High compression / ratio

[Andyman]

In terms of the engineering, how do you achieve the high compression? Is it a combination of decking the block, thinner head gasket and a skim of the head? or just a heavy decking of the block?

Got my block decked / bored and honed etc but the compression ratio measurements are coming in well lower than the quoted Wossner figures of 12.6:1 :S

 

[Dan519]

wossners come in at about 11.8:1 IIRC

 

[Andyman]

Do you find just skimming the block to bring the pistons up to height is enough usually ?

 

[NorthloopCup]

wossners come in at about 11.8:1 IIRC

I thought they offer 11.8:1 and 12.8:1 compression ratios anyway so op may have a set of 11.8's in the first place?

 

[Meek_racing]

My engine is running those pistons with a heavily skimmed head and its well over 13:1cr. If you skim the head you might need a bigger idler pulley on the belt, Fred had to source one for me, its an upgrade from standard plastic Renault one

 

[Meek_racing]

Their figures are always under what they state.

 

[NorthloopCup]

Their figures are always under what they state.

My experience of wossner's is that they are very different to what they state from being higher and lower than what they say! And in the same set of 4 'matched' pistons as well! Lol

 

[Andyman]

Is this right there are two different compression ratios in high comp form ?
The code number on the box says K9045D130 and googling it, it says these are 12.6:1.


Meek, do you have any more details on the pulley? part numbers or anything?

The head i will be using has a 10 thou skim on it so this will bring the compression up but no where near as high as Wossner state which agree, seem a little high.

Did you use a OE Renault head gasket?

 

[Meek_racing]

Best bet will be to call Fred next week when he's back off holiday. It's an all steel component with needle bearings so well up for the job and not too pricey.

As far as I'm aware he used standard gaskets. There were no issues with the head being skimmed substantially apart from the belt being slack, thus larger idler. He's using them on quite a few of his new builds so more than likely stocking them.

 

[Dan519]

Shouldn't need a heavy skim to bring compression up, the pistons are just not what they claim, and never have been. I've used iapel in Pete's racecar engine. More money but a better piston and better quality rings supplied. Wossner quality is OK, but you can't take things for granted. I've used them a lot with no problem. I've been told I'm wrong countless times when I've said they don't make claimed CR though