Quoted from the Helms manual:

"When the difference between the fuel pressure and the manifold pressure exceeds 43psi [for b18b], the diaphragm is pushed upward, and the excess fuel is fed back into the fuel through the return line."

This enables the fuel pressure to be 43 psi at atmospheric pressure. But at say 9 psi, the fuel pressure would be 51 psi, right?

Just checking to see if I have this right.

 

I also was wondering how the stock fpr acted under boost. I was told I should leave it open to atmosphore, because with a 12:1 fmu I would run really rich, also that I want the 12:1 fmu to react to the boost and the stock not to see boost. What do you guys think?

 

Also, couldn't I run check valves to it to make it not see boost? I'd rather not up the pressure so that I can keep the pump flowing as good as possible.

 

Mine rises under boost 1:1, some people say they don't some do. I've verified mine with a in car fuel pressure gauge.

 

yeah.....that sounds right.....thats what I figured it would do....thanks.

 

best way to verify is with an in-car gauge. the FPR on the '99-00 civic Si only rises from vacuum up to atmospheric, and does NOT rise under boost, but it's quite possible that the LS FPR acts differently.

-Xerxes

 

very interesting. if my FP gauge went high enough, or my cartech had a marking ont he rise rate adjustment, i would check this out. there is probably a certain point beyond which it is incapable of raising the pressure...

 

XERxes, how can a regulator not rise under boost 1:1 if it has a line hooked up to the manifold. that doesnt make sense

 

I think the question is:

Is the the stock FPR's diaphragm already fully closed at atmospheric pressure or is there more room to block the fuel to the return line with positive boost pressure?

 

To The Top

 

correct. the stock sping in the frp is pretty weak so the fuel pressure does raise. I see about ~56psi of fuel pressure at 15psi with the stock fpr. Its pretty much 1:1.

liam

 

I was looking at the design in the Helms manual more and it HAS to go up 1:1. Thats just how it works: it compares fuel pressure to air pressure.


[Modified by 00SilverLS, 4:04 PM 11/28/2001]

 

Right, but it is limited. The FPR will eventually close the return line off completely and the pressure will not be able to further rise with boost pressure. In other words, the fuel pressure will stay at a fixed psi (in liam821's case 56psi) until the boost pressure falls back down.


[Modified by quick108, 1:13 PM 11/28/2001]

 

ya i have never seen it go much higher then that.

liam

 

My stock FPR does not rise under boost. I verified it with an in-car fuel pressure gauge. I've seen the same behavior on 3 other 99+ Civic Si's as well as 1 2000 ITR. Yours may rise under boost....the only way to tell is to test.

Sonny

 

i have a greddy fuel in-car fuel pressure gauge...and the pressure does increase with boost. Although i have a sohc engine. Maybe the fpr in the b-series engines are stronger? Anybody know?

liam

 

You guys do understand that the 1:1 FP increase is not enriching fuel right? It is just compensating for pressure in the manifold to keep fuel delivery constant.

Dustin