True Injector Sizing...

[Big Al 389]

Ok this may sound stupid but...If a 1G 5 speed injector is 450cc's @36.3 psi of fuel pressure then if the there installed in a 2G at 43 the will be very close to 540 cc's...Correct? Or are they rated at 450 cc @ 43 psi and if so why not just use the same psi fpr and change the sizing?Just curious!

Al

 

[DSM90AWD]

Ok this may sound stupid but...If a 1G 5 speed injector is 450cc's @36.3 psi of fuel pressure then if the there installed in a 2G at 43 the will be very close to 540 cc's...Correct? Or are they rated at 450 cc @ 43 psi and if so why not just use the same psi fpr and change the sizing?Just curious! Al

Fuel injectors are "generally" flow tested at 3 ATM (43psi). I say generally as manufacturers some will test at higher levels to make their Injectors sould larger than they are. Stock DSM injectors flow 450cc @ 43psi.

FYI.. the formula for calculating the new injector flow rate at a different base fuel pressure is SQRT (New PSI / Rated PSI) * Injector Size at Rated PSI.

Stock 1G FP (SQRT (37psi / 43psi)) * 450cc = 420cc
Stock 2G FP (SQRT (43psi / 43psi)) * 450cc = 450cc
50psi Base (SQRT (50psi / 43psi)) * 450cc = 485cc

 

[Nanan]

You will encounter problems with some injectors when you boost the fuel pressure. Injectors can be either ball or disc type, which will effect their performance at different fuel pressure rates. Ball type injectors tend to seize up at high fuel pressure due to the force of the fuel upon the injector being greater then the force of the solenoid. Disc type injectors will work better at higher pressure rates then they will at lower.

If you kick the fuel pressure to 50 or higher psi on the stock ball type injectors you will likely lose fuel flow on the injectors due to cavatation in the flow at the port nozzel.

If you need more fuel flow then you can spike it up a bit by increasing fuel pressure a little. If you need more then a 10-15% increase then you should just step up to the next largest injector size such as 550's.

 

[DSM90AWD]

You will encounter problems with some injectors when you boost the fuel pressure. Injectors can be either ball or disc type, which will effect their performance at different fuel pressure rates. Ball type injectors tend to seize up at high fuel pressure due to the force of the fuel upon the injector being greater then the force of the solenoid. Disc type injectors will work better at higher pressure rates then they will at lower.

If you kick the fuel pressure to 50 or higher psi on the stock ball type injectors you will likely lose fuel flow on the injectors due to cavatation in the flow at the port nozzel.

Actually there are three types of injectors. You forgot Pintle-Style which is what our stock ones are as well as all Denso/Greddy injectors.

Some history, Buschur took 4Banger into the 10s years ago with Denso 660s at ~50psi base FP so guess it was ok for him

 

[tstkl]

Fuel injectors are "generally" flow tested at 3 ATM (43psi). I say generally as manufacturers some will test at higher levels to make their Injectors sould larger than they are. Stock DSM injectors flow 450cc @ 43psi.

FYI.. the formula for calculating the new injector flow rate at a different base fuel pressure is SQRT (New PSI / Rated PSI) * Injector Size at Rated PSI.

Stock 1G FP (SQRT (37psi / 43psi)) * 450cc = 420cc
Stock 2G FP (SQRT (43psi / 43psi)) * 450cc = 450cc
50psi Base (SQRT (50psi / 43psi)) * 450cc = 485cc

so I just bumped my fuel pressure up to 46psi, and I had my car tuned with my gm maf/maft combo. it was set at 450cc, but according to you it should have been set at 420cc, either way I got it running right at 450cc, but now that the base pressure is up from 37 to 46, what should I change my global by to get my tune right. using a straight ratio says I should use 560cc settings, using your equation above says 470ishcc, thats a huge difference. my low fuel trim jumped from 107% to 114%, should I disconnect the battery anyways to reset all my fuel trims now that the base fuel pressure has changed? I changed it to 480cc's but havent driven it yet, that was just my wild guess before I came here to do some research.

I have a headache... didn't try and start the car for long enough with the fuel pump disconnected...

what do you think I should run at?

450/37=560/46
420/37=520/46
the square root (that is sqrt, right?) of 46/43 * 450 = 470
sqrt (46/37) * 450 = 500

i think 500 should be right, but I'd like someone else to agree with me.

 

[DSM90AWD]

i think 500 should be right, but I'd like someone else to agree with me.

Yep, I get 507cc as well.

Remember, this is based on your car running perfectly on 37psi base pressure. As I've heard from several others running the MAFT in blow-thru, the actual compensation can vary +/-20% due to the MAF itself.

Reset your ECU and datalog your fuel trims to verify your results and "tweek" if necessary

 

[tstkl]

im not surprised, so far nothing has been close with a maft in blow through. I was hoping I could simply change my global scale, but Ill be ready for the uber shaft again.

my mid is at like -15%, wot at -25% and idle at +25% I think Ill just change it to 500cc, and if it runs ok at that, wait until I get my wideband o2 sensor installed to make any other changes. no point in doing it the long way when I have the short way sitting right in my lap... just have to get that bung welded and I should be good to go.