higher fuel pressure better spray pattern?

turboterror · Jan 7, 2007

I was speaking to an engineer at Motorworx (local shop). anyways he was saying that he thinks my static fuel pressure (vacuum line off) was too low..static at 44 psi. He said as I upgrade with larger cams (272s or larger) that the idle will become harder to tune at a lower pressure. He said the standalone will become less sensitive to changes and be easier to tune at part throttle if I raise the pressure. Also he said the higher pressure in boost I might actually pick up power as the higher pressure atomizes better. I asked him how high is too high of pressure in boost. He said he doesnt build mitsu's so he doesnt have much experience with em. Mainly toyotas, and nissians, but he said that the static pressure of a Nissian skyline is 60 PSI for a reason. He said the engineers got it right. He said that his engines regulary run twin walboro 255s and see fuel pressure of 100 PSI or so. I just think thats crazy!!! what does everyone else think?

will higher pressure atomize or have a cleaner burn? I mean Sheppard Racing is running what 58 pounds of boost? so even at 36-44 static, that still is 94-102 psi! thats alot!! what is everyones opinions on that?

so how much total fuel pressure is safe? and is it worth it?

greenstreak · Jan 7, 2007

I would imagine that each type of injector is made to operate efficiently within a certain pressure window. I noticed no difference in idle or tuning when going from 42psi to 50psi static.

turboterror · Jan 9, 2007

greenstreak said:
I would imagine that each type of injector is made to operate efficiently within a certain pressure window. I noticed no difference in idle or tuning when going from 42psi to 50psi static.

good point. but what style of injectors would be better at higher pressures u think and why? so i take it your top fuel pressure was in the mid 70s somewhere in boost?

destrux · Jun 25, 2008

Old post, but just wanted to add some info, as I'm researching the same thing for my car right now...

Almost all injectors are rated for static fuel flow at 43.5psi of pressure (which is 3bar). That means that at stock fuel pressure, the stock 450's in the car are only actually flowing 415cc/min (at 100% duty cycle). Note that fuel flow change based on fuel pressure change isn't linear (10% more fuel pressure doesn't mean 10% more fuel flow, although it's pretty close). There's a formula to calculate it, found it in an old issue of SCC. It doesn't account for the specific gravity being slightly different in different fuels (ie- race fuel), but that doesn't affect it enough to bother.

Same goes with 550's. Drop a set of 550's in at stock fuel pressure, and max flow is only about 500cc/min.

For example... if you run the stock 450cc injectors at a base (static) fuel pressure of 60psi the injectors will flow 528cc/min max. BIG difference.

Actually, any fuel pressure changes, even 5psi, WILL effect your tune, especially at WOT (or any open loop conditions). Under normal driving conditions, the ECU will retune (somewhat) to compensate for the extra fuel... so you might not notice it. It's always important to check your trims and retune after any pressure changes though.

Now, my only questions I have left before I crank up my fuel pressure are...

1. What pressure can the injectors handle before the fuel pressure overcomes the injector driver and holds the injector shut?
2. What pressure can my pump (a denso 180LPH from a 3000GT VR4) handle before it locks up or otherwise fails?

Now, I know deadhead test pressure on the pump is 95psi... so it should be able to handle at least that... but the injector question is still unanswered. I haven't been able to find anything anywhere about it.

The_EE · Jun 25, 2008

turboterror said:
good point. but what style of injectors would be better at higher pressures u think and why? so i take it your top fuel pressure was in the mid 70s somewhere in boost?

Rule #7 Its in my Sig.

Shift key needs to be used and U is not a substitute for the word YOU.

Don Boosted · Jun 25, 2008

The_EE said:
Rule #7 Its in my Sig.

Shift key needs to be used and U is not a substitute for the word YOU.

Haha that post was from 2007

U need to read the posts before u criticize them

Black_ bullet · Jun 26, 2008

destrux said:
Old post, but just wanted to add some info, as I'm researching the same thing for my car right now...

Almost all injectors are rated for static fuel flow at 43.5psi of pressure (which is 3bar). That means that at stock fuel pressure, the stock 450's in the car are only actually flowing 415cc/min (at 100% duty cycle). Note that fuel flow change based on fuel pressure change isn't linear (10% more fuel pressure doesn't mean 10% more fuel flow, although it's pretty close). There's a formula to calculate it, found it in an old issue of SCC. It doesn't account for the specific gravity being slightly different in different fuels (ie- race fuel), but that doesn't affect it enough to bother.

Same goes with 550's. Drop a set of 550's in at stock fuel pressure, and max flow is only about 500cc/min.

For example... if you run the stock 450cc injectors at a base (static) fuel pressure of 60psi the injectors will flow 528cc/min max. BIG difference.

Actually, any fuel pressure changes, even 5psi, WILL effect your tune, especially at WOT (or any open loop conditions). Under normal driving conditions, the ECU will retune (somewhat) to compensate for the extra fuel... so you might not notice it. It's always important to check your trims and retune after any pressure changes though.

Now, my only questions I have left before I crank up my fuel pressure are...

1. What pressure can the injectors handle before the fuel pressure overcomes the injector driver and holds the injector shut?
2. What pressure can my pump (a denso 180LPH from a 3000GT VR4) handle before it locks up or otherwise fails?

Now, I know deadhead test pressure on the pump is 95psi... so it should be able to handle at least that... but the injector question is still unanswered. I haven't been able to find anything anywhere about it.

I think you can could run into fuel pump overrun issues.

Considering pressure rises 1:1 with boost, starting at a riduculously high pressure like that will get out of hand by the time you reach full boost.
I wouldnt run anything more than like 55 base psi of fuel pressure max, and there would have to be a reason to do it anyways.

Also consider that the fuelpump actually starts to flow less the higher you crank the fuel pressure despite injectors flowing more... So different setups will call for more or less fuel pressure depending on injectors/ fuel pump.

I run the N/T FPR which gives a 48psi base and made my 450s flow like 505cc which helped run a little decent boost on the 16g. Im running FIC 850s now and still the same fuel pressure just with the over rall flow rate compensated in on the chip. Car runs great, and with over 900cc worth of flow, If we ever get e85 down here I should be good for some good numbers...

na94eclipse · Jun 26, 2008

Don Boosted said:
Haha that post was from 2007 U need to read the posts before u criticize them

I caught the same thing but I was gonna let it go... NO HARM NO FOUL! :dunno:

MuffinMan7580 · Jun 27, 2008

Gains by increasing fuel pressure are not linear, I agree, but there is an actual limit when you start talking about rediculous amount of pressure, stay around 49-55 for you base fuel pressure. Reason being, you can actually damage injectors (permanently) from running crazy numbers.

boominmypants · Jun 30, 2008

Well I have some actual feed back seeing as I just raised my base fuel pressure from 38psi to 42-43 or so. I'm running 750cc injectors, a maft, and a chipped ecu. At 38psi base, and at wide open throttle the IDC's were awful at 108%. The low and high fuel trims were 100% or so, and 94% or so.
With the 42/43psi base and a retune on the maft, the wide open throttle idc's dropped to about 84%(still high I know.) I left the base settings on the maft the same, except for taking 5% or 1 click out of the idle knob. The fuel trims dropped to 81% or so for both trims.

spoolnbreak · Jun 30, 2008

destrux said:
Old post, but just wanted to add some info, as I'm researching the same thing for my car right now...

Almost all injectors are rated for static fuel flow at 43.5psi of pressure (which is 3bar). That means that at stock fuel pressure, the stock 450's in the car are only actually flowing 415cc/min (at 100% duty cycle). Note that fuel flow change based on fuel pressure change isn't linear (10% more fuel pressure doesn't mean 10% more fuel flow, although it's pretty close). There's a formula to calculate it, found it in an old issue of SCC. It doesn't account for the specific gravity being slightly different in different fuels (ie- race fuel), but that doesn't affect it enough to bother.

Same goes with 550's. Drop a set of 550's in at stock fuel pressure, and max flow is only about 500cc/min.

For example... if you run the stock 450cc injectors at a base (static) fuel pressure of 60psi the injectors will flow 528cc/min max. BIG difference.

Actually, any fuel pressure changes, even 5psi, WILL effect your tune, especially at WOT (or any open loop conditions). Under normal driving conditions, the ECU will retune (somewhat) to compensate for the extra fuel... so you might not notice it. It's always important to check your trims and retune after any pressure changes though.

Now, my only questions I have left before I crank up my fuel pressure are...

1. What pressure can the injectors handle before the fuel pressure overcomes the injector driver and holds the injector shut?
2. What pressure can my pump (a denso 180LPH from a 3000GT VR4) handle before it locks up or otherwise fails?

Now, I know deadhead test pressure on the pump is 95psi... so it should be able to handle at least that... but the injector question is still unanswered. I haven't been able to find anything anywhere about it.

Maybe this would help somehow...I inadvertantly found the max of a Wally 255. It's 110psi; my FPR failed and locked shut and that's the point where my mechanical fuel gauge on my rail stopped before the fuse burned. Ha, I still remember that sound

WHIIRRRRRRRRRRrrrrrrrrrrrrrrrrrrrrrrrrr *thack*

higher fuel pressure better spray pattern?

turboterror

greenstreak

turboterror

destrux

The_EE

Don Boosted

Black_ bullet

na94eclipse

MuffinMan7580

boominmypants

spoolnbreak

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