Map sensors

[FLSRT8]

Can someone educate me on the differences between a 2 and 3 bar? Why some tuners feel they can use a 2 bar instead of a 3 to run boost over 14 pds. They say they can cut the tables in half and get better results since the PCM can detect (Sh** wish I wrote this down) something sooner and apply quicker power or can tell its going into boost while a 3 bar has to wait for the power curve to move up the table before it see it? Hope one of you guys can help fill in the blanks.

[BJB]

Can someone educate me on the differences between a 2 and 3 bar?

3-2=1 :pounding table: Is that the answer you were looking for??

This was explained to me once. Could not go into the details. Maybe Wilson will be on here over the weekend. He would be the one to explain this.

[FLSRT8]

We both are running forced induction and we both know that 1 is not the right answer!

[BJB]

Sorry Couldn't resist!! :D

[QIKBRIK]

1 BAR is the same as the following:

760 mm Mercury (Hg)
29.92 inches Hg
14.7 psi
101.3 Kpa

Which are all measures of atmosphereic pressure on a "standard day", 15 degrees celsius, 50% relative humidity. Change any of those pamaters, temperature, pressure, or humidity, and it is NO LONGER 1 BAR.

A 1 BAR MAP reads pressure up to one atmosphere, or 14.7psi. All N/A engines operate at a maximum of 1BAR becuase thats the maximum pressure that it will ever see. N/A motors run on the principle of high pressure always flowing to areas of lower pressure, so its the atmosphere actually pushing the air into your cylinders, not the cylinders "sucking" air in. This is why DA has such a huge impact on performance.

A 2 BAR MAP reads to 29.4psig, or 2 atmospheres relative to total vacuum, which is equivalent to 14.7 pounds of "boost"... boost being defined as any pressure in excess of normal atmosphere.

MAP sensors read the outside air pressure and send an equivalent voltage between 0-5 volts to a computer. There are only so many voltage paramaters that the sensor can send to the computer for interpretation. If the range of the sensor is increased, such as going from 1 BAR to 2 BAR, there are half as many voltage points for a given amount of pressure. If you go from a 1 BAR to a 3 BAR, you still only have a range of 0-5 volts to play wit, for now tripple the amount of pressure range. Accuracy of the sensor suffers. You will always have better operating parameters and easier tuning with lower BAR sensors. If you dont need to go over 15 pounds of relative boost then no need for a 3 BAR.

More than likely whoever your tuner is, is either clamping the voltage, or else just dumping massive amounts of fuel into your engine whenever the MAP reads its maximum pressure. This is a way to guestimate that your engine is safe if you exceed your MAP. It not real safe, and you may experience a lot of unburnt fuel, black smoke, etc, over time.

When your guy is saying that the 2 BAR is "faster", or whatever you were trying to say, its probably that he means that the 2 BAR can read more accurately for a given amount of Delta-P, or change in manifold pressure, or the RATE of that change. And indeed, will react quicker than a 3 bar, which needs more change in pressure to provide equivalent voltage feedback to the computer. For a mildly boost engine, this is nominal. But for imports that run 30psi, this is insane and should be running a 3 BAR, what kind of car are you putting this thing on?

Initially when you hit your throttle on a 3 or 4 BAR MAP, the engine will have a lean spot as it transitions to boost. This is the lag time he may be referring to before the tables richen up.

[FLSRT8]

I have a 06 Jeep 426 twin turbo, SCT tuner, 2 bar map. I'm currently using SCT for tuning but have the option to change to Diablo this week???? At 10.71 boost I'm making 748 AWHP. I would like to reach 1000 AWHP and will have to increase boost to over 15 or so to achieve this.

[HarryBallz]

Get the SCT out of there Chris.... have you seen anything powerful Hemi wise being tuned with a SCT? After Winston mde the switch, his truck just runs a whole lot smoother and better. MAKE THE SWITCH!! Did you change the intercooler out yet?

[FLSRT8]

Jeep down for new fuel system. Not sure what that will be. Stage6 was to call and give me a price but they never did, so they are out. Still working on the intercooler. Tuning still not figured out. Hope I can get all this done by May 3rd.

[FLSRT8]

So for you tuners, is there a solution for the lack of power down below when using 2 and 3 bar maps?

[Wilson]

I agree with almost everything qikbrik said. But the response is not dependant on the range of the sensor. The Neon SRT 4 actually uses a 3bar scaling on it's tables even with the factory 2 bar calibration. You can rescale the tables in the CMR software to read as high or as low as you want. When you install a new MAP, you are only increasing the range that the MAP sensor will read, you are not affecting the responsiveness of anything. All you are doing is changing the relationship between voltage and pressure. A 1 Bar sensor just reads 14.5PSI of atmosphere (0 boost) at 5V while a 2 Bar reads 29.0psi (14.5psi of boost) and a 3 bar reads 43.5psi (29psi of boost) at the same 5Volt signal. So if you were running a 2 bar MAP sensor, you would read ~2.5V at 0 Boost (Assuming a linear sensor).

Now, some people may argue that you will lose resolution in the table and this is true, but you can bias the resolution to the lower end of the scale to improve driveability. Larger break point differences are possible when you are in boost because you don't operate at part throttle high boost very much.

One other thing to realize is that just because you have a 3 bar MAP doesn't mean you need to have the tables scaled for the full range. You can scale the tables for 2 bar, 2.5 bar, 3 bar or anything in between. My reccommendation would be to use the 3 Bar and scale the table for the appropriate amount of boost you want to run. Keep some margine incase you get overboost just to be safe. A good calibrator should be able to handle this no problem.Feel free to PM me if you have any questions.

W

[Wilson]

So for you tuners, is there a solution for the lack of power down below when using 2 and 3 bar maps?

Your power should not change depending on what MAP you are running. If it does, your calibration needs to be adjusted. It should run the same at 12psi with a 3 bar as it does with a 2 bar at 12psi.

BTW, I've never heard anyone having luck with the SCT stuff. I would recommend the Diablo stuff. It's a proven product and they have very good product support. Not to mention it is available almost anywhere in the country.

W

[FLSRT8]

Thanks Wilson, I will switch to Diablo and a 3 bar next week. I will also be looking for a tuner before the May 3rd event. I was told this was the site to find the best.

[FLSRT8]

What about a 2 1/2 bar map sensor? Has anyone run this on their vehicles?

[Blown-WK]

I hope you can get it all sorted out Chris. Too bad Johan doesn't have an AWD dyno or you could get him to tune it out.

[FLSRT8]

I'm sure he could find one if he wonted.