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Simon Hitchen 01-18-2020 08:19 AM

swapping injectors
HI Guys,

Looking for a bit of engine advice please. Im running two Pmags and I'm very happy with their performance. Im able to run significantly LOP very smoothly but thats brought up another issue.

My GAMI split is in the order of 0.8 to 1.0. Not ideal. Cylinder 4 peaks first followed by 3, then 2, then 1. I end up with Cyl 4 running at 90 LOP and CYl 1 at 10 LOP. That generally gives me 180 mph at 7 Gph. The engine runs very smoothly due to the electronic ignition but id like to even it up a bit.

My question is, before i go down the GAMI injector route should I try swapping the injectors around a bit? The reason i haven't yet is because with my current set up cylinders 1 and 2 run the hottest because they're closer to Peak EGT and being up front they get the best cooling. Cooling isn't an issue really, I'm normally running around 310 CHT.

Any advice appreciated, Thanks

JonJay 01-18-2020 08:33 AM

Moving injectors wonít do anything as they are all the same size.

Send your data to Don at Airflow Performance. He can then advise what injector you need. The injectors are only about $25 each of I remember correctly. Then, you can always put the originals back in if it doesnít produce the result you want.

Bavafa 01-18-2020 09:17 AM

I am not sure what the following means
"My GAMI split is in the order of 0.8 to 1.0."
what is the fuel burn difference between when your first cylinder peaks and your last cylinder. Ideally, you want this to be at or less than .2G and I believe this is the factor to keep in mind whether any of them need to be changed.

Papa 01-18-2020 09:34 AM

Yep, Don helped me with this exact issue...after a few trial runs with new injectors on the two cylinders that were running rich, I got the spread down to between .1 and .2 GPH. I cruise LOP and, for example, flew home after last xcountry at 173 KTAS burning 7.3 GPH. I can give up a few more knots and get the burn into the 6s. Works great.

tommylewis 01-18-2020 09:39 AM

my response
If it were me, I would go to Airflow Performance web page and order two restrictors, one .0275 and one .0270, and change out number 1 cylinders restrictor with the .0270 and number 2 with .0275. Those are your two richest cylinders.

Or follow Dons advice on this page and send him the data and follow his suggestions.

Toobuilder 01-18-2020 10:34 AM

7 GPH is pretty low flow for a 360 unless you are really high or don't have the throttle wide open. What MP are you seeing at your 7GPH?

The reason this is important is because mechanical FI uses a fixed orfice for each injector tied to a common hydraulic source. At high fuel flows the restriction in each injector means the backpressure is an effective metering method and ensures each injector flows the same amount of fuel. At low flows the backpressure drops and it's real easy for the fuel supply to favor some injectors over another. My 200 HP will show a big split starting about 8.0 GPH, but can be rock solid if Im at lower altitude/higher fuel flow.

It's possible to reduce the injector nozzle sizes down to provide a crisp distribution at very low fuel flow, but the flip side would be that the fuel pump would need to provide several hundred PSI to be able to flow enough fuel for takeoff at sea level.

The point is, it's tough to get mechanical FI to provide the 17GPH a 360 needs for takeoff AND get a crisp Gami split at 7GPH for LOP cruise. Remember that the critical condition is the takeoff event, and any nozzle changes need to support that.

Papa 01-18-2020 11:49 AM

This is from my IO-360 RV-8 a couple days ago. 171 KTAS, 6.3 GPH, .1 GPH spread between cylinders. Note all cylinders running between 23 and 26 degrees LOP. 52% power calculated by the Dynon D180. This was stabilized flight with the autopilot engaged. I also have no issues with takeoff power...I had Don help me and have two of the cylinders slightly restricted.

Toobuilder 01-18-2020 11:57 AM

That's a great data point Mark. Are you able to get the .1 GPH spread at this fuel flow (6.3), or was that tight spread at a lower altitude/higher fuel flow? What is your TO FF?

Simon Hitchen 01-18-2020 01:41 PM

Thatís exactly what Iím looking for. Thanks guys, Iíll give Don a call.

Papa 01-18-2020 03:23 PM


Originally Posted by Toobuilder (Post 1401130)
That's a great data point Mark. Are you able to get the .1 GPH spread at this fuel flow (6.3), or was that tight spread at a lower altitude/higher fuel flow? What is your TO FF?

That was leaned to LOP at altitude. I will typically lean a little on climb, but not go to LOP until I reach cruise altitude. I was curious about my FF at takeoff due to a different thread, so I looked at it a couple of days ago. My home airfield is at 2100 feet (KVGT), so I donít have a number for sea level, but on takeoff at that altitude I was showing 15.6 GPH.

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