Head Gasket thickness selection

[Chello]

Ahh damn, well maybe a couple of weeks lol, I think I have to go to Ballarat end of next week for work for a few days anyway.

I have stuff I am doing on the Hilux at the moment anyway so a bit of extra time will be fine

[Needboost]

i soon will be taking my block an head to be machined for a mhg what Ra values should be done. and what exactly are Ra values? and i am planning on running probe pistions and saw on the thread that dish changes compression also. i guess im just confused on the compression ratio i would like to stay as close to stock to prevent problems. sorry if this is off subject

[eraezer]

Needboost: it's a arithmetic mean value of the surface roughness.


Now I need a little help to decide on a MHG.

As far as I know there is no MHG size between 2.0mm and 3.0mm, is this correct?

My block is now: 197.4 or 197.6mm (I don't have the exact number in my head, but somewhere in between).
My head is now: 116mm (unsurfaced so far)

Stock piston protrusion: 0.5mm
My protrusion value: 0.5+ (198.5-197.4) = 1.6mm (Max. value)
My protrusion value: 0.5+ (198.5-197.6) = 1.4mm (Min. value)

Combustion chamber volume: 37.5cc (forums) or 40cc (Arias)
I have been grinding away some hotspots so my combustion chamber is a bit larger than stock.
And I'm not sure which stock value is correct? On the piston paper from Arias, they say 40cc

Let's say that during surfacing of my head I'll end up removing 0.5mm
Let's also say that the combustion chamber opening is the same as the stock bore: 83mm. Just to keep it simple.
The volume removed will be:
pi*r^2*removed material = pi * (83/2)^2 * 0.5 / 1000 = 2.705 cc

So 2.705 cc is removed if the head is shaved 0.5mm
Let's say that my grinding has added 1cc/cylinder
This gives me:
Min : 37.5-2.705+1 = 35.795 cc
Max: 40-2.705+1 = 38.295 cc

Piston Dish: 19cc (stock)
My piston dish: 16.09cc (Arias)

If I would use a 2.0mm MHG I will have the following clearance between piston and head:
Min = 2-1.6 = 0.4mm
Max = 2-1.4 = 0.6mm

And with a 3.0mm MHG:
Min = 3-1.6 = 1.4mm
Max = 3-1.4 = 1.6mm

The stock clearance is 1.37-0.5 = 0.87mm

How much does the Eagle rods stretch during max rpm?

The cylinders are now 83.49 mm

gasket bore is 86mm

With this calc: http://www.csgnetwork.com/compcalc.html

and these values:

Enter Cylinder Bore Size 83.49
Enter Piston Stroke Length 90.98
Enter Head Gasket Bore Diameter 86
Enter Compressed Head Gasket Thickness 2
Enter Combustion Chamber Volume In CCs 35.795
Enter Piston Dome Volume In CCs Negative For Dished Pistons (Use '-') -16.09
Enter Piston Deck Clearance Negative If ABOVE Deck (Use '-') : -1.6

I get the maximum static compression of
With a 2mm MHG 10.10526513241693 : 1
With a 3mm MHG 9.231210911947521 : 1

and these values:

Enter Cylinder Bore Size 83.49
Enter Piston Stroke Length 90.98
Enter Head Gasket Bore Diameter 86
Enter Compressed Head Gasket Thickness 2
Enter Combustion Chamber Volume In CCs 38.295
Enter Piston Dome Volume In CCs Negative For Dished Pistons (Use '-') -16.09
Enter Piston Deck Clearance Negative If ABOVE Deck (Use '-') : -1.4

I get the minimum static compression of
With a 2mm MHG 9.543791078210202 : 1
With a 3mm MHG 8.769627288645353 : 1

Since the combustion chamber, according to arias, is 40cc and that is bigger than my max
I added a static comp ratio for that too:

I get the minimum static compression of
With a 2mm MHG 9.30101738082517 : 1
With a 3mm MHG 8.568338122041688 : 1

Until I have measured my final combustion chambers, these are the values I have to work with.

My max. static comp. ratio with a 2mm MHG is 10.105:1
My max. static comp. ratio with a 3mm MHG is 9.231:1

My min. static comp. ratio with a 2mm MHG is 9.301:1
My min. static comp. ratio with a 3mm MHG is 8.568:1

I'm not planning on using huge amounts of boost.
I will use my supra mostly on the street and on the occasional track-days.
The largest turbo it will see is probably a GT-35 or BW S200.
It's already stand-alone
BC stage 2 cams, BC valve springs+retainers and 1ZZ-FE COP's are on it's way.

What's the closest piston to head clearance I can run?

Should I just go with a 3mm MHG and be over with it?

What's your suggestion?

Thanks/Marcus

[Ekmo]

Bump for answer

[eraezer]

I went with a 3mm MHG.

The easiest equation is stock block + stock head + stock gasket - new block - new head = new HG
This should give a comp ratio slightly higher than stock and since I'm using 9:1 pistons so I should be around that.

[nofx230]

ok bare with me here, my heads already been shaved .020 from PO and is probably going to need another .015-.020 taken off thats almost 1mm of thickness problem is i wanna run a composite head gasket because pulling the block isn't an option right now, but with 1mm of thickness to make up due to machining whats my CR going to be at? also can i even run the car like that and what would i need to do to actually get it running properly

[Needboost]

ok i have had my head and blocked machine and decked. block is bored .20 over

HEAD BLOCK stock head gasket 1.37mm before total- 315.87mm
before-116mm before- 198.5mm after total- 313.918
after- 4.560in. = 115.824mm after 7.799 in.-198.094mm equals = 1.952 mm gasket that i need?

if i have the caculations correct what head gasket will i need?

[IJ.]

2mm will do it fine if your math is correct.

[Needboost]

2mm will do it fine if your math is correct.

ok i have had my head and blocked machine and decked. block is bored .20 over

HEAD BLOCK stock head gasket 1.37mm before total- 315.87mm
before-116mm before- 198.5mm after machine total- 313.918
after- 4.560in. = 115.824mm after 7.799 in.-198.094mm equals = 1.952 mm gasket that i need?

if i have the caculations correct what head gasket will i need? the machine shop did the measurement for me but i feel like i have made a misake some where

i added the stock head+block+headgasket size to get my total of 315.87mm
then dded the after machine work of head and block then subtracted the amount 313.918
to get 1.952

head
before- 116mm
after 4.560in = 115.824 mm

block
before-198.5mm
after- 7.799in= 198.094mm

stock headgasket. 1.37mm

before- 315.87mm
after machine work- 313.98

315.87mm-313.98mm= 1.952mm

[Needboost]

2mm will do it fine if your math is correct.

with the cylinders being bored .20 over what difference does that make on compression and do i have to get a certain kind of gasket since the block was bored. sorry for the ignorance on this just trying to get everything correct for the first build and learn in the process thank you.