high fuel pressure/stock injectors
08-12-2002, 10:33 AM
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high fuel pressure/stock injectors
I am in the process of increasing the boost to 17-18psi and want to know if increasing the fuel pressure could cause the stock fuel injectors to fail (or get stuck open or closed). 4-6psi is what I have heard is a safe amount of fuel pressure increase (according to AFPR instructions). I'd like to increase the static fuel pressure to no more than 45psi at idle. BTW, the fuel injectors are nearly brand new so they should be healthy. Anyone have any firsthand experience with this? TIA
08-12-2002, 06:12 PM
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You should have no problem running that pressure are far as the health of the injector goes.
HOWEVER - that's a BIG HOWEVER - bumping up your fuel pressure is not the way to go when increasing boost. It's a brute force way of getting more fuel into the cylinders.
Let's say you want to fill up your swimming pool. You can take your regular garden hose, and somehow increase the water pressure that is feeding it. Or you take a bigger hose that is designed for that kind of application (fed by the appropriate water source) and flow a lot more water, with a lot less pressure. Make sense?
When you're running that high psi, you're doing two things - maxing out your injectors, and maxing out your turbo (somewhat). Maxed out injectors (if maxed out enough) will make you go lean - pinging and detonation. Maxed out turbos are inefficient, leading to much higher charge air temperatures, again leading to possible pinging and detonation.
So, to conclude: Yes your injectors will be fine at 45 psi, but you're at their limits, so you might want to think about bigger injectors and a bigger turbo before you put a hole in a piston.
HOWEVER - that's a BIG HOWEVER - bumping up your fuel pressure is not the way to go when increasing boost. It's a brute force way of getting more fuel into the cylinders.
Let's say you want to fill up your swimming pool. You can take your regular garden hose, and somehow increase the water pressure that is feeding it. Or you take a bigger hose that is designed for that kind of application (fed by the appropriate water source) and flow a lot more water, with a lot less pressure. Make sense?
When you're running that high psi, you're doing two things - maxing out your injectors, and maxing out your turbo (somewhat). Maxed out injectors (if maxed out enough) will make you go lean - pinging and detonation. Maxed out turbos are inefficient, leading to much higher charge air temperatures, again leading to possible pinging and detonation.
So, to conclude: Yes your injectors will be fine at 45 psi, but you're at their limits, so you might want to think about bigger injectors and a bigger turbo before you put a hole in a piston.
08-12-2002, 10:27 PM
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[quote]Originally posted by Jax951:
<strong>bumping up your fuel pressure is not the way to go when increasing boost</strong><hr></blockquote>
Ok, thanks for the info.
I'm actually ditching my APE II chips in favor of SteveR's new 3bar chips. Apparently they are developed for a near stock 951S running 17-18psi boost and 42-46psi of fuel. I'm hoping the new chips will be better mapped for my setup. (Street car only with 93 octane.)
I'm also replacing the MBC that I literally installed last week in favor of a Profec B, so that I can more easily go between 14psi and 18psi when needed.
I'll keep an eye (and ear) on things too. I may be at the ragged edge of reliability, but I don't want to be TOO carefree about it. :-)
<strong>bumping up your fuel pressure is not the way to go when increasing boost</strong><hr></blockquote>
Ok, thanks for the info.
I'm actually ditching my APE II chips in favor of SteveR's new 3bar chips. Apparently they are developed for a near stock 951S running 17-18psi boost and 42-46psi of fuel. I'm hoping the new chips will be better mapped for my setup. (Street car only with 93 octane.)
I'm also replacing the MBC that I literally installed last week in favor of a Profec B, so that I can more easily go between 14psi and 18psi when needed.
I'll keep an eye (and ear) on things too. I may be at the ragged edge of reliability, but I don't want to be TOO carefree about it. :-)
08-12-2002, 11:35 PM
#4
Also - don't forget to monitor your duty cycle. You shouldn't go above 80% in Va. when it is hot. You will get a sufficient temperature decline in winter to overcompensate for the remaining 20% margin in fuel capacity.
