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Depends on the mods you have or plan to go to.. and also the injectors the ITB's are designed to use.
I run 560cc Bosch injectors in my TWM's they run at about 60% under full load. I use about 1 litre per 1/4mile run, return trip and 10min of idling.. so I get about 2-3mile per gallon
 

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non vtec said:
Depends on the mods you have or plan to go to.. and also the injectors the ITB's are designed to use.
I run 560cc Bosch injectors in my TWM's they run at about 60% under full load. I use about 1 litre per 1/4mile run, return trip and 10min of idling.. so I get about 2-3mile per gallon
He's talking about a full race car.

Personanlly, I'd say go for the 550's. The worst thing you'd want is to run out of room with the 440's. Play it safe with the 550's. Ron has said he's seen no loss of daily driveability when 550's are used.
 

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yes, we ran RC 550cc injectors in a completely stock RSX-S for six months straight with no problems whatsoever. Both Bigdawg and [email protected]/Speedwerx have been running on these injectors too since they upgraded cams.

Hondata has stopped carrying 440cc for the RSX and stocks 550cc, 650cc and 750cc RC high impedance saturated injectors.

-Ron
 

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What is the stock injector flow rate? :confused: Would 720cc injectors be way overkill? For N/A
 

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NickZED20 said:
stock on RSX-S is 310cc, on all other USDM K-series its 270cc

and 720cc is WAY overkill... thats for mild to moderate extreme turbo setups
do you have info on the stock tsx injector cc? would it be 310 the same as type s or bigger? and what is the type r cc?
 

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OK here's my pov backed up with a bit of maths :)

This is based on information contained within the book 4 stroke tuning by A. Graham Bell. Which is turn is based on real world experience of hundreds of hours of testing on an *engine* dyno. This is not specific to the K20 but the princples remain the same. All hp numbers are crank NOT wheel which is the way it should be.

An engine will make the best power with correctly phased sequential injection when the duty cycle is 60 – 70% - this only applies to sequential not batch where there is no difference between running 65% up to 85%

The formula given for calculating the approx. amount of fuel flow needed per cylinder for petrol burning engines is:

Fuel flow (cc per minute) = HPxK/C where HP = max horsepower K = 4.6 for NA engines and C = number of cylinders. So if 250hp was the target the answer would be 287cc. The next step is to find what injector size needed to provide that flow while keeping within your desired duty cycle so:

Injector static flow (cc per minute) = TFx100/NxM where TF = theoretical flow, N = number of injectors per cylinder, and M = injector duty cycle percentage

So TF = 287, N = 1 and M = 65

287 x 100/1 x 65 = 442cc injectors.

Now how do these formulas actually work with what Honda has given the K20. Honda of course has to worry about emissions, cost etc as well as peak output. If we run the numbers again using a 75% duty cycle for a 200hp engine we end up with an injector size of 307cc, which in my book validates the above formulas.

There is also a formula for calculating the effect of raising fuel pressure to save money on buying new injectors (presuming that your fuel pump can maintain a sufficent fuel flow).

Basically it say’s not to go above 4 bar and @ 4 bar we can expect a figure of 331cc running the standard 310cc injectors (formula is to tricky to lay out here) – this is based on them being rated at 310cc @ 3.5bar. So we’re still screwed…

Now the moral to this story is not to run injectors that are to large for your desired hp target. You will lose power! This is because your duty cycle will be to short for the best fuel atomisation and engine cooling. But 440cc injectors are right on the money for around 250hp.
 

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Looking at the underlying theory can be useful to give you a place to start or to explain results, but nothing beats empirical observation: on my NA engine 650cc injectors made the most power. On the dyno there was not much difference between injectors ranging from 440 – 750 cc (stock 310 cc were too small), but 650cc injectors made the most power, by a very small margin.

For most serious NA engines 550cc injectors work the best (better than 440cc injectors in all characteristics); for forced induction 650cc or 750cc injectors.
 

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Rubber Chicken said:
Looking at the underlying theory can be useful to give you a place to start or to explain results, but nothing beats empirical observation: on my NA engine 650cc injectors made the most power. On the dyno there was not much difference between injectors ranging from 440 – 750 cc (stock 310 cc were too small), but 650cc injectors made the most power, by a very small margin.

For most serious NA engines 550cc injectors work the best (better than 440cc injectors in all characteristics); for forced induction 650cc or 750cc injectors.
I completely agree, these are generic formula's but they give a good starting point. Something else that I need to confirm (maybe it's in the manual) does the K20 switch from sequential to batch injection as rpm rises (sequential injection is useful for emissions at low rpm)? If this is so (and I *think* it is) then running up to a 85% duty cycle will not make much difference in power compared to say 60% - this also ties in with my calculation based on a 75% duty cycle for a stock K20. If batch injection is used then you can get away with smaller injectors at little or no cost power wise (subject to confirmation on the dyno). In saying that your practical experience has proven otherwise...
 

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The ECU runs sequential injection under all conditions (except for when the crank or cam sensors are faulty).

I don't think changing duty cycle is a big influence on power. Moving the injector further upstream might be a better place to look.
 
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