Ralls

iTrader: (32)

I will be using my stock 94 pcm (OBDI) and Speed Density once I finish the car. I bought a 3-bar map sensor. Even though I plan to run around 15psi of boost, I may be able to push a few more PSI. So that's why I went ahead and got a 3 bar so it will read past 15psi. But I have seen tid bits of information saying the LT1 computer cannot read a 3-bar map sensor. Is that true?
Is it because the computer won't read past 15psi or it won't read the sensor all together?

Another thing. Has anyone had a chance to tune Racetronix's 79lb high impedance injectors? I know they are fairly new to the market so I didn't know how they would handle for low speed street driving. I'm just afraid I'll max out 60's.

moehorsepower

iTrader: (3)

I pulled off my supercharger and was running NA with the 85lb injectors, No problems...Still running MAF and just dialed it in and tuned the rest..

Ralls

iTrader: (32)

But I wonder if it only worked because your using the MAF. I don't have a MAF so it's relying on the MAP and IAT only. So you are using a 3-bar MAP?

moehorsepower

iTrader: (3)

No, Sorry, I was using a 2 bar......

Ralls

iTrader: (32)

That's what I'm trying to find out. I know a 2 bar will work. But how are people tuning their cars if they are running 15+ psi and speed density?

edcmat-l1

iTrader: (10)

With either a 2 bar or 3 bar, with the OBD1 computers, you have to fudge the VE table. With a 2 bar, you cut it in 1/2. With the 3 bar, you cut it by 1/3. Personally, I would go with the 2 bar. Even if you go to 18 psi or so, you should be able to make that up in PE. With the 3 bar, you will loose alot of the resolution in the table.

It ain't easy.........

Ralls

iTrader: (32)

Good info. If I'm not mistaken, do you have to cut it by 1/3 with 3-bar because the voltage varies 3 times as fast as a 1-bar? Something like that?

I'm still iffy whether to use 60 or 79lb injectors. I don't know if 60's will support 700hp with a single walbro 255... maybe if I boost reference it.

edcmat-l1

iTrader: (10)

60's would be fine at that HP.

You have to cut it by 1/3 because you're referencing 3 bar in the same amount of voltage as the 1 bar. Has nothing to do with how fast it varies.

Both are 5 volt referenced. The way it's set up, it's measuring 1 bar. You want it to measure 3 bar. The voltage will be no different.

Ralls

iTrader: (32)

Oh, I saw a comparison of a 1-bar and 2-bar, and the 2-bar increased at a faster rate. I must of interpreted it wrong. Well thanks.

poconojoe

iTrader: (43)

The value that is represented by each tenth of a volt increase will be more. For and example on a 1 Bar MAP the range will be minus 14.7 PSI to 0 PSI, on a 2 Bar the range will be minus 14.7 PSI to plus 14.7 PSI since they both have an avaliable output range of 0 to 5 volts, the 1 bar sensor will output 1 tenth of a volt change for every 0.294 PSI of pressure change, where the 2 Bar sensor will output 1 tenth of a volt change for every 0.588 PSI of pressure change, if you threw a 3 Bar sensor in to the mix it will output 1 tenth of a volt change for every 0.882 PSI of pressure change As you use a sensor with more range you lose the resolution, since each voltage increase represents more change, so you shouldn't use a 3 Bar, if a 2 bar will do the job, or use a 2 Bar in the motor is NA

Ralls

iTrader: (32)

Makes a lot of sense now. Thanks man.