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Old 01-21-2004, 07:24 PM   #1
Wombat North
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Default Upping USDM STI fuel pressure

Upping the fuel pressure on STI.

I would like some feedback on below figures based on these numbers posted by AZscoobie and Kingpin.
http://forums.nasioc.com/forums/show...5&pagenumber=1
http://forums.nasioc.com/forums/show...ighlight=rrfpr


Upping fuel pressure by 10psi to 53psi.

Stock STI injectors tested by APS flowed 480cc at 43psi

Using 5cc per hp and 80%IDC as safe factory spec the figures go like this.

480cc injectors x 4 # of injectors= 1920cc

1920cc divided by 5cc= 385 crank hp at 100%IDC

80%IDC=307 crank hp which is close to the 300 crank hp STI comes stock.


Now if we bump up the fuel pressure to 53psi the figures go like this.

53 divided by 43= 1.23

480cc injectors x 1.23= 590cc at 53psi

590cc injectors x 4 # of injectors= 2362cc

2362cc divided by 5cc=472hp at 100%IDC

80%IDC=377 crank hp

85%IDC=401 crank hp

90%IDC=428 crank hp

IMHO
Assuming my figures are correct the FPR mod is a very cheap way of getting 400 crank hp safely out of the stock injectors with no mods to them. Yes I know engine management is required. Yes the Perrin mod is out but as yet no real data on flow pattern or flow differences between injectors just internet spin.

FWIW
I live at 4000ft altitude and 400hp up here would be great. I have to boost almost 2.5psi more than sea level to get the same hp that sea level gets. I have AVO 450hp turbo.

20psi here is 17.5psi on the coast.

Comments please and be nice I just became a grandpa.
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Old 01-23-2004, 03:25 PM   #2
hippy
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My feedback is that the mod is for wrx's. I would think the sti already has upped fuel pressure(could be wrong though).

peace
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Old 01-25-2004, 03:17 AM   #3
odin1
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I would be interested in this as well. Hi wombat. Question-why would upping fp need engine management-stock ecu should be able to compensate for > fp-no?
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Old 01-25-2004, 03:21 AM   #4
odin1
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Wombat-where do you get the 5cc per hp figure? thnx.
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Old 01-25-2004, 03:44 AM   #5
odin1
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Wombat-I believe it's 532.8cc. You have to take the square root of 1.23 which equals 1.11x480cc=532.8cc's. square root of (x/y) x ccie 53/43=1.23 square root=1.11. But the again it's late and I'm no math wizard. Sounds like a great idea tho. Anyone know the fuel pressure that the stock sti fuel pump is good for? Walbro is like 73psi iirc. thnx
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Old 01-25-2004, 04:25 AM   #6
odin1
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Does anyone know for sure that stock fuel pressure on sti is 4psi-same as wrx? It's poss. we already have the dimple jdm sti regulator?
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Old 01-25-2004, 04:38 AM   #7
odin1
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Quote:
Originally posted by odin1
Does anyone know for sure that stock fuel pressure on sti is 40 psi-same as wrx? It's poss. we already have the dimple jdm sti regulator?
If we reverse think this thing-yeah I know it's late-Dan of godspeed pulled 312 awhp and said the sti injectors were close to being maxed on stock sti turbo-injectors,pump. If we assume a normal 20-25% awd driveline loss=390-416 crank hp. 53 psi fuel pressure=533ccx4/5=426 crank hp-using wombats figures-at 100% idc. hmmmm-anyone know stock sti fuel pressure?
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Old 01-26-2004, 09:49 AM   #8
TurboRex
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I have been running my car with more fp for a few months now exactly as you described. However, the stock fp cannot hold the extra psi. On my car, psi would drop to 55 at wot. I installed a walbro pump and the problem was fixed.

I have a safc to control ipw and it seems to be working just fine (the car hasn't blown up yet....haha). I think it is an easy cheap mod until we can get some larger injectors that have a decent price. The 850cc's seem too large for my setup (too much maf change to get proper fuel without screwing up timing).

Greg
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