Got my gm stage 2 installed and love it. Thought a nice vibrant 3" exhaust would compliment it. But thats a big negative. Definatly pulls harder at high rpms but cant cruise up hills anymore with low rpms. Anyone else have a similar set up? What should i do next.......

 

This is due to losing exhaust velocity at lower rpms... this happends due to using a 3" exhaust on a setup that does not flow enough air to utilize it... It actually hinders performance.

 

yaeh i figured this after searching the threads. I just wanna know the next step in mods so i can utilize my exhaust...

 

The only real option is to live with the reduced torque or switch back down to a 2.5-2.75" exhaust. I've actually been contemplating that myself.

As for taking advantage of it - 2.7" (or smaller) pulley and 60# injectors. That's my next step.

 

eh thats not really what i wanted to hear.. So am i actually losing hp with the 3 inch exhaust? whats the smallest pully i can run with the gm stg 2? and will in require a new tune?

 

DO NOT switch back to a smaller exhaust. That's counter productive. Switch to a smaller pulley and it will come back.

Lower torque helps you get out of the hole better

 

If you are running a stage 2 pulley try running a 2.9 or maybe a 2.8 pulley.

 

Thats exactly what I was thinking, I would prefer this. Just get a smaller pulley if you "need" it back.

 

That's what I've been told as well, but how does that work? You're not making boost at low RPM so a smaller pulley shouldn't do anything beneficial as far as low end, unless I'm missing something.
It helps you not hop while launching, but at the same time means you have to launch harder to get a reasonable 60' (and I still haven't found that sweet spot yet). Though I admit it feels like it's pulling a lot harder on the top end now.

Smallest I'd recommend on 42s is a 2.9. Anything below that and you're going above 100% IDC.

 

When you switch to a super big exhaust without dropping down a pulley or two you're just alleviating all the backpressure that the stock system creates. The engine now is more efficient because it can push all the air through faster then with the stock exhaust. By adding more boost it just creates that whole cycle again with not being able to push it through fast enough.

 

I bet the OP could get a better 60' time than most people with more low end torque because of less wheel spin and hop. This is my experience, when I had less torque I could get a better 60', until I got used to the extra TQ and learned how to launch, but then I was back to the same 60' time (******* street tires!), that was until I got DR's ofcourse.

Ok when you larger you are pushing out more air, but that is not always good. Exhaust needs to scavenge to work properly, if the exhaust is too large then you will lose some low end, but you should gain it back at a higher RPM. Bigger is not alway better if you dont have the HP to utilize the larger exhaust.

 

With the instant boost of the eaton it's not bad to goto a super big exhaust. IF i still had my LSJ i would run a shorty header into a 3" catless DP into a 3" Custom exhaust along with a 2.8" pulley.

My turbo setup is getting a 3.5" catless DP into a 3" catback. I want 20 psi to spool like no tomorrow.

 

If you can go with as big of an exhaust as you want, why is he losing low end? The scavenge process doesnt seem like it is happening until later in the RPM range... He has a 3.1ish pulley, not a 2.8. The 2.8" might be able to handle the large exhaust, hence why he is losing low end.

 

He needs to switch to a 2.8" and 60's then.

 

Exactly... But he just paid for GM stage 2; therefore, I believe he is trying to keepp a warranty...

 

That's entirely possible. When I got my exhaust switched over I also upgraded my clutch. Before when I would get on it from a stop I could make it hop or chirp without any issue, now it grabs way too easily and tends to bog. I'm guessing my error is more in learning how to launch it than the exhaust. (but even on the street it tends to feel a little sluggish at low RPM)
This is my experience as well. It kinda sucks at low end then takes off like a bat out of hell once I get higher in the RPM range. I plan to drop to a 2.7 or 2.6 sometime soon, that should make things interesting.

 

60's 2.7 Port head

 

so if i go and buy a 2.9 pully and bolt it up am i good to go? or do i need to retune the ecu?

 

a tune would be recommended

 

I think a tune is a must. You will probably lean out top end, depending on the previous tune. Better safe than sorry.