Injector question

[blk_srt]

Does anybody know the formula for converting psi to cc's? I got offered a set of slightly used injectors and he said the were 42 lb injectors and that doesnt mean a whole lot to me. so any help would be good

[EDMUND65]

I'm a dumbass, looking around online i foudn a conversion website, so i posted... proly have reply in morning...

http://www.convert-me.com/en/bb/view...hp?p=5466#5466

[kjewer1]

Most poeple use 10 to 10.5 as a conversion factor. The problem is that none of the simple conversions take into account the specific gravity of the test fluid. I like touse the SG of pump gas or race gas depending on what the primary use is going to be. I can run through the calculations for anyone that may be interested. There is no easy way to do it in this case, since the SG of the test fluid is not mentioned, but if it was the other way around we could do it (cc to lbs). We'll assume a SG of .76, which is approximate for pump gas, for the sake of exercise.

That number would be 42 lbs/hour. Water is 8.33 lbs/gallon IIRC, so at a SG of .76 that's 6.33 pounds/gallon. 42/6.33 is 6.63 gallons per hour. That converts to metric easily enough, 23.96 liters per hour, or 23960 cc/hour. Divide by 60 to get to minutes, 400 cc/min. The "conversion factor" in this hypothetical example is 9.5, but again, without knowing the accuracy of the SG figure of the test fluid actually used, it's still a rough guess. A safe guess though, odds are these injectors do a little better than 400 cc/min.

www.rceng.com used to have some calcs. Yup, still there. They use 10.5 as a factor. This gives us 440 cc min, roughly stock DSM size. But again, it's just a guess.

I personally only like to buy injectors that are rated in VOLUME flow, as opposed to MASS flow. You can then use the calculation I did above knowing the exact SG of the fuel you intend to run and it's balls on every time. For example, I use .76 for pump gas, and .724 for Sunoco 117 octane race fuel (the SG for just agout every race fuel is online), and it's always accurate to a surprising degree. At any rate, I prefer volume measurements for injectors. If you send the injectors out for cleaning and testing, you'll get the volume measurements, which is a good way to be sure the injectors are what you thought they were, without risking your setup.

[blk_srt]

Originally Posted by 95 GSXracer

Most poeple use 10 to 10.5 as a conversion factor. The problem is that none of the simple conversions take into account the specific gravity of the test fluid. I like touse the SG of pump gas or race gas depending on what the primary use is going to be. I can run through the calculations for anyone that may be interested. There is no easy way to do it in this case, since the SG of the test fluid is not mentioned, but if it was the other way around we could do it (cc to lbs). We'll assume a SG of .76, which is approximate for pump gas, for the sake of exercise.

That number would be 42 lbs/hour. Water is 8.33 lbs/gallon IIRC, so at a SG of .76 that's 6.33 pounds/gallon. 42/6.33 is 6.63 gallons per hour. That converts to metric easily enough, 23.96 liters per hour, or 23960 cc/hour. Divide by 60 to get to minutes, 400 cc/min. The "conversion factor" in this hypothetical example is 9.5, but again, without knowing the accuracy of the SG figure of the test fluid actually used, it's still a rough guess. A safe guess though, odds are these injectors do a little better than 400 cc/min.

www.rceng.com used to have some calcs. Yup, still there. They use 10.5 as a factor. This gives us 440 cc min, roughly stock DSM size. But again, it's just a guess.

I personally only like to buy injectors that are rated in VOLUME flow, as opposed to MASS flow. You can then use the calculation I did above knowing the exact SG of the fuel you intend to run and it's balls on every time. For example, I use .76 for pump gas, and .724 for Sunoco 117 octane race fuel (the SG for just agout every race fuel is online), and it's always accurate to a surprising degree. At any rate, I prefer volume measurements for injectors. If you send the injectors out for cleaning and testing, you'll get the volume measurements, which is a good way to be sure the injectors are what you thought they were, without risking your setup.

Kevin, you are a genius. Correct me if I am wrong but aren't stock injectors 450cc but only flow up to 30lbs/min?

[kjewer1]

STockers are 450s, what airflow they support depends on several factors, like fuel SG and target AFR. 30 lbs sounds about right for a typical example if I remember correctly. People have pushed them farther on race gas and very lean AFRs, but most poeple aren't interested in running like that. The 42 pounders definitely don't sound like something a turbo DSMer would looking to install...