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239 Posts
Discussion Starter #101
Long time since i posted,because i was sorting out the fuel pressure drop at full boost.Atlast it has been sorted out.took a month by trying to figure out where was the hinderance to fuel feed.
The datalogues showed very lean AFR's at 1 bar boost and injectors were at 100% duty cycle at top.i was using AEm 310 LPH fuel pump and 1000 cc FIC injectors which should be fine near 800 hp but mine was near 400 hp+-.After raising fuel pressure still no avail.
Already i have a mechanical fuel guage in engine bay but could not see the fuel pressure inside the car while driving.So to figure this out i installed a digital fuel pressure guage inside car and which told the whole story.

The pressure dropped at full boost,from 4 bar to 1.5 bar.very lean under full boost (15.4 Afr,Thank God engine did't blow)
Initially i thought the OEM feed lines were smaller diameter inside.
The inner dia is 5.2mm(Equals -AN5). But outer fitting is 3/8(equals -AN8) which is should be near 9 mm. So that means Honda used thick plastic here which reduced inside diameter.

So i bought new PTFE -6An steel braided line and installed it from here to engine.(i thought the OEm feed lines have many bends in them so a staight line will help)

All way to engine bay,but still no benifit.

So next i searched and found that may be the OEM wiring is not thick enough so fuel pumps is not getting its desired ameres to fully pump the fuel.
Got a 12 AWG thick copper wire and passed all way from battery too fuel assembly.

I used a 4 prang relay,40 Amps, the digram used

OEM feed line cut. The wire end coming from ECU will join Relay 86 and the wire to the fuel pump will join realy 87. Number 30 of relay will join my new 12 awg wire. 85 is ground which i attached to rear seat belt bolt.also 12 awg thich copper wire here.

As the wiere from battery to relay was thick but still from relay to fuel pump was OEm thin i added another wiere to it

Relay wired


Done.and tugged

But the promlem persisted.same fule pressure drop.
now i was frustrated. I thought my return(OEm EVAp) line is restrcition. So i drilled it to bigger bore.

Underside of my reutn line

Drilled with 6 mm bit

Aaaaaand still no benefit.same pressure drop.
I was thinking may be my fuel pump is not enough and i was ordering a 450 walbro. But online seaches showed 310 LPH pump should be good apto 800 hp.
Frustrated i opened the fuel assembly again to look may be some loose O-ring or some other season.
and by close imspection i found the OEM feed is quite complex.almost 180 bends and too many factors playing.and the fuel pump pumping in a closed space,not in a pipe


239 Posts
Discussion Starter #102 (Edited)
After removing the pump,lets cut the OEM feed mechanish and install a direct new feed line

New PTFE line

Installed on fuel pump.

Dont worry that the pump pump is held only by zip tie,there is a strong plastic plate underneath the fuel pump which holds it tight. I used zip tie to make it extra stable

Another view

Now lets open up the OEM fuel feed hole

Removed the check valve,(now i will have to be extra cautious of driving with near empty fuel tank)

Still frustrated that no factor should be un left now,i opned a hole saw hole under bottom where fuel filter will be.Now the fuel pump will not depend on this hole for feed,it will directly pick up under bottom of fuel tank.(no more worry of driving with low fuel tank)

After every thing is done.removed all extra parts in that closed OEm feed space,although now its does't matter as i have bypassed it.

Aaaaand i am so happy that fuel pressure is not dropping anymore.instead it rises with boost with 1:1 as it should be. The AFR were below 10. I had to tune and had to remove near 40% fuel and still duty cycle is only 48%. So i am so glad that the problem sorted out.

A pic during my self tuning session

So now that i have experimented all this.if i had to do this what i will do in this order.
1. Use OEm feed lines,Oem EVAp line a s return.
2: Install fuel rail,injectors, FPR.
3:Open fule pump assembly,install feul pump and install a direct feed line by bypassing that Honda close fuel compartment altoghather.
4:drill out OEm EVAp (our return) to big hole
This should be enough to support near 600 Hp.
5: Remove the back check valve
6:Optional... Remove the underside plastic where fuel filter is
7 Optional :Upgrade fuel pump wiring.I think it was not needed in my case but now its done.(i have read that late honda models OEm wiring is quite enough).

So here we are.completing the fuel setup atlast.i am booking my time with dyno and tuner in next week may be. i am hoping near 550 hp.
i will keep posted InshaAllah.
and in future i may install oil cooler.That is the last on my mod list in this build.the oil temps are with in normal range now but i think when it will be 500+ hp,i may need seperate oil cooler.
Sorry about spelling mistakes as i have no time to prrof read.its getting so late and i had so busy day with all this stuff.very tired also.but was worth the effort ☺

239 Posts
Discussion Starter #103
Atlast dyno tuned. 4 port boost solenoid was giving problems controlling boost.So we stopped at 450 WHP,397 WTQ. Equals 511 BHP

Here is video of dyno
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