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bumpin up th fuel pressure

 
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tarmac-



Joined: 29 May 2006
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Location: New Zealand.

PostPosted: Sat Mar 24, 2007 9:47 am    Post subject: bumpin up th fuel pressure Reply with quote

whats a good safe pressure to up the presure to without effecting spray patterns etc to muchh. just trying to get some more boost outa the old r33. rising rate of 1.1

cheers
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Nunook



Joined: 17 May 2006
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PostPosted: Sun Mar 25, 2007 2:40 am    Post subject: Reply with quote

i was going to raise my fp from the stock 43.5 to 50psi with 0 vac.
I dont think goin anyhigher is good.

if I do that then my 370cc will act like ~400cc and should afford me alittle more boost. Smile
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tarmac-



Joined: 29 May 2006
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Location: New Zealand.

PostPosted: Sun Mar 25, 2007 7:19 am    Post subject: Reply with quote

yeh ok. i was thinking more 60psi. hmm.
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cb_drift



Joined: 04 May 2004
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Location: New Zealand

PostPosted: Sun Mar 25, 2007 9:43 am    Post subject: Reply with quote

cant remember where i saw it - but i had a table of injector flow rates at various pressures

all the nissan injectors on it were listed with 3 pressures - highest being 3 bar where the 440's become 550's the 380's become 440s and so on....

try 3 bar - from the sounds of it - it seems that the injectors will do that - not sure how well or for how long or anything tho - ive always had the factory fpr and just swapped in bigger injectors when needed...
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LMQT



Joined: 06 Aug 2005
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Location: France

PostPosted: Sun Mar 25, 2007 8:54 pm    Post subject: Reply with quote

The formula is quiet simple Razz

[code:1:eca94dfc26]square_root(new_fuel_pressure/old_fuel_pressure) * old_injector_flow = new_injector_flow

[ SQR(3.60bar / 2.50bar) ] * 370cc = 444cc[/code:1:eca94dfc26]

so instead of swapping your old 370cc by some new 444cc, you can just increase your fuel pressure from 2.5bar to 3.6 Wink
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tarmac-



Joined: 29 May 2006
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Location: New Zealand.

PostPosted: Sun Mar 25, 2007 11:16 pm    Post subject: Reply with quote

yeh upping the injector size would be my prefered choice, but sidefeeds are just so expensive. i might just go 3.5 bar, if i blow it, ill just put the 30 block in :p.


sidenote, im running 23degrees advance at 12psi on a rb25det with S5 RX7 turbo in GTS-t exhaust housing, and front mount intercooler. i cant hear any detonation, but is this safe on 98 unleaded gas. its been fine for a while, im presumming its sweet and i think i could probly push for more timing, but just want some ideas. next im wanting to run around 17-18psi or what ever the injectors will let me flow.

cheers!
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skyshack



Joined: 09 Feb 2006
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Location: Burton on Trent, UK

PostPosted: Sat Aug 11, 2012 11:13 am    Post subject: Reply with quote

[quote="LMQT"]The formula is quiet simple Razz

square_root(new_fuel_pressure/old_fuel_pressure) * old_injector_flow = new_injector_flow

[ SQR(3.60bar / 2.50bar) ] * 370cc = 444cc

so instead of swapping your old 370cc by some new 444cc, you can just increase your fuel pressure from 2.5bar to 3.6 Wink[/quote]
Better late than never.

You would find it's a bit lean and still needs excessive injector opening times. The pressure ratio is absolute not gauge.

square root ((New pressure + atmospheric) / (Old pressure + atmospheric)) x old injector flow = new flow.

SQRT((3.6 + 1) / (2.5 + 1)) * 370 = 424cc

That can be used to set a new K value. More useful is the re-arranged formula to find new pressure for desired fuel flow (up)rate.

New pressure = [(new flow / old flow) x (old pressure + atmospheric)] - atmospheric

[(444 / 370) * (2.5 +1)] - 1 = 4.04 bar

4.04 bar = 59.4psi
(near enough to 60psi same as Tarmac's value)

Peak Injector fuel pressure = pressure with 0psi + boost.

1bar + 4.04bar = 5.04 bar = 74psi
1.2bar + 4.04bar = 5.24bar = 77psi

I don't know what pressure injectors start to dribble or can't open/shut properly but could be possible with high fuel pressure.
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swapnali



Joined: 09 Sep 2017
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PostPosted: Wed Jan 31, 2018 6:59 am    Post subject: Reply with quote

hello all,

nice place to be here, i see nice comments and nice people as well, i will make it a point to come here more often to read and post comments so people and myself benefit.

Cheers!!!
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