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Cars tunned, Now upgrading fuel system


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Hi all

My cars currently tunned with OE intank fuel pump setup (uprated pump) r32 skyline rb25det

Im building a drop in surgetank/bosch 044 setup which is going to be in the usal spot in the boot and will work in conjunction with the intank unit

stock fuellines at this stage still in use, Adjustable fuel pressure reg fitted to car with my base at 50Psi current tune

Im guessing the fuel pressure reg is going to maintain pressure with the 044 in use but would like a tunner on here to confirm this
Also if there will be any fuel flow differences from this change?

I know what afr my car is sitting at at idle, WOT/highest load and between etc

I hope to simply check and confirm my afr (LM2) on the road and track with my new fuel system, and try to avoid highering a dyno if i can lol


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If fuel pressure stayed the same under all conditions after upgrading then you would not need to change any of the tune.  However this is probably unlikely depending on how good the old system was.  Usually the old system was a bit marginal (otherwise you wouldnt upgrade) so you will probably find that your old fuel pressure was dropping away under high load/boost and now with the bigger pump it will probably stay closer to where it should.  This will make it run richer at the top end.  Usually if the regulator etc is good quality you will probably not see much difference at idle/low loads. 

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the old system is perfectly up to the job as it is, i dont have an issue with fuel pressure dropping off at higher load points as we made sure of this last dyno,

simply adding a surgetank set up with 044 for track work ; )

will my sard regulator be up to the task with this added flow/pressure at lower load and idle etc?

thanks adamw

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  • 1 month later...

.....managed to get out a check fueling with new setup and did a short amount of logging, prior to that

Fuel pressure at the regulator gange seemed to stay the same as what it was with old intank fuel system which was good

while out on road AFRs seemed to be leaner below 130- 140 kpa between 2000 and 4000 rpm lower load areas
While at higher rpm and load afrs are on tracking well and AFR starts driffting rich which was to be expected

also car did not sound of the usal tone also seem just a touch unresponsize then usal.

Basicly 'seems' as if the old intake walbro was holding higher pressure at lower rpm and load (5psi-) then the 044 currently is.....

Fueling at high rpm and boost levels seems to track as it should and eventually getting richer beyond 5500rpm which was to be expected based on the the 044 stable flow data

voltage at 044 terminals with engine running at idle is 13.58v

No real other fuel plumbing changes have been made apart from moving the stock filter in engine bay to the boot where my surge tank setup is

Base pressure at regulator set by tunner last time on dyno is 60.4 psi which is high due to the car only having 440cc injectors and the poweroutput

will edit logfile and upload shortley

opinions on this link forum??...  :-)


Edited by Builtingarage
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Obviously the ECU will still be commanding the same injector pulsewidth so the only thing that can change AFR is either a change in air flow or a change in fuel pressure.

Since you have done little that would influence air flow I think you can jump to the conclusion that fuel pressure has changed. 


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