Injectors

[mattyb]

Read this and thought... that needs to be on the forum.

So, how much power is this injector good for? That depends on the air/fuel ratio that is used, but a good rule of thumb is to divide this flow figure by 5 to get a hp capability. So, 322cc divided by 5 = 64hp maximum fuel flow with this injector. If you want to be pedantic, it's the mass of the fuel (not the volume) which is the critical factor. Assuming a "normal" fuel density, the mass of the fuel in pounds per hour can be worked out by Dividing the cc per minute figure by 10.5. For this injector, that gives a mass flow of 30.6 pounds/hour. To convert from pounds/hour to horsepower capability, multiply the figure by 2.04. So 30.6 pounds/hour multiplied by 2.04 gives a horsepower capability of 62.4hp - the same as we got from the cc/minute figure.

The power ratings discussed above are for each injector. This means that you need to multiply this rating by the number of injectors that are to be used. So, if you were using the Impulse RS 322cc injectors in a 4 cylinder engine (with one injector per cylinder) the max power that the injectors could deliver fuel for would be about 249.6hp. All of these figures are assuming that you are running an average fuel pressure of ~43psi and at 90% duty cycle.

Conversions

500cc per minute is approximately equal to 49lbs per hour which is equal to approximately 100hp.

lbs/hour = cc per minute / 10.5

lbs per hour = HP / 2.04

cc per minute = lbs per hour x 10.5

cc per minute = HP x 5

HP = cc per minute / 5

HP = lbs per hour x 2.04

[jim985]

I thought id test your info out.

If we take 42Lb injectors, which ppl claim max at 350 RWKW.

42 * 2.04 = 85.68 HP

85.68 * 6 (injectors) = 514.08 HP

using a BHP to KW converter = 378 KW

So if you take into accout losses between the fly wheel and the rear wheels being approx 20% then you get 302.4 RWKW.

If instead you convert 42lb/h to cc/min first

42 * 10.5 = 441 cc/min

41 * 6 injectors = 2646 cc/min

2646 / 5 = 529.2 HP = 389 KW

approx 311.2 RWKW

Did I do something wrong with my calculations to get 2 different answers?

[IH8TOADS]

You would need to convert to 4bar base fuel pressure. 441cc is at 3bar.

IMO it's very well known what size injector these cars require for X amount of power.

[PHANTMXR6]

Are all calculations done based on 100% efficiency, or something lower?

[mattyb]

Maybe one of the tuners cn elaborate on what I found. It's not my work, just something I found and thought could draw some info and eyes to the subject here on the forum.