Have a few mods done to the 305, has a catback system, K&N air filter, some aftermarket chip, the air foil, throttle body water bypass, smog pump and lines removed. I think thats it, would i benefit from siamesing the runners and base? How much would i loose on the bottom?

You can port the base a little, but from what I understand, you don't really want to siamese the ports any.

....as for the runners, you can't siamese or port stock runners since they're aluminum tubing that has been bent and welded to the flanges. Most aftermarket runners are cast aluminum, and although some may "Look" like they have seperate tubes, they are in fact cast, and can be siamesed. IIRC, TPIS/ASM runners are significantly oversized, but also use actual tubing, and like stock, can't be siamesed. Edelbrock/SLP/Accell are all cast, and CAN be siamesed.

http://www.thirdgen.org/siameseport

this is what i was thinking about, i thought he did it with the stock runners

BUT im sure u know more about this than i do lol

Those are SLP runners, not the factory runners.

Well i guess i won't be doing anything to my intake lol. So much for a cheap time consuming upgrade. Damn is there anything cheap i can do to get a little more power?

Headers would get you alot farther than intake parts will, for the same or less money in the end.

What would a set of shorty headers do for me? Will they bolt up to the Y pipe thats in the car now?

I don't know of any that will bolt up to the existing Y-pipe, but all of the good shorty sets have Y-pipes available specifically for those headers.

A set of headers will HUGELY improve the breathing of the engine on the exhaust side. Headers will let the engine push out more spent exhaust gas with much less resistance (backpressure), which means more HP and torque, and usually a little better fuel economy as well. The exhaust manifolds on these cars are really bad, a big restriction. Replacing them with a good set of headers will improve power and torque dramatically, improve the fuel mileage a little bit, and will sound really nice. Not uncommon to get around 20hp from doing headers, matching Y-pipe, and 3" catback. You already have the catback appearantly. All you'd need is the headers and Y-pipe set.

I'd recommend the Hooker 2055 shorty header set and the matching Y-pipe. That Y-pipe has a 3" outlet on it, so it should match up to your catback if its a 3" system as well (most are).

The Hedman 68470 headers would be good too, but the Y-pipe supplied with them have a 2.5" outlet. That can be changed to 3" by an exhaust shop, but its just an extra cost. These are the headers I have, and I like them.

you can siamese a little bit in the flange area of the runners that is bolted to the upper pleneum

next time I have mine apart I will post pics

its not much but it will smooth out the airflow from the pleneum to the runners

it also alows you to knock out the walls in the pleneum between the runners