I'm working on lowering the CHT's on my recently completed 9A. I have an O-320 with 9:1 pistons, one P-Mag and
one Slick. I can't operate at any DA at full throttle without the CHT's climbing above 425. I don't know just how
high they would go as I throttle back to cool them off. The engine has 13 hours on it and has used less than a quart
of oil in the 13 hours.
I've researched quite a bit and have read many threads where people have enlarged the main jet so I asked my
engine builder for his take on it. He said that at full throttle I should get a minimum of 125 degree rise in
my EGT's in order to be rich enough. I get exactly that on several tries. I'm flowing about 12.5GPH at full throttle.
I've done all the baffling stuff to ensure that the air is going where it needs to and believe that it is sealed well
as evidenced by oil temps being a max of 190 with OAT's in the 80's to 90's.
I've also read that on high compression engines that even Lycoming suggests base timing of 20 BTDC instead of the 25
that my slick is timed at and the P-mag's total advance is more than that.
I do have the jumper in the P-mags for the lower advance curve and last evening, after some study of P-Mags literature,
I disconnected the manifold pressure line, which is supposed to retard the curve to about 26BTDC. I haven't had a
chance to fly it as the weather won't co-operate.
I guess my question for you engine gurus or someone with some HC piston experience is two fold. Is 12.5GPH enough
fuel at full throttle and should the base timing be retarded because of the high compression pistons?
It's a little frustrating that I can't climb, even at 120 knots, very long and even at 10,000DA I can't run at WOT.
Any suggestions will be much appreciated.
one Slick. I can't operate at any DA at full throttle without the CHT's climbing above 425. I don't know just how
high they would go as I throttle back to cool them off. The engine has 13 hours on it and has used less than a quart
of oil in the 13 hours.
I've researched quite a bit and have read many threads where people have enlarged the main jet so I asked my
engine builder for his take on it. He said that at full throttle I should get a minimum of 125 degree rise in
my EGT's in order to be rich enough. I get exactly that on several tries. I'm flowing about 12.5GPH at full throttle.
I've done all the baffling stuff to ensure that the air is going where it needs to and believe that it is sealed well
as evidenced by oil temps being a max of 190 with OAT's in the 80's to 90's.
I've also read that on high compression engines that even Lycoming suggests base timing of 20 BTDC instead of the 25
that my slick is timed at and the P-mag's total advance is more than that.
I do have the jumper in the P-mags for the lower advance curve and last evening, after some study of P-Mags literature,
I disconnected the manifold pressure line, which is supposed to retard the curve to about 26BTDC. I haven't had a
chance to fly it as the weather won't co-operate.
I guess my question for you engine gurus or someone with some HC piston experience is two fold. Is 12.5GPH enough
fuel at full throttle and should the base timing be retarded because of the high compression pistons?
It's a little frustrating that I can't climb, even at 120 knots, very long and even at 10,000DA I can't run at WOT.
Any suggestions will be much appreciated.