I recently purchased an 86 Z28 with a 305 that's locked up, not sure what the problem is just yet (spun a bearing I'd say). The car is a factory carburetor car and is only rated at 165 hp. Question is, looking for experience and advice on these engines here, is this engine combination worth rebuilding to keep it a numbers matching car or would I be better off to drop a 327 or 350 in it and be done? If rebuilt, are there any tips to get more than 165 horses without dropping a lot of $$$$??? Thanks in advance, I've never messed with a 305 engine before.

 

Unless the car is 100% absolute mint, then it's probably not worth keeping it as a numbers car.

It's either rebuild or 350 time. Depends on how bad it's messed up and how deep the pockets go. Figure out how much you're willing to spend first, then decide on what you're willing to do. A core block doesn't cost much at all, either block would require machine work. If you snagged the 350's rotating assembly from the junk yard as well, that might also be usable - pending inspection and necessary machine work. Simple rebuild kit and it's pretty much good to go. Not much involved that's not going to be required for the 305. Of course, this is all pending a tear down and inspection of the damage to the 305. If it were me, I'd start shopping.

 

The biggest restriction on HP isn't the engine it's the exhaust from the heads to the tail-pipe.

Anything you put in front of it will be terribly restricted. Putting a V8 in front of a single 2 1/4 inch pressure bent pipe system is bad enough, let alone the tiny manifolds.

You needs headers with 02 sensor provision if you're keeping the computer controlled carb. No less then 3" mandrel bent exhaust with hi-flow cat or test pipe.

With 350 blocks being so readily available you should be able to get a workable core for 50-100$. Thats a small cost for the extra potential you attain.

That being said your 86' 305 engine is a decent platform as far as 305's are concerned. It has flat-top pistons and above average cast heads.

 

There's really no reason to rebuild the original 305 now if you don't want to. If you're concerned about keeping it original you can always save it to rebuild and install somewhere down the road. If you can pick up a nice running 350 for a decent price I would go that route. Even if you decide to go with a rebuild I would just go out and get a 350 core and start with that since you can basically build a 350 for the same price as a 305.

Right now these cars aren't at the point where originality matters for a 305 '86 Z28 unless is it's a lower mileage car. Actually, the car would probably be worth more with a 350.

 

Thanks for the advice. I plan on keeping the car carburated. I also know that headers and a cam will help the HP's. But I'd rather help a 290 hp 350 than a 165 305.

 

one other option would be a vortec 350, the heads are way better than anyother stock casting and with alittle bit of work they can be a great head for the money.

have talk to local yards and they are about 200 bones running with 50- 100,000 miles, the only down fall to just putting it in is I don't think the is a mechanical feul pump boss on the block.

 

The 305 is not 165hp. It probably makes more hp then most stock 350's once you get rid of the McDonald's straws it calls exhaust and put something a performance vehicle should have.

Theres an article out there where one of the car mags took a 305 turd and showed how much it netted in power after each mod and the first thing they did was headers/exhaust and it freed up 40hp (if memory serves) with no other mods. This isn't performance territory by any means but doing anything else before this is counter-productive.

Also if you search around theres a couple stock headed 305's on the boards in the 12's, which is an accomplishment with just about any motor with stock cast heads, let alone a lowly 305.