I just got my new 350 to replace the 305 in my 1986 Z28. The engine is still the stock bore and stock heads. Want to try and get 300 hp. What do you guys think I need to do to get to 300? Like what size cam? Do I bore it out or not? Haven't built a motor in 20 years. Bought this car for me and my son to rebuild together.

 

A lot depends upon what the 350 came from, especially the heads. The vast majority of factory 350 heads are not conducive to producing 300 HP, at least not efficiently.

Whether or not to bore depends upon the condition of the cylinders. If you have dished pistons and want to replace them with flat tops to raise compression, then it makes sense to go ahead and bore to the next oversize, assuming the cylinders aren't already overbored. This is just for a good ring sealing surface, not to increase the displacement to achieve the 300 HP goal.

Is the 305 carb or TPI? Do you have to keep it emissions legal? (Well, you "have" to keep it emissions legal according to federal regulations, but do you have to go through emissions testing and/or inspection?)

If carb, the power level is a little easier to achieve for less money. If TPI, still possible, but more expensive.

Assuming the heads you've got are performance junk (a pretty safe assumption), I'd suggest starting here http://www.sdparts.com/product/SD806...merIntake.aspx if carb. Your stock carb, ignition, etc. will fit on it except for EGR. If TPI, then http://www.sdparts.com/product/SD806...keHeaders.aspx . You'll need aftermarket runners. Or, just get the upgraded Vortec heads and a Holley/Weiand 7542 Vortec Steath Ram intake.

With good exhaust, like Hooker 2055HKR headers & 3" cat on back, and a cam like a Comp XE268, you'll easily make 300 gross flywheel HP.

BTW, love to hear of father/son projects. Keep us updated on the progress.

 

The motor is a stock 1973 350 . Stock heads never been bored . The 305 is carberated and I do not have to do emission testing.

 

Junk 350 heads confirmed.

Carb = good. It'll easily support 300+ HP.

LG4 exhaust = all bad - replace every piece of it.

Forgot to mention air cleaner. LG4 single snorkel = bad. Dual snorkel much better. You can make one (tech article linked from the thirdgen.org homepage), try to find a factory dual snorkel (becoming more rare and expensive), or get a kit from ramairbox.com (also a bit pricey, but flow better than either of the above). The underhood temp of our cars make open element type air cleaners less desirable.

See sig. I keep thinking I'll do that S-D Vortec head kit, other projects keep it from happening. Perhaps when the 383 project commences. . .