2 bar map sensor questions to help better my tune on my D1SC...

I currently have a 95 Z with the stock PCM (single bar map sensor). From what I understand if I were to upgrade to a 2 bar map sensor, it would be easier for my dyno tuner to re-tune my supercharged Z in my sig, plus, it would probably run better. I am aware that ultimatly a complete FAST system would be ideal, but don't really want to spend the $ involved with that.

My question is, what exactly is involved with switching to a 2 bar map sensor? I am not even sure where it is located in my car. Can I just go to GM and order one for $40?, and then install it right before I have my car dyno tuned?

Are you doing a 2 bar Speed-Density tune or simply 2 bar and keep the MAF?

If you're keeping the MAF, it won't be that big of a deal to drive it with the wrong MAP sensor. But, that's sortof a rigged way to do it since the computer fueling will still be blind to boost.

If you want to do a 2 bar SD tune, then your tuner had better be good. I have only heard of 1 car that actually made this work on the stock ECM, and it was a '93 which worked a little different in the base case.

Mike

I guess I don't know much about the whole thing and am still learning here. I know the LS1 cars have two or three bar map sensors and are much better to tune accuratly. Especially over 600 RWHP.

So, basically you are saying in order for me to do this right, I need to run my car speed density without a MAF, and then go to the 2 bar map sensor?

If that's correct, how do I properly take out the MAF from the car to have it set up correctly?

The more info the better for I don't know much on this and would like to.

Best to talk to a PCM tuner. Like Madz. They can tune out your MAF and adjust your VE tables so they should be close.

If you doing this to a Daily driver, then one big downside i hate is weather and alt. are very noticable with a SD tune. Since you adjust most of the tune by the VE tables, when it gets hot or cold out, your tune is off. With the MAF the computer can tell extactly how much at is coming so weather has a much less effect on the tune, weather still will effect it though.

The LSx's run 2 and 3 bar tunes because they are able to replace the OS in the ECM and it'll do whatever you want. It's not so easy on an LTx.

Yes, to really do it right, you would get rid of the MAF and run a 2 bar MAP sensor, but very few people have gotten this to work.

If FAST or BS3 is too expensive, take a look at MSII. It includes most of the same features, including full-throttle WBO2 feedback control, but for $400 instead of $2000.

Mike

when it gets hot or cold out, your tune is off.

Not if it's done right. Cars ran on Speed Density for years and they did fine.

Mike

I'm planning to attempt this same thing with a 3 bar GM sensor I picked up off ebay for around $50. Since I'm only boosting 7 psi right now, I could have used a 2 bar, but I thought I might eventually get up above 15, although unlikely. To gain back the resolution lost by going to the new sensor, I'm planning to incorporate an adjustable scaling circuit (just a non-inverting op-amp circuit with potentiometer) to maximize use of the PCM tables to get most of the resolution back. Obviously I will have to adjust all of my MAP related tables and constants in the PCM also. I have no idea if it will work well or not, but it'll be a fun winter project anyway.

Well after talking with my tuner, it sounds like I will be keeping my 1 bar, and my MAF. Without going with a FAST or similar system, it sounds like swapping to the 2 bar and going speed density is much harder to do after all as far as tuning it goes.

Thanks for all the inputs.

To gain back the resolution lost by going to the new sensor, I'm planning to incorporate an adjustable scaling circuit.

There really isn't much reason to do this. The LT1 ecm has way, way more VE cells than the aftermarket ecm's. Even when you half it, you still have plenty of resolution.

There really isn't much reason to do this. The LT1 ecm has way, way more VE cells than the aftermarket ecm's. Even when you half it, you still have plenty of resolution.

That's interesting, I didn't know that about aftermarket ECM's. Will there still be enough resolution for shift points, etc? Whether it's necessary or not, I still plan to try just for the fun of it. With the 3-bar MAP that I have already, I'd be cutting my resolution to 1/3 of stock without the scaler.