SharpZ28

Hi guys, I just put a Paxton SN2000 kit on my stock engined 1992 Z28 350TPI. The car pulls good at first, but then seems to surge in the upper rpm's. Could it be running lean? I am also going to install an MSD 6AL ignition to insure good spark. The instructions say that no modifications are required to install the supercharger, but I think this is B.S. Thanks for any help or info.

LBSZ28BLOWN

SharpZ28,
I had the same thing happen to me also, and I just installed
a sn2000 on a friends Z28 and his did the same thing.

The problem is not enough fuel, you'll need a bigger (higher flow)
pump to start with.

SharpZ28

Thanks, I was thinking this would be the problem. I put an Auto Meter air/fuel ratio gauge on also with the supercharger and when at wide open throttle it seems to be pegged in the lean zone. I guess next on the shopping list would be hi-volume pump, adjustable pressure regulator, and fuel pressure gauge. Should I be o.k. with the stock injectors? Thanks again for your help.

Willie

iTrader: (1)

You've heard the saying, "One thing leads to another."?? This applies here! With substantially more airflow comes the need to add substantially more fuel. Check your fuel pressure under load as I suspect it is decreasing. Assuming this is the problem, the fix would be to replace the in-tank pump (the best solution) or add an in-line (band-aid).

Now, are the stock injectors good enough? Probably not. A couple of simple calculations to determine duty cycle is needed. If you're exceeding 80-85 percent, they're not large enough. However, this is NOT going to be the primary problem, it's secondary.

Primary problem:
The stock MAF or SD system cannot "see" a boost condition. Therefore, how can the ECM add more fuel if it doesn't know to do so? The simplest fix I can think of is to change the 1-bar MAP to a 2-bar. Accordingly, the EPROM MUST BE CHANGED.

A can of worms? Yes, but very well worth the effort.

SharpZ28

Thanks Willie, the guy I bought the supercharger from also said he had an Accel 2 bar MAP sensor and a custom burnt Jet chip, which I got from him also. I was going to see how well it would run stock first before changing anything, but I knew that with an increase in air also comes the need to dump in more fuel. Will the 2 bar MAP sensor tell the computer to richen the mixture under boost? Should I swap out the stock MAP sensor and get a better in tank pump to start with, and work from there? Thanks again.

Willie

iTrader: (1)

You might already know this but felt I should explain just in case>> The term "1-bar" refers to one atmosphere. Its range is from ~30 inches of vacuum to zero inches (also known as zero atmosphere or no vacuum). A 2-bar's range extends the one bar into the pressure side or 14.7 psia (pounds per square inch atmosphere). So a 2-bar MAP will see ~30 inches of vacuum PLUS boost up to 14.7 pounds! To extend this, a 3-bar MAP will see up to 29.4 pounds of boost (14.7 x 2).


Will the 2 bar MAP sensor tell the computer to richen the mixture under boost?

Yes, but only if the EPROM is burned accordingly. You definitely cannot run a non-boost app EPROM calibration with a 2-bar. I don't think the engine will even run!

I was going to see how well it would run stock first before changing anything....

A good engineering approach! Gotta love it.


Should I swap out the stock MAP sensor and get a better in tank pump to start with, and work from there?

The very first thing I'd do is install a fuel pressure gauge. Monitor it to make sure your pressure is good under boost. Note that fuel pressure should increase slightly with boost, about one pound of pressure for every pound of boost. I cannot overemphasize to build boost gradually. Try five pounds or so maximum at first. Watch the pressure. If it's okay, go to seven pounds or so. If the pressure does not rise or even decreases slightly, replace the pump. Once this issue is no longer an issue, move on to the next step.

Above all, the best engineering philosophy is to make only one change at a time. This will allow you to evaluate that change. This is why I would not replace the MAP sensor until your fuel pressure is sufficient. Replacing the MAP sensor/EPROM will further aggravate the fuel pressure problem because it will demand the pump work even harder -- even more fuel.

Willie

83 Crossfire TA

iTrader: (2)

Well, not exactly, The stock map can actually "see" slightly into the positive pressure range, but the ECM isn't really programmed to deal with it. The MAF doesn't care about boost at all but the mass of air passing through it, so until you reach the flow limit of the MAF and you have a table to look that flow number up in the chip it will meter "work."

To be strictly technically correct, 1 bar = 14.5psi, not 14.7

Will the 2 bar MAP sensor tell the computer to richen the mixture under boost?

Yes, but only if the EPROM is burned accordingly. You definitely cannot run a non-boost app EPROM calibration with a 2-bar. I don't think the engine will even run![/b][/quote]

The output range of a 1, 2, 3, 5… bar map is the same, it's just the voltage that a specific pressure results in is different. A 2 bar map will have half the granularity of a 1 bar, but it will be able to measure over 2x the range. If you plug a 2 bar into an ecm with a chip programmed for a 1 bar map the ecm will think that the manifold pressure is changing at about ½ the rate that it actually is.

Well, a good engineering approach would be to know exactly what you need from the start and design a system that works perfectly for that… Since we don’t have that luxury and don't really have adequate data acquisition available to do that, one thing at a time is best…

SharpZ28

Thanks for all the technical stuff, but this is a bit over my head. My car is speed density, and I need to know what items are needed to get my car to run at its full potential with the supercharger? I know that the stock in-tank fuel pump is now inadequate under boost. I am going to get a fuel pressure gauge to verify this. Thanks for the help.

antoine

i have a sn-93 paxton on my camaro paxton says bolton not had to change to bigger injectors,walbro fuel pump,colder sparkplugs,msd btm etc.

Raiden

I had the SAME expirence! It was like the car crapped out above 35-3800rpm's. I put in an 255l/hr pump and fmu which solved the problem. Pulls up to 5500rpm's strong!

B4Ctom1

right on! I think this is a great place to start. call it square one. there are many that will suggest that you do a huge computer mod and do the whole $58/749 ECM workover to sense boost and add fuel though bigger injectors, and they are correct. but that is such a huge jump for most people. consider the fuel pump and FMU thing to get a feel for how you like this project. graduate to the ECM prom buring when you are ready or when it is required by your power/versatility needs.

Willie

iTrader: (1)

I always thought that one bar equals one atmosphere or 14.7 psia (called Standard Atmosphere). I only had to take one fluid dynamics course in college (and hated it). I just looked at the book (I kept all my engineering & math books) and it makes no mention of a "bar". So if it equals 14.5 psia, where does this value originate and why 14.5??? You got me curious....

Willie

Blown87

iTrader: (1)

For what it is worth, I am running a SN2000 with a stock fuel pump and #30 injectors. The engine runs fine all the way up in the 5000 RPM range, although in the future I do plan on upgrading the fuel pump.
Mine is MAF and has a PROM that is configured for the upgraded injectors and boost.

SharpZ28

I found my problem! The vacuum block off hose I had on the intake manifold blew off the first time I came up on boost. I took out the vacuum fitting and screwed a plug in it's place. The car now runs fine, although I am still going to up-grade my fuel system. Thanks for the help everyone.

SharpZ28

Blown87, what pulley size are you running for 11lbs of boost and have you run any 1/4 mile times with your set up?

Blown87

iTrader: (1)

It is a 3" pulley on the compressor. I just purchased it (about 4 weeks ago)from Paradise wheels. I have not run it on the track yet, it will be there in a few weeks.
One thing to keep in mind is that the SN2000 has a compressor redline of 38500. With the three inch pulley, that equates to an engine speed of about 4700 RPM. I have my rev limiter set to 5100 RPM. So I am exceeding the compressor redline. Even though I have to watch the engine speed, I like the new pulley. It gives me more "usable" boost under normal driving conditions. The boost now comes in at much lower engine speeds, which gives me more kick when not at wide open throttle.

SharpZ28

Thanks for the info, I need to put in some 3.73 gears in the rear like you have, mine are 3.23. Mine seems to be sluggish until it gets rolling. I will measure my pulley tomorrow, it is putting out 6psi right now. I am trying to get the car in the 12's, before the supercharger I ran the car for the first time at the track, it went 14.34 @ 95 mph. This was on the worn out Firestone radials I have on there now. My next visit to the track will be on some drag radials and hopefully a 12 second timeslip.

anesthes

iTrader: (12)

Remember, WOT under boost on a '730 will be in PE mode, which is open loop. Even if the ve table scaled differently, I dont think you'd get the fuel you wanted.

'749 here - woohoo!

-- Joe

83 Crossfire TA

iTrader: (2)

Blame the metric system, 1 bar = 1 x 10^5 Pa (pascals)

91TPI5.7

[QUOTE]Originally posted by Willie [QUOTE]
Willie, you are correct in saying that 14.7 equals one atmos. at sea level. All guages are calibrated to read 0 at sea level (PSIG)
So 1 PSIG (mind you all is done at sea level) equals 15.7 PSIA.
And the conversion to bar goes as 1-bar = 14.50377377302092 PSIA. That reads in at .2 (about) PSIA under 1 atmos. So a 1 bar map cannot read into the positive. Just thought I'd share thishttp://www.csgnetwork.com/automotiveconverters.html Awesome site for any conversion calculation you need.