Injector Sizing Calculator

[0HP930]

Along with all the other stuff I have been trying to figure out lately is what size injectors I will need for my FI mods.

Since I know some of you are thinking about tweaking your injection systems I thought you might find the following resource helpful.

Not only do they give you the scientific equations to estimate your FI needs but they also have a convenient calculator at the bottom of the page.

http://www.rceng.com/technical.htm

Enjoy

[HybridSS]

Yeah...saw that. I think those calculations are a bit conseravtive..although there is nothing wrong with that. Better safe than sorry when fuel is concerned. Mainly about the 80% duty cycle...I dont want to approach 100% but I am not afraid to run at 90-95% for short periods. If I were starting from scratch I would use exactly what they prescribe here. That way your guarenteed to have ample fuel.

[Matt Vassallo]

so wtf did you choose to go with anyways


100% is for men

ive never had one of my injectors stick open

[0HP930]

Since the auxillary injector controller I just bought has a two injector harness and I am looking to go about 200 HP over what the stock system can handle it appears I will need 2 650 cc injectors.

Anyone have a couple for sale?

[Mr 2]

my 72lb(750cc) injectors seem to be right for me, but I have aready seen all these calculators

[ghuey]

Also if the motor is supercharged you need to account for the horsepower it takes to spin the charger.For example,gsr 200 hp at the wheels should equal about 235 at the crank.But is actually closer to 255 at the crank.So you need to adjust for paristaic loss when figuring the size injectors you are going to run,I imagine the vehicles accessories should be figured in the equation as well..Maybe that is why rc's estimates seem a little high..



~Guy
AE

[HybridSS]

ghuey.....I now what your saying but I believe all that is accounted for. The HP figures are for the motor and the BSFC changes will approximate added losses or ineffiencies for supercharged or turbo motors. As for accesories I am not sure.

[Matt Vassallo]

well it all makes sense that if you put the engine and only the engine on a chassis dyno or whatever it is called ( you know the kind that hooks straight to the crankshaft)

that the calculations will probably alot closer to what they are in real life.. as for me i feel theres only three real sizes of injectors that must be needed.. or hell.. anybody can get away with 720ccss. they always seem to idle good with a good sequential ecu..

[0HP930]

I agree with mattback since any good modern ecu can control FIs well enough to make a set of 750s run great on a motor that doesn't need even need half that much.

Then again, the big injectors are usually more pricey so it makes sense from a financial and engineering standpoint to get a set matched for your max output.

With so much controllable variance on a turbo it certainly makes sense to run bigger sizes than what you think you might need.

If the cost is not much more I just may buy a set of 750s even though I'm calculating I can get by with a set of 650s so I have some extra fuel if I need it.