This should be a quick one, basically when my engine was built and the power FC installed the guy who built the engine used an FD 2bar map sensor when i specifically asked for a 3bar, the vehicle was tuned on the 2bar, but i'm wondering, since i DO plan on running more then 15psi, how hard is it and what is involved in changing it to a 3bar?, i presume the vehicle would have to be re-tuned all together?...

thanks!...

 

Should be able to scale everything over. A slight retune will be needed though.....but basically a check over to make sure everything is fine. Not a big deal.

 

the FD MAP sensor reads up to 17psi, but the factory calibration from Apex'i is inaccurate. It will read about 1-1.5 psi too low as you boost it, with the inaccuracy increasing as boost levels increase. For example, I have a friend with an FD that runs about 14psi, but with the inaccurate MAP sensor calibration it reads about .9 kg/cm^2, or ~12.75psi . I didn't bother recalibrating the MAP sensor for his car because I didn't feel like retuning it, which could affect idle as well, so I just used 14psi timing in the 12.75 psi area of the map. If you change anything MAP sensor related, either the sensor or the calibration, it will need at least a minor retune unless your tune is so pig rich/conservative that you wouldn't notice a difference.

Your situation is further complicated by your high altitude. You may find your PFC Commander does not read close to "0" for boost with the car off. Ideally the MAP sensor would have some kind of calibration next time you tune it. One number you could tell your tuner to use is "scale 35800 offset 3900" if he has the older version of the datalogit software, or "scale 5375 offset 3900" if he has the newer version of the software. That will at least make it read more accurately under boost, although it won't be matched to your altitude exactly.

Anyway, the direct answer to your question is, no you don't "need" a new MAP sensor, and yes you could "get away" without even changing your FD MAP sensor calibration depending on how your maps are set up. I would have to see the tune the guy put on there, and that would require you having a datalogit. If you think your car is running right at this point just leave it alone.

honestly though, if you raise this issue with your tuner, there is a 90% chance he will say "oh don't worry about it," probably because he wasn't even aware of the issue. Besides the PFC self-tuners on this forum (like myself), only specialty Rx-7 tuners know about the FD MAP sensor issues.

 

i'm looking at upgrading my BNR3 turbo for my new T04R and would like to run 16psi, since you said the FD map sensor reads to 17psi should i be alright?, and i doubt the tuner did the calibration on the sensor....

regardless, if i had to stick with the FD sensor, what psi would i be safe to run here in alberta, canada.... what would you guys recommend....

 

depending on the fuel you're using and you're level of bravery (and money) 15-16psi is about the practical limit (which on a t04-R is VERY fast....) That can be raised with better octane, whether you deliver it in the gas, or by auxilary injection.

 

i'd be considering 15psi with the T04R, however the 2bar map sensor ordeal is kind of worrying me, when you say 15-16psi is practical do you mean in general?, on a stock engine?, on a 2bar map sensor?...

my engine is built with 2mm RA seals, not sure if i mentioned prior, aswell it has a complete fuel system from RX7store, etc....

last piece to the puzzle would be the T04R....

 

It is always better to be safe than sorry. Being cheap will always cost you more in the long run. The 3 bar sensor will give you room to grow with your setup. Where as the FD sensor is like playing with fire.

 

so, what exactly happens when the boost surpasses the 2bar map sensor?, is there zero change in fuel mapping and resorts to "base" mapping or does the mapping stop at the bottom of the grid where the "15psi" would read....

 

I would need to see your map to give you a better answer. On stock FD MAP sensor and scaling, the highest row the Power FC will read up to is row P19, or 1.2 kg/cm^2 of boost (17psi or so). At that point the MAP sensor is reading right near 5 volts. So if you run 20psi, the ECU will still only read 17psi and deliver the same fuel and timing as 17 psi. You will lean out and your timing will be too advanced by at least 2 degrees.

Set your boost target to .95 Kg/cm^2 and you will hit fuel cut at 1.20 kg cm^2 (fuel cut = boost target + .25 kg/cm^2), right before you overrun the map sensor. I don't know why you are sweating this so bad. a GM 3 bar sensor is like $60. I bet you could get Banzai Racing to sell you just the sensor and harness adapter, or otherwise buy the sensor from ATP turbo and wire it in yourself.

 

i run an apexi 3 bar map sensor...
i just liked the idea of apexi doing the calibration, where there are no variations between tuners (GM 3 bar)... and i hate the idea of a sensor reading its peak... or near its peak alllll the time... what if you have a 1 or 2 psi variation and thats all it takes for **** to go bad? after all... there is only one right answer...

 

If you exceed the limitations of the FD sensor, (arghx's example) running 20psi it does not stay at the 17psi row, it defaults to row 20. This is the reason there are some tuners that will push the stock sensor to 20-22 psi, since they can set up row 20 with loads of fuel and proper timing. It is basically a work around and the wrong way to tune a car.

Basic rule of thumb, when using a 2 bar sensor do not exceed 1 bar of boost. I do not care if someone has tested the FD sensor to 17psi, there is a margin of error. If you want to put your motor and turbo on the line because someone on a forum told you it was OK to exceed the limitations of a sensor, that is cheap to replace with the correct one, that is your call.

Pushing 7-10 psi is not nearly as dangerous as 17-20, all it takes at the higher boost ranges is something small to be incorrect and you lost a motor. No one needs to see your PFC map to tell you this.

We do not sell the GM sensor and FC harness individually.

 

thank you for the clarification.

 

problem being is that i just spent $450 on a tune for the power FC and now recently read that i need a 3bar and to have the entire thing retuned, it's frustrating considering i told the initial builder to USE a 3bar sensor....

how can i convert it from 2bar to 3bar?...

 

You should have had this tuning mixup straightened out as soon as it came up instead of sitting on it.

you convert from 2 bar to 3 bar by wiring in the GM sensor, which is 3 wires I believe, and then there is all the PFC stuff you have to do like change the scaling and double check the tune.

 

yeah on the FD sensor there are three wires connected.... if it's simple enough to wire in the 3bar it shouldnt be that big of a problem, i'll run the T04R @ 15psi i figure and when i'm ready for more boost i can get it re-tuned....

nothing wrong with running 1bar on a T04R is there?... besides, any idea what my limits should be with a race ported engine with RA super seals?...

:P

 

You are going to need access to a datalogit to enter the offset and scale for the GM 3 bar.

What PFC do you have? The AP or the FD with our install kit?

 

i'm not sure, i want to say the AP however it was a rare unit specifically built for the FC so it was plug and play utilizing the factory FC coils....

 

That's too bad, if it were our kit then your would already have the settings in the base map that we supplied, to run the GM 3 bar, on option 2

...and our kit uses the factory coils, just the trailing ignitor needs to be modified.

 

i thought i was doing myself a favor buying the power FC for the FC....

frick....

 

in that case
go buy the apexi 3 bar map sensors
it plugs in directly and look better anyways...
thats what i use....

 

yeah it will be more expensive but it will work, you should still double check that the tune is ok though.

 

i will check when i swap map sensors for sure....

theoretically though, i should be able to run 15psi on a T04R without problems though with the 2bar, correct?....

 

yes, 15psi is done on that sensor all the time

 

excellent.... then it will be a fun summer for sure....

:P