of GA engines, and even an untrained eye will tell you, it ain't gonna take too much more speed. Case in point, Lycomings used in helicopter applications, have reduced TBOs simply because they are required to spin faster that their conventional flying brothers. Exhaust designs are always a hot topic of discussion. In reality, they do not add or make power, unless other components are in harmony. They will only pin point power. Given the operational speed of our engines which is no more than 300 or so rpms, it would take a sophisticated dinomometer to design a pipe the will make all it's power at that speed, and even then it won't be much more, if any, than the engine already has.
Other factors include fixed ignition timing, fixed pitch props, and the worst carburator design of all time , the updraft carburator, which BTW, won't be found even in lawn mowers. One last feature, is the tolerance used in a typical GA engines.
A few days ago, I measured the bores of an O200 Conti. Piston to wall clearance was an acceptable .013. New tolerance for the O200 is .009 to .011. Maximum allowable is .019 to .020. By comaprison, a Briggs and Stratton lawnmower, has ,003, max .006. As you can see the AC engine will have constant blow by, as well as oil consumption. My Chrysler T&C as well as many other autos, has .0005 piston to wall clearance and max .002. Your O320 is a little wider than the little Conti, new .010 to .020 max.
Bottom line, we fly engines with technology out of the Jurassic age.
What can we do to improve them?
As with all engines, our dinosaurs notwhitstanding, holding those tolerances as close to new as possible is the first step. I've done this on my old Cherokee 140 (O320) as well as my old Arrow (IO360)
Piston to wall clearances held to new tolerances, as well as ring gaps, lifter bleed down clearance held at ,050 +- .005 for the 320, .060+- .005 for the 360. Ignition timing per specification , but just because the mags match on the timing marks doesn't mean it's woking. Point gap must be set to allow maximum coil saturation for the strongest spark possible. With the 140, it's maximum speed as published was 142 mph. it rarely would do much over 120. Airframe rigging help a bit to barely nudge 125. Prop pitch had been decreased, so I had increased back to specifications and increased it to the legal limit of 1 in. It's published top speed of 142 was finally realized. With the fixed pitch prop. altitude was always a limit but it did reach it much faster than before the changes. Climb was also improved by as much as 300 fpm over published specs, 800 fpm over 500 fpm.
On the Arrow (180) much the was done in addition to LASAR. Fuel injectors were properly flowed to specs. Before the Arrow rarely saw more than 128 to 132kts in cruise, after 140kt to 145kts in cruise (top speed 147 kt) Due to C/S prop and managed ignition timing. Climb was dramatically increased particularly at higher altituded 11K to 13K yielded more than 750fpm while at lower altitude avaraged 1100 fpm. Spcs 800 fpm from SL. In both cases, oil was 15/50, and mogas helped as well though the Arrow was not approved due to FI, however, though illegal, it did improve performance, when tried.
Could more have been done, probably so, but as stated, with poorly designed intake ans exhaust conduits, poor combustion chamber, overly heavy valve train, unbelivable sloppy engine tolerances, it would have taken insurmountable funds. In the end with the low engine speeds, I doubt that much more could be gained accecpt for a massive reduction in oil consumption (to none), and yes, reduction in oil consumption in itself would translate in HP increase, performance, and economy.
If you have the time and funds, even the dinosaur can be made to soar.
We are after all experimental, so give it a shot, but don't be too disappointed if what you're looking for evades you. At least the learning curve will be rewarding.
T88
RV10