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swapping injectors

Simon Hitchen

Well Known Member
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
 
Moving injectors won?t 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 doesn?t produce the result you want.
 
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.
 
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.
 
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.
 
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Mike,
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.
Mark
 
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'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 don?t have a number for sea level, but on takeoff at that altitude I was showing 15.6 GPH.
 
Pretty impressive Mark. Gives me hope for the -8 yet. In my experience the Bendix system goes haywire below 2GPH/per cylinder, so I'll have to do some more work.

Also, 20 inches of MP at 11.5 is something to be proud of. It seems you have a well scienced combination.

BTW, you will see my -8 "Old Crow" tied down at VGT transient in a few days.
 
Great results

Thanks for the help guys. I contacted Don at Airflow performance, he recommended four new injector nozzles of differing sizes based on my Gami data.
I installed them last night and went flying. Took less than 10 minutes and $112.
The results are exactly what I wanted. All cylinders balanced and peaking at the same flow. I’m able to in 50 to 100 lean of peak smoothly and balanced. GAMI spread 0.1.
BEFORE
C60-D0-E3-D-1-AF9-48-A9-9-CFA-3-ACDDE4714-C5.png

AFTER
62-B0-DE6-A-C211-41-EA-87-CE-0-CA3-D239-BD2-E.png
 
Sizes

I went with 0.024” on cylinders 3 and 4,
0.023” on cylinder 1 and 0.0235” on cylinder 2.

Stock injector size is 0.028” so I enrichened the servo mixture slightly to Ensure I get adequate flow on take off. It seems to work as I get 17.0 gph on take off and a 50 rpm rise when aggressively leaning at 1000 rpm ground idle.

It may be my eager imagination but I’d swear it runs smoother too :)
 
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It may be my eager imagination but I’d swear it runs smoother too :)

The smaller injectors increase the downstream fuel pressure from the servo and help better atomize the fuel. It also helps a little in reducing the boiling point temp at low RPMs. Don recommended .024's for my 320 and 025's for my 540.

Larry
 
The smaller injectors increase the downstream fuel pressure from the servo and help better atomize the fuel. It also helps a little in reducing the boiling point temp at low RPMs. Don recommended .024's for my 320 and 025's for my 540.

Larry

Yes, and I am (or was) running .022 in my IO360 on 91E10 fuel for that same reason. I had to boost my fuel pressure to the servo in order to get good takeoff fuel flow, with electric pumps and an adjustable regulator.

I'm currently in the process of installing the SDS EFI system.
 
What made you change from the Bendix to the SDS?

More precise control over mixture distribution and ignition timing, especially LOP at high altitude where I spend a large amount of time. The RSA-5 and Lightspeed Plasma was good - the SDS is just better.

I did the install plus a full panel rebuild and annual inspection, and got the first engine start this afternoon on the new system. Tuning it now and I'll get some airtime tomorrow.
 
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