I've seen a couple of group buys for Fuel Pressure Regulators and plenty f people asking what they are and what they do to your S.

An FPR is the device which controls the fuel pressure in the fuel rail which serves your injectors. Right?

So if I buy one of these FPR's and set it to 47 or 46 psi what difference will it make. If I were to tune it on a dyno, what would I be able to achieve then?

Anyone?

 

A bit more power has been found on the leaner side.. 43 - 44 psi.
http://www.s2000online.com/forums/showthre...hp?threadid=266

 

Why do you think Honda didn't lean it out from the factory? It probably would get better mileage by running leaner and quite possibly better emissions this combined with more power would be a no brainer don't you think? Is it possible they are worried about it running too lean and melting a piston. Possibly when tuned to that fine an edge it does not leave a margin of error for when your fuel filter gets some miles on it and some dirt in it?

I don't think this is an issue of them trying to save some money it is after all just as easy for them to dial in a leaner mixture.

Makes me wonder why they did it anyway.

 

Beig, the factory regulator is the same cheap regulator Honda has used since 1990. This regulator is mechanical and it is nothing near precise. If you look into the service manual, you should note that in the fuel press. rating, the manual gives a range ( I don't remember exactly but it's like 43-51) Why? because the regulator is not accurate.

 

Ok that makes sense.

 

Hey Aus, someone went way deep into this on this very board just a couple of days ago...take a look around...they were talkin' way over my head, but you might be able to make heads or tails of it.

 

Ok guys... I have been waiting for someone to explain this as well. I have always thought the purpose of the fpr was to provide enough fuel to the injectors to meet their needs... in other words make sure they did not starve for fuel thereby not keeping up with the demand. I thought the injectors and the ecu controlled fuel flow to the cylinders. The ecu controlled the start and stop of the injectors and the duty cycle that they were open. I have yet to understand how you can manipulate this by reducing pressure, unless you are starving the injectors. In older gm cars, I have seen the actual ecm programming where fp was regulated to 40 and the ecu would shut down the system and go into limp home mode when pressure was less. It would seem to me... that reducing the fp will artifically lean the engine by starving the injectors... causing the ecu to increase the duty cycle while trying to compensate for the programmed fuel delivery vs the apparent lean condition that the sensors should be telling it that the car is experiencing. It would seem that a controller that could modify the fuel maps would be a more efficient method to do this. On the other hand... if we were talking about FI, then the fpr would be a no brainer so as to allow for increased fuel pressure to meet the needs of the injectors to match the increased volumn of air into the cylinders.

 

As I understand it, the mixture is variable and regularly adjusted (reading the oxygen sensors) under the control of the ECU, but at WOT is controlled by a preset mapping.
With this design there is some room for tuning for a couple of reasons.

Since there is such a big variance in conditions that with fixed WOT fuel mapping Honda had no choice but to tune so that the engine would not go lean. This means that at WOT in very warm climates the mixture may be a bit rich.

The fuel pressure regulator is reportedly a pedestrian part that has been around for years and is not known to be extremely accurate. The factory range for the fuel pressure spec is 7psi wide.. not very precise.

Fito and Pepe started fooling with pressure thinking as they change the engine it may need more fuel. What the found on the dyno was quite a few HP by leaning the mixture. They have since made a recommendation that a few of us have tried.

I have concluded that the recommendation of 43 psi is great for 80F and above but maybe too lean for colder weather. A few drives and I decided to move closer to the middle of the factory range for the 35F I have been testing in. I will use a one gear test timing (as recommended by Luis) since I won