I took my engine to get rebuilt. 350 TPI out of an 89 IROC. The machinist wants to bore it 60 over. I have heard that this can make the cylinder walls weak. How true is this? How weak? Should I let him. I mean he seems to really know what he is doing and has done a lot of work that I have seen, he's recommended. Is this a good thing for my engine? ALSO what would the displacement of the engine be then after getting bored.

 

Before going .060 I would have the block sonic tested to make sure the cylinders are thick enough to go that far.If you go .060 on a street engine and the walls get to thin then you can have a real problem trying to cool it.I have seen alot of engines that have run on the street .060,but I would make sure the block can take it before I gave the order.Nothing like have'n your fresh built engine togther and running only to find out that it runs way to hot and you can't cool it.

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Superman
Rev'n to Seven

 

Has he sonic checked the walls? .060 seems like a lot but if the wall thickness -overbore is enough then it should be fine. Why does he want to go .060? An overbore that big makes future rebuilds impossible.

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82 z28 350cid, vortec heads, comp 262h cam, Holley 600cfm carb, 2in twice pipes, MSD ignition, turbo 350 trans, 3.73 posi

 

I don't know why in the world he would want to bore it .060 over. Unless the previous owner already over-bored it without you knowing, or the cylinders are EXTREMELY tapered, or therer's a big gash in one of the cylinders, there's absolutely no reason to bore it out that much.

 

You should only bore as much as you need to, generally .030 is the first step, and will clean up just about anything. I agree with everyone else, why so much?

 

82 Z you are exactly right. Sorry I forgot to mention it. the previous owner had already had bored .040. But all in all said this should be alright over all? Or not?

What would be the displacement of the engine then be?

 

I knew a guy that a had a Ford truck it has a 300 6cyl in it and it is 4 wheel drive and he bored it .80 over and has really used this truck it has alot of power and had no problem with it and we have pulled dump trucks and hauled 25 foot trailers wtih other trucks and not to mention some major 4 wheeling. But i have not heard of any one doing this to a SBC but i am sure some one has took one .80 over before.

 

OK, here is how to figure out your displacement. The formula is: radius of the bore squared x pi (3.14) x stroke x number of cylinders. A 350 has a 4 inch bore, the radius is half the bore, so in this case it is 2. To square that you multiply it times itself, 2x2=4. Then multiply this times pi (3.14), 4x3.14=12.56. This is the area of the bore. Multiply this times the stroke, which is 3.48 inches on the 350, 12.56x3.48=43.7088. This is the displacement of each cylinder. Multiply this times the number of cylinders which is 8, 43.7088x8=349.6704 (350) cubic inches. With a 4.060 inch bore (.060 overbored) your displacement would be: 360.23918

 

Is there some reason you are so attached to this block? I mean hell, in this neck of the woods(almost northern Canada), used 350 blocks go for about $150 Cdn(about $100 US). Four-bolt blocks go from $200(truck donor) to $350(car donor). Hell, Summit will sell you a brand-spankin new four-bolter fer $599.

The block you got; don't sound like it deserves a reprieve from the guv'ner! Sounds like throwin' good money after a bad block.

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He who hesitates,... is lost!

 

Iroc,

According to my books, MOST 350 blocks will go to .060 - but not ALL. So, sonic testing would be in order. Here are the problems:

-By the time you paid for the sonic testing, you'd have an even more expensive block that could never be rebuilt.

-going .060 is like turning a crank .030/.030 - yes, you can do it, but when seasoned 350 blocks are going for $100, WHY ?

.060 over = 360 Cu. in.

I'd recommend buying a standard bore seasoned block from a salvage yard - or for that matter, ask your machinist if he has any for sale. Good luck.

BOR