30th droptop

iTrader: (-1)

We have an LS1 motor at the machine shop now. The machinist says the bores will clean up by honing them to .010 over. I've read that GM recommends that as the maximum oversize.

But our machinist says that the bores can be opened up bigger with no problem, and that there standard replacement pistons available up to .030 over. He said he's built LS1 motors with these .030 oversize pistons, and that there isn't be any problem at all. And when I look at the liners, they seem to have some beef to them. When you think about it, .010 over is only .005 per side - basically the thickness of a piece of newspaper!

Assuming I can get pistons in a .010 oversize, that's what I'm planning to go with. I won't go any bigger than I have to. But I am just curious if the bigger oversizes are safe.

Mike94ZLT1

iTrader: (3)

.005, have you ever seen how thick the sleeve is? .030 over and you will be in a water jacket.

30th droptop

iTrader: (-1)

Let me get straight up front that I'm not trying to argue with anyone. I just want to understand this:

Why is Enginetech, a machinist's supply house, offering .020 and .030 oversizes for LS1 pistons. And my machinist said he's done .030 with no problem, and that Enginetech recommends these oversizes.

Mike94ZLT1

iTrader: (3)

The stock bore on an LS1 block is 3.9 inches. Maximum recommended overbore is .005 inches, for a total bore of 3.905. It's even less for earlier blocks. If you want larger than that then you either need a wet sleeved block, or to go to something like an LQ4 or LQ9, or LS2 block. The machinist may not know a damn thing about LS1's.

http://www.gmhightechperformance.com...1_stroker.html

My 383 is a 3.903 bore (.003 over stock, not .030) with a 4.00 inch stroke.

MPHmotorsports

iTrader: (18)

acturally its 3.898 bore and 7 thousands is where the 3.905 number comes from. I have seen 10 thous before a few times but why?
For the extra 1 cubic inch?

30th droptop

iTrader: (-1)

Yeah, that's what Eagle is now telling me - that the 3.905 oversize is the only availability for the stroker pistons (we're building a 383). The .010 came from the machinist - I think he's accustomed to thinking in terms of even numbers for oversizes. I'm now trying to get him to commit that the bores will clean up at .007.

jermzz

iTrader: (18)

Maybe he either said wrong or you misunderstood three thousandths .003 to thirty thousandths .030

I wouldnt think anyone who had ever done an ls1 would ever recommend .030. Iron blocks dont even go past .030 without sonic testing.

billc5

iTrader: (1)

make sure you understand what type of piston you are using, for example the Lunati 4032 forging is a high-silicon design which expands very little and needs less clearance, .003 to .004 over the piston size. Do not over bore your engine or you will hear about it latter, it is very common for a machinist to over bore the LS6 block.

http://www.gmhightechperformance.com..._engine_build/

The next thing is that it is also common for the bearing clearance to be too much and cause low oil pressure at idle.

If the machine shop is recommending .010 over then you need another machine shop.

DONAIMIAN

iTrader: (18)

Early blocks can go out to 3.905 and later blocks to 3.910. Gen IV blocks can go out .020. The .030 pistons your machinist are finding are for when you want to make a 370 iorn block. (4.030b x 3.622s)

30th droptop

iTrader: (-1)

Thanks for the info, everyone.

I definitely didn't misunderstand the machinist - he said he's bored to .030 and that those pistons are available. I checked the Enginetech catalog myself, just to be sure. But, like DONAIMIAN said, those could have been for iron blocks, I guess (although the Enginetech catalog specifically listed them for Camaro/Firebird).

I'll definitely use your advice. Our block is a 1999, so I guess it's an early block and shouldn't go more than .007 over? It's hard to believe the bore size difference between .007 and .010 can make a critical difference in engine durability. That's like .0015 per side - like the thickness of a human hair! There. Now I've said it. Let the lead fly.

PREDATOR-Z

You'll be ammazed how critical .003 can be in a motor, especialy the LS series.
3.905 is max bore safely on LS1/6

Stang Killer

iTrader: (27)

ok.....so my machinest just bored my 6.0 liter .060 over....is that possible for that block!? or am i kinda screwed? haha

PREDATOR-Z

He should have sonic tested it. If not, it is a crap shoot, you have about a ~40% chance of getting by.

Stang Killer

iTrader: (27)

im not really likeing that percentage..... are there other guys you know that have done it sucsessfully with out any problems?

URLOSN

iTrader: (29)

I have talked to several people and have said that @ .060 you need to sonic test the block and it should be used mainly for N/A or a small shot <100. But then again, i know of a person running a 4.045 bore and is spraying over 300 shot on it, and having no problems. so i guess the little bit of difference in the bore makes a lot of difference in longevity. Just my .02 not worth much, lol iron blocks i am speaking of also

PREDATOR-Z

The last time I used a .060 overbore 6.0L iron, my shop went through 6 blocks before they found one that was solid enough to handle what I wanted to throw at it.
Definately wise to sonic test.

Stang Killer

iTrader: (27)

well im going to be running boost....so basicallly i need to get a new block then.....and have him punch it .030 then??

jermzz

iTrader: (18)

Tell him to sonic test it, it's failry cheap.... Make them comp it cause it was his bad to do it without you telling him to. It might pass. If it passes Sonic check, you should be fine for boost.

The only problem with going .060 on an iron block is that after this, there is no room for error later down the road. It's at it's MAX bore, so basically if something happens to the block, it's garbage.

Stang Killer

iTrader: (27)

yea ill have him check it...hopefully its not fu-bar'd.....ahh..i really just wanna buy a new block so i dont have to buy all new internals when something breaks.......

Spellbound

I bought a used iron short block thinking I could freshen it up. Well, once the engine was tore down...the pistons were crap, the skirts were severely scuffed and once the block was sonic tested, we found out the bore was 4.060 instead of the 4.030 the previous owner thought it was. Also, two of the cylinders were less than the recommended hundred thousands between the bores... The block shouldn't have ever been used.

He did get over 380 1/4 mile passes out of it before he pulled it though.