Here's the dilema: I just built a fresh 400 small block with MiniRam for my brother's 87' GTA. I have all the hardware bolted together and installed in the car. What I DON'T have and WON'T have for several weeks is the SOFTWARE to run it- a custom chip.

I have 2 sets of injectors available: stock 22lb units and a fresh set of 32s that the new chip (which I don't have yet) will be programmed to work with.

So I only have a stock 1987 350 TPI chip avaialbe right now to run this Frankenstein. I just need to get it running well engough to get it out of the garage and maybe drive it around the block to break in the motor. I will NOT be beating on the car in any way during this period. Idle and light throttle only. It's a 400 with good heads, Miniram, and a mild 270 grind cam- nothing wild but very different from a stock TPI.

SO....... Should I drop in the 32s and hope the bigger cubes will take the extra fuel they will deliver or drop in the stock 22s and crank up the fuel pressure? I am sure the ECM will EVENTUALLY learn how to run the engine reasonably well with either set of injectors (it uses a mass air flow sensor which is more tolerant of stuff like this) but I want to minimize any problems on initial startup. I'm leaning towards using the 22s right now.

Comments?

 

do not run the 22s. you will be extremely lean in open loop. that 400 will be moving too much air for 22lb injectors. in closed loop it might compensate for it some, but 22lbs would be too small for a 400. just put in the 32s.

 

Well, let's think about that a minute.....

Yes, the 400 will want more air and therefore more fuel, too. But this engine uses a Mass Airflow Sensor so it SHOULD have the ability to compensate for the extra airflow to a larger degree. If I use the larger injectors it would OVERcompensate for the extra airflow. Right?

Keep in mind I know the 22s are way too small to make power with but this engine is NOT going to full throttle until the correct chip arrives.

I also know once the O2 comes on line it will learn its way to a livable fuel curve eventually but I want no startup glitches like flooding the motor.

 

wrong. if your gonna fire it up with the stock computer, and you use the 22lb injectors then you are gonna be considerably lean until your car warms up completely and goes into closed loop, and after that, the computer can only compensate for it so much. the 22lb injectors just arent enough to feed a 400 period. its not a wise decision. but if you put in the 22lbs and ruin a head gasket cause of detonation youd be pissed. the mass airflow isnt used until its in closed loop. the 400 will be pulling way more air than the computer thinks it is. the computer thinks its filling 350 cubic inches with fuel and air. there is a certian point to where the 22lbs injectors wont be able to put out any more and you wont be able to richen up the mixture anymore (computer or manually by raising pressure)

 

and here is something else to think about. with the 32s, the worst that could happen is you run rich and foul some spark plugs. run the 22s and if you run lean, you could be burning the tops of your pistons, exaust valves and destroying your head gasket. the results speak for themselves.

 

Damon, what HP do you estimate the engine of producing?

At about 44 psi and 80% duty cycle, the 22# injectors can keep up at WOT with about 300HP engine, up the pressure to 50PSI and you can support like 360? Don't recall, but a quick look at the injector flow rate and calulator program, will let you know...I'm just going by memory.

Now, since you're using the 350 chip which is calibrated for 22# injector, I'd use it and the 22#'ers and bump up the pressure, my concern with a new motor and 32# injectors would be lack of lubrication due to excess fuel, not so much the fouling of the sparkplugs.

Go to www.racer-x.f2s.com (best damned garage on the net) and look through the TPI stuff he has, and you'll find the injector calculator.

The GM injectors are rated at 44 PSI, so you can plug in what they're capable of, then also look at them with more pressure.

Now you won't be doing any WOT blasts, and maybe it's just best to run the motor under no load without driving it, monitor the O2 voltage, if it seems lean, shut it down.

My .02 anyway.

 

I'd run the 22's with maybe a fuel pressure increase. The 32's on a stock chip are just gonna drown the motor in fuel. Even in open loop the fuel supplied is based off the MAF and it will be just fine for breaking the engine in and tooling around town.