Amount to skim to raise compression

[blitzracing]

Does anyone know how much you can skim of the std Rover 3.9 heads to reach 10:1 ? I gather the composite head gasket drops the CR by .6 over the metal one but whats the thickness difference (once compressed)?

Thanks

[purple helmut]

Going back to my engine building days I seem to remember the formula for calculating this is :-

swept volume of cylinder / (required) CR - 1

for example :-
on a 4 litre engine

3950cc / 8 = 493.75

493.75 / 10-1 = 54.861

so the total chamber volume must be 54.861 cc to get a 10:1 compression ratio

From this subtract all the volumes that do not reside in the cylinder head, eg gasket wolume, dish in piston, volume above piston at TDC (due to piston not coming even with the block deck)you will then be left with the combustion chamber volume required to give you a 10:1 compression ratio.

When you have this, put the spark plug in, set the cylinder head up on a level surface (must be level) then take a burette graduated in cc using paraffin put the ammount into the cylider head combustion chamber.

Then measure with a vernier (or depth micrometer)from the head surface to the liquid and that is the ammount to skim off to get a 10:1 compression ratio.

If your not into this, I would suggest calling one of the specialists like V8 Dev. (they will have a lot of experience in this type of stuff)

[blitzracing]

Thanks for the info.

Mark

[v8 racing]

There are a few varibles from manufactures etc.. but if the engine is totaly standard you would need 24 cc heads with a composite gasket= skimming 80 thou from the heads, if you are fitting tin gaskets you will need 30 cc heads = skimming 32 thou off, you have to be carefull skimming this amount due to valve to piston clearence and the inlet manifold not fitting

[Boosted LS1]

Iirc a tin gasket compressed will be about .025". Composite will be .040" but I may have a fuzzy memory You can always clamp an unused part of the gasket and measure that once it's at the correct torque.

Boosted.

[v8 racing]

composite are 47 thou, factory composite ie 4.6 gasket is 52, tin gasket is 12 thou, if you are doing this for performance reasons then you would be better off going with the tin gasket as you have a much better squish clearence

[blitzracing]

Thats the sort of info Im after. I had bought the Haynes David hardcastle book on tuning the RV8, but it has very little factual data for the home tuner, just lots of examples of what other people have tried and its now somewhat out of date. Im sure there must be better books or web sites out there.

Thanks

Mark

[v8 racing]

blitzracing said:

Thats the sort of info Im after. I had bought the Haynes David hardcastle book on tuning the RV8, but it has very little factual data for the home tuner, just lots of examples of what other people have tried and its now somewhat out of date. Im sure there must be better books or web sites out there.

Thanks

Mark

I am half way through doing one!! should be really good as i have done various combinations of engine build etc... basicaly what works in the real world! just need to find a publisher?

[trackcar]

Wow Rob that would be a great book to read .. I wish you success with that one.

Can't Steve Heath help you with getting it published?

[Boosted LS1]

v8 racing said:

blitzracing said:

Thats the sort of info Im after. I had bought the Haynes David hardcastle book on tuning the RV8, but it has very little factual data for the home tuner, just lots of examples of what other people have tried and its now somewhat out of date. Im sure there must be better books or web sites out there.

Thanks

Mark

I am half way through doing one!! should be really good as i have done various combinations of engine build etc... basicaly what works in the real world! just need to find a publisher?

Get loads of pics Rob! Publishers, readers like those.

Boosted.