Alright, I've got a b20v with a GSR head that I'm looking to run off of stock 240cc injectors for a while. That is until I can afford a pump, bigger injectors, NepTune RTP and tune. And I would love if someone with more knowledge and experience would be able to provide me with some guidance in my findings.

That being said, I have purchased a new AEM FPR and gauge and I'm already running a Wideband.

Essentially, I'm trying to properly calculate the estimated amount of fuel pressure I'll need to run, in order to satisfy my AFR's on a Phearable Basemap.

Conservatively speaking, I estimate my power to be ~180 to the crank (being fully bolted, stock internals/cams, 2.5 exhaust). In using a P28v ECU which comes from the 92 Civic Si, we know they produced ~125HP.

180/125 = 1.44%

Which provides me with a need for 44% more fuel than that of the base Si.

I've read that the rule of thumb is to utilize the square root of the pressure difference and the quotient will equate to the percentile change in fuel delivery.

Essentially, I need to square the percentage increase:

1.44 *1.44 = ~2.1

Lastly, to produce a fuel pressure estimate, I multiplied the squared product of 2.1 and then multiply by 35 , which is the PSI for a 92' Civic Si.

2.1*35 = 73.5PSI

I do understand that running the stock injectors at this pressure is (quite) poor for the fuel's atomization, so that is another hurdle I would love some opinions over.

Thank you for any input.

 

If you have a wideband, why do you need to guess at your fuel pressure? Set it at 40psi, do a pull and watch your afr's. Adjust pressure as necessary and repeat.

Did you not tell the person that made the basemap what your setup was? I would think a stock GSR map should get you pretty damn close. At least enough to drive around on.

 

Yes, I gave Phearable all the pertinent information. I'm just over-thinking things as I always do. Really it was just a means of figuring things out theoretically and then apply the logic.

 

You don't go by vacuum connected fuel pressure, you go by vacuum disconnected at the FPR for base pressure since this will be the condition under WOT. I assure you that you won't need 44% more fuel at idle on your setup, but theoretically it would be possible for that fuel requirement increase at WOT.

It is neat and all you are trying to figure stuff out on paper before hand, but in this world of modification it will only get you so far and is almost pointless. It is great to very roughly get you in the ballpark and adjust accordingly. Stock injectors absolutely do not like high fuel pressures especially at low duty cycles. You need to have the car properly tuned on a programmable EMS rather than play games with your engines welfare.

 

here is a good webpage from rc. it has some tech info and a calculator too

http://www.rceng.com/technical.aspx?...JwJPlAF1sCF5ld.

that said, yes you set the fuel pressure with the vacuum to the regulator disconnected. i was in the same boat as you (wideband,regulator,stock injectors and a motor that needs more). i used the rc website to figure out about how big id need the injectors to be and then how much pressure to run to make them behave that size.

as previously said, do a pull, monitor afr, adjust accordingly, rinse and repeat.


lastly, the fuel pressure is pretty broad, and applies across the whole rpm range. if you ecu is programmed for an engine that makes power at a different rpm point than you new engine, to get your afr right in some parts of the rpm range it may be too rich in others. this is why the best way is still to get a tuned ecu so you can take all that into account.