I started the thread knowing that these engines are on planes and air boats. Thinking that someone would share a prep template. As it appears that the guys actually flying them dont visit this site. Probably too busy flying . The result is a lot of conjecture about how bad this idea is ,based on desk top calculations and no real world experience.
FWIW using more RPM will result is lower operating temps at the same power level. More cool Air in , less cylinder pressure per revolution etc. The redrive allows this. Direct drive may work OK at reduced power output. Ilike the 103 planes and the direct drive is less optimal for slow flight. None of these engines are designed to have a large Gyro hanging off one end or the other.
I like electric start. I will keep some sort of flywheel to accommodate it and some charging system .
My time frame is about one year . I will start with the best deal i can find on either the big single or the baby twin. The twin shows really nice on the front of an old AC tho.
I can direct load my dyno load cell for reference against a known good value . That may be the Hirth 389 @ 30HP or the Cuyuna 430 @ 37HP.
For the guy inverting his engine . really nice research BTW. Most inverted engine struggle to control the oil ring drain. The oil is supposed to drain from the bottom of the piston. Inverted makes it very hard to get rid of the oil. You will need a large drysump pump to vacuum the case, or the oil burn will be too much to tolerate.IMHO. Thats one reason why the big radials burn oil .
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There really isn't a need to reinvent the Wheel. Engines for Part 103 probably need to be under 65 lbs Complete ( Motor, Redrive, Exhaust, Electric Start). For the most part that means Singles. Some of the Small Block V Twins 470-627 in Direct Drive could also work. You're never going to appease all the Arm Chair Mechanics, the hate mongers. You have very valuable Data to look at on these Go Kart Sites on what they did to make these engines almost Bullet Proof! Almost all of these Part 103 and Small Kit Planes their MTOW fall into the 540 lbs (32.8hp) to 660 lbs (40.1hp).
Based off the 460 Dyno Sheet 37.37hp@5000rpm, 458cc/37hp = 12.4cc to make 1hp.
Spec's: 34mm Carb, 11.0cr, 307 CAM, 40/32 Valves, K&N, Tuned Header!
Based off the 420 Dyno Sheet 33.4hp@5000rpm, 420cc/33 = 12.7cc
Spec's: 34mm Carb, K&N, Tuned Header!
I would use 12.4cc as a base and make up a chart. Very few Planes will use less than a Honda GX390 (389cc) 389/12.4 = 31.4hp@5000rpm since most Planes need a minimum, 25+hp. 40.1hp being the Max any Part 103 would need, 40.1 x 12.4cc = 497.24cc (500cc) Engine needed.
While you can CUSTOM Build any Engine up to a (100mm x 86.5mm) 679.6cc, it's going to be easier, faster, cheaper, to just upgrade the most common off the shelf Engines, like GX390's 420's, 440's, 460's. Which you can buy at Harbor Freight, Home Depot, Lowes, eBay, Amazon, NH Northern Tool, etc.
Template for All Singles and V Twins:
1. Disable Governor.
2. Disable Low Oil Sensor.
3. Install 34mm Carb for Singles.
3. Install K&N Airfilter.
4. Install Billet Rod.
5. Install Billet Flywheel.
6. Install Tuned Header.
7. Install Hi-Rev kit.
8. Install a Better CAM for peak hp@5000rpm.
9. Mill Head for 11.0cr.
10. Install Billet Needle Bearing Racker Arms.
For more hp.
11. Use Bigger Valves
12. Port & Polish the Heads.
Chart showing Approximate hp@5000rpm upgraded!
