Aerovee Turbo Woes...again x 3
Posted: Fri Mar 17, 2017 10:48 amI flew the prior Sunday with the best performance to date. I had been studying the effects of the factory air filter. I tested flying with the factory air filter, no filter and a high flow K&N filter. The test involved tuning the engine mixture and then doing 2 passes up the runway at 1,000 ft agl @ 34" followed by a max climb rate to 4,000 ft. I tracked IAS, CHT, EGT, VS on climb.
Results: The factory filter is a choke on the engine, it's the bottleneck into the turbo. It resulted in 200+ rpm loss, higher temps and much lower speeds. The K&N tuned slightly rich achieved 168mph IAS (yes, IAS) on the level upwind, 1,500 ft/min climb with a max CHT of 395 degrees. At 4k cruise and 31.5" I was able to cruise at 6.1gph and achieve 156mph TAS average over 45 min of flight. And that cruise flight was with a 706lb nose dragger, 13g fuel and my wife with me...
I cannot climb over 950fpm on the stock filter without CHT spiking.
So, after 120 hours, I am once again working on my engine. This will be the third time. During my annual the next day, I found the following compression readings:
1- 10/80
2- 30/80
3- 20/80
4- 78/80
It is very apparent the leak is not in the rings this time (that was tear down #2), but the exhaust valves. We put in a borescope and the valves look clean and there are no burn marks, apparent carbon, etc. We tried a few mechanic tricks to achieve better seals, but were unsuccessful. Below is the pic of exhaust valve on cyl #1. Nice and clean.
Frustrated and reaching out to a few other Aerovee owners, I was not surprised to hear several people have gone though 2-3 pairs of heads over 200-300 hours due to the same issue. That got me thinking, something just isn't right. I tried to reach out to Sonex, but tech is shut down for the week and didn't care to send another email. Plus, I'm sure it's my fault again... :roll:
I called a few of the top bug tuners in the country and received their insights. I wanted to share with the larger group to get your thoughts on what they say is clearly the problem:
1) We are running too hot of a plug (AL-4163) and recommends a cooler plug (Denso 24)
2) The valves need to be 3-angle ground to get a better seal and need to be hardened stainless steel
3) We should be using dual springs, not the stock spring. At minimum, a heavier racing spring
4) They recommend a valve size of 42/37 or 40/35 for a high torque / low rpm application
5) They all said our 92mm bore is wrong for our application
The last bullet was the most shocking for me. A 92mm bore is the hottest running bore out there (according to 2 bug tuners). He strongly recommended moving to a matched / forged 90.5mm bore as it doesn't require new heads or block. It increases wall thickness, helps with torque, and significantly improved cooling, which should result is much longer head life. The 375-400 degree + temps on climbs are putting too much stress on the heads between 1 and 3.
Although we lose some cc's, we shouldn't notice much difference in speed because we are running such low RPMs. He said we need the engine built for torque, not increased HP. And with a turbo, we can just increase throttle to make up for the cc loss. He said a big prop and such low RPM is putting too much torque on the engine for a 92 bore. A 90.5 bore paired with 42x37 or better yet a 40x35 valve setup will give us more torque to move the prop efficiently.
He makes ported, matched heads for about $800 with 3 angle valves, dual springs, with dual plugs.
He also has split heads (so we can pretend we are a real airplane engine) which are also dual plugs and awesome looking on the roller rocker, but the cooling fins are smaller and may cause heat issues with the turbo engine. He believes the ported heads will be better for us. But, they would solve the valve issue flexing as the stress across cylinders becomes non-existent. (I'm tempted to try a set, but they are $1,400...ouch, and risky if they overheat on climb).
Questions:
1) What are the valve sizes?
2) Are the valves sodium filled or solid stainless?
With that info, I'd love some opinions...GO!
Results: The factory filter is a choke on the engine, it's the bottleneck into the turbo. It resulted in 200+ rpm loss, higher temps and much lower speeds. The K&N tuned slightly rich achieved 168mph IAS (yes, IAS) on the level upwind, 1,500 ft/min climb with a max CHT of 395 degrees. At 4k cruise and 31.5" I was able to cruise at 6.1gph and achieve 156mph TAS average over 45 min of flight. And that cruise flight was with a 706lb nose dragger, 13g fuel and my wife with me...
I cannot climb over 950fpm on the stock filter without CHT spiking.
So, after 120 hours, I am once again working on my engine. This will be the third time. During my annual the next day, I found the following compression readings:
1- 10/80
2- 30/80
3- 20/80
4- 78/80
It is very apparent the leak is not in the rings this time (that was tear down #2), but the exhaust valves. We put in a borescope and the valves look clean and there are no burn marks, apparent carbon, etc. We tried a few mechanic tricks to achieve better seals, but were unsuccessful. Below is the pic of exhaust valve on cyl #1. Nice and clean.
Frustrated and reaching out to a few other Aerovee owners, I was not surprised to hear several people have gone though 2-3 pairs of heads over 200-300 hours due to the same issue. That got me thinking, something just isn't right. I tried to reach out to Sonex, but tech is shut down for the week and didn't care to send another email. Plus, I'm sure it's my fault again... :roll:
I called a few of the top bug tuners in the country and received their insights. I wanted to share with the larger group to get your thoughts on what they say is clearly the problem:
1) We are running too hot of a plug (AL-4163) and recommends a cooler plug (Denso 24)
2) The valves need to be 3-angle ground to get a better seal and need to be hardened stainless steel
3) We should be using dual springs, not the stock spring. At minimum, a heavier racing spring
4) They recommend a valve size of 42/37 or 40/35 for a high torque / low rpm application
5) They all said our 92mm bore is wrong for our application
The last bullet was the most shocking for me. A 92mm bore is the hottest running bore out there (according to 2 bug tuners). He strongly recommended moving to a matched / forged 90.5mm bore as it doesn't require new heads or block. It increases wall thickness, helps with torque, and significantly improved cooling, which should result is much longer head life. The 375-400 degree + temps on climbs are putting too much stress on the heads between 1 and 3.
Although we lose some cc's, we shouldn't notice much difference in speed because we are running such low RPMs. He said we need the engine built for torque, not increased HP. And with a turbo, we can just increase throttle to make up for the cc loss. He said a big prop and such low RPM is putting too much torque on the engine for a 92 bore. A 90.5 bore paired with 42x37 or better yet a 40x35 valve setup will give us more torque to move the prop efficiently.
He makes ported, matched heads for about $800 with 3 angle valves, dual springs, with dual plugs.
He also has split heads (so we can pretend we are a real airplane engine) which are also dual plugs and awesome looking on the roller rocker, but the cooling fins are smaller and may cause heat issues with the turbo engine. He believes the ported heads will be better for us. But, they would solve the valve issue flexing as the stress across cylinders becomes non-existent. (I'm tempted to try a set, but they are $1,400...ouch, and risky if they overheat on climb).
Questions:
1) What are the valve sizes?
2) Are the valves sodium filled or solid stainless?
With that info, I'd love some opinions...GO!