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Old 01-18-2020, 09:19 AM
Simon Hitchen's Avatar
Simon Hitchen Simon Hitchen is offline
Join Date: Apr 2006
Posts: 296
Default 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
Simon Hitchen
Port Perry, ON, Canada
7 Tip Up, Titan XIO-360, Dual P-Mags, Airflow Performance matched Injectors, Sensenich FP Prop, Dynon Skyview, GTR-200, GTX-327
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Old 01-18-2020, 09:33 AM
JonJay's Avatar
JonJay JonJay is offline
Join Date: Jan 2007
Location: Battleground
Posts: 4,348

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.
Smart People do Stupid things all the time. I know, I've seen me do'em.

RV6 - Builder/Flying
Bucker Jungmann
Fiat G.46 -(restoration in progress, if I have enough life left in me)
RV1 - Proud Pilot.
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Old 01-18-2020, 10:17 AM
Bavafa Bavafa is offline
Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,435

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.
N825SM RV7A - IO360M1B - SOLD
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Old 01-18-2020, 10:34 AM
Papa Papa is offline
Join Date: Apr 2007
Location: Las Vegas, NV
Posts: 124

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.
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Old 01-18-2020, 10:39 AM
tommylewis's Avatar
tommylewis tommylewis is offline
Join Date: Jan 2005
Posts: 773
Default 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.
Tom Lewis
RV7a N967BT 1900 hrs.
RV10 N143EB 960 hrs.
Granbury, Tx
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Old 01-18-2020, 11:34 AM
Toobuilder's Avatar
Toobuilder Toobuilder is offline
Join Date: Jul 2009
Location: Mojave
Posts: 4,716

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.
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
Harmon Rocket II -SDS EFI
1940 Taylorcraft BL-65
1984 L39C

Last edited by Toobuilder : 01-18-2020 at 11:36 AM.
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Old 01-18-2020, 12:49 PM
Papa Papa is offline
Join Date: Apr 2007
Location: Las Vegas, NV
Posts: 124

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.
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