Hi....Im looking for someone with some know how on the GM efi system with maf and a dis. (no crank senser style) Because i am building a yard style 225 turbo blow through system with efi and havent got this far yet but I am thinking when I let off the gas pedal and the blow off valve dumps the air dumped will have been meseured and accounted for by the computer but never makes it to the cylendar. ok?? Heres where the problem comes in. In theary this is where a lean condition comes in. A potensial problem of the engine dieing when going around a corner. So my question to myself and anyone that might know is.....can i use the maf systen and add a map sensor and still use the prom from the maf system? will the computer recognize the map sensor or do i need to rethink the air metering system i am useing.? Like use a prom from a 3.8 turbo setup and eliminate the maf system to go with a map system.?? Also I am thinking of ways to run the ignition timeing and have it retard with boost. ( im useing a solid lifter 225 so the knock sensor mite not proove to be a reliable sorce for detination controle. ) and yes thears lots of aftermarket stuff i could by to corect any and all of these problems but im trying to use my head more than my pocket book. Unfortunetly they are boath empty. ha ha he he. Thanks for all and any constructive ideas and criticizums.

If the blow-off dumps the air charge after it's measured by MAF then the pcm will still inject fuel for the "full" amount - so you'd have a momentary rich condition. AFAIK, the factory Buick turbo system was a blow-thru throttle body but didn't use a blow-off valve (mild system). I don't know if you can route the discharge from the blow-off back into the air inlet duct ahead of the turbo or not.

You can't pick & choose what sensors you want on these OLD factory computers. All these EFI 3.8L used MAF, but none had MAP (until the series II in mid-90's- & that wasn't for fuel control). You could try a different computer system for a different engine that was MAP but your fuel/spark maps would be out the window (& not even close for a boosted engine.)

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63 Valiant Wagon
225 - 4 bbl

I will interject here. The GM ecus from the late 80's to the early 90's were anazing devices. But by the tlme you buy the programers, burners and what nots to reprogram them, you may be money ahead going with a Megasquirt or something simular.

Yep, the GM "P4" computers weren't that bad (once they figured out how not to have them break- I replaced LOTS of them back in the day)- they used "cal-pak" modules with all the eng calibration info burned into them. It would be more work to modify all the needed sensors to a /6 but it's a much nicer system- esp the MAF sensors.

The earlier 3.8L (up thru '87) - including the batch-fire "distributor" type used the older "C3" computer with just a PROM chip for calibration - does anyone still "burn chips" these days? Let's not forget the "hot-film" MAF's - better carry a spare.

None of these old OEM systems are close to the adjustability of most aftermarket units.

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63 Valiant Wagon
225 - 4 bbl

Ah yes I stand corrected. This would create a ritch condition. Maybe i should get the EFI up and running before i introduce the turbo. humm... Also i should add that the only reason i am thinking i might need a blow off valve is only because i have no idea how the turbo i have will spool with the slant. ( could be too mutch,-early RPM - could be not enough- late RPM).... I hope its the later. because this would fit into the end resault better for me.
Another question i had was what type of signal does the knock sensor make when it is ratteled. My first guess is it grounds. and makes a square wave via the timming controler and moduel. Any body know? And the reason i ask is because I am thinking if i could mimic this signal i could controle timming via the ECM with a simple electronic device. Thanks again.

instead of using a bov you would need a redirection valve commonly used on jap cars. it will redirect the bled pressure back in front of the turbo behind the maf sensor. they are pretty common.

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1966 Plymouth Valiant, 225, 3 on the tree, 8 1/4 3.21 sure grip, hyperpac, holley 650dp, holset h1c

thankyou. That sounds like a good idea , and veary nice car.

Knock sensor is a piezo-electric device, it generates a variable AC voltage. The EST module is programmed with engine specific "knock signature" info (it determines what's knock & what's "noise" for that engine)- it sends a signal (square wave?) to the ecm to retard timing if it thinks there's knock.

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63 Valiant Wagon
225 - 4 bbl