[oldman]

Here is an example of a "free mod". The stock cat is 1.8 ID, it is crushed down to about 1.6 ID just before the O2 and has a boss that supports an 02 sensor that sticks into the flow to boot. When I'm done it will be 2.0 ID, the boss will be milled smooth, the 02 will be spaced outward for minimal protrusion and the front entrance which has abrupt transitions of 1.8 ID will all be tapered and smoothed. Once welded back together (just like the LS1 twin-wall exhaust manifolds), it will look stock to all but the most diehard fans. HP? dunno near enough to CA front cat deletes.
So from me to anybody that claims how fast "stock" cars are, really don't know what they are talking about.


Here is a link to the Callaway "high flow Cold Air Intake", there are more comments below but since I don't have a LT4, I don't know what pivoting the MAF is all about. https://www.camaro6.com/forums/showthread.php?t=541269

So there you go, LT1 two free mods that can add up dunno say up 10 HP, probably more on an LT4. Any good brokanic could do it in a day. Heck I would not be surprised to find that add in boost bleed to the MAP, ported supercharger etc on the GT500, if you got bucks a shop could do so much stuff in a week, including porting the heads, cams, ported supercharger TB, off-road pipe, modified air induction, E85, bigger / smaller pulley (or (just mill up another one) off another OEM application... the list of tweaks is endless.

Stock mods:
ported cats or just cut them all off and replace with straight pipe: 6 to 8 HP on LT1
Cut box, green filter, maybe the pivot that EDFHobbies is talking about, remove the front air baffle: 6+ HP while moving
E85 25 HP with tune
ported heads 30 HP maybe even more if you toss in milling for 12.3 CR
small cam 30 HP
What are we at now? closing in on a 100 HP on a completely stock looking and stock sounding, "stock" engine... before the 416 stroker....

that is on a LT1 (which I have), I assume the LT4 is even MORE insane "stock" and the GT500 / LT5 is even MORE insane "stock".