AeroVee Tubo - Correcting low MAP at full throttle
Posted: Wed Oct 13, 2021 11:31 amNoel Wade posted excellent info on the root cause and corrective actions of his turbo not achieving full MAP at full throttle. His original post can be found at viewtopic.php?t=4323&p=49134#p49124, and is summarized below.
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The definitive solution to my issue [low MAP at full throttle] was that the White spring in the wastegate actuator was too weak. Switching to a blue spring (per the image/chart) gave me an extra ~5 inches of boost at full WOT.
Since that is about 2" more boost than spec, my solution is going to be to limit throttle travel at low elevations. With the white spring I could slightly change the max boost by adding pre-load to the actuator; but in the end the blue spring with no preload was the only way I could achieve the 40" MAP called out in the manual.
If you look at the spring chart I linked to above, the white spring is rated for 0.3 bar (and will start actuating at slightly less pressure). This is equivalent to ~8" - 9" of mercury. Add that to sea level pressure on a standard day (29.92) and you get ~38". Which is close to what I was seeing. The blue spring is rated for 0.5 bar (and again, starts actuating slightly below that), which is equivalent to ~11" - 14.7" of mercury. This would put max boost between 41" & 45" at sea level on a standard day - this is beyond what Sonex/Aeroconversions specifies, so I would urge caution to anyone who follows in my footsteps. I think that for many AeroVee Turbos, some preload and/or frictions in the system cause the effective spring rate of the wastegate to be just a touch higher than what is spec'ed for these springs; thus many folks can achieve 40" MAP right out of the box. But variance in setup and the exact spring strength (i.e. unit to unit variance) may leave a few folks 1-3" short.
I bought my blue spring on Amazon.com, but reviews vary. If you Google the part number shown in the chart you can find the exact spring for sale directly from Kinugawa (the manufacturer of the wastegate actuator that came with my AeroVee Turbo): http://shopping.kinugawaturbo.com/kinug ... bar-1.aspx
Note that the Kinugawa units come in different styles, with two different types of spring - the straight spring (which I linked above) has an actuator that can be adjusted via preload on the wastegate arm. They also sell a more-adjustable wastegate actuator that uses conical springs. I have no idea if Sonex has changed the parts they source/use for the wastegate system over time, so double check the actuator & spring style you have before ordering one of these blue springs.
I would urge you not to assume the wastegate actuator is the issue unless you've done testing and eliminated other potential causes (such as induction leaks, exhaust manifold leaks, throttle-travel limits, assembly errors in the wastegate actuator system, and instrumentation errors). If you can record engine data with your EFIS/EMS, warm up the engine for a minute or two and then slowly sweep the throttle up to full over ~5 seconds, and then smoothly pull it back down. Pay attention as you advance the throttle - do the MAP and RPM stop rising before you hit the throttle stop? After engine shutdown, grab the engine data and look at a graph of the MAP. If you see it plateau or have a small drop before the engine RPM starts to decline, that may be an indication the wastegate is opening too soon.
[original image located at: http://shopping.kinugawaturbo.com/image ... l/4.56.jpg]
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The definitive solution to my issue [low MAP at full throttle] was that the White spring in the wastegate actuator was too weak. Switching to a blue spring (per the image/chart) gave me an extra ~5 inches of boost at full WOT.
- 4.56.jpg (102.74 KiB) Viewed 7498 times
Since that is about 2" more boost than spec, my solution is going to be to limit throttle travel at low elevations. With the white spring I could slightly change the max boost by adding pre-load to the actuator; but in the end the blue spring with no preload was the only way I could achieve the 40" MAP called out in the manual.
If you look at the spring chart I linked to above, the white spring is rated for 0.3 bar (and will start actuating at slightly less pressure). This is equivalent to ~8" - 9" of mercury. Add that to sea level pressure on a standard day (29.92) and you get ~38". Which is close to what I was seeing. The blue spring is rated for 0.5 bar (and again, starts actuating slightly below that), which is equivalent to ~11" - 14.7" of mercury. This would put max boost between 41" & 45" at sea level on a standard day - this is beyond what Sonex/Aeroconversions specifies, so I would urge caution to anyone who follows in my footsteps. I think that for many AeroVee Turbos, some preload and/or frictions in the system cause the effective spring rate of the wastegate to be just a touch higher than what is spec'ed for these springs; thus many folks can achieve 40" MAP right out of the box. But variance in setup and the exact spring strength (i.e. unit to unit variance) may leave a few folks 1-3" short.
I bought my blue spring on Amazon.com, but reviews vary. If you Google the part number shown in the chart you can find the exact spring for sale directly from Kinugawa (the manufacturer of the wastegate actuator that came with my AeroVee Turbo): http://shopping.kinugawaturbo.com/kinug ... bar-1.aspx
Note that the Kinugawa units come in different styles, with two different types of spring - the straight spring (which I linked above) has an actuator that can be adjusted via preload on the wastegate arm. They also sell a more-adjustable wastegate actuator that uses conical springs. I have no idea if Sonex has changed the parts they source/use for the wastegate system over time, so double check the actuator & spring style you have before ordering one of these blue springs.
I would urge you not to assume the wastegate actuator is the issue unless you've done testing and eliminated other potential causes (such as induction leaks, exhaust manifold leaks, throttle-travel limits, assembly errors in the wastegate actuator system, and instrumentation errors). If you can record engine data with your EFIS/EMS, warm up the engine for a minute or two and then slowly sweep the throttle up to full over ~5 seconds, and then smoothly pull it back down. Pay attention as you advance the throttle - do the MAP and RPM stop rising before you hit the throttle stop? After engine shutdown, grab the engine data and look at a graph of the MAP. If you see it plateau or have a small drop before the engine RPM starts to decline, that may be an indication the wastegate is opening too soon.
[original image located at: http://shopping.kinugawaturbo.com/image ... l/4.56.jpg]
