Hello everyone, was wondering how much hp and tq do you think an after market header with 2.5" collector tube, 2.25" full exhaust with cat delete and cold air intake would add (may get a what pen!s intake if that works better)
Any guesses would be appreciated.

I personally think a header will add 3-6hp, exhaust will be 3-6 also and the air intake may be 0.5-3. So all together around 7-14hp ish. and the torque may be 3-8 ft-lbs more?

 

A D16Y8 will make 127 Flywheel HP stock... a big 2.5" collector header will make NO more power than a small 1.75" collector header... and the former may even lose a few ft/lbs of torque in the mid-range too. The 2.25" cat-back may make a HP or two... but it is really too big for your application. If you like the sound... get it. The "Whale Pen1s" style intake is a TERRIBLE choice and typically LOSES power over a properly sized straight-tubed intake. A 2.5" tube is actually about right for a Y8... use a quality brand filter element and it will add 2-3 HP.
If you gain 5 wheel HP from your I/H/E upgrades, you will be lucky... especially without tuning.

 

What size exhaust would you suggest? I also saw a header with 2" collector do you think that would be best.

 

Yes, the 2" collector will be best and an exhaust system sized in the 2 to 2.25" pipe size will be perfect.