how big can chevy 350 be bored out?

[NCC1701]

A friend of mine has a chance to get a chevy 350 that has been bored 30 over. Everything I have been told says that 30 over is the max for this engine. He is asking me for my opinion on getting this engine. He has a budget build up article from one of the car magazines where they take a 350 and bore it 60 over. What do you guys think? Is it a good idea to bore out a 350 this much? I was always told that anything 40 or over you run into overheating problems.

Have I been misinformed all these years???

Thanks In advance

 

[Vendor Defendor]

.060 is the biggest most people go, but i think i have heard that someone did .075 over once...

-neil

 

[gofstbuick]

Like Vendor Defendor says, most max the overbore to 0.060. Personally, I would sonic the block before having it bored 0.060 over. Those that bore a SBC more than 0.060 over are using bowtie or some other HP block. I had my block sonic tested prior to overboring 0.030. Mainly because I was building a 383. If he does decide to build the 350, I would definetly recommend the 6.0 inch connecting rod. This requires no changes to the block unless it is stroked. Just MHO.

 

[myclone]

Depends on the year block and what it will be used for. Ive bored early 350s (~1970ish) to .060 without probs back in my chevelle/camaro days. They had adequate cooling though with big radiators, mechanical fans, etc.

The machine shop I deal with now wont bore a late block (~1985 and later) any further than .030 unless they sonic check a pile of blocks to find one that has a decent cylinder thickness.

IMO (in my OPINION) if the cyl pressure is kept low (no N2O, turbo, or blowers) and the cooling system is sufficient you could get away a with .060 over bore on a later engine just fine. Just be aware that if you beat on it then you may very well run into ring sealing probs due to flexing/wobbley (is that a word?) bores at high RPM or high cyl pressure.

 

[TurboBuickSix]

I got an 88 K5 Blazer that had a just rebuilt jasper motor with a mysterious coolant into oil leak.Turned out the motor was .060 over and I figured out to my ace mechanic father in laws dismay that the coolant was coming in through the cylinder sleeves where the had pinholes in spots from rusting on the cooling side of the sleeve.He still insisted it only needed a head gasket but compression was 150psi or better across the board.Since been pulled and replaced and he took it to a machine shop and what do you know,they agreed and said .060 was way big for that year SBC.I have also seen the older ones(pre 76'?)go that big without problem.Best insurance is to get the sonic test done as suggested earlier.

 

[NCC1701]

Thanks guys

I really appreciate the information