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Tha stock LT4 OBD11 is pretty hot as stock.I do know the GM Hot Cam really wakes it up and let's it really breathe along with Long Tube headers.and maybe the Corsa exhaust.. 40-50 HP + gain.
Well... in CA, he can't do the LTs and the Hotcam is questionable. It has a tendency to throw misfire codes, so that would be bad.
I agree with STL94LT1, change gears. That engine is pretty hot from the factory... add a cat back (Corsa is a good choice), high-flow cats never hurt and an open lid air box or some form of intake.
The LT4 is very receptive to upgrades, but they are not "bolt on".
Another trick is to install an Impala SS head gasket. It's thinner.
- K&N filter with open air lid
- Rear end gears in the 3.90 – 4.10 range.
- Get the stock throttle body ported/polished to 52mm. Find/get a air foil port matched with it. Don’t waste your time/money dealing with the Holly or BBK units.
- A good catback exhaust
- Longtube headers
- Computer reprogrammed for the above mods
- Dyno it, just to make sure the air/fuel ratio is correct
- Hurst shifter
- NGK TR55 spark plugs, depending on age/condition good plug wires