A65-8 TO A75-8 ?

jack duncan · Post by **jack duncan** » Thu Nov 08, 2007 08:02

I'm going to overhaul my champs A65-8 this winter, and am thinking of converting it to a A75-8, I need to hear from some of you who have been down this road, and have some thoughts or opinions on this subject. Is it worth it? will I really get ten extra HP? or is that just sales hype? will there be any noticeable performance differance? or should I leave it like it was designed? I think I know the answer to some of these questions but, let me hear from you. thanks, Jack

Paul Agaliotis · Post by **Paul Agaliotis** » Thu Nov 08, 2007 08:52

Jack,
Most people will add the A75 mods for reliability reasons. The horsepower
increase is the result of a higher RPM. This will increase the fuel burn by atleast 1GPH. To get the RPM you need to run a propeller that doesnt provide the best performance for a Champ.
If you need the power increase I would look to the C series engines.
Now with all that said, there is nothing better than floating along in a 65HP Champ @2100 on a spring day in California.
Paul

Post by **joea** » Thu Nov 08, 2007 15:46

I had a converted A-75 and can second Pauls findings. The power was good only really during takeoff and climb, otherwise not needed.

Am very happy with my C-85 but then it came with the airplane when purchased.

Joe

marklamon · Post by **marklamon** » Thu Nov 08, 2007 19:41

Jack, This is from Harry Fenton

There is more to read about it at http://www.bowersflybaby.com/tech/fenton.htm#A65_uphp

A65 Horsepower Increase
What is the best way for me to get about 80 to 90 hp out of my A65 engine? I have an A65-8 with 42 smoh that I need to tear down and inspect since it has sat for 2 years without being run since I have it tore down. Maybe I could bump the compression or whatever. Please let me know the best most reliable way to do the HP upgrade.
The easiest hp increase with the minimum amount of work is the conversion from the A-65 to A-75. The change is pistons, connecting rod work and carb re-jetting. To get more than 75 hp will require welding to the A-65 case, extra studs, and special experimental pistons. The A-65 would need a flange crank as the taper crank is not capable of supporting much more than 75 hp. Along with the above, you really need to magnaflux the crank and zyglo the case and balance the reciprocating components.

Upping the output of the A-65 is not a casual affair. If you compare the A-65 to the C85/O200 you will see how lightly the A-65 is constructed in comparison. Some homebuilders have dropped in experimental 9.5:1 pistons, turned up the rpm to 2700 to 3000 and accept the unknown risks. Consult lycon.com for info on the pistons.

I hope this helps, Mark

Jody Wittmeyer · Post by **Jody Wittmeyer** » Fri Nov 09, 2007 03:17

Just for testing sake, I did all the mods required for the A-75, then put A-80 pistons in. A-75 and 65 pistons have @ 6.3/1 compression ratio, A-80 have 7.4/1 cr. Running the same carb, same jets and the same prop, I picked up 150 RPM. I have a Sensenich 76AK-2/44 prop and now get 2200 rpm on climbout at 60 mph, 2400 in full throttle/level cruise and cruise 92 mph at 2200 rpm, burning 3.6 gph.
With the A-65 pistons, 1970rpm on climbout at 60mph, 2250 at full throttle level cruise and 88mph at 2200rpm cruise, burning 3.8 gph.

mike newall · Post by **mike newall** » Fri Nov 09, 2007 18:16

Look for a C-85, do the mod as per the Service Letter - no dorsal, no fuselage mods, if you are on a McCauley prop it needs trimming by 3" to avoid harmonics.

The result - Marvellous

You can still float along, now even quieter because you will have swapped exhausts.

Takeoff and climb improved.

Fuel marginally more.

A lot smoother engine.

jack duncan · Post by **jack duncan** » Mon Nov 12, 2007 08:41

Thanks for the comments folks, I think I'll do a "by the book TCM overhaul" and enjoy it. thanks again. Jack

National Aeronca Association Bulletin Board

A65-8 TO A75-8 ?

A65-8 TO A75-8 ?

A65-8 to A75-8