rebuilding 302, 306 worth it?

[beaver2489]

I'm rebuilding my 302 that has 140,000mi+. I'm putting the setup in my sig on the shortblock. For another $300 I can make it a 306...is it worth it, or should I just put all new bearings and rings, and have all the other machine work done? I know a 306 is only worth 4-6hp over a 302, but if the cylinder walls are in decent shape we should just hone them and save the $300 right? Thanks

 

[TIMMY2734]

I would do it if i were in your shoes. Thats unless your cylinder walls are in pristine condition. You really dont wanna skimp on the bottom end if at all possible. I dont know what kind of budget your on, so that may be the determining factor.

 

[IndyBlk5.0]

i seriously doubt that your cyclinder walls are ok after 140,000 miles. have the machine shop check them, but dont be surprised if he tells you there is too much wear in the cylinder walls. i would say around 1000/1100 for a complete shortblock rebuild decked, the whole bit and built to lower intake. thats a decent deal... ask about it.

 

[beaver2489]

i seriously doubt that your cyclinder walls are ok after 140,000 miles. have the machine shop check them, but dont be surprised if he tells you there is too much wear in the cylinder walls. i would say around 1000/1100 for a complete shortblock rebuild decked, the whole bit and built to lower intake. thats a decent deal... ask about it.

He'll do it all for $750

 

[SmockDoiley]

The point of boring is not to get more horsepower. Its to re-round the walls. Your walls are always taking side loading which makes for an egg shaped cylinder wall. Rebuilding an engine will almost always require boring. Not only do you have unround cylinders but you may have developed a good ridge at the top of the cyliniders too. I'd say at 140k, its mandatory.

 

[IndyBlk5.0]

sounds like a good deal to me beaver, is that built to the shortblock only? new timing chain and oil pump?

 

[SuperStang83]

Most likely you will have to get it done after all those miles! It's not a bad thing though. Just don't bore it out anymore than that or you have a possibility of overheating problems!

Jakob

 

[beaver2489]

ok, I'll just have him bore it .030" and make it a 306. Ya, all the machine work to the shortblock, all bearings, hi vol oil pump, timing chain, and new pistons he can get me for about $700-800. His best friend owns a machine shop and he's got friends in the parts department...damn I'm ready to get my car back running lol.

 

[MustangMulch]

It might be good for only 4-6 hp stock, but isn't it true that mods like heads and cam will respond better on a 306, than on a 302 meaning more hp gains? I sure hope so, because the guy i bought my car from said he bored it to a 306 when he had it rebuilt. I'm not sure if this is true, but i hope so.

 

[SmockDoiley]

He had it bored because thats what you are suppose to do when rebuilding an engine. Rarely do you see an engine that can get away without boring. The only real time a bore comes into play is when you see those racing classes with limitations and cube limits. So the racer of course is going to take full advantage anyway he can to squeeze every horse out of the engine as he can. As far as it making more horsepower, I doubt by doing dyno tests with a 302 and then a 306 your going to see power gains. The added power comes from having a fresh rebuild or better parts like coated or fully floating pistons and perfect balancing or blueprinting. I see the bore as a means to get the engine able to run again and properly seal. Another reason to bore is to correct factory imperfections and get a perfect round for boosted applications. But I really hope people arent out there boring engines or looking to buy bored engines because they think they are getting a power gain out of it. If anything, once you bore a 302 30 over, you really dont want to bore it again because the walls start to get thin and you can run into weakening of the block, or overheating of the oil. Overboring can especially be dangerous for strokers because stroking an engine leads to greater side loading of the cylinder walls. I'm not saying a bored engine is inferior, just that they shouldnt be looked at as a power gainer. I just bought a clean 30 over 460 for 50 bucks, but Im going to have it rebuilt and bored again so I know its fresh. But I'm not going to walk around telling people I have a 470 or whatever itll come out to, but rather that I have a rebuilt 460. I personally dont think its anything to brag about.