Stock fuel pressure on 2JZ and 1JZ

[2JZR31]

Thanks Chuck. I will set it at 38psi with the vacuum hose disconnected.

[BMWTurbo]

Thanks Chuck. I will set it at 38psi with the vacuum hose disconnected.

I was thinking about aiming for 40psi base with mine Denis... running aroudn 18ipsi I should be adding roughly 30psi to the base... I'm happy with 70psi being high enough over the std to not need the STD ECU to run into boost cut ast 18psi (MAP sensor max)

You are runnig 550's though I believe?

[2JZR31]

Yeah I am going to run 550's. This is why I need to know stock pressures etc, so I know exactly how much extra fuel I will be injecting at any given manifold pressure. This is important in terms of ignition advance since I will be running a SAFC to trim down mixtures.

Also. Do malpassi FPR's minus 1.7psi per negative PSI when the manifold is pressure goes below 0psi (at cruise etc)? Some people tell me they do others say they behave like a 1:1 when manifold pressure is negative.

[BMWTurbo]

MY understanding is they are 1:1 below atmospheric, but 1.7:1 above it... There isn't too much ifnormation around.

[oldcorollas]

send me one and i'll test it

or you could do the same... get a couple of bike tyres and tubes and crap.... (or compressor)
hook up one to the vac ref, and one to the fuel inlet.... or use syringe to pull vacuum.. then see when it starts leaking, and what pressure it holds...

oh, need a couple of gauges too.. (or even better, 1 gauge and one pressure differential gauge)

[thechuckster]

what little i know of the malpassi RR FPR is that of NMWTurbo's - is only rising rate above atmospheric (and i have one as well).

[2JZR31]

Cheers guys. A mate told me he had to run is malpassi in series with his stock FPR because it was subtracting fuel pressure at a rising rate below atmospheric. Maybe his was stuffed?

Anyhow. The NZ supra site says that a 2JZ runs 42psi base pressure and pretty much all the info on the US supra site says 40-42 base pressure.

[Ribfeast]

So an idle vacuum of around 15psi on a 1JZ is not so crash hot? This is at 630rpm, snapped it while in D, waiting for the traffic lights to change.



Wouldn't a higher figure give you better throttle response?
Compression is around 167-175 approx across all cyls.

[thechuckster]

engine under load in D - you really need to see the pressure in N or P with the AC and other ancillary stuff off.

[Ribfeast]

Hmm I'll give it a shot It sits in the 20's when I'm coasting down a hill at medium speed with my feet off the pedals...

Does vacuum have much to do with throttle response? You would think the closer you are to boost or positive pressure at all times, the better right?

[oldcorollas]

for a start.. the gauge is Psi on the RHS, and inHg on the left hand side..

second. 1 atmosphere is 14.7psi.
it is very hard to go below 14.7psi.... in fact it is impossible
say (roughly) 1atm = 101kPa... our vacuum furnaces go down to about 10^(-8)kPa (ten to the minus 8 pascals), but that is still not less than 14.7psi vacuum

in absolute kpa, idle could be from around 30-40kPa to 60-70kPa (unless you have huge cam and ITB.. then higher), and on decel, could go down to 20kPa or so...

[oldcorollas]

Hmm I'll give it a shot It sits in the 20's when I'm coasting down a hill at medium speed with my feet off the pedals...

Does vacuum have much to do with throttle response? You would think the closer you are to boost or positive pressure at all times, the better right?

engines idle cos there is very little air going in. if the manifold had positive pressure at all times... that means you are boosting at all times, and the engine eats a lot of air and makes a lot of power at all times...

not too acceptable in todays society where there are stoplights and stuff

but.. positive pressure in the pipes before the throttle will decrease the transition time, and help response a bit...
usualy you have 1atm pressure ahead of the throttle... if you had an SC setup and set it to have 5-10psi ahead of the throttle, then you would have better response.. at the expense of power drain all the time when you are not on the throttle.

[Ribfeast]

Hmm so if I had my boost gauge referencing from around the exit of the turbos, it wouldn't see so much vac? I guess the throttle body would be a huge restriction when you let off the loud pedal, hence the vacuum reading...

[oldcorollas]

you would only see vacuum there if the engine was trying to pull more air than the turbos could provide (WOT from idle maybe?) but not much..

throttle body IS loud pedal .. and engines usually are sucking against a vacuum....

ie, manifold is always in vacuum, unless you have pedal pressed down far enough to go to atmospheric pressure (WOT for NA), or boost (less than WOT for FI).... unless you are pushing pedal enough to be WOT for NA or more (for boost), then the manifold will ALWAYS be in vacuum....


unless it's a diesel

oh, and the whole point of throttle is to be a restriction.. otherwise you would be at WOT all the time.. fun but.... (diesel engine speed/power is controlled by fuel, not air..)

[Ribfeast]

Thats good info man Make sense now that I think about it.

Here's my vacuum in N or P:



Does that look OK, or should it be lower?