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I would just like to hear any and all opinions about going with a turbo system in order to get to a HP requirement I need for my chosen Zenith version (CH 640).
Now, before you throw on your negative nancy glasses, realize that the Sling 4, a similarly sized EXP, is powered by a Rotax 914 UL/F @ 115hp. People said it was underpowered. So they came out with the Sling TSi, which is now powered by the Rotax 915 TSi @ 141hp. People are raving about the power now. To accomplish this, it is paired with an AirMaster variable prop system, something that I would want to do as well with the Corvair.
So what I want to do is build a 3300 Corvair and put a turbo system on it to reach 150hp on takeoff (at any airport altitude!) and then dial the manifold pressure back for cruise to save abuse on the engine. Basically a turbo-normalized engine, but with a boosted phase for takeoff. Paired with a VPP, it should prove to be quite the econo-cruiser.
Okay... NOW. Go ahead and let me have it...
I don't think it is being a negative nancy to point out that the Corvair heads are going to be marginal in the regime you're talking about. If you're making Hp, you're making heat, and that heat has to have some way of getting out.
The big VW cylinders only gets you up to 3100cc. How will you get to 3300? A longer crank?
Yes, the stroker crank, and don't forget, the factory corvair was turbo boosted to 180hp on the Monza.
Yes, but how long could you stay on that 180Hp? Typical cruise driving requires about 30Hp.
My plenum is keep my CHTs around 150F in my 3100cc, so you can get it done with proper oil cooling. But, getting the heat out is a real concern.
Out of what? The oil? I believe ww sells an auxiliary oil cooler, correct? Bill Clapp is flying a turbo-boosted corvair in his plane. It definitely can be done. The question is, for how long.... i.e. what should be TBO on this thing.
I'm only wanting 150hp for 5 minutes of takeoff and climb, then dial it back to turbo-normalization.
The oil and the CHT. I've got my CHT's under control, but my oil is at 275 on a 95 degree day, which is what I consider to be the red-line. I'm using two of the folded fin coolers in the stock position. I've made a modification to the plenum, as the first iteration was about as aerodynamically bad as it could possibly be, but I've not had time to test it. But, unless you heat soak the engine before takeoff, I don't see you stressing it too much in 5 minutes. Definitely doable.
My feeling from all the reading I've done combined with destroying way too many engine parts: Keep the oil below 275 and CHTs below 300 on all cylinders. Do NOT exceed 32 degrees of advance, and then ONLY above 2700 RPM. Got the melted piston to prove that one. Expect to re-torque the heads at 25, 100, and 500 hrs, and any time that you feel power is dropping. I then think you can expect 500 reliable hours as a minimum. The highest numbers of actual flying time I've heard are around 1200hrs.
So, you are talking as if your engine is turbo, is that correct?
No. I don't have a turbo, but the advice is independent of intake pressure. If you're keeping the temperatures down, you're keeping the metal strong. The thing I've come to understand is that the ability to handle combustion pressures is no unlimited. Adding a turbo just gives you more ability to push the engine beyond what the metal can handle.
If you're only using the turbo for a few minutes, then there shouldn't be a lot of time to bake the heads. . . but, you still can.
BTW, the 3100 is heavier than the 2700. Saturday morning, I touched down at 60mph, and the nose came down hard, in large part due to that weight. It broke my bungee, and then the tips of my Warp Drive prop succumbed to a bump in the asphalt. (add crying emoji here). I'm going to be looking for ways to reduce nose weight, even without the turbo.
Sorry to hear about your prop strike. Multiple sources say the 3100/3300 is lighter than the 2700 because the VW cylinders are actually lighter than the GM Corvair ones. A total of 6 lbs. But I don't think it is an issue because the CH640 I'd designed around a 0-320 or 0-360. Much heavier than a corvair. I plan to make that weight up with an AirMaster prop system.
Where are you measuring the oil temp?
Why are you re-torquing the heads so often? Do the head fasteners actually loosen up?
I'd have to double check, but I'm pretty sure that the sensor is between the filter and oil cooler.
I've put together a different air duct that has some deflectors to direct airflow more evenly across the radiator. I had one short flight to test it, and it seemed to drop the temps down into the 230s. I won't be solid on those numbers until I've had a chance to get at least an hour long flight on it, though.
I think you're asking a bit much of the Corvair. The factory turbocharged Corvair engines made 180 HP at 4000 RPM. Unless you run a reduction unit you won't be able to use the power. 150 HP may be achievable direct drive with a turbo but you'd be adding weight and complexity and trading off longevity and reliability. Maybe you should consider the Viking 180 for your CH640.
The weight is not as concerning to me, as the plane will support up to an 0-540. So there's a lot of room to add a turbo system to an engine that weighs as little as the Corvair comparatively speaking. Complexity? yeah... But while it is more complex on the front end (installation), the result would be a lot simpler flight operations with no worries about density altitude, taking off from high airports, etc.
But I am sorta coming around to everyone else's conclusion that getting 150hp out of the Corvair, even the 3300 stroker, is going to be a cooling nightmare. Now, the Sling TSi is a similar plane in gross weight and configuration, and it takes off fully loaded with a Rotax 915 turbo that makes 141hp for the first 5 minutes, and then 135 after that, so the POWER seems doable. Granted, the Rotax is water-cooled, so that's an advantage over the Corvair.
I don't know.... still thinking on it.