Smaller injector nozzles, and maybe higher fuel pressure? - Fuelly Forums

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Old 04-19-2010, 12:42 AM   #1
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Smaller injector nozzles, and maybe higher fuel pressure?

I was talking to an engineer friend about heating the gas line, for better atomization, and he didn't really like the idea, saying that if the heat could be closely regulated, it could work, but there are too many variables. However, he reminded me of an idea I had a while ago. My car's injectors flow 220cc/ min, and I have a spare set for the same engine block that flow 180cc/ min.
I'm pretty sure that I can put the 180cc nozzles on the 220cc injectors.
I can set the engine management computer to flow the right amount for my target AFR.
My car begins to miss at idle at about 16.5:1.
I think that the 180cc nozzles will atomize the fuel better, and wanted to get your thoughts about it before I tear it all apart. I can also get an adjustable fuel pressure regulator, and raise the pressure, then the EMS would shorten the injector pulse.
What do you all think?
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Old 04-19-2010, 05:06 AM   #2
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Quote:
Originally Posted by fowljesse View Post
I was talking to an engineer friend about heating the gas line, for better atomization, and he didn't really like the idea, saying that if the heat could be closely regulated, it could work, but there are too many variables. However, he reminded me of an idea I had a while ago. My car's injectors flow 220cc/ min, and I have a spare set for the same engine block that flow 180cc/ min.
I'm pretty sure that I can put the 180cc nozzles on the 220cc injectors.
I can set the engine management computer to flow the right amount for my target AFR.
My car begins to miss at idle at about 16.5:1.
I think that the 180cc nozzles will atomize the fuel better, and wanted to get your thoughts about it before I tear it all apart. I can also get an adjustable fuel pressure regulator, and raise the pressure, then the EMS would shorten the injector pulse.
What do you all think?
What I have found to work very well is to run a smaller injector and raise the fuel pressure. So this case you could run your 180cc/min injectors at 67psi to get the same fuel flow that your 220 cc/min injectors would at 43psi.
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Old 04-19-2010, 07:09 AM   #3
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Sounds like a plan and just don't try varying the pressure while you are running or it will drive the ECU trims crazy. You should definately get better atomization with the higher pressure. Also running some Iridium plugs with a larger gap should help ignite the lean A/F mixture better too. It also helps to index the plugs towards the intake valve where the richer A/F mixture is due to the fuel coating the cooler intake valves.
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Old 04-19-2010, 09:06 AM   #4
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Good ideas, but where could you find an engine vacuum operated fuel pressure regulator set for 67 psi. Would it need to be custom made, or could you just cut one open and change out the spring inside?

Or would you use a static pressure regulator- one that did not vary fuel pressure with engine vacuum?
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Old 04-19-2010, 10:51 AM   #5
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You buy an adjustable FPR... Basically it lets you screw/unscrew to set it for the pressure that you want. It still can change pressure based on vacuum/boost.

I was using a SARD FPR like this one on my turbo Regal:



It is adjustable from 200-800 kpa (29.0-116.0 psi)
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Old 04-19-2010, 11:23 AM   #6
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Originally Posted by Erik View Post
Good ideas, but where could you find an engine vacuum operated fuel pressure regulator set for 67 psi. Would it need to be custom made, or could you just cut one open and change out the spring inside?

Or would you use a static pressure regulator- one that did not vary fuel pressure with engine vacuum?
Here's one that I have had good luck with.

http://aeromotiveinc.com/products-pa...le-regulators/

One more thing when running at these high fuel pressures it is harder on the injectors themselves. It can shorten the life on them, but I personally haven't notice a difference.
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Old 04-19-2010, 04:23 PM   #7
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Wow- very interesting. I'll be waiting to hear how it affects fowljesse's mpg.
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Old 04-19-2010, 07:41 PM   #8
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Thanks for all the input!
I can get the 180cc injectors for next to nothing, so I'll stock up How do I know when they're starting to fail? I'll have to keep an eye on the duty cycle in the high rpm. The engine peaks HP at about 7K rpm right now, and will be higher soon.
Through experimentation, it was found that this engine does best with plain ol' NGK V-Power plugs. I have them indexed, and gapped to max. I'm getting coil packs, so I should have stronger spark.
Thanks for the link pgfpro.

I'l post up results as soon as I get them. Right now, I'm doing so much to the car, that I can't get any kind of baseline.
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Old 04-19-2010, 10:39 PM   #9
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This sounds like an interesting idea.
Here's a couple of tips: Some fuel pumps have a pressure relief valve to keep the pump from burning out. Some popular Denso and Walbro pumps are set to open around 65 to 75psi.

Adding fuel pressure also increases injector deadtime, or latency. It's a small ammount but it'll throw off the fuel trims a little.

A friend is using the Sard AFPR on his EVO running 30psi of boost and 43psi base pressure, so it's capable of handling high pressures.
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Old 04-19-2010, 11:12 PM   #10
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Hmm..
I have a Walbro 255L/ Hour @ 40psi pump. I'll read up on it's relief valve, as well as injector dead time (latency), and fuel trim.
I've learned, and am still learning as much as (if not more than) I do on other forums which are catered to tuning.
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