injectors

[twilightprotege]

hey guys.

can someone confirm the size of the p5's fuel injector??? ditto with the mazdaspeed injector???

the reason i ask is that i'm sure i've read somewhere that we have a 220cc/min fuel injector

now working through some formula's i have (the bible - sport compact car hehehehe)....i have a few interesting facts that might prove a few people's horsepower claims very very very wrong (or their engine is about to melt...one of the other)

later

 

[sal002]

Based on your above assumption - what are the facts?

 

[boostisgood]

The MSP has 285 cc injectors. the same as the P5. The MSP Fuel Pressure Regulator is set to 43 lbs per hour. (this from Chojin at Mazdaformance)

 

[Micah]

yep, - and just for reference, the ES, p5, MP3, and MSP all have the same size injectors. You can bet that the LX and DX probably will also, though I haven't had a chance to check yet.

Last night it was explained to me by Nick that with our stock injectors, the safest HP you could run would be about 180, which fits up just perfectly against the HP of a stock MSP.

However, with a Fuel Pressure regulator and a larger MAF Sensor, and maybe even a larger throttle body......

I'm still learning.

 

[twilightprotege]

well......horsepower of an engine is limited to the amount of fuel it can burn...more fuel, more power (with appropriate more air ofcourse)....less fuel, less power.

now, assuming a duty cycle of 80% on 285cc/min injectors, the maximum amount of power in n/a trim the engine should produce is around 173hp. 100% duty cycle is 217hp.

now for turbo charged engines...this is where is gets interesting. because turbo engines have more air, they need more fuel. on 285cc/min injectors, the max power on 80% duty cycle is between 144 and 173, 100% duty cycle is between 180 and 217.

so that leaves me with the assumption....either people are bending the truth, or, their engine is about to go into terminal meltdown

since i'm in australia it's 11pm and i'm about to go to sleep...i'll explain more about this tomorrow....

 

[Micah]

yep, what he said - exactly. Dyno shoot out is coming though. I'm sure someone will bring a stock MSP, ES/P5, MP3.

Now someone lend me their P5 and a sawsall, I'm gonna make a truck!

 

[twilightprotege]

ok. further to my comments previously.

to work out a given injector size for the amount of horsepower you want to create is a simple formula.

( ( Horsepower * BSFC ) / (Number of injectors * Duty cycle) ) * 10.5

this will give you the cc/min you require to make a given horsepower for ANY engine.

now what is BSFC? that stands for Brake Specific Fuel Consumption. basically what that is is a rating of how much fuel an engine required for a given horsepower output....in other words the amount of fuel per hour an engine needs for each horsepower it makes. typically a well tuned 4 cylinder naturally aspirated engine uses 0.5lbs of fuel per hour for each horsepower it creates. a well tuned 4 cylinder turbocharged engine uses 0.6lbs of fuel per hour for each horsepower it creates.

Duty cycle? Well most injectors can only handle 80% duty cycle, that means it will flow 80% of what it is rated safely...anything above that and you're asking for trouble. for example, most injectors will only open halfway above 90% duty cycle...what does that mean for your engine? not enough fuel....lean burn....no, very lean burn...terminal engine meltdown.

now back to the formula, we want to work out what size injector we need to safely make 300hp in turbo trim....so we just plug the figures in :

( (300 * 0.6) / (4 * 0.8) ) * 10.5

= 590.63cc/min

now if we rework the formula so we can find out what the maximum power an injector size can create safely we get :

Injector Size / (BSFC / (Number of injectors * Duty cycle) ) / 10.5

so using the stock injectors in n/a trim...we get

285 / (0.5/(4*0.8)) / 10.5

which equals = 173.71hp

before some people start to argue the fomula, it is 100% correct. it is not my design or anything, ask some professionals and they'll give you the same if they know what the formula is.

so this leads me back to my previous comment. there are 3 issues i have with some peoples horsepower claims.
1) the injector size we have is not 285 (which i would find very hard to beleive that mazda would put larger injectors than that for the n/a cars, maybe a little larger for the mazdaspeed)
2) they are bending the truth a little, or
3) terminal engine meltdown is only seconds away.

later