This is likely something the people tuning my ECU will know, but since I want to understand how my 91 Q works, let me ask. How does Nissan/Infiniti monitor boost in thier turbo cars?

Is it a MAP sensor, even though the intake air is measured by the MAF?

I know the z32 ecu doesnt. It just goes on airflow and a few other variables, and has no real indication of what boost is. There are some boost solenoids which switch off if detonation/cold engine/less than a predetermined time running (3mins?) are sensed, this closes the bypass allowing the manifold pressure to go directly onto the wastegate spring opening at about 5-6psi which they term safety boost.the boost is controlled simply by boost jets in the hoses near the turbos. There is a thing which looks like a map sensor near the firewall but thats just to give the boost reading to the gauge on the dash and has no bearing on the engine control. I can only assume most other nissans do the same.

I think some model RB25DETs have some sort of map sensor because I had heard that there is a black box (no cliche intended) that controls the boost and would have to be removed when installing an aftermarket boost controller.

EDIT: To clarify what I meant, I think this is only used for the boost cut, As far as the actual EFI, they just use MAF sensors in the RB-series. The same is true for the VG and all other production fuel injected Nissan engines I know about.
Modified by SSDwellah at 7:17 PM 12/27/2006

The 300ZX just uses actuators that are set at a preset boost level, and the MAF measures the amount of air.......

The ECU on a MAF based car DOESNT CARE what boost you are running, it only cares how much air is entering the engine

You dont have let the ECU know what boost you're running.... Just put your MAF on the pressure side.... IMO you dont want to have the MAF on the intake side like it comes on the twin turbo Z because you have to be COMPLETELY FREE of boost leaks... Even if you have a tiny boost leak its going run really crappy... plus instead of assuming the air going into the turbo via the MAF is the same as exiting, you are measuring the amount of air that ACTUALLY enters the motor.

So the way Id set it up is you have your turbo with air filter somehow hooked up to it (or them ), run it up to your intercooler and then on the charged air piping throw in your MAF before the TB...

Im reasonably sure this is how JWT recommends doing it.... The only reason they dont run it this way on the twin turbo Z is because theyd need 2 MAF.

Thanks Wes. The advice on putting the MAF between the turbos and the TB is good info, and will be easy to do.

Curious about ignition retard as boost comes on, how does the ECU handle this function?

There are several problems with blow through MAFS setups though. Some major ones are turbulence due to the turbo, BOV, and throttle closing. Also I don't know how this will affect the readings with air recirculation and all the above issues.

I have always heard that the preferred setup with Nissan MAFS is ...

Air filter ---> 6 inches of pipe (or as much as you can spare, second segment is more important) ---> MAFS ---> 12 inches of pipe (more important than first segment) ---> turbo compressor inlet ---> turbo compressor outlet ---> BOV ---> some amount of pipe ---> optional intercooler ---> some length of pipe (BOV recirc enters here) ---> throttle.

This is on a single turbo, single intake manifold system e.g. SR20DET.

YMMV

on a single turbo setup that would definitely be easier IMO... maybe im just brainwashed thinking the only way to go is with 2 turbos! it would certainly require a LOT more custom piping to run a single MAF on a twin turbo setup with the constraints listed.

Im not sure if the turbulance problem would really come into play i mean ive seen people run open MAF with no problem on turbo cars.... Im pretty sure JWT recommends the blow through MAF with their ECUs (at least for the VH45 boost ECU), but their ECUs are pretty conservative anyway so it may mask any potential tuning issues....

I can see your points though, that under sudden throttle closing the ECU sees an instant drop in voltage and the car stalls.... im not sure how that would be any different than an N/A car..

Still it seems to me that when youre actually pounding down the streets in boost that you would get a more accurate reading in a blow through system and those other shortcomings would be easy to deal with...

we pulled the air filter of the 450 on the dyno, filter goes right onto the maf adapter then to the maf, i ran alot worse that way (no filter)

Next time try a big f*ck off trumpet