I think I have uneven airflow....

[DanH]

An aside...although we may believe the sump to be the root of all evil, until somebody actually puts a sump assembly on a flow bench and measures all four runners, nobody really knows.

It could just as easily be four very different intake ports and valve seats, for example. Some custom shops flow bench cylinders and correct the asthmatic, others don't. Bring the low-flow cylinders up to the level of the best, and the result is more power.

Break.

The ROP reduction in fuel burn is an interesting benefit. The ROP comparison shown here was taken at two different altitudes (and apparently on two different days), but they're close. If both setups were referenced to the same ROP value (say 100 ROP for the leanest cylinder, for example), balance means the richest cylinders are no longer running a lot richer than 100 ROP. I point this out because folks often think of GAMI spread as a LOP tool, but it extends to best power mixtures too.

[carrollcw]

Originally Posted by DanH

The ROP reduction in fuel burn is an interesting benefit. The ROP comparison shown here was taken at two different altitudes (and apparently on two different days), but they're close. If both setups were referenced to the same ROP value (say 100 ROP for the leanest cylinder, for example), balance means the richest cylinders are no longer running a lot richer than 100 ROP. I point this out because folks often think of GAMI spread as a LOP tool, but it extends to best power mixtures too.

Exactly. Cylinders 2/4 were significantly trimmed leaner which results in more economy when running ROP. This technology results in the engine running better, but also better fuel economy running ROP and LOP. It will take me a few more flights to get an idea of just how much more economical it is now.

[Toobuilder]

Originally Posted by DanH

An aside...although we may believe the sump to be the root of all evil, until somebody actually puts a sump assembly on a flow bench and measures all four runners, nobody really knows.

It could just as easily be four very different intake ports and valve seats, for example. Some custom shops flow bench cylinders and correct the asthmatic, others don't. Bring the low-flow cylinders up to the level of the best, and the result is more power....

The flow bench would certainly give plenty of info, but it still wont tell the tale concerning the interaction between all the cylinders in a dynamic state. And if we think back to the gearhead days when all cars had carbs, plenum volume was a major discriminator in how they performed. Big plenums used to be reserved for big inch, big RPM race engines - but that was with a "wet" flow. With the advent of EFI and "dry" intakes the plenum volumes went way up. Look at the plenum volume of the 200 and 300 HP Lycomings compared to the 180 and 260 versions.

The updraft sump may not be the root of ALL evil, but I suspect that it at least has a bad disposition.

[Toobuilder]

Originally Posted by Weasel

Would you design the system with a filter after the servo?

I'm thinking that the servo would remain in the exact same location in space, so the existing filter and inlet would be retained. Not a practical solution for many airplanes, but it will allow for a fairly easy addition to my Rocket - just to test the theory.

[bpattonsoa]

Actually Ross's new system is a complete engine flow bench. Assuming (I hate that word) the exhaust system is reasonably well balanced, the individual injector adjustments are the airflow imbalance.

With a healthy engine, which it appears he has, to get equal EGT's you have equal AFR's. I know the fuel injectors are usually very close from experience getting a set cleaned and calibrated.

[rv6ejguy]

Originally Posted by DanH

An aside...although we may believe the sump to be the root of all evil, until somebody actually puts a sump assembly on a flow bench and measures all four runners, nobody really knows.

It could just as easily be four very different intake ports and valve seats, for example. Some custom shops flow bench cylinders and correct the asthmatic, others don't. Bring the low-flow cylinders up to the level of the best, and the result is more power.

Break.

The ROP reduction in fuel burn is an interesting benefit. The ROP comparison shown here was taken at two different altitudes (and apparently on two different days), but they're close. If both setups were referenced to the same ROP value (say 100 ROP for the leanest cylinder, for example), balance means the richest cylinders are no longer running a lot richer than 100 ROP. I point this out because folks often think of GAMI spread as a LOP tool, but it extends to best power mixtures too.

A flow bench may tell you nothing of the operational dynamics on the engine. It could point you in another useful direction though. Cylinder head / plenum flow is not constant state and as Don already mentioned, exhaust can have a huge effect on intake flow and scavenging. We won't be sure about the cause of all this without peeling back some more layers through testing and elimination, one variable at a time.

Dave Anders will have a SD plenum on his with flow benched heads and equal length exhaust. If that one shows very close spreads, we'll know we're on to something about balanced airflow.

For many years, some of the top engine builders in the auto race world have used pulsed and wet flow benches to more accurately understand what really goes on inside an engine. Not sure what top race shops like Sky Dynamics and Lycon use in the Lyconental world though. You can learn a lot on a flow bench and carry that forward to final validation of your theories and mods on the dyno. When I was building race engines, I built one of each from scratch and spent a lot of time testing and testing. My level of understanding massively increased within a couple of years of having those tools readily at hand in my own shop.

One point which Dan has stressed several times in the past is that EGTs may not be the same even in an engine with well balanced heads, induction and exhaust components but should PEAK near simultaneously, indicating they are at the same AFR under those conditions of rpm and throttle angle/MP. We can see this in Clark's data here even with a 0 GAMI spread.

I want to thank Clark and Rusty for getting these test flights in so quickly and gathering and posting this data. Most interesting and it validates our work in the lab.

[rv6ejguy]

Speaking about intake manifold designs, I posted the photo of the stock 540 vertical sump earlier to show the very small plenum volume and vastly different intake runner angles and lengths to illustrate a likely poor design with likely unequal flow to each cylinder. It breaks every rule we know in this regard.



Here's some photos, courtesy of Dave Anders, of his EFI install on his RV4 with the Sky Dynamics induction. Note large plenum volume, equal entry angles, tapered runners, with bell-like transitions and near equal lengths. This is best practice from the performance/ racing world. And I'd expect this to work better than the stock Lycoming vertical sump. Time will tell.

[rv6ejguy]

This is a very poor intake manifold. Off 320 Lycoming I believe. Compare to the SD one above.

[rleffler]

Originally Posted by Kahuna

Assuming your 1.5 is 1.5gph difference between first and last peak. If this is the case, fix this first. this will pull the engine cylinders into a closer tolerance in everything.

I just finished this with the assistance of a few friends and ended up with a 0.2 gph spread on my IO-540. It may even be smaller, but it's darn near impossible to move a throttle quadrant in 0.2 gph increments.

G3i EI On 2300 RPM Map 22.7 7500 ft

Size 0.025 0.0255 0.0245 0.0245 0.025 0.025
F/F Cyl 1 Cyl 2 Cyl 3 Cyl 4 Cyl 5 Cyl 6
12.8 1368 1409 1401 1422 1473 1442
12.6 1371 1409 1401 1415 1469 1446

In emails with Don, he shared that this resulted in 1.3% total spread in airflow between cylinders.

I might add a shameless plug for Don's upcoming FI 101 class in March. http://www.vansairforce.com/communit...d.php?t=134194

[rv6ejguy]

Originally Posted by rleffler

I just finished this with the assistance of a few friends and ended up with a 0.2 gph spread on my IO-540. It may even be smaller, but it's darn near impossible to move a throttle quadrant in 0.2 gph increments.

G3i EI On 2300 RPM Map 22.7 7500 ft

Size 0.025 0.0255 0.0245 0.0245 0.025 0.025
F/F Cyl 1 Cyl 2 Cyl 3 Cyl 4 Cyl 5 Cyl 6
12.8 1368 1409 1401 1422 1473 1442
12.6 1371 1409 1401 1415 1469 1446

In emails with Don, he shared that this resulted in 1.3% total spread in airflow between cylinders.

I might add a shameless plug for Don's upcoming FI 101 class in March. http://www.vansairforce.com/communit...d.php?t=134194

Good numbers. What sump are you using?