Fuel Pressure?

**dsp26** · 07-06-2007 08:13 AM

Originally Posted by Mr_will

fair to say that the rising rate regulator might make more of a difference if you have msd?

bit of a noob when it comes to fuel pressure stuff so willing to stand corrected

as i said an afpr has never really been considered a 'performance mod'. the factory fpr is also rising rate like most other cars just not adjustable.... it will richen/lean fuel mixtures across the entire A/F curve which is why it is labelled a "temporary band-aid fix" until a car is actually tuned by a proper ecu to richen/lean mixtures at different rpm points.

you will gain power somewhere in the rpm range where you have a trouble spot at the cost of power somewhere else... kind of like putting high rpm aggressive cams in a non-vtec car.... they will lose power down low and have a lumpy idle as a price to get top end power and vice versa.

***EDIT***
as stated by this honda tuning dedicated site:

Originally Posted by http://www.phearable.net/tech/efibeginnerguide.html

"What is an fmu?:
A Fuel Management Unit (FMU) is a special rising rate fuel pressure regulator placed in the fuel return line of the fuel injection system. This is a very common approach to handling the increased fuel demand required by turbo kits and supercharger kits. It does work. It will make the injectors flow more fuel than their rating. These are used in addition to the factory or aftermarket fuel pressure regulator and only have an affect under boost.
FMUS are rated by the ratio of fuel pressure to boost pressure. For instance, a 10:1 FMU will give you 100psi fuel pressure at 10 psi boost pressure. "

What he is talking about is a seperate rising rate unit on top of an fpr... the SARD unit is already an adjustable rising rate (or whatever the original poster has... looked like a SARD)
The only thing he is wrong about is the "Flow rate" part as it technically doesn't increase flow.. just forces out more fuel through injectors for every pulse width.

That explanation with the boost is also why i said the above 10% formula isn't exactly correct and only applicable to the rising rate/vacuum operation... and again that 10% figure is skewed by boost pressure in the intake. The rise in rate of fuel pressure is controlled by intake vacuum as well as the fuel pump... each pump provides a certain pressure already which is why the Walbro + AFPR = ???psi shouldn't be taken as gospel either.

**beeza** · 07-06-2007 05:03 PM

Great Input Guys!
I think it's fair to say your just really guessing the psi until you get on a Dyno or hook up a wideband then.
Just out of curiousity If I bump it up a bit how will I know that I am running to rich?

'Black soot in the bumper' = Too rich? Does this mean Blowing black smoke?

**dsp26** · 07-06-2007 07:06 PM

Originally Posted by beeza

Great Input Guys!
I think it's fair to say your just really guessing the psi until you get on a Dyno or hook up a wideband then.
Just out of curiousity If I bump it up a bit how will I know that I am running to rich?

'Black soot in the bumper' = Too rich? Does this mean Blowing black smoke?

like you said no-one can really tell you without a dyno... HOWEVER... i'm not condoning it BUT I was gauging mine based on exhaust pop under a certain load under a certain rev. not willing to dyno now as i'm waiting for one more mod and an ecu so i can spend my $100 on a before/after of the ecu.

Heres another example though... i know my car was more responsive in the midrange at 30psi to lean out compared to stock 37psi with vac line on (vac line off is +~10psi)... however coz pressure was too low.. it's soooo hard to start sometimes so just put to like ~34psi.

***EDIT***
sorry about the emphasis on a few words... just making MY method for MYSELF clear so the nazi's don't go flaming me for dangerous methods.