Hey Guys I was wondering with the GM stage two kit can you step down in pulley sizes anymore without needing a re-tune or go larger injectors? I know cooling mods are needed. I'm just wondering with the GM setup injectors/tune how much flexing around you can do with the boost before it starts leaning out. I hear the GMS2 is a 3.0 pulley. Wondering if it could be stepped down to a 2.8 within tuning problems.
Thanks for the help guys.
I"m really enjoying learning to tune this car. it's really different from the 4g63 cars i've tuned in the past.

 

pretty sure it's 2.9.

 

^^correct. 2.9 is the lowest you want to go on ST2.

2.8 and under, it's advised that you get bigger injectors, cooling mods, and retune.

 

which is what i plan on doing very soon. haha! roadrage06, how does yours run? have you had it dynoed? did you get tuned through ottp or zzp? your mod list looks about identical to what mine will look like when i move up to ottp stage 2.

 

3.067

 

Thanks for the info,
I was thinking of going GM because my car only has 28K miles on it and it's still got a little warranty left but now I think i'll go OTTP Stage two plus the heat exchanger it looks like it has a 2.8 pulley on it's setup if i'm reading the info right on their page. and i figured 2.8 is where i want to be.

It looks like you can e-mail them your tune and put it back on again. Can i higher end OBD2 scan tool push and pull programing off the cars ECU?
I would like to not have to pull it out and send it in.

 

1.3"

 

my old set-up: GM S2, 2.85 pulley, one step colder plugs, 3 in. intake and the stumod=Cooling mod is a must especially here in the south.

ran perfectly fine until winter when the temperature dropped to around freezing. It didn't like the cold thin air compared to driving around all summer with high humidity. Just swapped to a 3.0 pulley and it smoothed back out.

 

im pretty sure you need hp tuners to get the tune off your ecu. an obd 2 scanner wont do that.

 

Hmmm so if i want to pull the tune for OTTP i'm going to need to find someone that owns an HP tuner

 

Woah...I have the exact same setup on my car lol. Complete coincidence too haha. I measured the stage 2 hub to be exactly 2.444in in diameter. The s/c snout is 2.318in. Just not sure how much bigger a pulley has to be to fit that.

 

My mods are in my sig. Only difference is I am HP tuned. My injectors are fine tho. I might buy new ones just because I had my 42's in there for 70k. I think it's time for new ones lol

 

I'm running a S3 2.99 pulley and I wouldn't go any lower than 2.9

 

Thread revival

 

70k is nothing.... don't waste your time/money.

 

So.. let me get this right. I am running the Stage 2 kit, with the 3.067" pulley. Without re-tuning I can swap off the 3" pulley for a 2.9" without changing anything else? Would the engine run too lean? Would the performance benefit ouweigh the increase of heat buildup in the supercharger?

 

Ive been running a 2.85 for about 3 years on a GMS2. I ment to get tuned but kinda lost interest in the cobalt. and just drive it to and from work, but i still romp on it daily.

I personally think its safe ,it actually still run rich (last time i got dynoed it was around 11 to 10 @wot lol) There has been talk in the past about the 42lb injectors being over 110% duty at wot on a stock GMS2 tune, which just sounds odd to me. 42lb injectors @ 60psi flow like 50lb injectors , 50lb injectors should be able to support alittle over 330hp @ a 86% duty cycle. But i'm not a tuner so what do i know.



When i went from a stock stage 2 to a 2.85 my trap speed went from 99-103 to 103-106 (i also added an heat exchanger at the time) so the power increase is evident, the most noticeable difference is the mid range.

 

Is it safe for most to all people to go as low as a 2.85" pulley? It seems like 2.9" might be a safer size? (The reason I ask is because you are in FL and I am up in PA. We have some pretty different weather)

I would imagine the reason for this is because the stock GM Stage 2 tune is a conservative tune?

 

Correct.

Not many people know, or understand this.

 

Staged07SS; do you have any knowledge or experience with running a 2.9 or a 2.85 on a stock GMS2 tune? Can this be done safely?

 

I've run even smaller with 42's, but not on the GMS2 tune (not recommended).

I don't recommend going below the GMS3 76mm on the GMS2 tune w/o custom tuning.

You won't blow the engine running a 2.9 or 2.85 on the GMS2 tune, but your parameters will be off, and you won't see the max potential from the additional airflow.

 

76mm is 2.99xx inches, probably not much different from a 3.067 inch pulley if I were to swap them, right?

If i wanted to try a 2.9 or 2.85, I may not be unleashing the maximum potential, but would the performance increase?

 

yeah weather plays a big part. thats why my trap varies. in summer when its like 89-90+ out with 80+ humidity the car will trap about 100 to 99. in winter (for Florida ) when its in the 50s or lower and next to no humidity the car become a different animal trap jump to 106ish, i haven't got any logs but like everyone says the GMs2 tune is pig rich...I really need to get this thing tuned...In a colder climate i can see concern for running lean or sending the injectors static. If i had to do it over id deff get at lest a tune.

 

IMO you can run a 2.8. The only think you cant do is consecutive pulls in the car.

How do i know this, i monitored mine on the 2.9 and 2.8 with HPT. 2.9 was fine and consecutive pulls could be done but add a 2.8 with no cooling mods and 1 pull is gonna be it before it cools back down.

So for eveyone saying you can run it i just dont agree. You can and i did and no i did not fly by the seat of my pants. It was monitored and tested. Just have to follow the rule of not doing one pull right after the other and your good.

Just my two cents.

 

I think the question is more geared towards the safety of the tune it self with a smaller pulley. heat soak is gonna be a problem regardless of the tune with no cooling mods.