Map

[wlarson861]

I upgraded to the turbo AeroVee and have never seen more than 36 inches of manifold pressure. my cruise is spot on with others and climb is good, so why the low max power number? I take off at about 35.9 inches and climb at 7 to 9 hundred feet per min solo. I cant get anywhere near 40 inches of manifold pressure. Any ideas? I am using auto gas and compression is set at 7:1

[Rynoth]

I am using auto gas and compression is set at 7:1

Could this be part of the problem? I thought the Turbo was required to be run with 100LL.

[marsolgp]

My guess(es) would be either indication problem (what does MAP read when engine is not running?) or waste gate partially open. Did you preload the waste gate controller to hold waste gate closed?

By the way Bill, I went ahead and installed a 'vent grate' in my cowling above the turbo, to let heat out after landing….. works good and no ill effects during flight.

[wlarson861]

When the turbo was being developed it was always stated that auto gas was ok in the lower compression engine builds. Talked with Joe who said they were testing auto gas in the test cell but something took priority and they had to delay the auto gas.
As to the waste gate, I don't think I did anything to pre-load it. I'll have to check that. It makes sense that the gate is opening too soon since it has all the right performance at the lower settings.

[wlarson861]

[quote="marsolgp"]My guess(es) would be either indication problem (what does MAP read when engine is not running?) or waste gate partially open. Did you preload the waste gate controller to hold waste gate closed?

Good call. Removed actuator rod end from waste gate and turned 1/2 turn tighter. Didn't see more that 36 inches on take off. Level at 2500 I added throttle and watched it go to 44 inches before full throttle was reached. Pulled back to 40 inches for a few seconds and then back to 30 .8 inches. after landing I took off again and the MAP went above 40 inches as I climbed out at 80 mph. It appears I didn't have enough tension on the waste gate to hold it closed at high power settings. Further flights should tell if this the case. I am encouraged.
Thanks Geary

[Sonerai13]

You don't want to put too much tension on that wastegate controller. You want to set it so that you get 40 inches MAP for takeoff, but you want it to do it's job and limit MAP to about 42 inches max. Too much tension on that controller arm will allow MAP to go well above 42 inches, which is not what you're looking for. A half turn one way or the other when you're close makes a significant difference. Err on the low side rather than the high side.

[marsolgp]

Waste gate springs are calibrated with proper preload figured in..... You do not adjust manifold pressure with the preload, that is done with the correct spring installed in the waste gate controller. The spring installed in the supplied waste gate controller is a white one, this is the 'lightest' spring made for this waste gate and is set to STARTopening at approx 40" MAP.... It doesn't fully open til about 44" MAP. This why you have to pay attention with throttle setting, because this turbo will produce more boost than you need or are allowed.
Oh, and you're welcome Bill.....

[Sonerai13]

Geary,

The amount of pre-load does indeed make some difference. We played with this in the test cell and found out that the MAP at which the wastegate would open would vary somewhat with the amount of pre-load we placed on the rod.

[marsolgp]

I don't disagree….. this is an old trick from street racers to easily increase boost by keeping waste gate closed past the springs boost setting, because you are essentially changing the spring tension…. My point is, with the proper spring and proper preload, 'adjusting' preload should not be needed, nor used. This turbo installation will easily produce 44-45" at sea level when adjusted properly. The pilot needs to use throttle to control this.

Now, to get a little deeper into the subject, I didn't like the idea of pulling my throttle back during T/O but it was necessary because as you roll down the runway, the RPM and Boost do increase. So what I did was install a 'helper' spring on the outside of the waste gate controller (with an adjustable collar) that effectively cancels out some of the tension applied by the white waste gate controller spring. I now have everything adjusted so that when I apply full throttle, my turbo only goes to 40-41" and I can concentrate on my T/O and climb out.

[wlarson861]

I don't think I have any "pre-load" on the actuator. I think before it was not fully closed and was opening too far. The maximum MAP I was seeing was 35.80 in.