i have my car set up for a 2.8 and on a 2.8 tune, i just put a 2.7 pulley on sould i be alright to drive it till i get it retune?

 

Yeah youll be fine just dont go WOT.

 

wat injectorz?

 

yea def not gunna go wot and i on 60s y

 

ok, just wanted to confirm.

 

correct me if I'm wrong, but I thought the only thing pulley size affected was how much you could boost. Obviously that can affect how much fuel your pcm's gonna dump, but .1" difference doesn't sound like much.

 

my rough math says its about a 3% boost increase

 

In theory you will be fine even in wot. Your maf should see the air changes and make the adjustments for you. I went from a 2.8 to a 2.7 with no changes at first. Im always logging/tuning my car when I have some time for it though. The only thing is you might hit some cells farther down your maf table. This is my experience and I tune my car.

 

i hopefully get a retune this weekend so a week not hard to wait for.

 

air and fuel might be fine, make sure you adjust timing, dont want any nasty knock creepin up on you

 

yeah, but my point is that if you're going from a 2.8 to a 2.7, it wouldn't affect your fuel tables that much. So why would you need to re-tune?

 

It would effect ur fuel tables 3% @ WOT.

I'll let the end user judge if thats significant or not.

 

The car is going to try to push out the same AFR thats commanded regardless of how much boost you are pushing.

 

right, and with 3% more boost yielding approx. 3% more airflow you'll need 3% more injector pulse width.

If this pushes your IDC's past whatever threshold you deem 'safe' it might be cause for concern for you.

 

i getting it retune because i putting meth on it plus the tune was not very aggresive.

 

Because if you didn't change the tune, your missing out on what your car COULD be doing. Tuning fine tunes everything so your car runs better and stronger. A smaller pulley will also cause more heat.

Don't go into boost and you should be fine.

 

I'd imagine if you had 60's, you wouldn't be pushing your IDC until you run something smaller than 2.5

yeah, but we're only talking about a tenth of an inch. I rolled with a 2.8, and then a 2.7 (both with an aftermarket h/e). So heat wasn't an issue. And as far as fine tuning goes, I would think our cars aren't going to run any more efficient with a tune for a 2.7 pulley and a 2.8 pulley. Not saying you're wrong, but we're not talking about a drastic change like converting to e-85 or turbocharging.

 

True true, but I personally wouldn't wanna risk any harm. Better to do it the right way than just hoping it don't go boom. Like someone said already, injectors might go over the "safe point" and start to become static.

 

Just puttin it out there.

No argument intended.

Just information, in case anyone ever asks...


I logged 126% max duty cycle on 42lb injectors in combination with a 2.8 pulley and a stage 2 tune (no boost limiting) on someone's cobalt.

 

y do idiots go with 42z and a 2.8. 60z are a little more lol my duty cycle with 60z wot at 19 lbs 2.6 pulley r 79% when warm and 84%_ when cold lol I'm also pushing a total of 20 in both timing maps and when pe kicks in at 10lbs I get a extra 6 at 19lbs and when iat2z reach 135 I take timing out and have a afr at wot starting at 12.5ish to 11.3 at top end and I have no kr. I've tuned people running 2.8s and 42z and limited there boost till they got the 60z becuz I told them they were stupid lol. The most duty cycle I seen was also in the 130 range but this was when it was cold and car made 16lbs .......



But going from a 2.8 to a 2.7 won't hurt junk..... The PCM will command a afr of 14.7 when cruising until u go into pe table unless all u use is the ve and or the maf only. Your ltft will be off and so will your stft but your car will compensate 1lbs of boost... There will be tuners that argue. But it won't hurt, tuning the 2.7 is prob the better idea because your air coming in will be quicker but the tune u have now won't be far off for the 2.7