I HAVE INSTALLED A DEZOD 2.75" EXHAUST ON AND AM NOT SURE I FEEL THE "OFF THE LINE" POWER I DID B4 I PUT IT ON, TOP END I FEEL IT MORE BUT WAS WONDERING IF ANYONE ELSE NOTICED THIS?

 

What you're talking about can be applied to any setup in which you create more available flow without directly upping the flow on the intake side such as a smaller pulley or a more efficient intake manifold.

The stock exhaust size allows enough flow up top for what you would do on the street (as well as what the engine is capable of flowing in stock form) while optimizing the velocity at which exhaust gas can exit your engine.

It's all give and take, however, it is possible to get close to a perfect combination of flow mods. With your 2.75" exhaust, if you would now modify the head and intake manifold etc., and possibly up your boost a bit, then just like after any other modification your powerband would change slightly and you would notice that the 2.75" is now working for you by allowing all of the new air to flow efficiently; although you would need to adjust your driving technique and concentrate on keeping your car in higher revs the benefit would be worth it if you can get used to driving it.

 

why do you always use caps

 

Why Does It Matter? Also I Love The Hi Revs Lol Quicker Response From The Car. Also I Am Goin 2.7" 60#ers And Some Other Things I May Get Meth Inj And Get The 2.6 Pulley

I Love Caps, Makes Me Seem Louder!!!!! Lol All My Sn's And Pw's Everything On My Comp Is Done W/ Caps So Why Take It Off

 

That is typical. Actually going too big can cause the supercharger to make significantly less boost and build boost slower. The rule of thumbs is 2.5 inch is usually good up to about 400 horsepower. Anything bigger than 2.5 on a cobalt is simply overkill

 

yep i went through the same **** with that exhaust.

 

could be the spark/fueling tables aswell. Remember with a bigger exhaust you will be flowing more air, therefore your car will follow a different path on both tables.

Some tuning will definitely help.

 

you think a tune just for the exhaust?

 

yup, my buddy just installed a honed header and when I log him now he's on a different part of the table, not crazy different but enough to notice.

I fixed him up.

 

sucks cuz my lowend is shot i only ran my usual 1/4 time once advice on a parts list to get into the 12's?

 

what's your setup?

 

there is a balt in the 12's with i believe intense stage 3 and maybe an exhaust. search its around here some where

 

stock aside form the xhaust, was about to start ordering parts next week but dont want to make a mistake,

 

He wasn't tuning his exhaust cause that honestly makes no sense. He changed tables to achieve better power in the lower part of the powerband.

Exhaust is the air and fuel mixture that is left over after the power stroke. What happends during the exhaust stroke and sending the exhaust out isn't effected by your computer. Changing your ignition timing is changing your ignition timing, it may effect how much fuel is left over and how well the fuel is being ignited but the issue at hand has nothing to do with the computer...it has to do with the exhaust velocity of the airflow.

The tables you're changing in the PCM is making up for the power loss...that's it.

 

Hey Adam were you on the J-Body forum awhile back with the red sunfire with white wheels??

 

Yes.

 

I see what you are saying but you must remember the easier the exhaust can get out, the less amount stays in the cylinder during a cycle as there is always some exhaust that re-burns. So the more air you can get out of the cylinder the more you can get in which is a direct relationship to the MAF reading and the maf reading along with the rpm is the only factors used in calculating cylinder airmass and of course spark is based on your cylinder airmass calculation.

When I upgraded by exhaust from stock to 3" (no cat or resonator) I picked up 4lb/min off the maf.

That's my theory and your welcome to dispute but I have plenty of log files to show that upgrades on the exhaust side directly affect the MAF reading.

 

I noticed the same with my 3". But as far as i know.... its expected

 

LOL well long time no talk man! I had the yellow '04 Cavi & I used to talk with you quite a bit & got a few parts from you. Didn't you buy that underdrive crank pulley from me?? I think my name on there was FWECOTEC. As you might remember I traded my Cavi in on a '05 SRT-4. Got that thing well into the 11's and now shooting for the 10's. I recently bought a '06 Balt for the wife, and well I'll be damned if I'm not itching to make that thing fast. Anyways good to see your still around! How quick did you get that sunfire?

 

No offense to you but I honestly don't remember. I talk to ALOT of people and have dealt with alot of people in the past so excuse my bad memory.

If you want to talk more, you can PM me here or you can join up at ecotecforum.com and PM me there.

 

Just because you have more flow potential does not mean you have more flow all around; with a 3" exhaust you would not utilize it until higher rpm where it's possible that you make enough boost (and therefore exhaust output) to compensate for the loss in exhaust velocity.

No need to prove it changes the MAF signal; it's a fact that any airflow modification will change the MAF's output because airflow will be different at different rpms.

Spark is based on crank position and adjusted by MAF signal. Therefore, since the car will build boost more slowly due to lower intake velocity, a way to compensate is slightly adjusting timing advance and fuel in the lower rpm range to suit the condition. The best starting point is a 12.5:1 AFR as that is the mixture at which gasoline creates the largest amount of BTUs.

 

this post should be stickied for all the naysayers on the GMPP catback.

bigger is not always better.

 

x2 think about where you put your 02 sensor for your wideband , anything that is after that doesnt matter AT ALL