perception opinion on a .040 block

[Bossgold]

Have to at least ask. Got specs to from my engine shop. Thrust side of the cylinders are .249 - .187. pretty decent from sonic test. The block cylinders are .033 from standard bore. I wanted to stay below .040 and engine shop says why? 

Perception! ...if we can machine the cylinders correctly would it be worth keeping below .040 from a Perception value $$$ stand point. Or am I wasting my time fighting this and just go with .040. I know many people don't like original blocks bored over 30 thousandth. A 340, depending on thickness, should be OK at 40......but I Know as we all do the smaller the size the better.

So should I stick to keeping  it below 40 and do custom pistons/rings or just do the 40 thousandth.....and make it easy. My engine guy thinks I'm crazy....Am I wrong to consider this and if it was your block would you stick to smaller is better.

I know in other worlds (Ford Boss 302) 30 over is pretty much the limit and dramatically reduces the value if you go over on the block/engine because of overheating.

[Cuda Cody]

Is it a #'s matching block?

IMO, if the sonic test comes back good I'm fine with them at .060 over.  And if it's a #'s matching block, I would just sleeve it if I had to to keep it running good.  But to answer your question, .040 is fine in my book and no different in price to a .030. 

[6bblgt]

..... but what is considered "good" VS. "thin" for wall thickness & likely to cause excess heat?

his minimum thickness thrust side is .187" & he'll lose another .003-.005 on an overbore to .040" over

[Fastmark]

I have sonic tested a few blocks in my life. I had a 340 TA block that was matching number to a car I had at the time. It was .030. The trust on a couple of cly was at .090! I eventually sold the car to a friend and his guru that did all his work wanted to bore it .060. I warned him about the cly and thankfully, he listened. Knowing him like I did, I'm surprised. He went with .040 and it gave him no trouble with overheating issues. .187 on the trust at .033 over sounds good to me. .003-4 more won't hurt. Honestly, I would keep the sonic sheet from the machine shop to prove it was that thick. That sounds thick for a 340. When I do one, I have 12 locations in each hole so I am very thorough. They may not have done that many spots. 

[Chryco Psycho]

I remember a drag race team that would bore the blocks .002 -.005 & then have custom pistons made , this way they could use a block for decades , virtually any block needs very little material cut to straighten the bores but due to the cost of custom pistons everyone just uses .030 , 040 or .060

[blown motor]

My 340 is bored .060. That's the way it was when I bought the car. The engine blew and we had to sleeve two cylinders. That was 7 years ago and it runs strong and stays cool. 

[RUNCHARGER]

Go .040 and fuggitaboutit.

[aussiemark]

I think it will be fine at .040 but what are the bores like now, bolt on a torque plate and get it measured with a bore gauge to make sure there is no taper and they are round if this all checks out ok you could give it a light hone and use .030 forged pistons they will be ok with .005 clearance. If you have .033 now just a light hone to deglaze the bores and .030 should be good. I understand your theory I have a std bore 340 and went with .020 pistons rather then going straight to the more easy to find .030 it has a fair amount of wear and there is a light rust stain in one bore where water sat in there for a while but it will clean up on .020 so why go further?

[Bossgold]

Cody - yes...its a numbers matching block. The car sat for many years due to a small leak of water in the oil. It turned out to be a simple fix. I guess the previous owner could not find it and thought the engine was toast so he put in a standard 340 block. I bought the car thinking anything can be fixed...... The sonic check came in good as I said with the relief side at 119-126 and thrust side at 187 -249 thickness. I wanted to machine the cylinders just enough to get them round and then stop cause I know you can get custom pistons (.037, .038) and file the rings. And yes I know its splitting hairs when you divide both sides of the bore but to many saying the bore is .037 vs 40 thousandth just sounds better.  That's why I ask your opinions....cause Original blocks are hard to come by and the more metal the better.  My engine guy .....well he's not sure if I have all my cards.      And I will most definitely keep the sonic sheet.

[js27]

My 67 GTX was bored 40 over 10 years before I bought it and I was able to just freshens it up with a hone. I guess they didn't drive it much. I ran the car for 27 years with NO problems at all. Never overheated. Had a 180 thermo in it and it ran at 180 even in hot summer traffic. It was a all stock 440 with no mods to it.
Do it !
JS27

[torredcuda]

I can`t see .0035 per side being a big deal unless you were already on the edge of wall thickness or going .060 over, .040 over is no problem in my opinion

[RUNCHARGER]

Sorry: 1 to 2 thou a side is just not going to change your life. Hopefully your engine guy will keep working with you.