Max PSI on stock fuel system KA24ET

[kyle1911]

Whats the max psi I could run on the stock fuel system of my ka24e if I were to turbo charge it?

Also whats a good car to look for in a junk yard to rape for a Turbo (decent sized so I dont have to buy another to support 250whp) and FMIC?

[toki]

5psi stock from a generic T3 like it sounds like you are looking at, 7-8 psi with a 2:1 FPR i'de be willing to bet.

A Z31 (early generation 300zx) T3 turbo, and a 1:1 FPR, you should be ok for the 6psi I believe those turbos are set at stock.

I'm not talking from expierence, just from what the consensus is from what people have actually done, and from what calculations show. There is a guy who ran 8 or 9 psi on his stock fuel system in a hardbody (KA24E) and had no problems. But it depends on a number of things, mainly of which are your compressor size, and your fuel pressure.

[Checkered-Member]

5psi stock from a generic T3 like it sounds like you are looking at, 7-8 psi with a 2:1 FPR i'de be willing to bet.

A Z31 (early generation 300zx) T3 turbo, and a 1:1 FPR, you should be ok for the 6psi I believe those turbos are set at stock.

Those ratios don’t make any sense…

Bone stock…4 psi

With a little help from a high pressure fuel pump, high flow fuel filter and an 8:1 FPR…6 psi

[kyle1911]

FPR = Fuel pressure regulator ?

1:1 ratio? hows that different from stock?

is there any turbos that are in factory cars that dont have a internal wastegate? what about fmic's? conquests and sarions are a rare item around here let alone junkyards.

can a Z31 T3 support enough air for 240whp without creating to much heat/topping out at around 5k rpm?

ca18det injectors are needed to special order would they be worth my time? also if i did get them would i have to buy a SAFC ? or aftermarket fuel management? will the MAF sensor support that much air?

[toki]

disregard my post, I somehow managed to forget how an FMU worked momentarily. haha.

point was, with the stock fuel pressure (40 or 43psi), you should be good to 5psi, if you bump the fuel pressure up to 50 or 55 psi, you should be fine for 7. But when you add fuel pressure to a system not designed for it, you will add wear to the system.

and by 1:1, I meant a FPR that raised fuel pressure 1 lb for every 1lb of boost.

[Checkered-Member]

point was, with the stock fuel pressure (40 or 43psi), you should be good to 5psi, if you bump the fuel pressure up to 50 or 55 psi, you should be fine for 7.

50-55 that’s not nearly enough....try 80-90, I read that at 100 psi the injectors can no longer open…

[kyle1911]

so from what you say the 8:1 FPR Checkered-Member recommended would let me run 8psi of boost? that seems a little high to me, unless my impression on how a fpr works is incorrect.

now that thats is sort of sorted out how about those junkyard questions?

[Checkered-Member]

so from what you say the 8:1 FPR Checkered-Member recommended would let me run 8psi of boost? that seems a little high to me, unless my impression on how a fpr works is incorrect.

An 8:1 ratio means that for every 1 psi of boost you will raise the fuel pressure by 8psi

so if you are running 6 psi, you will raise the pressure by 48psi (8x6=48)

I read many time that 12:1 and 10:1 are too rich, even 8:1 can be allot, personally I would stick to 6:1

[toki]

90psi = broken injectors

a 1:1 is all the most people with proper fuel need, and 'technically', we have proper fuel for 220whp I believe from the numbers i've run in the past.

btw, I was under the impression a FRP has to first account for stock fuel pressure, it will never decrease it, but it also has to first be sending out stock fuel pressure internally before it starts raising it. For example, and 8:1 wouldn't start boosting fuel pressure until after 5 psi, because at 5psi, it was just getting to 40 psi in the fuel system? See what I mean? I forgot that little tidbit earlier.

[Checkered-Member]

a 1:1 is all the most people with proper fuel need, and 'technically', we have proper fuel for 220whp I believe from the numbers i've run in the past.

btw, I was under the impression a FRP has to first account for stock fuel pressure, it will never decrease it, but it also has to first be sending out stock fuel pressure internally before it starts raising it. For example, and 8:1 wouldn't start boosting fuel pressure until after 5 psi, because at 5psi, it was just getting to 40 psi in the fuel system? See what I mean? I forgot that little tidbit earlier.

they don’t make a 1:1 FPR the lowest is 4:1

nope i don't understand what you are saying…

[toki]

I know they make a 1:1 FPR, I own one, as does a friend on mine in his FC....

you are thinking on a vortec FMU. Which is different than a fuel pressure regulator.

The FMU is placed after the FPR, so on a stock fuel system, it will see 40psi. The FMU will never lower fuel pressure, only adjust up. It raises at an 8:1 ratio. So at 1 pound of boost, it internally wants to send out 8 pounds, but it's already seeing 40, so it does nothing. 5psi on the 8:1 will get you stock fuel pressure, so only AFTER 5psi, will it start to raise fuel pressure...get it?

[Checkered-Member]

I know they make a 1:1 FPR, I own one, as does a friend on mine in his FC....

you are thinking on a vortec FMU. Which is different than a fuel pressure regulator.

The FMU is placed after the FPR, so on a stock fuel system, it will see 40psi. The FMU will never lower fuel pressure, only adjust up. It raises at an 8:1 ratio. So at 1 pound of boost, it internally wants to send out 8 pounds, but it's already seeing 40, so it does nothing. 5psi on the 8:1 will get you stock fuel pressure, so only AFTER 5psi, will it start to raise fuel pressure...get it?

that makes sense...FPR & FMU are different things, even thou many use the terms interchangeably…blah…

[Def]

The design of the stock FPR makes it a 1:1 ratio.

[hannibal]

I thought a FMU increased fuel pressure over the base setting. With a stock 3bar (43psi) FPR and a 8:1 FMU at 5psi, your fuel pressure would be 43 + (8 x 5) = 83psi. I think thats why 7-8psi is the max. At that boost level, your max fuel pressure is hitting 100psi [43 + (8 x 8) = 107psi], which is not the most reliable setup.The Nsport kit runs 7psi and uses a 7:1 FMU for fuel mgmt.

[ftrs13]

yes, I believe that is correct. which is why the FMUs are BAD, even though I have one as a bandaid for right now

[huguetpj]

I thought a FMU increased fuel pressure over the base setting. With a stock 3bar (43psi) FPR and a 8:1 FMU at 5psi, your fuel pressure would be 43 + (8 x 5) = 83psi. I think thats why 7-8psi is the max. At that boost level, your max fuel pressure is hitting 100psi [43 + (8 x 8) = 107psi], which is not the most reliable setup.

You are right. Toki is wrong. Plus the BEGI unit has a starting pressure once the intake mani hits 0PSI the fuel pressure jumps toi a preset setting then starts climbing 7:1 from there.

Not a great thing to run, I'm also running it as a band aid when I saw the kinda AFRs I was running with a stock fuel system. And I did run 7PSI on the stock fuel system for a while... just a bit lean for my taste.

[ziggy682]

Toki, I think you're spreading some information that isn't correct.

First of all, the stock FPR is a 1:1, meaning it will raise fuel pressure in the fuel rail 1 psi for every 1 psi of positive manifold pressure.

Also, I don't know where you're getting the numbers for the stock injectors being able to support 220 hp. In fact 370cc injectors can only safely support around 240 hp or so.

Personally, I would never recommend that someone run 6 psi on the stock fuel system. I wouldn't want my advice to lead to a blown engine.

[toki]

I guess you missed me making it clear about 100 times that my information is a big mix of what others have said and claimed to do.

The 220whp figure came from a 'calculator' the determined the maximum supportable horsepower based on some basic engine and fuel system stats.

But like I said, people claim to have run 8 psi on a stock fuel system. It may be possible, it may have been bull****.

http://www.capa.com.au/vortech_fuel.htm

read thier breakdown of the FMU..it's exactly what I said, minus the 1:1 of the stock FPR, I wasn't under the impression our stock FPRs dealt with positive manifold pressure...but I'm a big noob.

[huguetpj]

But like I said, people claim to have run 8 psi on a stock fuel system. It may be possible, it may have been bull****.

I haved runned 7PSI with a completely stock fuel system and ignition (including 20°BTDC). But as ziggy said... I would not recommend it to anyone cause I don't wanna be the responsible of a blown engine.

[im two techno]

LOL FMU companies should sell fire extinguishers along with their FMU! 100psi in a stock fuel is asking for it.

[ftrs13]

I carry one, haha

[AN89HATCH]

I haved runned 7PSI with a completely stock fuel system and ignition (including 20°BTDC). But as ziggy said... I would not recommend it to anyone cause I don't wanna be the responsible of a blown engine.

Why can some people run 7 psi on a stock system, and other people blow there engine at 5-6 psi, is it luck?

[ftrs13]

its the condition on all the components. and its lluck. one person may have a better spray pattern. and maybe another hascarbon deposits that raise compression a bit. its all engine dependent.

[C-Kwik]

Most 240's will barely handle much more than 7 psi with an FMU. I've never heard of an injector opening failure from too much pressure with this kind of set-up. I know it can happen, but I've just never heard of anyone running into that problem. And typically, a stock fuel pump would max out before it can provide a full pressure at 7 psi as you near redline. When this happens, one of two things has to happen. Fuel pressure will drop, or fuel flow will decrease. I'd guesstimate that fuel pressure will likely max out near about 80-90 psi on a stock fuel pump. It can vary from pump to pump. This is probably one of the bigger contributing factors to why one car might be able to handle more. The most I've heard of anyone running on a FMU is 9 psi with a higher output fuel pump. I believe he eventually blew his motor though.

And just a side note, as far as the injector's ability to handle high fuel pressure, it will not be the rail pressure that is important, but the relative pressure. Under boost, the intake is pressurized. So if there is 100 psi of fuel pressure and 7 psi of boost, then the relative pressure between the manifold and the fuel rail will be 93 psi. So there is a slight cushion. And this is not exactly going to make a huge difference, but it;s just one more thing to think about...