Alot of misinformation has been going around lately about pulley sizing and A/F ratios. So let's clear things up.

• Your car will attempt to provide the A/F ratio that your tune wants. This is based on amount of incoming air.
• Changing to a smaller pulley increases the amount of incoming air. The injectors then (based on your tune) try to match what is specified by the tune for the amount of incoming air.
• Many people experience lean conditions from pulley downsizing as a result of increased airflow that was not accounted for in the original tune.
• The tune you are using is optimized and intended for a certain pulley size and amount of air. When changing pulley size and increasing airflow, the tune is not optimized any longer which is why a new tune is always recommended.
• A 2.9 is the safest recommended pulley size for the S2 tune/injectors (as stated by Nate)

If you have anything to add, PM me and I'll add/edit

 

um...misinformation? a smaller pulley does lean out ur car...not ur tune yes..but ur car will lean out if u drop pulley sizes and stay on the same tune..its not because ur injectors cant keep up..its because ur maf tuning is off after the bigger amount of air coming in over before..u have to re-adjust ur maf to have ur actual afr match ur commanded again...

 

From my understanding (not perfect, but I believe accurate, correct if im wrong), a smaller pulley will not largely affect AFR unless the smaller pulley produces a mass of air large enough that the fuel requested from your tune is less than the injectors can provide.

We also see alot of people needing 60lb injectors when running 2.8's or lower which backs this up. Let's get more input to get correct info out there for everyone and i'll update for future references.

 

if u add 60lb injectors to a stage 2 cobalt just because u want a higher head room for ur idc's will cause ur car to run rich..u have to tune for everything..u can fart infront of a cobalt and it will effect the tune...just like ur supposed to tune at night so u dont run lean at night from tuning during the day..alot effects our cars that are "tuned"...u can add a 3inch intake and exhaust and u will lean out a bit..

 

lmao at farting in front of car will have an effect...

i didnt know about the tuning at night, that makes alot of sense

and technically it is leaning out ur car, but not changing your tune. and they are going lean because theres more air being pulled then the injectors can provide for fuel

 

its not that the injectors cant keep up..its that ur maf is out of wack and u need to re tune it to get it dailed in to the afr u are commanding..

 

trying not to interfear here. i have a small question. i have a stage 2 kit installed. can i safely go to a 2.9 inch pulley. a)will i notice a difference in the car, b) will i do any damage to the car if i do not get a new tune. c) can i use the stock wireing harness that i have in the car. d) will i need a new belt or can i use the one from stage 2 kit?

just trying to avoid damage to the car. thanks for the answers

 

Why would you have to re-adjust the MAF? If it's properly calibrated across it's whole spectrum pulley size doesn't affect how it reads only what value it's reading. Simply drawing more air through it will not cause lean conditions if the whole table is reading the correct value for X amount of airflow.



The above image is a shot of the MAF table for my silverado but it's the exact same concept that applies to our vehicles (I've created the markings on it purely for example, I have no idea what the actual airflow value for the two pully sizes is). You can see that if the curve is properly configured across the whole graph changing pulley size simply moves the MAF reading higher up in the graph where it is properly configured to read the correct amount of air and thus used to calculate an accurate fueling rate. Where you have issues are when this table is not properly calibrated or as stated already the max pulse width of the injector supplies insufficient amounts of fuel to meet fueling demands for a given airflow.

 

u'll be fine alot of people run it...ur belt will work up to 2.7..alot of people notice a difference...i dont know what u mean by stock wiring harness..

they are speaking on a gm stg2 canned tune where the maf isnt dialed in to that car..but what u said is correct

 

i heard that when you run 60lb injectors you have to buy a new wireing harness for the injectors.

 

yes, unless you can find some 60's that use the existing harness you will need an adapter harness.

 

BWHAHAHAHAHAHAHHAHAHAHAAHAH



::breathes::

BWHAHAHAHAHAHAHAHAHAHAHHAH


ok. im done.

i have logs to prove other wise.

:::slams head into desk:::

 

intttttttteresting

 

Area47 could you please explain. Im not at all saying Im right, notice the part where I said from my understanding and not perfect, but as Ive never tuned a car in my life finding good solid answers are hard as **** especially on these forums. I spend tons of time on the forums researching but half of the **** on here are repeated questions and misinformation. I talked to NJHK about this concept (what makes smaller pulleys cause lean conditions) and that was what I got out of it. I may have mistaken what he was saying but either way it goes, I'm looking for an explanation so A) I understand, B) Everyone else can see it and I can update my post for anyone who references this in the future. Could you post what evidence you have and give an explanation so those who don't know can learn? I sent RavenSS a PM asking for an explanation but got no response either haha. Just trying to figure out how it all works. Thanks in advance

 

Tuning Q&A -> http://www.hptuners.com/forum/

 

I know about the hptuners forums, but Im not really asking about tuning itself. Moreso about what ACTUALLY happens when downsizing pulleys. Why do people experience lean conditions on smaller pulleys. People on stage 2 tunes that downsize to stage 3 don't seem to have as extreme lean conditions as those on 2.9's, 2.85's or 2.8's from what i've seen posted (keep in mind I haven't seen dozens like others on the forum may have so dont jump on me).

My question is What actually happens when downsizing pulleys and why? (very basic and dumbed down question, but a legitimate answer from someone who knows could clear it up for the 200+ viewers of this thread that may not know for sure)

 

It's all there, on the HPT forums.
Using their search button works too...

 

do this experiment.

stick a stage 2 pulley on the car. set your afr to 11.3

go drive it.

then drop sizes, to say a 2.8. watch the afr. without making any changes to the map itself. the car will run leaner.

more air requires more fuel. this is a given. you have two options to counter act this. maf scaling. increase the number, or work the pe table to adjust for the added air flow.

 

theres 2 of us...ravenss and raven ss i never got a pm...

ur adding more air in when u drop pulleys..which means u need to re-scale ur maf since it is now reading more air its out of wack for the previous maps..or..u can just do the math and tune in pe

 

That explains the PM . Thanks. And yeah that's what I was figuring after what has been said. I'll edit my original post for everyone's future reference and thanks. I want to get into tuning bad but have to wait on the funds. Thanks again guys.