[Scott Stoneburg]

Guys, looking for input from the expert or just very knowlegable...I checked the deck height on my 535. Currently pistons are .025 in the hole. I thought I checked it wrong at first, so I checked again. No mistake in the measuring so I did some research, if using the butler gaskets, 4.39 bore size, .039 crush thickness, my pistons have 17 cc dish-valve reliefs , heads have 70cc chambers. I'll need the piston .015 in the hole to get below 12 to 1. Is .015 in the hole going to cause any issues? I looked into what the so called experts are recommending for quench. I read that .040 is the minimum but that too much quench could also create detonation too. So where is the sweet spot? Between .040-.050 ??

[pastry_chef]

.040 would be a conservative minimum.

I'd put the sweet spot .035 to .045.

Once you get to .050 the benefit is negligible.

Steel connecting rods?

[steve25]

There is nothing carved in stone in regards to quench clearance!

Many Super Stockers and high level builders run the piston .005" out of the hole,

The rule of Thumb is the lesser amount of quench area the Head has the smaller your quench clearance should be to get some good turbulence taking place.

It's the turbulence that the quench area makes that creates a more homogeneous air and fuel mixture that burns faster and more complete.

People that have ping or knock issues with a given amount of quench clearance just do not realize that now with faster burn they need less total timing!

You want the fastest burn you can have because once the piston gets down the Bore even just to a distance of 25% of the motors stroke the push ( hot air expanding ) on the piston top has already provided its most usefulness!

[Scott Stoneburg]

Originally Posted by pastry_chef

.040 would be a conservative minimum.

I'd put the sweet spot .035 to .045.

Once you get to .050 the benefit is negligible.

Steel connecting rods?

Yes, steel rods. Trying to keep the compression low enough for pump gas.

[ponjohn]

By using the piston in the hole to reduce compression, is that best practice?

I thought zero deck was the starting point and then adjust other parameters to reduce compression?

[mysticmissle]

lots of engines doing just fine with the piston in the hole a little

[Scott Stoneburg]

Would it be better to get close to zero deck and go for a thicker gasket? I may also see if my pistons can be machined a little to give them a larger dish.

[mysticmissle]

everyone has an opininion and mine is no better than my machine shop, that being said, i started using a new guy a few years ago on my last build up, and he is also is getting the IA2 build i dropped off to him last week.
Zero deck is not a bad thing, and it helps more so in pump gas lower cylinder pressure builds, than large camshaft high cylinder pressure hi performance builds.
however, if space exists, and you can get the piston to sit low 10-15 thousands with the parts you have (rods, pistons, deck height) the rings will seal better, with the lower height. the ring pack sees Less heat, more of it is taken at the top of the bore/block. this is his opinon, i am an engine assembler not a builder. It makes sense to me, however i do not think there is alot of power to be had, it may be a longevity thing. The last motor he did the machine work and speced pistons for, I had the crank and rods and block, he designed the piston to be in the bore. I believe it ended up about .015 but would have to refer to my notes.
He has built eveyrthing form top alcohol to x275 procharged, hemi show car stuff to concourse triumph rebuilds. I saw him dyno a triumph 4 cylinder. I think it made 87 hp. they were ecstatic because it put out something like 70 hp in 1972! its the details. I have no idea what the piston to deck was in the triumph
fwiw he hates total seal gapless rings too. the convential ones are fine, I went with BWE rings last time and will again.

[LATECH]

Originally Posted by Scott Stoneburg

Guys, looking for input from the expert or just very knowlegable...I checked the deck height on my 535. Currently pistons are .025 in the hole. I thought I checked it wrong at first, so I checked again. No mistake in the measuring so I did some research, if using the butler gaskets, 4.39 bore size, .039 crush thickness, my pistons have 17 cc dish-valve reliefs , heads have 70cc chambers. I'll need the piston .015 in the hole to get below 12 to 1. Is .015 in the hole going to cause any issues? I looked into what the so called experts are recommending for quench. I read that .040 is the minimum but that too much quench could also create detonation too. So where is the sweet spot? Between .040-.050 ??

So I am guessing you are running an aftermarket block @ 535 CI yes- no?

Too much gone awry here to worry about quench now.

.025 in the hole -game over
dish pistons - game over
70 CC -game over

Block should have been zero decked, which means you should have calculated your stack height (Piston pin height + rod length) and cut the block deck accordingly

Then you need flat top pistons to utilize a quench pad that a cylinder head has

That being said, the heads need to have a quench pad area.If you have no quench pad area, then the whole point is moot

70 CC heads are waaay to small , even with a 17 CC dish, to get to 9.5 to 1 static

As it stands, your combo is almost 12 to 1

You need around 100 CC heads to get your combo down to 9.3 ish to one

98 CC would put you at 9.49 to one

Time to rethink a bit here

You could run a Iron head ,say a 6x , or a 7K3- 400 4 barrel (96 cc) , or a set of 4x or 4c heads from a 400 may fall into range. Best to CC any head before you buy to see where it is at. It may have been milled already so chambers may have shrunk due to milling .50 year old heads....you just never know

[LATECH]

Mystic muscle makes some good points with his post on running .015 in the hole with a piston.food for thought.

[Scott Stoneburg]

Originally Posted by LATECH

So I am guessing you are running an aftermarket block @ 535 CI yes- no?

Too much gone awry here to worry about quench now.

.025 in the hole -game over
dish pistons - game over
70 CC -game over

Block should have been zero decked, which means you should have calculated your stack height (Piston pin height + rod length) and cut the block deck accordingly

Then you need flat top pistons to utilize a quench pad that a cylinder head has

That being said, the heads need to have a quench pad area.If you have no quench pad area, then the whole point is moot

70 CC heads are waaay to small , even with a 17 CC dish, to get to 9.5 to 1 static

As it stands, your combo is almost 12 to 1

You need around 100 CC heads to get your combo down to 9.3 ish to one

98 CC would put you at 9.49 to one

Time to rethink a bit here

You could run a Iron head ,say a 6x , or a 7K3- 400 4 barrel (96 cc) , or a set of 4x or 4c heads from a 400 may fall into range. Best to CC any head before you buy to see where it is at. It may have been milled already so chambers may have shrunk due to milling .50 year old heads....you just never know

Yes aftermarket block. IAII. I bought a package of parts at the same time.
*2 sets of pistons. 1-flat top, 1-w/17cc dish.
*Heads are 70 cc chamber. CV1s(no haters please)
So they are what I'm using. I dont want 9.5 to 1. Looking to get just under 12 to 1., 11.75 to 1 is the goal. If it stays at 12 to 1 then I might as well use the flat tops and go 13.5 to 1. If I'm going to run race has the why not. Looks like if I can get the dish milled to 25cc on the piston.(8cc more than they are now) I'll be at 11.5 to 1.

[slowbird]

Plenty of guys running round or spherical dishes that don't offer much if any quench making good/great power without issues

[LATECH]

Originally Posted by Scott Stoneburg

If it stays at 12 to 1 then I might as well use the flat tops and go 13.5 to 1.

Pretty much..

[ponjohn]

Originally Posted by Scott Stoneburg

Yes aftermarket block. IAII. I bought a package of parts at the same time.
*2 sets of pistons. 1-flat top, 1-w/17cc dish.
*Heads are 70 cc chamber. CV1s(no haters please)
So they are what I'm using. I dont want 9.5 to 1. Looking to get just under 12 to 1., 11.75 to 1 is the goal. If it stays at 12 to 1 then I might as well use the flat tops and go 13.5 to 1. If I'm going to run race has the why not. Looks like if I can get the dish milled to 25cc on the piston.(8cc more than they are now) I'll be at 11.5 to 1.

Can you get E85 there?

[Scott Stoneburg]

Yes. E-85 is available a a couple different stations locally. But ive heard you really need to check that to make sure the content is consistent.

[Richie Hoffman]

I like 0 deck but have run .010 to .020 down on NA applications just dish pistons to get my compression ratio Inboost application I run .050 in hole with a dish all have run cool and made good power

[Richie Hoffman]

You can also open the chamber in heads up to get your compression you want and run a thin Cometic gasket to get proper quench

[AG]

I always measure deck height of the block and order custom pistons with a CH so it takes less than a 0.010"" deck height for a zero deck. You are stuck with what you have unless you get new pistons so maybe a slight cut off the deck to minimize the deck height.

[steve25]

What you can get away with quench wise and still make good power also is a factor of the motors piston speed as it approaches TDC.

A 4.210" stroke motor has over a 12% greater piston speed then a 3.750" stroke motor for example and as such the the 4.210" stroke motor makes a 12% higher level of turbulence when the piston parks itself at TDC.

In short longer stoke motors are fine with a less then optimum quench clearance.

[Jay S]

I would not be concerned about being .025 quench on a 535 versus a tighter quench. With the bigger cid and the longer stroke that quench area is a smaller percentage of the compressed volume. Piston speed is high too. What Steve said.



I would find someone to mill about 8 more cc into the pistons, get the SCR into the upper 10s and run it.