Increase CR by skimming head

[Radugns]

Hello,

When I rebuild my engine I was forced to remove 0.15mm from the head and 0.05mm from the engine block for having a good surface.
Does this skimming of 0.2mm increase the CR so much that I need to remap the car?

Thanks,
Radu

 

[JamesBryan]

0.2mm sounds like a lot...

Could use a Megane head gasket to bring compression down again, they're thicker I believe.

 

[Radugns]

The meg gasket is 1.3mm and the clio is half.
That one could lower too much, i think.

 

[robzracing]

You can buy Athena head gaskets in varying thicknesses, although I doubt you’ll see much difference in the behaviour of the engine with that amount of skimming anyway but if you want to be sure go up to a 0.75 or 1mm.
If you have the engine apart it’s relatively simple to calculate the CR by taking a few measurements.


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[Radugns]

Th

You can buy Athena head gaskets in varying thicknesses, although I doubt you’ll see much difference in the behaviour of the engine with that amount of skimming anyway but if you want to be sure go up to a 0.75 or 1mm.
If you have the engine apart it’s relatively simple to calculate the CR by taking a few measurements.


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Athena is a little too expensive for this project, but I find that Elring one is 0.7mm thick, so the overall skimming will be less than 0.15mm.

Thanks for your reply!

 

[NorthloopCup]

You need to be careful how much you skim off the head as it can, and will have detrimental effects on the cam timing. Skimming a head to raise compression is not the done thing.

 

[Radugns]

You need to be careful how much you skim off the head as it can, and will have detrimental effects on the cam timing. Skimming a head to raise compression is not the done thing.

Hi Mark,
I did not want to raise the compression, I took the head from machine shop and the less material was 0.12mm or 0.15mm (need to look again). I also have some small grooves on the block am skim by 0.05mm for a good surface.
I know it does affect the timing, the tensioner cannot tension a longer belt.
I only want to know if someone skim to around 0.2mm, the final CR will be around 11.27 if I am right. Or 11.2 with Elring head gasket.
The Athena 0.85mm gasket will bring to original CR but is too much for my project, or maybe not?

 

[NorthloopCup]

Hi Mark,
I did not want to raise the compression, I took the head from machine shop and the less material was 0.12mm or 0.15mm (need to look again). I also have some small grooves on the block am skim by 0.05mm for a good surface.
I know it does affect the timing, the tensioner cannot tension a longer belt.
I only want to know if someone skim to around 0.2mm, the final CR will be around 11.27 if I am right. Or 11.2 with Elring head gasket.
The Athena 0.85mm gasket will bring to original CR but is too much for my project, or maybe not?

11.2:1 CR will be fine, but you’ll need to run on decent Ron fuel, or have it mapped conservatively for whatever fuel is readily available over there mate. You’ll need a different set of plugs to the standard 172 items as well ideally.

 

[Radugns]

11.2:1 CR will be fine, but you’ll need to run on decent Ron fuel, or have it mapped conservatively for whatever fuel is readily available over there mate. You’ll need a different set of plugs to the standard 172 items as well ideally.

I always use 100RON fuel in my Clio, so I will stick with it.
You mean spark plugs? Aren't the PFR6E-10 not good enough?

Radu

 

[NorthloopCup]

I always use 100RON fuel in my Clio, so I will stick with it.
You mean spark plugs? Aren't the PFR6E-10 not good enough?

Radu

They may not like the extra heat from the raised CR mate.

 

[Radugns]

They may not like the extra heat from the raised CR mate.

Have you got any suggestion mate?
I mean you sure have
Maybe R PFR7Z TG from 197?

 

[NorthloopCup]

Have you got any suggestion mate?
I mean you sure have
Maybe R PFR7Z TG from 197?

They’re what I was going to suggest funnily enough