Hey Guys
Hey I was just trying to get some advice. I have a 1992 z28 with a messed up 305 in it. It has a head leak and it also is sluggish, I bought it an got raped pretty much . I was going to just scrap the motor and go with a 350 or 383 but then after talking to my buddies and then giving it alot of thought I decided it would be pretty cool to have a built 305. I think it would be cool to stick with the original motor, let alone whoop people with a 305. I know so many people talk so bad about the motor. How much potential does it have? I know that 302's and the mustang 5.0 and 4.7 are pretty powerfull for there size. I am wanting to get started in the near future with the swap or rebuild. I was just wondering how wise it would be. As long is the block is in good shape I would like to bore it like .30 over or more. What is the most I can bore it out and still be safe running NOS or forced induction. Also I was wondering how much I should worry about getting forged parts. Like the crank and pistons. I will definatly put like a 100 shot at least on, let alone my dream of putting a procharger or the banks t-tubo kit thats coming out soon. I am going to be busy for awhile with pulling out my motor and stripping it to the block so I have time to get this all figured out. What should I look for when I do purchase one as far as strength? What would I need to change out other then what is in the rebuilding kit when I rebuild it? I hope you guys can help me out. I really appreciate it! Thanks!

 

First it's .030, not .30, and second you want to bore the block as little as possible in order to true up the cylinder walls. There really isn't any benefit to boring past what's necessary. If it only needs to go .020 to clean it up than that is all you do. The more you bore now, the less meat is left if you ever need to rebuild again.

 

Thanks for your imput. About boring, I was always told you can bore a block out to get alot more power, I saw a rebuilding kit that was for a 305 bored to .030 over in summit, am I not going to get more power from boring it out more then it is now?

 

Ok let's think about this logically. A Chevy 350 block bored .030 over actually displaces 355 cubic inches. That's only 5 cubic inches more, which isn't much. On a 305 a .030 in. overbore is worth even less cubic inches. If you want more power get a different set of heads, and a better camshaft. A few cubic inches doesn't amount to squat. And remember you can only bore so much, so the more you bore this time, the fewer times you can bore in the future. The max you can bore a 305 sbc is probably around .060 (although I could be a bit off). Doesn't it make sense to leave as much there as you can? That's my opinion anyway.

 

The difference between a .030"-over 350 and a stock bore 350 is 5.27 cubic inches. The difference between a .030"-over 305 and a stock bore 305 is 4.92 cubic inches.

The power benefit of an overbore is getting the rings to seal better to the cylinder.

The power benefit of a 350 over a 305 (either standard bore or overbore) is 45 more cubic inches. If your upgrades produce one horsepower per cubic inch, that's 45 more HP. That is significant.

The other part about a 350 vs. a 305 is the larger bore allows more flow through the valves because the cylinder wall is farther away from the edge of the valve. You can also put larger valves in a 350's bore for this reason. Bigger valves = more flow which = more power than just the difference in displacement.

You need to decide before you build whether you're going to spray this engine. Little things such as piston choice, compression ratio, ring gap, etc., are influenced by the use of nitrous.

TPI has inherent power disadvantages. When on top of a 305, those disadvantages are magnified. Nitrous helps overcome those disadvantages, but the effect of nitrous is magnified when applied to a 350 vs. a 305.

Finally, blowing someone's doors off with a 305 is kind of like wetting your pants when you're wearing dark pants: It gives you a warm feeling, but nobody else notices. Blowing someone's doors off with a nitrous-ized 305 is like wetting those pants twice in the same day.

(I'll apply my sig just so you know the truth about my "anti-305 bias"...)

 

I agree with five7kid on this one. There really isn't much reason to rebuild a 305 if you can get your hands on a 350 block. It's no cheaper to rebuild the 305 than the 350, and 45 cubes is a significant difference.

Basically what I meant to get at was that boring .050 over vs. boring .030 or .020 over won't make much of any difference. Bore as little as needed. Upgrading to a 350 however will make a world of difference.

 

i have a 305 that has been bored over .030 and my car does feel strong, but for the money i spent on the machining and labor work, it would've been cheaper on buying a 350

 

Thanks alot guys I really appreciate it

 

It's good you're considering the 350. It's a good choice, and certainly the better one.

Try not to get caught up in the "my car makes 2 HP/Liter" like the import guys just to be "different".

True..... the 350 may be everywhere, and a lot of people use them. But there's a reason for that.

Want to be different and build a 305? The guy in the next lane who's got his ordinary 350 will more than likely beat you. So that will make you different. He'll be the winner and you won't.

Overall, it may cost more to build a 350 from scratch, but the benefits far out weigh the costs.

 

Yeah that sounds like what I need to do, my problem is this. It seems like it would be a pain in the rear to put a whole other motor in my car, I dont know that much about hooking other engine into my computer, or do I buy another computer when I get a new motor? I was looking at LT1s and some others but I dont have any idea how I could get it to work on my car because it doesnt have all the emmisions stuff that mine does, or wires at least. Am I making to bif a deal out of it? It would be sweet to put an LT1 from a newer camaro in it but it seems like it would be really hard.