Will I be running too lean?

[19Cutlass94]

Ive been thinking about this, but would like to get some of your opinions. I plan on going with a 3400 ( which I bought today ) with a 3500 top end swap ( more than likely from the store here ) probably the street p&p and maybe? mill the heads +.050 since Im loosing compression from the 3400 heads to the 3500 heads. Ill also be using a stage 1 cam from mms. Now Ill be keeping the stock 3100 fuel rails and injectors and this will be running off the 3100 ecm ( obd 1.5 ) so I wont have a way to tune for it.

question is, will I be running too lean from this? Right now Id rather not swap over to obd2. That might come later on down the road, but not right now. I know I cant use the 3400 rails and injectors cause then Id probably be running wayy to rich. Or will I just have to try it and see what happens when I run it?

opinions? Thanks!

[torq455]

if you have a MAF the ecm should measure the air and give you the gas you need, however, i'm pretty sure those injectors will not work even if you up the fuel pressure--maxed out. you can not remove more than .020 from your heads. which unless you need it, i wouldn't do more than .010. by switching to the 3500 heads you will only loose .2 CR. with no way to tune, you won't get the most power and may cause drivibility problems. you can get away with bolt ons.

[IsaacHayes]

Nope he has no MAF, speed density on the 94-95 3100's.

I'd say run it and see. I don't think you'll burn a piston unless you are running super high revs sustained or something. Make sure you have a good new O2 sensor that will help more than anything. The computer will learn and adjust as best as it can to an extent. You won't be able to run the 3400 FPR/Injectors.

So you got .3l more displacement, better flowing heads, intake and a cam.

With the power increase it's like going from a 2.8 to a 3400. Maybe a touch over with the cam. It will run but not optimal. I think you'll be fine to drive it and when you get the bug you can upgrade to OBDII and get the rest of the power.

Maybe an AFPR as a temp fix... I wonder if there are any that you can adjust the WOT part separately? That and a wideband O2 would help you get closer to perfect when WOT...

[torq455]

thought so.

yeah the ecm will learn what to do during closed loop, but not WOT. pretty sure it will run way to lean unless he uses bigger injectors. kinda shaky w/o a way to tune. would be better to go the AFPR.

[IsaacHayes]

It does calc WOT off of the learned tables though. So if it learns decently while driving, it can guess at what WOT should be. (thats the reason why my car was faster after a new o2 sensor, even though it doesn't read it at WOT)

[3400-95-Modified]

its gonna run like POOP!

Mine ran like chit and that was with 22lb injectors and OBDII.

same setup, Stage 1 cam, with 3500 top end. I went to 28lb injectors and now I have reasonable injector PW numbers... 22's I was 80% duty cycle at wot... you'll max out the 17's in no time. OBD1.5 isnt going to like that cam either...

[Superdave]

I agree... you need bigger injectors, and a Wideband just to see what's happening at WOT.

having a bigger cam really makes your VE tables interresting. I'd switch to OBD2 and tune it, it would suck to put all that work into it and have it run lean and poop.


BTW, you can get better cams from the store here.. and pay less than Milzy

[sprucegagt]

thought so.

yeah the ecm will learn what to do during closed loop, but not WOT. pretty sure it will run way to lean unless he uses bigger injectors. kinda shaky w/o a way to tune. would be better to go the AFPR.

lol I can't believe what I'm reading here. The old myth that the MAF will readjust your fuel requirements does not work.

Yes the PCM will learn to an "extent" but it will be far from perfect or even close. Basically the car will run, but don't expect anything more. Gas mileage will suffer, not from the mods, but from a poor tune. Also as 3400-95-Modified mentioned, the car will run like a dog. You won't have the right fuel or timing profiles needed to get even a modest amount of available tq/hp from the new goods. Instead you'll be pissed that you spent that much money for something that really doesn't perform all that much better from what you already have. Instead I would just plan on upgrading to OBDII while you have the engine out and getting a tuner. I'll take time to learn, but in the end, you'll be happy you did it.

[IsaacHayes]

Yeah the cam will really mess with it.

[torq455]

lol I can't believe what I'm reading here. The old myth that the MAF will readjust your fuel requirements does not work.

it this true for all GM MAF cars? is there a difference on how what the ECM learns and MAF in OBD I, 1.5, and II?

i know someone that simply added a S/C with 6 psi with the stock chip and it ran great. the MAF measured the extra amount of air and gave it the fuel it needed. however, with a tune it ran noticeably better all around. if the MAF won't measure the amount of air to tell the ECM what fuel to give, then why is it on there?

[IsaacHayes]

MAF doesn't matter. It's just a different way reading how much air is coming into the motor. The computer still can only adjust so much outside of it's pre-set calibration. I'm guessing speed density reads the MAP changes to see air flow changes and load, and MAF cars read the MAF and use the MAP for sensing load only. But I have no idea, just guessing there.

The guy with the supercharger had to use a RRFPR/FMU. No way just the ECM was adding enough fuel for 6psi.

The MAF is there to measure amount of air coming into the motor, but the computer doesn't read that and say "oh I know *exactly* how much fuel the motor needs to operate". The computer is pre-programed with the parameters for the engine, and the little bit that it can self-adjust and learn is just to fine tune for different situations such as temp, air density, (climate) etc.

EDIT: Think of it this way. You edit the computer to the right amount of fuel and spark at X condition. The sensors tell the computer when it's at X condition, and the computer looks it up in its tables and squirts fuel and adjusts spark for that condition.

[95Grand-Am]

I don't want to sound like I'm stealing this thread but I have a simular question. I'm curently running a 3400 with a 95 intake and a 56mm throttle body, this really runs great on OBD 1.5. Do you think I could put 3500 heads on it and lower intake with a large port 3100 upper intake with a 56mm throttle body and the 3500 cam with out going lean useing the stock 3100 feul rail? This is a for a circle track car. Is the aftermarket cam the biggest down fall with OBD 1.5?

[torq455]

this guy with the S/C is my dad, so i know all the details of what that build was about. no, he didn't use a RRFPR/FMU. just the stock tune. there was enough adjustment in the programming parameters to give the fuel it needed for the increase in air. you can see the MAF DOES matter. i really doubt that GM, Ford, and the foreign auto makers would really put an expensive sensor on their cars if it didn't matter.

out of a How They Work article-
"The Mass Air Flow Sensor is probably the best way to measure the amount of air an engine takes in (engine load). This sensor not only measures the volume of air but also compensates for its density as well. Ford, GM, and many imports are using engine control systems based around this sensor."

[19Cutlass94]

Im currently looking into swapping it to OBD2. From all the things you guys have said, it isnt worth it to spend that much money and not have it run right. So for a little bit more money now, Ill be able to not only have it run the way it should, but I might be able to put a bigger cam in it as well and tune for it.

[sprucegagt]

it this true for all GM MAF cars? is there a difference on how what the ECM learns and MAF in OBD I, 1.5, and II?

i know someone that simply added a S/C with 6 psi with the stock chip and it ran great. the MAF measured the extra amount of air and gave it the fuel it needed. however, with a tune it ran noticeably better all around. if the MAF won't measure the amount of air to tell the ECM what fuel to give, then why is it on there?

Like I said, it's a myth http://wiki.60degreev6.com/index.php...une_Themselves

Yes it is true for all GM MAF cars. Like I said the car will run, but it will not get anywhere close to the most out of the mods. I'm sure the stock chip DID NOT give it the extra fuel it needed at WOT. That's why the car ran as you said "noticeaby better all around" after a tune.

Im currently looking into swapping it to OBD2. From all the things you guys have said, it isnt worth it to spend that much money and not have it run right. So for a little bit more money now, Ill be able to not only have it run the way it should, but I might be able to put a bigger cam in it as well and tune for it.

You"ll be happy with your choice. Just be patient with it cause it will take time to learn how to tune.