Fuel Injectors...
12-23-2007, 11:18 PM
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Fuel Injectors... Ok, I have 3 questions...one, what is the stock PSI for the fuel injectors on a 1997 Z28 LT1? I am polishing my fuel rails and figure while I have all this **** out maybe I can upgrade...next question, if I DO choose to upgrade, what would be a good psi to go with for a daily driver with a few performance mods like pacesetter headers, ported and polished heads, ported intake manifold, SLP Cold Air, 58mm TB, and a good computer tune? Last, what would those cost me????
12-23-2007, 11:40 PM
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Stock 1994-1997 injectors are 24#. Stock fuel pressure is around 42-47psi at WOT (without vacuum).
Stock cam?
Depending on how much power you're making, you might be able to squeak by with factory injectors, and/or bumping up the fuel pressure with an adjustable fuel pressure regulator. Depends on your current injector duty cycles. With a healthy aftermarket camshaft, many people upgrade to the 30# Ford SVO's. I've run them without any issues. They'll cost you roughly $350~$400 shipped to your door, unless you buy used or something.
Naturally, any change in injector size will require another tune to correct for the increased injector flow rate.
if I DO choose to upgrade, what would be a good psi to go with for a daily driver with a few performance mods like pacesetter headers, ported and polished heads, ported intake manifold, SLP Cold Air, 58mm TB, and a good computer tune? Last, what would those cost me????
Depending on how much power you're making, you might be able to squeak by with factory injectors, and/or bumping up the fuel pressure with an adjustable fuel pressure regulator. Depends on your current injector duty cycles. With a healthy aftermarket camshaft, many people upgrade to the 30# Ford SVO's. I've run them without any issues. They'll cost you roughly $350~$400 shipped to your door, unless you buy used or something.
Naturally, any change in injector size will require another tune to correct for the increased injector flow rate.
12-23-2007, 11:49 PM
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Ok, I have a stock cam for now...may upgrade way later...like sometime in 2010...lol. But not for a while. So I'll prolly stay stock...now how much does an Adj. Fuel Pressure Reg. cost and where??? And what should I bump it up to?
12-24-2007, 03:56 AM
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Haha! That's pushing it.
Well, forced induction engines can run better than .5 BSFC. The stock 24# injectors are actually listed at 24.91# in the factory tune. Mathematically, 24.91# injectors @ 43.5psi fuel pressure at 95% DC, assuming a conservative .47 BSFC could be achieved, would support 402.8 hp. (= 24.91 * .95 / .47 * 8). Bump the fuel pressure, and you could squeak out a little more.
Definitely far from a 'safe' idea -- especially on a forced induction engine!
Simple questions, but the answers require some explanation. Deep breath...
My only advice is this: if you're going to upgrade injectors, do it once, and do it right. You'll have to determine what your short and long-term goals are, and plan for the long-term. You may need even larger than 30# injectors if you run a radical head/cam package. For now, I think stock injectors will suffice.
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You won't really need an adjustable fuel pressure regulator -- I mentioned it only as a bandaid to help drop your injector duty cycles if they are getting above 85-90%. In the end, you should run proper injectors for your intended setup.
Regardless, to answer your question, there are some options to consider. Brands such as Holley and Aeromotive sell complete units which fully replace your stock regulator. Other brands (such as Metco? and the like) simply convert your factory regulator into an adjustable one, and will be about half the price. There may be other brands out there now -- I'm rusty. PM me if you need help finding vendors.
I use a Holley AFPR, which I believe cost around $150. I went with it because there were no complaints about them at the time. It works great, albeit I had to weld an extension onto the factory fuel line brace/bracket -- since the regulator's design happens to shift the fuel lines about 1/2" farther apart.
Another option is Aeromotive. I was hesitant to use Aeromotive in the past (due to all sorts of quirky problems they were having), but I know they redesigned their units a few years ago. Perhaps others can attest to their quality today.
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It's not really important, but to find how a bump in fuel pressure will affect injector flow rate, simply take the square root of (New fuel pressure / Old fuel pressure) and multiply by the flow rate of the OLD injector. Your answer will be the flow rate for the NEW injector.
For instance, a 24# injector (rated at ~3bar/43.5psi) will behave similarly to a 28# injector if it is run at 58psi of fuel pressure (4 bar)... not that I'd recommend doing that.
[sqrt(58.01psi / 43.5psi) * 24#] = 27.7# injectors (<-- can use psi or bar, just keep units the same. FYI, 1 bar = 14.504psi)
-You can then plug this back into the standard injector formulas to estimate new supported horsepower and whatnot.
Well, forced induction engines can run better than .5 BSFC. The stock 24# injectors are actually listed at 24.91# in the factory tune. Mathematically, 24.91# injectors @ 43.5psi fuel pressure at 95% DC, assuming a conservative .47 BSFC could be achieved, would support 402.8 hp. (= 24.91 * .95 / .47 * 8). Bump the fuel pressure, and you could squeak out a little more.
Definitely far from a 'safe' idea -- especially on a forced induction engine!
My only advice is this: if you're going to upgrade injectors, do it once, and do it right. You'll have to determine what your short and long-term goals are, and plan for the long-term. You may need even larger than 30# injectors if you run a radical head/cam package. For now, I think stock injectors will suffice.
---------------------
You won't really need an adjustable fuel pressure regulator -- I mentioned it only as a bandaid to help drop your injector duty cycles if they are getting above 85-90%. In the end, you should run proper injectors for your intended setup.
Regardless, to answer your question, there are some options to consider. Brands such as Holley and Aeromotive sell complete units which fully replace your stock regulator. Other brands (such as Metco? and the like) simply convert your factory regulator into an adjustable one, and will be about half the price. There may be other brands out there now -- I'm rusty. PM me if you need help finding vendors.
I use a Holley AFPR, which I believe cost around $150. I went with it because there were no complaints about them at the time. It works great, albeit I had to weld an extension onto the factory fuel line brace/bracket -- since the regulator's design happens to shift the fuel lines about 1/2" farther apart.
Another option is Aeromotive. I was hesitant to use Aeromotive in the past (due to all sorts of quirky problems they were having), but I know they redesigned their units a few years ago. Perhaps others can attest to their quality today.
---------------
It's not really important, but to find how a bump in fuel pressure will affect injector flow rate, simply take the square root of (New fuel pressure / Old fuel pressure) and multiply by the flow rate of the OLD injector. Your answer will be the flow rate for the NEW injector.
For instance, a 24# injector (rated at ~3bar/43.5psi) will behave similarly to a 28# injector if it is run at 58psi of fuel pressure (4 bar)... not that I'd recommend doing that.
[sqrt(58.01psi / 43.5psi) * 24#] = 27.7# injectors (<-- can use psi or bar, just keep units the same. FYI, 1 bar = 14.504psi)
-You can then plug this back into the standard injector formulas to estimate new supported horsepower and whatnot.
12-24-2007, 09:40 AM
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wow...haha, i think I'll stick with what I got stock and just get a new Fuel Pres. Reg. lol. All that math is killing me! HAHA, But all in all I think it sounds like I will be ok with what I have, I'm not gonna go "radical" with anything, like my cam isnt gonna make me lope or anything of that sort...So I think I'll be ok. Thanks Guys!!!
12-24-2007, 01:01 PM
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Yea, I'm surprised his injectors didn't crap out before his motor did. I don't plan any big upgrades, so whatever I do to my car my SVOs should suffice for quite awhile. Headers and intake work are all I foresee in the future.
