Jeff, I do have quite a few concerns about a number of things. The crank is a GPAS forged unit with the Force 1 prop hub. If any crank can handle the loads I think this is my best bet. My biggest concern is the case itself. I may have to go with a larger type 4 center bearing or go to something like the aluminum Scat "killer case".
Cooling the power will indeed be a challenge. The water injection will help but only testing will tell. Right now I am running it like the Revmaster turbos ran, without a waste gate. I may have to add one. I have noticed that once the boost is in, it does not take much more throttle to get more power. I have considered a throttle stop that is hinged to prevent a serious over boost that is deployed during takeoff and landing but I'm not sure how that will work out. I have looked at a few waste gates but none of them are programable. The would just be set to pop off at whatever pressure its set at preventing over boost. The ignition is also set up so that if an over boost happens the ignition timing drops to 0 but the mag is still firing at 25 degrees BTDC. Again, I am going to have to see how it works out. Joe at Revmaster said that the prototype KR2S was turbocharged and ran up to 6psi with the timing set at 25 degrees. If anyone knows anything about this please let me know! I did drop the compression from a little over 9:1 to 8:1 by installing larger shims under the cylinders. 8:1 is what Joe recommended. Its still higher than the 2.5l turbo in my Subaru car, but that is running about 14psi of boost (60"). If I recall, its CR is 7.5:1. There will be many test flights and inspections along the way. Initially, I'll normalize and then slowly work up to more power. The engine will have to be torn down next winter to see what the results are. The engine is being torn down next month to see what it looks like inside. Its got about 50 hours of full throttle operation at over 4000rpm's on it now and I want to see how it's held up to that. I'm in no big rush since I have the KR to fly. If the Sonerai takes all summer I am just going to race the KR at cruise power. Thanks! Jeff Lange On Mar 25, 2013, at 9:16 AM, "Jeff Scott" <jscott.planes at gmx.com> wrote: > Wow Jeff! You're making a ton of HP with that. Any thoughts on the effects > of adding 2.5" to the crank length plus running the additional HP? I have > only built one VW based aero engine, but I would question running that kind > of HP through the VW crank while multiplying the crank loads with an > extension at the same time. I would think the turbo boost will also degrade > the life of the VW heads, which are kind of a weak area for the engine as > well, but I'm sure you already know that trade off going in. The work looks > really good and should be a blast to fly. > > Are you set up with a programmable automatic waste gate, or is it set up as a > manual waste gate? The automatic ignition timing using the manifold pressure > to help with ignition timing mapping will be a big help with the boost. I've > seen a guy blow up the a turbo Subaru trying to run a manual waste gate. A > quick throttle response to a runway incursion while on short final and > suddenly while cursing the plane that cut him off, he found himself with a > closed waste gate and a serious over boosted engine and blew it up with > detonation before he recognized what was happening. > > I like your approach to the engine and cooling. Cooling will be the key to > longetivy of the heads. If you can keep the CHTs and Oil temps in the green, > you should be good to go. > > What about compression on this engine? The norm for a turbo boosted engine > is to lower the compression. With the turbo boosting, you don't really have > the need for high compression at the same time as you can make up for > compression with boost. Are you running relatively high compression pistons, > or have you lowered the compression down to go with the turbo boost? > > Overall, good job. It looks great and will undoubtely be a real rocket to > fly. > > -Jeff Scott > Los Alamos, NM >
