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Discussion Starter #1
Hiyas,

I have a set of CNC ported 241 heads. They flowed around 280 in, 243 ex.

I have a 3.908" bore in my LS1 as it had to be taken out 0.03"

This therefore reduces the possibilities for pistons which I can use. I have a set of Mahle with -4cc of valve relief in them.

Last night I checked PTV clearance and I have a ton, around 0.400" (exact figures are at home)

I am building this engine only for drag racing, it is going into a 125" altered (open wheeler)

I am chasing info on how far I can mill these 241 heads down before I run into issues of water.

I run ARP studs, 0.040" cometic head gasket, cam is 238/242 @ 108LSA I want as much compression as possible; preferable over 13:1 so I can run an alcohol based fuel.

Sorry for so much detail, but I wanted you guys to have all the facts.

Cheers
 

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Hiyas,

I have a set of CNC ported 241 heads. They flowed around 280 in, 243 ex.

I have a 3.908" bore in my LS1 as it had to be taken out 0.03"

This therefore reduces the possibilities for pistons which I can use. I have a set of Mahle with -4cc of valve relief in them.

Last night I checked PTV clearance and I have a ton, around 0.400" (exact figures are at home)

I am building this engine only for drag racing, it is going into a 125" altered (open wheeler)

I am chasing info on how far I can mill these 241 heads down before I run into issues of water.

I run ARP studs, 0.040" cometic head gasket, cam is 238/242 @ 108LSA I want as much compression as possible; preferable over 13:1 so I can run an alcohol based fuel.

Sorry for so much detail, but I wanted you guys to have all the facts.

Cheers
So what is the bore size? I don't understand the .030" over. 3.908 is .010 over.

That is a lot of piston to valve clearance. Are you sure you checked it properly?

You may consider some more port work, your intake port is a little weak.

As far as milling, if it is naturally aspirated, I wouldn't be afraid to mill them .065"
 

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Discussion Starter #3
So what is the bore size? I don't understand the .030" over. 3.908 is .010 over.

That is a lot of piston to valve clearance. Are you sure you checked it properly?

You may consider some more port work, your intake port is a little weak.

As far as milling, if it is naturally aspirated, I wouldn't be afraid to mill them .065"
Sorry, I got my figures wrong - you are correct it is .010 over making it 3.908

I am sure it was checked correctly. I checked it via dial indicator, and then checked it via the playdough method. I also had a friend here who has built afew monster SBC/BBC engines hmself who verified what I was doing is correct.
 

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To get to 13:1 you would need to mill the heads down to 48-49cc and that is probably near an 1/8" off. Not going to happen with head milling alone. You should have gone with a dome piston if you needed that much compression.
 

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Discussion Starter #5
To get to 13:1 you would need to mill the heads down to 48-49cc and that is probably near an 1/8" off. Not going to happen with head milling alone. You should have gone with a dome piston if you needed that much compression.
As above, no off the shelf dome pistons exist for 3.908 but thanks for the information.
 

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As above, no off the shelf dome pistons exist for 3.908 but thanks for the information.
4" bore block and its noooooooooo worries :)

i have a set of the new JE ayssm coming for a 13:1 std bore stroke deal now
 

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Discussion Starter #7
4" bore block and its noooooooooo worries :)

i have a set of the new JE ayssm coming for a 13:1 std bore stroke deal now
I am now thinking about bolting the head on, not milling it and in between next year's season order a set of custom dome pistons for this bore size, then mill the heads once I have them installed.
 

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that will work

just run it for now or even get another block and start piecing it togther
 

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not ideal, but I had a set of 243's milled to a 48cc chamber. They did leak a tiny bit with a GM .051 gasket. Its not uncommon to mill 243/241 .070-.080, mine were around .125
That was good for over 13:1 even with the thicker gasket. Ran them for an entire year and it never ate coolant but when I pulled the heads there was evidence it was starting to leak a little
 

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if you want to use them I would weld them up. The chambers is big and you have to cut them alot to get them down. Most Ive done was about 59cc plastic intake needed some work to fit and it was still getto with the std bolt pattern. it was something like .080 off.
theirs power in a better tighter chamber too
 

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They regularly angle mill 20ish cc off the 70cc chambers of the ls3 and ls7 stuff.

Might cost more but seems to work well for getting a lot of compression in these motors
 

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Discussion Starter #13
Thanks guys, I double checked yesterday using a dial indicator and soft springs. 0.427" intake / 0.397" exhaust
 

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Valve drop should be close to .200" so I am not sure how you have that much ptv clearance. Not that you should have any issue with that cam and 4cc valve reliefs. Just sounds way off.
 

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Discussion Starter #17
Why would that be? I'm using test springs and pushing the valve down until it hits the piston?
 

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Why would that be? I'm using test springs and pushing the valve down until it hits the piston?
You need to use the cam to open the valve and measure the clearance between the valve and piston. What you are measuring there is valve drop. If the cam was at full lift at tdc it would hit the piston as I am sure you have at least .600" lift and only .397" clearance.
 
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