Converting A-65 to 75Hp

[dehavalandb]

I am thinking about converting the ol' A-65 to 75 Hp. My A&P seems to think it is easily done. He said mainly just a piston change and a few other things. Is he correct and if so what is the normal cost of doing the change? I would like to hear from those of you who have had it done. Mainly concerned about the cost, time involved and performance enhancement. Thanks.

Jonathan Howells
N34236

[lktiller]

An old continental service Bulletin covers this. I'll find the number later or maybe someone else remembers it.
You'll also need to untwist the prop just a bit. The extra HP is available with more RPM. Your cruise rpm will be 2250 instead of 2150.
Get a promise of Field Approval from the FAA. the 75 is not listed on the Type Certificate.

LKT

[lktiller]

Oh, yeah, about the cost vs value!!!! My thinking is; it's worth it if you are going to do a major OH anyway.
performance of N95901: 800fpm climb @ 55mph off the hayfield, standard day, with me and full tank: Cruise 2250rpm @ 95mph. Static 2250rpm with warm engine.

[Forrest Barber]

75 & 80 hp

We have done all that here a few times. The A-75 & A-80 get their "horesepower" by merely turning he engine faster with a smaller prop.
The A-65 in my ship uses a 74-45 IF I wanted the full "75 horsepower" then I would have to use a 70-38.... check your ATC's for these engines for the proper RPM's etc for what you want to do...
Way back then when this was thought up; Cont. engines were changed according to the SB to use "waffeled" pistons , four rings, smaller wrist pins, different jetting & venturi in the carb, ( she will burn more fuel) .... the increased RPM produced problems with heat that required the piston & wrist pin change AND the rods were drilled to squirt oil onto the opposite skirt to help cool the engine ...

There is a rumor out there by "Publicious" that some people drill the rods, go to the other stuff too sometimes.... then use the old prop & cruise at 2250-2300 RPM. THAT is how "Publicious" got to OSH at over 100 MPH in his BC12D.. This does not increase Static RPM so take-off is the same. IF you need the increased HP at take-off then you need the smaller prop...

[stormman]

A65 to 75

Im not really sure its worth going from the nice tight 65 pistons with the big pins to the loose 75 and 80 small pin pistons
They use alot more oil and rattle more and im not sure the performace is really that measured that much more, at lest in the seat of your pants i found it very disappointing .
What say ye tribe members?

[Acroeric]

I had a BC12-D with the A75 and I was disappointed, so much so that I could tell absolutely no difference between it and the A65 it replaced. If you are going to go to the trouble put a C85 in it and be done with it.