FAST MAP sensor question for Craig/Lance

[njrob6]

Am i correct in saying that the 3 bar map sensor used in the FAST system will read up to about 30psi? My new combo will be boosting up to 36 psi and spinning the motor over 8,000. What do I need to do to tune it above 30psi?

My combo is a 388 SBC, Dart 18 degree heads, Procharger F-3R supercharger flowing through a liquid intercooler. Car is setup to run mid 7 secs weighing in at 3,100lbs.


Rob

 

[V6Power87]

I would like to know also..... I thought one bar was 14.7 psi?

So 3 bar would be 44.1 psi?

 

[bobc455]

Well 3 bar means 3 bars above a perfect vacuum- a NA car will use 1 bar (0 PSI boost= atmospheric pressure), a 15PSI boost will use 2 bars and a 30 PSI boost will be 3 bars.

Last I heard you could only use a 3 bar sensor (30 PSI boost) but I seem to remember ramblings about maybe expanding beyond that, so I'll leave to Craig/Lance to say...

-Bob
bobc@gnttype.org

(I don't think a 4-bar sensor can be used, if one even exists...)

 

[Craig Smith]

To date, people running above 30 psi have been doing so with a 3 bar sensor. You peg the cursor at the top of the screen so it only "knows" that you have 30 psi, but you can still do it - you just have to realize that from 30 psi and above you are running out of the same numbers in the VE, target a/f, and spark tables.

Here's the problem. A 4-bar sensor, contrary to what several people have told us, does not seem to exist. We have spent a lot of time trying to find one for these applications and cannot come up with a 4 bar sensor to save our lives. 5-bar sensors exist, but they seriously limit your tuning resolution since you have so much ground to cover, and they also cost several hundred dollars.

I would say that you could proceed with a 3 bar sensor bearing in mind that you are above the limit of what your MAP sensor can accurately read. If that sounds scary I understand. I don't know that I would do it that way with my own stuff, but I have talked to a lot of people who do and have good luck with it that it can't be THAT bad of a thing to do.

 

[Chuck Leeper]

3BARZ??

Anyone know how Kent R. does it? He MUST be at "40PSI and rising".

 

[ijames]

Could you use a tee with an orifice and a leak to air, like the stock y-hose to the turbo? Put the orifice to the manifold, put a 3 bar map sensor on one of the other two legs, and put either a very small orifice or one of those bleeder valves on the last leg. Put a little filter on the valve or plumb it in to the intake pipe after the air filter, because when the engine isn't making boost it will suck in some air. Anyway, under boost there will be a pressure drop across each orifice so the map sensor will see a fraction of the true manifold pressure (works the same under vacuum but the air is sucking in not blowing out). If the two orifices (plus the tubing restrictions) are the same size you should read half the pressure. Will take some tuning and you will have to calibrate your setup with an independent boost gauge, but it would let you expand the range as much or as little as you need to.

 

[bruce]

Re: 3BARZ??

That wild of combination, you might think of just going Alpha-N.

Going to a 4 bar sensor even if they existed, your low end table resolution is going to be lousy.

Using a 3 bar just means you running the same fuel and timing at 30 PSI as you are at 36, meaning you a little rich and slightly retarded at 30, which isn't going to be that big of deal, IMO.

On the oem MAF system, guys are getting away with going way past the oem resolution, and going fast. And they are wayyyy past the oem capacity.

 

[Craig Smith]

Alpha-N + turbo = engine parts on ground.

Forced induction systems have to run speed/density. At any given throttle position and RPM, you have no idea what the boost is going to be. Might be 5 psi or 25. Kinda tough to pick a pulsewidth and make it work for both.

 

[nightdiver]

What about the delco map sensor from Volvo truck F16 ?
I know their boost goes over 30 psi ??????????

 

[S2V6RACER]

Re: Re: 3BARZ??

Originally posted by bruce


That wild of combination, you might think of just going Alpha-N.

Going to a 4 bar sensor even if they existed, your low end table resolution is going to be lousy.

Using a 3 bar just means you running the same fuel and timing at 30 PSI as you are at 36, meaning you a little rich and slightly retarded at 30, which isn't going to be that big of deal, IMO.

On the oem MAF system, guys are getting away with going way past the oem resolution, and going fast. And they are wayyyy past the oem capacity.

I agree with bruce. Your A/F ratio and O2 correction will still be logged and accurate. I would just take it a little at a time and keep a eye on the #'s and add to the top VE #'s.