[mgarblik]

Originally Posted by 63Banshee

Block deck has huge influence on head stability and subsequently head gasket survival.

The block is important certainly, but don't forget the head bolted down to it. Case in point: Our very tall and stiff billet head has survived at 3000+ HP on both aluminum and iron IA II's for 8 years on one pair of head gaskets. No compression leak witness marks. That's with the stock 10 head bolt layout that everyone said could never be done. Clamp load is what it's all about. 9/16" studs torqued to 135 PSI. A solid head with lots of meat around every head bolt column. Use a light, flimsy aluminum head on an iron block with long, wimpy 1/2" studs at 95 ft. lbs and all you get is 10 pulled-up areas around each head stud and leaks all around, especially where the heat concentration is in the paired exhaust ports. Above 1000 HP, your asking allot of the head gasket IMO. Bore spacing doesn't help, but I am not convinced 4.840, or even 5.00" alone is an instant cure.

[Dragncar]

Originally Posted by mgarblik

The block is important certainly, but don't forget the head bolted down to it. Case in point: Our very tall and stiff billet head has survived at 3000+ HP on both aluminum and iron IA II's for 8 years on one pair of head gaskets. No compression leak witness marks. That's with the stock 10 head bolt layout that everyone said could never be done. Clamp load is what it's all about. 9/16" studs torqued to 135 PSI. A solid head with lots of meat around every head bolt column. Use a light, flimsy aluminum head on an iron block with long, wimpy 1/2" studs at 95 ft. lbs and all you get is 10 pulled-up areas around each head stud and leaks all around, especially where the heat concentration is in the paired exhaust ports. Above 1000 HP, your asking allot of the head gasket IMO. Bore spacing doesn't help, but I am not convinced 4.840, or even 5.00" alone is an instant cure.

One pair of head gaskets for 8 years, on and off with that kind of power. Thats interesting.
Your 9/16 studs at 135lbs. They don't pull up the deck in spots. Just because your head is so solid and stiff?
The separate exhaust has got to help a bunch too.

[Elarson]

The stiff head bridges across between bolts much better and applies better loading out in the unbolted areas.
Separate exhaust ports are a huge help to even out the temperature related distortions.
We had Darton custom-make replaceable sleeves for us so that we could fix cylinders at the track. Reverse Murphy's law....were prepared for that so we've never needed that. Sleeve OD is 4.5 so we only have .12 wall between cylinders but with the solid block, that's ok. The sleeve upper rim has a flat on both sides so they lock into their neighbor. O-ring grooves are in the upper rim of the sleeve. The counterbore depth in the block for the sleeve upper rim is a little short so that the sleeve stands proud of the deck by a couple thousandths assuring that we fully clamp around the cylinder.

Eric

[Elarson]

And yes, the block will flex up around the bolts but can only go a few thousandths so it won't permanently yield. And the replaceable sleeves float in the block slightly so they're less affected by block bore distortion.

Eric

[Stan Weiss]

Originally Posted by Elarson

The stiff head bridges across between bolts much better and applies better loading out in the unbolted areas.
Separate exhaust ports are a huge help to even out the temperature related distortions.
We had Darton custom-make replaceable sleeves for us so that we could fix cylinders at the track. Reverse Murphy's law....were prepared for that so we've never needed that. Sleeve OD is 4.5 so we only have .12 wall between cylinders but with the solid block, that's ok. The sleeve upper rim has a flat on both sides so they lock into their neighbor. O-ring grooves are in the upper rim of the sleeve. The counterbore depth in the block for the sleeve upper rim is a little short so that the sleeve stands proud of the deck by a couple thousandths assuring that we fully clamp around the cylinder.

Eric

Eric,

From the actual bore size you use. Is there an difference from what the Hemis run?

Stan

[john marcella]

I so wish people would stop categorizing cyl heads based on its flow numbers.

[63Banshee]

Originally Posted by mgarblik

The block is important certainly, but don't forget the head bolted down to it. Case in point: Our very tall and stiff billet head has survived at 3000+ HP on both aluminum and iron IA II's for 8 years on one pair of head gaskets. No compression leak witness marks. That's with the stock 10 head bolt layout that everyone said could never be done. Clamp load is what it's all about. 9/16" studs torqued to 135 PSI. A solid head with lots of meat around every head bolt column. Use a light, flimsy aluminum head on an iron block with long, wimpy 1/2" studs at 95 ft. lbs and all you get is 10 pulled-up areas around each head stud and leaks all around, especially where the heat concentration is in the paired exhaust ports. Above 1000 HP, your asking allot of the head gasket IMO. Bore spacing doesn't help, but I am not convinced 4.840, or even 5.00" alone is an instant cure.

I'm not forgetting the head. I wanted to point out the importance of block deck thickness. Something overlooked by many before 60+ boost numbers.