3 Bar map accuracy

[Big88]

anyone using a 3 bar map with a fast ? Mine seems to be a little off. On the laptop it is showing 26 - 27 lbs. of boost but my boost gauge and fuel press. gauge says 22lbs. Which one sould i belive? Anybody else seen this differance?

 

[Red Supra]

Yes, I have noticed the same thing on my car also. I would like to know which is right. Or maybe it's a value between the 2 pressure reading.

Does your boost gauge and fuel pressure gauge read the same?

Max
93 Supra turbo

 

[Big88]

The fuel gauge and the boost gauge are very close to each other. I would like to crank up the boost , but i don't want to break it.

 

[S10xGN]

I'd suspect the MAP, being close to it's maximum reading, is the inaccurate reading. A 3-bar MAP's maximum reading *should* theoretically be 29.4#, but all units will have some production "slop" tolerancing and may not be as accurate when close to the limits...

• 1 Bar = 28" vacuum to 0# pressure
• 2 Bar = 28" vacuum to 14.7# pressure
• 3 Bar = 28" vacuum to 29.4# pressure

As you can see, the more the "bar", the less resolution is available for a 0V - 5V signal, which is prolly making your MAP reading skewed a little.

 

[Big88]

Ok, It would seem to me, How well could you tune with a fast or any other managment system, that the psi reading is that far off?

 

[Reggie West]

I would trust the MAP sensor above all else.

You can check it against an air source but I would bet you will find the MAP to be much closer.

Remember the FAST unit makes all of its calculations off of that MAP sensor so that is the one to trust.

My Dads GN had a manifold with 5 or 6 leaks in it. It took us forever to figure out what was going on. The boost gauge would read 30 psi but the MAP was only reading 24 or 25.

Guess which one was right

 

[bruce]

Originally posted by Reggie West


Remember the FAST unit makes all of its calculations off of that MAP sensor so that is the one to trust.

That's all that counts.
That and remembering you tune to keep the motor happy, not tune to get a number. Just cause someone else runs 7s with 32 PSI at a 11.2 AFR means that your car will be fast with that tune.

Your's stand a 50/50 chance of wanting less, or 50/50 chance of wanting more, from anything anyone else reports. Don't fall prey to the numbers games. They are just some hints on what MIGHT work or even be true.

 

[TurboBob]

There are some odd 3bar sensors around, I think they have a yellow insert in the connector instead of orange. They were calibrated differently.

Bob