bring pistons 0.080 above deck with 0.080 gasket?

[HankL]

In the latest Engine Masters magazine 'teardown' section they show a trick where one of the builders decked his block so much that the pistons came out of the hole 0.080 inches. {maybe he lengthened his con rod instead}

He then used a 0.080 Cometic head gasket so that the piston land above the 1st ring was mostly in the head gasket section and had a very tight side clearance - so tight that at least one piston showed some rubbing marks.

I guess the idea is to reduce 'crevice volume' where unburned gasoline can 'hide' and not burn.

I also guess this would create the tightest possible quench - so much so that perhaps the combustion chamber needed some circle cut milling at each bore center to create a 'clean quench' ? {I have seen this done in the 70's on old 340 heads with as-cast rough quench surfaces}

Anybody tried this?

Pros, cons ?

Lighter engine block,
lighter cyl heads (must mill to to match) better rod/stroke ratio
perhaps the top of the bore is more rigid and won't deform as much if the piston goes as high as possible?

[dirty dan]

More squeeze
This is a good thing.
However you should Know 14.5 :1 is the max useable compresstion ratio.
After that they call it a desile.
I have acheived pluse 70 deck hiegth on a big block application.
Haveing said that I should point out that milling the edge of the piston diamiter is required.
I also use a 60 th copper head gasket.
There is power to be made from incressing compresstion.
But differant combos require differant cuts.
Just remember a safe number for both strandard and automatic trans aplication is 50 thousands piston to head clerance.

[6 packin]

Woulnt that all be much better to obtain with maybe Dome pistons and correct clyinder chamber volume, It just dont make sence having +.080 deck clearance then buying band-aid thick .080 head gaskets. to fix the mess up. How would that be any different than a zero deck engine? Dont sound like there Engine masters too me, sounds like a bunch of glue sniffing chevy heads went crazy with the mill?? 13.5:1 can be acheived with a flattop piston and stock heads, but will take some work, much better power that a 14:1 dome engine if you ask me........but you probably wont!

[23T]

I learned a looong time ago never to say you cant do that, it wont work. Now I just say you did that, how long did it last?

[dirty dan]

Originally posted by 6 packin
Woulnt that all be much better to obtain with maybe Dome pistons and correct clyinder chamber volume, It just dont make sence having +.080 deck clearance then buying band-aid thick .080 head gaskets. to fix the mess up. How would that be any different than a zero deck engine? Dont sound like there Engine masters too me, sounds like a bunch of glue sniffing chevy heads went crazy with the mill?? 13.5:1 can be acheived with a flattop piston and stock heads, but will take some work, much better power that a 14:1 dome engine if you ask me........but you probably wont!

Hey six packin
Trw dome pistons 11.58:1 were used in this application.
These forged pistons do wiegh a ton.
However they do have a good low dome design.
I'd like to have a push rod for every set of Ross's I have seen with 1/2 the dome cut off.
Not flat tops.
The reson for the thick (copper) head gasket is required is due to
O-ringing the block.
To handle the extra cylinder pressure .
When the block was origineally decked I itended to use a standard thickness gasket.
But with the use of NOS there was no way they could take it.

[6 packin]

Dome pistons can be very effective for sure. Its very important on the dome shape however in a wedge head engine. Hey whatever it takes to get you there I guess. Im running a set of 516 closed chambered heads that been milled .080 to get my squeeze up there. Because i have .080 negtive piston to deck clearance.

[deadhorse66]

These engine masters are not sniffing glue, six packin, they know what they are doing. If the same compression can be achieved with a flat top as with a domed piston, the flat top is the better route (in wedge, polysphere, and bathtub chamber designs), and I will tell you why: As mentioned earlier, domed pistons generally weigh more than flat tops. Also there is an issue called flame propagation. Propagation is the way the flame front of the igniting fuel travels across the crown of the piston as it burns. In a domed piston application, whether it be quench or squish, the flame front must travel across the dome to reach the side of the chamber opposite the spark plug. In doing that, the flame front loses speed, heat and momentum. This slowing of the flame front reduces effective force on the piston, and therefore reduces horsepower. If you look at your combustion chamber, it is easy to see. As the flame front travels on your wedge head, it runs into a bottle neck as it reaches the quench area--that is where the majority of the big push from the flame front takes place. With a flat top, there is a straight shot to the quench area, with domes, it is like the flame front has to work through a maze to get there. Granted, you have more squish with a dome, but if the flame front cannot build in the squish area, then it is useless. When you have to build one to the absolute ragged edge to compete with sanctioned parts, this is what you end up with. Personally, I would not try it because I have no need for such an engine and I have heard that it is really hard on the top ring (as in breaking it), but I would not put it past the guys who run N/PS--they do some wild things.

[dirty dan]

Originally posted by 6 packin
Dome pistons can be very effective for sure. Its very important on the dome shape however in a wedge head engine. Hey whatever it takes to get you there I guess. Im running a set of 516 closed chambered heads that been milled .080 to get my squeeze up there. Because i have .080 negtive piston to deck clearance.

Hey 6 packin
You are still missing out on a lot of squeeze.
Flat tops at -80. Wow what a gapeing gap .
Cutting the small chamber heads is a good idea.
But much more squeeze would be achived by decking the block
then the heads.
I perffer the open chamber heads 452 milled down to achive a 72cc chamber with 1.181 exh and 2.140 int valves.
But thats another story.

[dirty dan]

Originally posted by deadhorse66
These engine masters are not sniffing glue, six packin, they know what they are doing. If the same compression can be achieved with a flat top as with a domed piston, the flat top is the better route (in wedge, polysphere, and bathtub chamber designs) Also there is an issue called flame propagation. In a domed piston application, whether it be quench or squish, the flame front must travel across the dome to reach the side of the chamber opposite the spark plug. In doing that, the flame front loses speed, heat and momentum. This slowing of the flame front reduces effective force on the piston, and therefore reduces horsepower. If you look at your combustion chamber, it is easy to see. With a flat top, there is a straight shot to the quench area, with domes, it is like the flame front has to work through a maze to get there. Granted, you have more squish with a dome, but if the flame front cannot build in the squish area, then it is useless. When you have to build one to the absolute ragged edge to compete with sanctioned parts, this is what you end up with. Personally, I would not try it because I have no need for such an engine and I have heard that it is really hard on the top ring (as in breaking it), but I would not put it past the guys who run N/PS--they do some wild things.

Dead horse
Your quit rght
This is why I perfer a low dome piston.
Anyone can purchuse a set of ross 12.25:1 pistons and say there its a monster now.
But as you mentioned It's not that simple.