LEX with 440s, Tune with Fuel Pressure?

[rumptis]

I have never seen this discussed before, not like this anyways.

Basically everybody says if you go LEX you have to either get a piggyback or go with 550 injectors.

Here is the hypothetical setup.

1. LEX AFM
2. Walbro 255
3. Fuel Pressure Regulator
4. wide band to monitor a/f

Basically all the mods you would do minus the 550s.

Here is the question....

Could you tune with fuel pressure alone basically getting the same results as putting in 550s?

I would think bumping up the fuel pressure 25% or so would get you the same results as adding 550s....basically a rich safe tune.

Please serious answers only....

 

[Supracentral]

Injectors are rated at a specific flow rate. When you jack the pressure like that you beat the crap out of the injector and the spray patterns go to shit. Car probably won't idle correctly, nor run right at part throttle. Many injectors will also leak, or lock static when pushed with too much pressure.

Overall a bad idea. There ain't no such thing as a free lunch.

Related discussions:

Injector Sizing: http://www.supramania.com/forums/showpost.php?p=179880&postcount=7

AFPR: http://www.supramania.com/forums/showpost.php?p=203093&postcount=5

How to make power: http://www.supramania.com/forums/showpost.php?p=182731&postcount=23

The weak link in the 7M is the owner: http://www.supramania.com/forums/showpost.php?p=534193&postcount=8

 

[hottscennessey]

:word8kn:

 

[ATL88Supra]

just get the injectors there not much now days......

 

[supra_ed]

i would suggest getting injectors. but u can tune a lex afm with stock injectors using a afc neo if u have to and a WIDEBAND

 

[staticpat]

People just like the LEX/550 combo because you don't need to tune or do anything to it. It's the ease and convenience for most users.

I am using stock injectors with the lexus and an afpr to bump up pressure and an safc to fine tune. I make 360rwhp with no signs of going lean, but I won't push it anymore without bigger injectors. I also get like 26mpg when off boost .

It all depends on your horsepower goals. If you're just trying to get past fuel cut then you don't need to overkill for injectors. 550s are good for like 500rwhp, most supra owners won't be getting that.

HP (at the crank) =( flowrate (lbs/hr) * # injectors * duty cycle )/ BSFC (.55 for turbo engines)

So for stock injectors at an 85% duty cycle

HP =(42.2 * 6 * .85 )/ .55 = 391bhp

So if your shooting for over 350rwhp then get bigger injectors. If not your money could be spent elsewhere (ie. cleaning and flow testing your 20 yr old 440s).

 

[wardog]

Well how is it that jblmk3 is makin over 450 rwhp on stock 440s no tuning devices just with a fuel pressure regulator set at 42 psi and 18psi on a ct26/60 trim? can anybody explain?plz :1zhelp:

 

[bountykilla0118]

Well how is it that jblmk3 is makin over 450 rwhp on stock 440s no tuning devices just with a fuel pressure regulator set at 42 psi and 18psi on a ct26/60 trim? can anybody explain?plz :1zhelp:

Thats good question ......... But he was a bit on the lean side for pump gas.

 

[7MGTEsup]

Stock fuel pressure is 38psi fuel injectors are rated at 43psi so on a stock supra your 440's arn't even 440's. Putting on a Lex AFM and bumping the pressure to 43psi the car should run fine just make sure you have a wideband to confirm the setup and all your 440's are clean and flowing to spec.

 

[mkIIIman089]

Fuel pressure goes up with boost. Base FP may be 38, but not when it matters.

 

[shaeff]

and john lunsford has been in the mk3 game for a long time, and knows exactly what he's doing. would i do it? nope. but if you DO know what you're doing, you might be able to squeak by like John does.

also note that he's running a higher static CR.

-shaeff

 

[tte]

and john lunsford has been in the mk3 game for a long time, and knows exactly what he's doing. would i do it? nope. but if you DO know what you're doing, you might be able to squeak by like John does.

also note that he's running a higher static CR.

-shaeff

Thats right....if you are new to this game, it wouldnt be wise to gain valuable experience by blowing up your motor. Its better to seek advice from the more experienced guys and setup the car with a bigger safety margin.

Cheers,
Roy

 

[MDCmotorsports]

also note that he's running a higher static CR.

-shaeff

Correct.

 

[7MGTEsup]

Fuel pressure goes up with boost. Base FP may be 38, but not when it matters.

I'm well aware of that, but if your base fuel pressure is 43psi which is 5psi more than stock it will be 5psi more when it matters also :icon_wink

 

[jetjock]

Fuel pressure goes up with boost.

Well, kinda. Sort of. Not exactly. It actually stays the same. It has too or accurate metering would be impossible. That's what the word "regulator" in fuel pressure regulator is for. I understand you're talking about PSIG but I don't want others to get the wrong impression.

 

[mkIIIman089]

Well, kinda. Sort of. Not exactly.

LOL, this sounds shockingly similar to something a buddy of mine would say!

 

[jetjock]

Just playing with ya Colin. Fuel pressure has to change in order to maintain a constant delta P between rail and manifold. In a stock 7M it's 36 psid.