Does the TRD head gasket raise compression?

[Mr Revhead]

reading that hurt.
let alone working it out

think ill just email you what i want to know and threaten you with higher prices to get what i want

[sergei]

"Oh NO"

[pc]

It's simple math, and necessary to work out the current CR ratio and target CR. Combining all of the equation into one line makes it look a little daunting tho.
Don't forget to include the volume of the gap between the cylinder wall and the piston, from the top ring to the top of the piston... and also the volume of the top of the cylinder if it's not flat.

[Mr Revhead]

yeah my biggest issue is not the maths, its finding exact volumes

[pc]

I wasn't sure on the standard way of measuring the volumes of the piston & combustion chamber, but I used plasticine.
I filled the top of the piston with plasticine, shaved it off flat using a steel rule, then rolled it into a ball and put it in a measuring beeker with water and got the volume in ml (cc) that way. The same was done for the combustion chamber (with spark plug installed), and the rest was done with calipers and a calculator.
The engine reconditioner came up with the same figures as I did, so this method seems to work ok.

[sergei]

to calculate the compession ration you don't need to know the voluems of combustion chamber or piston shape, because it is constant and does not vary, all of those things can be considered as "combustion chamber volume" in my equation.
Infact you could simpilfy formula and exclude stock head gasket volume from it by replacing volume difference between new gasket and old gasket (+ with increase - with decrease).

[pc]

Ummm.... no you can't do that.

you still need to know the volume of the
combustion chamber
+ headgasket
+ piston dip thingie
+ gap around the top of the piston

To be able to add all of these things up, you will need to know what they are.

[Truenotch]

45 thou or 45 thousandths of an inch is just over 1mm.

dam.. guess i've got enough compression then heh

How does your smallport go with that much compression? I'm thinking about raising mine a bit.

[sergei]

Ummm.... no you can't do that.

you still need to know the volume of the
combustion chamber
+ headgasket
+ piston dip thingie
+ gap around the top of the piston

To be able to add all of these things up, you will need to know what they are.

I disagree with you. You don't need to know this. What you need to know is the change in that "static volume", wich is pretty easy - volume of new gasket minus volume of old gasket. That will give you a change. Treat rest of the volumes as one volume "x", because it is static it will not matter what it is composed of. ie Comubstion chamber stays the same, deck heigh stays the same, piston hight/depth stays the same, what only differs is the gasket thickness. So just add/subtract (depends if thicker or thinner) the difference of new gasket volume vs old to that X.

as in here:

old C.R. = ( Bore volume + X ) / X

new C.R = ( Bore volume + X + change in gasket thickness ) / ( X + change in gasket thickness )

knowing old C.R. and Bore volume, it is possible to find X - which is combined volume of comubstion chamber, deck heigh, piston dish/dome, stock gasket. etc. Then knowing X it is possible to reintroduce it in new C.R. equation and calculate new C.R.

Simple algebra.

[Mr Revhead]

just make a spread sheet and post it up

[JT]

just make a spread sheet and post it up

I'm working on it...


Sergei, to not confuse matters ( ) best to refer to your 'bore volume' as 'swept volume'

[sergei]

just make a spread sheet and post it up

I'm working on it...


Sergei, to not confuse matters ( ) best to refer to your 'bore volume' as 'swept volume'

Sorry about that, you know, english is not my first language

[AE85coupe]

45 thou or 45 thousandths of an inch is just over 1mm.

dam.. guess i've got enough compression then heh

How does your smallport go with that much compression? I'm thinking about raising mine a bit.

Goes bloody awesome, it loves it, won't run on anything but 98 mind you, and i had to retard the timing a touch (need some av gas haha)

[pc]

Ummm.... no you can't do that.

you still need to know the volume of the
combustion chamber
+ headgasket
+ piston dip thingie
+ gap around the top of the piston

To be able to add all of these things up, you will need to know what they are.

I disagree with you. You don't need to know this. What you need to know is the change in that "static volume", wich is pretty easy - volume of new gasket minus volume of old gasket. That will give you a change. Treat rest of the volumes as one volume "x", because it is static it will not matter what it is composed of. ie Comubstion chamber stays the same, deck heigh stays the same, piston hight/depth stays the same, what only differs is the gasket thickness. So just add/subtract (depends if thicker or thinner) the difference of new gasket volume vs old to that X.

as in here:

old C.R. = ( Bore volume + X ) / X

new C.R = ( Bore volume + X + change in gasket thickness ) / ( X + change in gasket thickness )

knowing old C.R. and Bore volume, it is possible to find X - which is combined volume of comubstion chamber, deck heigh, piston dish/dome, stock gasket. etc. Then knowing X it is possible to reintroduce it in new C.R. equation and calculate new C.R.

Simple algebra.

Ahhh... I see. You are assuming that the current CR is known (accurately)... I am assuming that it isn't.

[JT]

Ahhh... I see. You are assuming that the current CR is known (accurately)... I am assuming that it isn't.

If you don't know your CR then you'll have to do it the long way. Assuming it is known accurately (and the standard gasket is 1.2mm) I have calculated for a 16V with 9.4:1 standard CR a 0.8mm gasket with raise compression to 9.8:1 and a 0.5mm will raise it to 10.1:1

Would be interesting to know how much a standard gasket squashes when the head is tightend in place. The calculation depends on a few variables that we have to assume are constant.

Not quite sure how Jebus arrived at his figures?

Will sort out the rest of the 4ag series and some error margins of standard CR. This assumes the head and pistons are standard but I can calculate if you've had the head skimmed.

[TRD Man]

I think you're pretty close JT. At some point we did the calculations and determined that the 0.8mm gasket raised the ratio by about 0.3 roughly.

[JT]

hmm so when i took 45 thou off the head of my smallport how much did i raise the compression?

whats 45 thou in mm?

45 thou is 1.143 mm. If you used a standard gasket you'll have ~11.7:1

I think you're pretty close JT. At some point we did the calculations and determined that the 0.8mm gasket raised the ratio by about 0.3 roughly.

Yeah, 0.38 to be exact But thats for a bigport. Don't forget that the standard CR of an engine determines the CR with a new gasket so a smallport will have a slightly larger increase of compression of 0.47
For a silvertop it increases by 0.49 and for blacktop 0.55

[AE85coupe]

cool 11.7:1 eh, thats awesome, surprising i can still run it on pump gas hahahaha