I was told that the MPFI 660's fire in batch mode. I was wondering if there is another Gm ECM that we could use to change it to sequential.. All my buddies are telling me its better. Im not sure but it sounds like it would be. Any input is appreciated. Thanks, Baron

 

What's better about the SFI?

Not much, idle is generally a bit smoother, and SFI can provide an increase in fuel economy, but other than that, there's not much benifit to SFI.

 

Can use the 1227148 ECM. It is the sequential fire MAF based unit used in the TTA and turbo GN's. This ECM is also used in a bunch of regular 'ole Buick's, so it is easy to find. Lots of support on the GN boards for it too.

RBob.

 

If you want to go SFI, then you also have to add a crank trigger and Cam Sensor so that the ECM knows when you come up to TDC on #1 so it can fire the injectors correctly.

 

rbob, and map based sequentials? I'm about to the point of needing a custom chip, might as well make the move if I can

 

Yep... and SFI converts to Batch fire over 3000 rpm, anyway

 

So its pointless to switch basically... Thanks for the info

 

I wouldn't say it's pointless, but for the amount fo work that you're going to put into it, the idle quality and fuel economy aren't worth it unless you REALLY want it.

 

If we have an ecm thats a fairly simple swap, I'd do it. Normal running rpm for me is below 3000.

 

Yea, id do it too if it does improve mileage.
30mpg may be very possiable.

 

gumby, above mentioned ecm will work for you since your maf. However, if having to add cam/crank trigger is true, you would have to fab them up.


As for me, I'd like a MAP/SFI ecm. Since I'm on a 3.4 block, I already have previsions for them sensors. I'd just have to make a wire harness and run it to the inside.

 

The crank trigger is already present, the distributor. Correctly need to add a cam sensor.

I don't know of a MAP based 6-cylinder sequential ECM (other then a special GM racing ECM). So going seq, MAP, and 6 cyl., not sure what to recommend.

As for converting to batch over 3,000 RPM, the 1227148 does not do this. It is sequential through out the RPM range. My belief of this statement is that it is derived from WOT, where the PW DC% is large enough that it doesn't make as great a difference whether the injection is seq or simultaneous.

At part throttle sequention injection does make a difference.

The one great item to keep in mind, is that as soon as you mix-and-match engines and ECM's: is calibrating it. OTOH, this isn't as difficult as it is sometimes made out to be. The learning curve can be a little steep, but once at the top it really flattens out.

RBob.

 

There's no TDC signal from this distributor to sync the cam and crank. All of the motors that I have seen with SFI have some sort of TDC sensor so that the injector fires correctly on the intake stroke rather than the compression stroke. If it fires on the compression stroke, you'll be in the same position as you are now with the batch fire system.

Fuel will pool up on the back of the intake valve and you'll get decreased atomization meaning lower fuel economy. For that amount of work, you might as well just stay batch fire.

 

edit, n/m. I'm an idiot

 

This answered an age-old question I had about our setup. (When I looked at the Haynes manual and wondered why the injectors were in paralell.)

My next question is:

What advantage does MPFI have over TBI?

Is there an advantage to having the fuel sitting at each port? It's only for a few milliseconds.

I always felt the intake in our cars was the most restrictive thing I have ever seen. I took out the baffles under the air filters and noticed an immediate improvement in throttle response (And an annoying whistle). I always wondered why couldn't I use the Eldebrock setup with a TPI swap and get better performance? It seemed to me that Chevy milked the MPFI for all it was worth back in the 80's, and it was nothing more than a glorified TBI.

Any ideas?

 

Well that is wrong the MPFI which is a direct port is better because it delivers a precisly metered amount of fuel to each cylinder, TBI is basicly a hoped up Carb system and you cant control if one cylinder runs rich or if one runs lean only howmuch goes in at the beginning.

 

MPFI is the best hands down

TBI was the cheap 80s way of goin FI

 

The cam sensor signals when a particular piston is at TDC firing. Which particular piston depends upon where on the cam the sensor trigger is located. Can be any one of the six cylinders, but it will always be the same cylinder every two revolutions of the engine.

RBob.

{edit: 2_point8_boy, in your last post you quoted 2 sentences of mine. Please note the second sentence where I agree that a cam sensor is required to be added.}

 

With no intentions of starting a TBI vs MPFI war, the 'precisely metered amount of fuel' for MPFI is only good if the amount of air is also precisely the same (on a cylinder to cylinder basis). Which is not always the case.

RBob.