.040" over?

[87we410877]

Is there any dissadvantages of going .040 over? Also, what are the best rings to get for the diamond pistons for high HP applications?

 

[boostingbuick]

I've run .040 befor with no issues. Unless you are looking to make a couple more horse, I would stick to a .020 over. If your going to a high hp level I would go with another piston. I have had little luck with Diamond. They do make a good lower horsepower piston, but I run a J E piston. HATE, I mean HATE having to talk to someone there, but I had great luck with them.

 

[87we410877]

I've run .040 befor with no issues. Unless you are looking to make a couple more horse, I would stick to a .020 over. If your going to a high hp level I would go with another piston. I have had little luck with Diamond. They do make a good lower horsepower piston, but I run a J E piston. HATE, I mean HATE having to talk to someone there, but I had great luck with them.

Well im looing to go about as high as you can go HP wise on the 109 so would you care to elaborate on why you think they are bad for high HP levels. From what ive herd they are pretty good. And why not .040 over for high HP levels? whats wrong with that? Please a little more info.

 

[BlackBandit]

Well, I could take a stab at why not to go .040 over. First, unless you NEED to go .040 over to make the hole round it's pretty much pointless. I mean, you're talking about maybe a couple of cubes. (forgive me for not doing the math ). Also, if you think about it. The more you bore out the block the thinner the metal gets which makes it harder to keep cool (don't know how much harder, could be insignificant) and, more importantly, weakens the block. It seems to me that if you want to push the stock block you would want to stack the odds as far in your favor as you can. Of course if you like a challenge, why not .060 over. Just my .02. james

 

[87we410877]

Well, I could take a stab at why not to go .040 over. First, unless you NEED to go .040 over to make the hole round it's pretty much pointless. I mean, you're talking about maybe a couple of cubes. (forgive me for not doing the math ). Also, if you think about it. The more you bore out the block the thinner the metal gets which makes it harder to keep cool (don't know how much harder, could be insignificant) and, more importantly, weakens the block. It seems to me that if you want to push the stock block you would want to stack the odds as far in your favor as you can. Of course if you like a challenge, why not .060 over. Just my .02. james

We'll my cylinders were a little loose and are already .030 so thats why i have to go w/ .040 over. My block is gurdled and has 4 billit caps so im not worried about strength. On the other hand, i would still like to know more about why diamonds are not the best piston to go with as said above.

 

[87buickracer]

.040 over

I ran a .040 motor back in 1998. had no problems with car over heating with 160 thermostat.no problems at high speed.If building a race motor,I like the weber short block rotating assembly.give him a call on piston selection for your application.good luck...have fun.....

 

[Ormand]

The problem with 40 over is that not every single block can be safely bored 40 over. 20 over- never a problem. 30 over- probably Ok there, too. But there are a few blocks that because of production tolerances and the thin wall casting design, just don't have enough metal in the cylinder walls. You could get them tested with ultrasonics- but that is only useful if you can find someone who knows how thick is "thick enough".

 

[87we410877]

The problem with 40 over is that not every single block can be safely bored 40 over. 20 over- never a problem. 30 over- probably Ok there, too. But there are a few blocks that because of production tolerances and the thin wall casting design, just don't have enough metal in the cylinder walls. You could get them tested with ultrasonics- but that is only useful if you can find someone who knows how thick is "thick enough".

Oh we'll . Im going .040 over before i buy a new block. Just ordered Diamonds. I'll be sure to let everyone know how i like em. Thanks.

 

[SloGN]

well i have been running a .040 block with TRW pistons for 2 yrs now and have nnot had any problems with it heating up. i make @ 19-20 psi on pump gas it layed down 350/440 @ the reat wheels with the stock cam and rockers.



i got a set of kenne bell 1.65 roler rockers one the other day wonder what that will give me hp wise

 

[Ormand]

I don't think cooling is the big problem. The problem would be that with very thin cylinder walls, you get distortion and blowby, or blown head gasket, and in the worst case, you might get a cracked cylinder wall. If you're starting with a build, it makes more sense to get another block, since they are still not too expensive. But in this case, since the money for the girdle and the billet caps is already "invested", it's worth taking the chance on the bigger bore.

 

[boostingbuick]

The problem with Diamond pistons if that when you put a lot of heat to them they swell oblong. Then the pistons skuff the walls hard and score the bores. After that you end up with piston slap and poor sealing rings. I work at a performance shop and have seen this too much. We no longer use those pistons. That doesn't mean this will happen to you. Just my .02.