6bolt 4g63. Moving from .020 to .040 bore?

[Purple_Demon]

Ok I have searched but the answer to my question hasnt really been answered in other threads yet, so bear with me...

I recently purchased a built 6bolt block from a friend only to find out the wiseco pistons had cracks in them. So I took the block to the machine shop to have it cleaned/mic'd/magnafluxed. I picked the block up today while running errands and didnt notice a certain item until I got home...the cylinder walls have scuffs and scratches in them and one cylinder has a good sized nick that catches your fingernail. The machinist has already honed the cylinders but I see that will not do for this block.

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Now here is my concern...the block is already .020 over and the bores measured out as follows:

Stock: 3.346
.020 over = 3.366

Cylinder 1 : 3.3665
Cylinder 2 : 3.3665
Cylinder 3 : 3.3665
Cylinder 4 : 3.3760

Now with my block already being .020 over and the nicks in the cylinder walls catching my fingernail I know the block has to be bored again....But I have researched and gotten mixed responses and posts for .040 over on the 2.0L motors.


I am looking for first hand information, not "I heard" or "So and so did this..."
I need to know which of you are actually running .040 over, if you have any cooling issues, how you drive the car(track only, DD, mixed), and just any general advice.

My car will see close to 30psi on a holset hx35 or hx40, daily driven, and occasional track use. Should I expect any issues with going .040 over or will it be fine?

 

[XiKeiyaZI]

There have been several who have ran with a .040 bore and had absolutely zero issues. The reason that this is suggested is because it is feared that much more would endanger the integrity of the cylinder walls and weaken them. When making power you certainly want your walls to be as strong as possible. Now, it is suggested that .040 is the Highest you want to take it (though others have ran slightly more) if you want to keep within the safety range. You will not run into any drivability issues that will determine if it is a garage queen or a daily driver.

Remember, we like to set safety ranges with a little wiggle room for a reason. We wouldn't say ".040 is the highest you want to take it" if it endangered engines. Otherwise we'd say "Never go to .040 as it will destroy the integrity of your engine." We're too cheap and anal to take chances. Many have ran .060 without issues but many will agree that this is 'pushing it'.

 

[ChrisTheBuilder]

i am running 40 over and my temp is exactly as it was when i had my stock block. go for it!

 

[WES_393]

I'm running 86mm (.040) bore as well. She's running great so far (knock on wood). No overheating or anything like that and I drive her pretty hard. Before the trans went out she was seeing 30 miles of boost happy DDing and some hard races on the weekends.

I agree 86mm is the highest you should go, but I would consider taking the block to a different machinist for that. My machinist would have never let the block leave his shop with scores like that in the cylinder.

 

[toppertopper]

+2 on never leaving the shop with scores like that ..That looks like they bought the honing for drills.

 

[Bo0sTdTsI]

.040 over is just fine. I ran em 10:1 and doing the same set up again, i thought it was decent. You shouldnt have problems going that route.

 

[TSITurbo95]

Did the machine shop say anything about the scores? If they didn't suggest honing it more to get rid of the scratches, then I would be iffy about that machine shop.

 

[blizz99]

I'm currently running .060 on a 7 bolt stroker block =)

 

[Purple_Demon]

Well they were not supposed to hone it at all, and I wasnt charged for it either. They were only supposed to mic it to check for out of roundness, then magnaflux it for cracks IF the cylinders were not out of round.

I honestly did not even think to check, they came so highly recommended and my dad has used them in the past with zero issues. Im headed back there today to drop the 7bolt head off for cleaning so I will ask

 

[kdubbs]

I have question that is related to this topic and haven't found much info on people running a little out of roundness on their build. I currently have my 6 bolt block at the machine shop being built. It is .040 over with Mahle stroker (4032) pistons, eagle rods and 100mm eagle crank. I bought the block used already bored to .040 over. The shop honed the block and told me that there is a little out-of-roundness towards the bottom of the cylinder (last inch or so) that measure 0.0005". I know the spec is 0.0004" for the turbo blocks but if the rings will never see it will it be ok? The shop said it would be and if the rings did touch some of the out of roundness it would be lower like 0.0003". I would get a new block but wont because of money and the current situation so its not worth asking. Any suggestions would be helpful. The only changes I will be making are a new SBR G50 and shooting for 400-450 whp.






-thanks, Kevin