Piston dome height

by **clee** » Mon Dec 11, 2006 1:14 pm

In the engine manual it quotes two for the Z7U .The ones I have are of course 3.60 .............

8.6 CR = 3.60mm
8.0 CR = 1.57mm

Now can you guess where I'm going with this :?:

Is it possible :?:

by **mitchella** » Mon Dec 11, 2006 1:31 pm

clee wrote:Now can you guess where I'm going with this

Straight onto a metal working machine of some sorts that can relieve you of 1.63mm of metal? I'm seeing lowered compression ratio, thereby allowing higher boost to be run thereafter... and those volvo head gaskets will not cause a problem even if they are a bit under 1.7mm. .. but I am still learning the business of GTA tinkering so I could be completely wrong :oops:

by **clee** » Mon Dec 11, 2006 1:37 pm

I'm learning the hard way as we all are :lol:

But if the piston interior depth is the same on both then a reduction in dome height shouldn't be a strength problem should it ? Perhaps not the full difference ,maybe 1 mm :?:

by **mitchella** » Mon Dec 11, 2006 1:55 pm

[quote]
Straight onto a metal working machine of some sorts that can relieve you of 1.63mm of metal? [/quote]

Spot the accountant!! 3.60 - 1.57 = 2.03!! Doh.

I guess the real answer to your question lies in what thickness the crown of the piston has. If you are lucky then perhaps both of these pistons are made from the same casting/forging/whatever process and then just machined down to final spec, Can you measure how thick the existing material is? That would give you a clue as to what percentage you are taking away and perhaps a better view as to whether it will wreck the overall integrity of the part or not.

by **clee** » Mon Dec 11, 2006 2:01 pm

It's depth-mic central so I can easily check them .But yes I can't see them using different castings for just that difference

But it was France in the early Eighties ,so they may be :lol:

by **David Gentleman** » Mon Dec 11, 2006 2:18 pm

clee wrote:It's depth-mic central so I can easily check them .But yes I can't see them using different castings for just that difference But it was France in the early Eighties ,so they may be

But the 8:1 pistons came 4 years later, so I don't think they are related...If it was done to solve a problem, I would assume it was reengineered rather than just lopping a chunk off the top..

by **clee** » Mon Dec 11, 2006 5:52 pm

I've ordered the Volvo gasket kit, when it arrives I'll measure it up .Whatever the thickness I think it'll be safe to take that 0.30mm diff off the pistons at least .There's always a degree of safety built in all bits

@ 8.6cr the psi will be 170ish ? @ 8 it'll be 160 ish , 6% less

It's all relative :lol:

He said .........................Kaboom of Leicester ,innit mate

by **Alpineandy** » Mon Dec 11, 2006 8:08 pm

you could take a bit more off and try this out?
http://www.poetonaptec.co.uk/xtreme.htm

by **David Gentleman** » Mon Dec 11, 2006 8:09 pm

clee wrote:Whatever the thickness I think it'll be safe to take that 0.30mm diff off the pistons at least .)

C'mon, think about it....it will be more than 0.30mm off the top of the piston won't it... :wink:

by **clee** » Mon Dec 11, 2006 8:15 pm

I know of Poeton ,they do a lot of specialised finishes for ali .I looked at some of their products for a project .Apticote is hard anodising I think .

by **Alpineandy** » Mon Dec 11, 2006 8:17 pm

Apricot is what

by **clee** » Mon Dec 11, 2006 8:18 pm

Alpineandy wrote:Apricot is what

Fruit

by **clee** » Mon Dec 11, 2006 8:30 pm

David Gentleman wrote:
clee wrote:Whatever the thickness I think it'll be safe to take that 0.30mm diff off the pistons at least .)

C'mon, think about it....it will be more than 0.30mm off the top of the piston won't it...

Please explain

by **David Gentleman** » Mon Dec 11, 2006 8:30 pm

clee wrote:
David Gentleman wrote:
clee wrote:Whatever the thickness I think it'll be safe to take that 0.30mm diff off the pistons at least .)

C'mon, think about it....it will be more than 0.30mm off the top of the piston won't it...

C'mon, think really hard.... :oops: