Stock injectors with supercharger...low level boost?

[markd79ta]

What can I expect using my stock injectors with 4.5psi of boost. I don't expect there to be too much of a problem, but I thought I would ask. Additionally, the altitude is over 5,000 ft so I have low levels of air anyway. I am looking at 30lbs or 36lbs injectors later this summer.

Oh, preference on plugs?

[wako29]

It would have fuel starvation before anything. You shouldn't have to much trouble, but I would recommend reprogramming after you get the injectors and all. That is just general car advise though...

For plugs, I dunno. I use NGKs on practically everything, never had problems.

[Injuneer]

Depends how your S/C system adds the extra fuel. Many low boost applications use a "fuel management unit" (FMU) to add extra fuel by increasing fuel pressure in proportion to boost levels. This generally works fine, and does not require additional programming of the stock PCM. If that is the way your blower setup works, stock injector size will be fine.

You also have to consider the fact that because of your 5,000-ft altitude, the stock injectors live a relatively relaxed life, since they are only called upon to produce about 83% of the HP that the rest of us enjoy at sea level, giving them a strong reserve capacity on the stock, normally aspirated motor. Your 4.5# of boost on top of a relatively stock LT1 is only going to be making about 300flywheelHP total. I would think you would want to go a lot higher than 4.5psi boost at that altitude.

[fastTa]

I am also a little inquisitive about why you are only planning on 4.5 psi. At your altitude and with that low of boost, you are only looking at a 40-50 hp gain if that.

Which one of your cars is this going on?

[markd79ta]

Originally posted by fastTA
I am also a little inquisitive about why you are only planning on 4.5 psi. At your altitude and with that low of boost, you are only looking at a 40-50 hp gain if that.

Which one of your cars is this going on?

It is going on the '97 T/A...it has 95,000 miles. My thought was putting the unit on the T/A with the 4.5 pulley for now and using a 9psi pulley later when I rebuild the engine with 9.5:1 pistons. However, I will use a 6psi pulley for now.

How would that 9psi pulley work with the FMU and the 10.5:1 pistons at this altitude? Do you think it will grenade it? All of my driving occurs between 5.000 and 7,000 feet. Anyhow, my main thought of buying this kit is to counteract the powerloss of the altitude. I know I am not going to get big numbers out of my stock motor at this altitude. However, I don't have the time or money to build the engine the way I want.

[fastTa]

With 9 psi and your stock 10.4:1 compression ratio you will be OK.

[Injuneer]

Just keep in mind.... when your stock 10.5:1 engine completes its compression stroke at 5,000-ft altitude, the combustion chamber has the same mass of air in it as if the engine had a 9.1:1 compression ratio at sea level. You should not have to reduce your static compression ratio to run a blower. As boost levels go up though, the need for after cooling becomes more important. I've seen a 9.0:1 engine run 20# boost, through a very large intercooler. And it was running racing fuel, but would still run on 100-octane on the street.

[markd79ta]

Originally posted by Injuneer
Just keep in mind.... when your stock 10.5:1 engine completes its compression stroke at 5,000-ft altitude, the combustion chamber has the same mass of air in it as if the engine had a 9.1:1 compression ratio at sea level. You should not have to reduce your static compression ratio to run a blower. As boost levels go up though, the need for after cooling becomes more important. I've seen a 9.0:1 engine run 20# boost, through a very large intercooler. And it was running racing fuel, but would still run on 100-octane on the street.

Another problem with this altitude is that we have horrible gas 85,87, and 91. It is hard to find high octane fuel up here. I guess they decide that since the air is so thin, there is no need for it...kinda stupid.

I think I will start off with the 6psi, and buy an aftercooler later along with a 9psi pulley and programming...it will be an interesting project.

Oh, what should I set the timing retard at. It is usually 1 degree for 1psi of boost. Should I set it lower, say 5 degrees for 6psi of boost. Also, another question, what are the stock injectors rated at 19lbs?

[Injuneer]

The need for "octane" drops with the increase in altitude... I think it may be about -0.5 octane units per 1,000-ft. So there is no need for them to sell anything better than those grade fuels.

Stock injectors on a 94-97 LT1 are 24#/HR nominal, and programmed for 24.9#/HR in the PCM. They are good for up to 400flywheelHP. Some people have pushed them even higher, but I wouldn't.

I wouldn't pull any timing initially... assuming you can put a scanner on it and monitor the PCM for knock retard. If you see retard, pull a little timing to eliminate it. I would focus on setting up the FMU to give you peak power without going overly rich. Its probalby a case of setting the AF ratio first, looking for knock retard, and if you get some, looking at whether you get rid of it more effectively by adding fuel or pulling timing. One of those may give you better power than the other.

When reading my advice on blowers.... notice I do not run one.... I'm a "nitrous" type.... but a couple of my friends have done a lot with blowers, ranging anywhere from the 4.5# setups to the monsters.

[markd79ta]

Originally posted by Injuneer
The need for "octane" drops with the increase in altitude... I think it may be about -0.5 octane units per 1,000-ft. So there is no need for them to sell anything better than those grade fuels.

Stock injectors on a 94-97 LT1 are 24#/HR nominal, and programmed for 24.9#/HR in the PCM. They are good for up to 400flywheelHP. Some people have pushed them even higher, but I wouldn't.

I wouldn't pull any timing initially... assuming you can put a scanner on it and monitor the PCM for knock retard. If you see retard, pull a little timing to eliminate it. I would focus on setting up the FMU to give you peak power without going overly rich. Its probalby a case of setting the AF ratio first, looking for knock retard, and if you get some, looking at whether you get rid of it more effectively by adding fuel or pulling timing. One of those may give you better power than the other.

When reading my advice on blowers.... notice I do not run one.... I'm a "nitrous" type.... but a couple of my friends have done a lot with blowers, ranging anywhere from the 4.5# setups to the monsters.

Your advise is good as gold to me! It doesn't matter what you run, you know a lot more than I do!

What is a good setup(software & cable) to put on my laptop? I don't have a scanner yet, but I was hoping to set up my laptop this summer.

[fastTa]

One other thing to note is that a centrifugal type blower is not a positive displacement compressor like a roots type blower. So at your elevation, the impeller within a centrifugal blower will not be as efficient at producing boost as it would at a lower elevation. Say you have your particular head unit pullied to make 4.5 psi, it will actually make considerably less boost given the inefficiency of the impellar in thinner air.

Just something to consider.

[markd79ta]

Originally posted by fastTA
One other thing to note is that a centrifugal type blower is not a positive displacement compressor like a roots type blower. So at your elevation, the impeller within a centrifugal blower will not be as efficient at producing boost as it would at a lower elevation. Say you have your particular head unit pullied to make 4.5 psi, it will actually make considerably less boost given the inefficiency of the impellar in thinner air.

Just something to consider.

I pretty much hate living here. It is such a pain. It sounds like the 9psi is the way to go. I will play with the 6psi setup for awhile so I don't blow anything up.

[Flash 97 WS/6]

I live at about 700ft above sea, run a powerdyne with a 13psi rated pulley (actually supposed to only make 11# on an LT1), I'm running a 2-core ATI intercooler (long story ) and still running stock 24# injectors without problems. No re-programming done other than fan temp and rev limiter, just using the FMU for extra fuel pressure.

Now, if you look at my sig. you will notice that this is a weekend warrior car, not a lot of miles, but it sees max boost (about 8 psi with the intercooler) at 6k rpms EVERY time I drive it .

With altitudes of 5k+ I would not even consider the 6psi pulley... it's only going to make about 5psi (if that) and that barely makes up for the reduced air mass at that altitude... basically you'll be getting the power of a stock engine at sea level. Even without an intercooler, I would go for a 9# (11#) pulley.

Powerdyne Warning: Powerdyne calls it an 11# pulley because they are rated based on the furd 4.6, be careful about this little trick if you go powerdyne... take a look at some part numbers carefully, their normal 6# pulley is that same one they use for the LT1 4.5 kit, the 9# is the same as the LT1 6# kit etc... they sometimes have a "Truck" rating...THAT is what you want to look for as it more closely reflects a 350 ci engine. What they call 11# actually makes 9# at sea level on our cars even though they don't officially support more than 6# on the LT1. (confused yet? )

I'd get the LT1 6# kit (biggest LT1 kit PD offers, comes with fuel pump and FMU) and an 11# pulley, you'll make around 7# (just guessing) and you should be able to run 90-91 octane OK.

* * Oh yea, and it will be %@*&$ FAST compared to what you are used to !

[markd79ta]

Originally posted by Flash 97 WS/6
I live at about 700ft above sea, run a powerdyne with a 13psi rated pulley (actually supposed to only make 11# on an LT1), I'm running a 2-core ATI intercooler (long story ) and still running stock 24# injectors without problems. No re-programming done other than fan temp and rev limiter, just using the FMU for extra fuel pressure.

Now, if you look at my sig. you will notice that this is a weekend warrior car, not a lot of miles, but it sees max boost (about 8 psi with the intercooler) at 6k rpms EVERY time I drive it .

With altitudes of 5k+ I would not even consider the 6psi pulley... it's only going to make about 5psi (if that) and that barely makes up for the reduced air mass at that altitude... basically you'll be getting the power of a stock engine at sea level. Even without an intercooler, I would go for a 9# (11#) pulley.

Powerdyne Warning: Powerdyne calls it an 11# pulley because they are rated based on the furd 4.6, be careful about this little trick if you go powerdyne... take a look at some part numbers carefully, their normal 6# pulley is that same one they use for the LT1 4.5 kit, the 9# is the same as the LT1 6# kit etc... they sometimes have a "Truck" rating...THAT is what you want to look for as it more closely reflects a 350 ci engine. What they call 11# actually makes 9# at sea level on our cars even though they don't officially support more than 6# on the LT1. (confused yet? )

I'd get the LT1 6# kit (biggest LT1 kit PD offers, comes with fuel pump and FMU) and an 11# pulley, you'll make around 7# (just guessing) and you should be able to run 90-91 octane OK.

* * Oh yea, and it will be %@*&$ FAST compared to what you are used to !

OK, I am probably going with the Powerdyne for now...I will put the kit on the Roadmaster later when I can afford to do a wild ATI Procharger and engine build. What is the part number for the 11psi pulley that you are talking about...what should I look for on their site. I have found the 9psi pulley.

Thanks for the info!

[markd79ta]

Originally posted by Flash 97 WS/6
I'd get the LT1 6# kit (biggest LT1 kit PD offers, comes with fuel pump and FMU) and an 11# pulley, you'll make around 7# (just guessing) and you should be able to run 90-91 octane OK.

Is this the pulley you are using?

http://www.proficientperformance.com...ode=D10045-270