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I just received PowerFlow's eBook on tuned exhausts. According to the O-320 chart data on page 19, the question I raised about higher HP at the tuned RPM and possibly lower HP at different RPM is not correct. The test data reflected in the chart do not appear to be independently validated but if we take the chart at face value, the PowerFlow increases HP across the entire usable RPM range. I'm trying to figure out how this can be true, even based on PowerFlow's explanation of how HP is gained. There may also be differences in efficiency gains between carburetor and fuel-injected engines.

Anyone have any thoughts?

BTW: Generalizing from O-320 data, it would appear that the PowerFlow puts our aircraft into the high performance category. Hmmm.

Powerflow told me that the peak benefit in the DA40 was between 2300-2600 with peak somewhere around 2500-2550ish (depending on altitude, temperature, etc).

DavidS wrote:Mine came OEM with that exhaust, but I have flown non PF exhausted DA40s as well. I believe that there's a notable difference.

Between the electronic ignition and the PF we picked up 10-12 knots (depending on power setting & altitude). I can't comment on how the Powerflow would have done on it's own as we already had the Electronic Ignition.

Replacing a perfectly good, recently overhauled propeller (required for PF STC) was not a happy thing for me to do. Someone should pitch me an offer for the prop as it's in perfect shape and sad to be off of the airplane.
hartzell-aluminum-2-blade-prop-spinner-4300-t5298.html

you replace your hartzall alluminium prop for trhe power flow system, but with the link you send you have the 7495 model and they are compatible with the power flow stc.... or you change it to have an composite prop

Enrouk wrote:but with the link you send you have the 7495 model and they are compatible with the power flow stc....

You should take another look at the datasheet and you will see:

Note 1. NOT COMPATIBLE with Power Flow exhaust system per Power
Flow Systems STC SA03281AT.

I replaced the Aluminum Hartzell with another Aluminum Hartzell that looks identical but has ever-so-slightly thicker tips.

I upgraded last yr on my 2003 with MT prop and there was a noticeable difference in climb rate and approx 4 to 6kt at cruse. On the downside the systems is louder but you get used to it very quickly.

3 things to watch out for with PowerFlow exhaust on a DA40 (most of which have been mentioned here before):

1. At every annual the exhaust must be removed and put back with anti-seize compound on the movable joints. Otherwise the exhaust risers will crack.
2. The fiberglass muffler inserts ("glass packs") will degrade over time and literally disappear, with your exhaust getting louder in the process. Expect to order new muffler inserts from PowerFlow to reinstall every 300-400 hours.
3. The thick rubber strap that holds up the exhaust pipe tends to break, causing the exhaust to pivot and rub/touch against the white composite engine cowling, causing burn marks and/or paint bubbles.

I had all 3 of these things happen to our DA40 in the first 600 hours of ownership.

CFIDave wrote:3 things to watch out for with PowerFlow exhaust on a DA40 (most of which have been mentioned here before):

1. At every annual the exhaust must be removed and put back with anti-seize compound on the movable joints. Otherwise the exhaust risers will crack.
2. The fiberglass muffler inserts ("glass packs") will degrade over time and literally disappear, with your exhaust getting louder in the process. Expect to order new muffler inserts from PowerFlow to reinstall every 300-400 hours.
3. The thick rubber strap that holds up the exhaust pipe tends to break, causing the exhaust to pivot and rub/touch against the white composite engine cowling, causing burn marks and/or paint bubbles.

I had all 3 of these things happen to our DA40 in the first 600 hours of ownership.

The rubber straps are relatively inexpensive. Order several at a time.

Other than noise, what is the consequence of losing the fiberglass pack?

rwtucker wrote:Other than noise, what is the consequence of losing the fiberglass pack?

Hi Robert -

AFAIK, the only other consideration is that the polished stainless tip gets discolored from higher temps. At least, that is what has happened to mine.

The big problem with the insert is that eventually the perforated metal tube warps into a pretzel and constricts flow. Several years ago Power Flow changed to a thicker gauge tube which is much more resistant to deformation.

Chris