Any Turbos running 8:1 CR?

[NWade]

Hi All,

My AeroVee Turbo kit should be shipping from the factory in early August, so I've started planning ahead for the assembly... In the newer DVD, Joe Norris builds a 7:1 turbo and claims that the turbo makes the power output pretty similar, regardless of the CR. (And yes, I've seen the thread talking about the MAP & CR & HP differences)

The way its phrased in the DVD, the 8:1 CR is not explicitly forbidden. Its just generally stated that 7:1 works fine for them at Sonex Aircraft, on an AeroVee Turbo. So I'm wondering: Has anyone out there in the Sonex community run 8:1 on a turbo? ...Either as a new build or by converting an existing AeroVee to a Turbo. If so, have your experiences been OK or have you noticed anything we should be concerned about?

Thanks,

--Noel
Sonex #1339
TD, Center-Stick, Acro-Ailerons, Flush pulled rivets, AeroVee Turbo

[radfordc]

Are you trying to tweak every last HP out of your engine? Seems that a lower CR might be easier on the engine in the long run.

When I had my Sonex I started with 8:1 compression and then later on rebuilt the engine and changed to 7:1 so I could run MOGAS. I couldn't tell any difference in the performance of the engine. Same rpm before and after as far as I could tell. My plane with the 7:1 CR and Bob Mika's plane with 8:1 performed almost identically...we were always within 1-2 mph of each other at the same rpm.

[Bryan Cotton]

Makes perfect sense that if your RPMs are the same, and the prop is the same, the performance would be the same. I would expect with lower CR you would notice lower RPM at low speed, like in climb. Was this not the case?

I love running auto gas. I have a lot of towing time in a Pawnee & PA18 burning auto gas. Plus our club C140 never used to get fouled plugs on car gas but the old C85 hated 100LL. My home airport has both mogas and the blue stuff. I was going to set up for 100LL because it is everywhere and the promise of more performance. Seems odd if there is truly no benefit and I wonder why.

[Brett]

I'm running 8:1. Runs great with plenty of power on take off. I have to be very careful to not over boost over 40"map during takeoff. Most of the time I usually take off somewhere between 32" to 36". It climbs out so well anyway I rarely bother to take it to the max.
Only thing I'm struggling badly with is heat in the engine bay. My temps never exceed 380 now I have done some big changes in the cowling but the turbo roasts everything. I have the blanket on and wrapped the exhausts as required but it isn't enough. I'm now making or made heat shields for the trigger modules as they have both swollen due heat, im onto my 24th engine mount now as they keep melting so making furthur shields and waiting for a 3M aluminuim shielded sticking insulation to try and cover and save the mounts. Last flight melted the bushes in a record time off 45min. They don't melt during flight but seem to after shutdown. Im concerned about other key electrical components so tying to shield them also.

[radfordc]

Makes perfect sense that if your RPMs are the same, and the prop is the same, the performance would be the same. I would expect with lower CR you would notice lower RPM at low speed, like in climb. Was this not the case?

Yeah, that was a dumb statement wasn't it... :oops:

But, when Bob and I did formation takeoffs there didn't seem to be any difference in performance there. I assume we were both at full power.