Working Out Compression ratios

[Daniel306]

Anyone know how i workout compression ratios and how much i want to skim to lower it? this is for working out Xud and 205 1.9 Gti compression drop's

[ginge191]

Google it mate, pics an diagrams explain it more.
You need to work out a number of heights on your conrods, the fuel and air etc. obviously, if your using a modified car, it varies to standard.

I can get you the standard CR if you need, but as I said, google has a much better answer. As for lowering the compression, you can get various headgaskets or forged parts.

[daddyfixit]

swept volume divided by (clearance volume + combustion chamber volume)

[Ruan]

Try working out the combustion chamber volume with an IDI engine

It's very, very difficult.

[darrenjlobb]

Heh this subject confused the crap out of my brain for a good week when trying to work it out, I found a good calculator tool thing in excel that helped alot, not sure where I found it though....

[daddyfixit]

indirect engines or even petrol engines are a pain;
with the head on a bench upside down--valves closed and pointing upwards, a pippette is used to measure in amounts of liquid in c.c's until the level of the liquid is level with the cylinder head. the liquid will obviously fill the entire area so thats about the most accurate way---performance heads are also measured this way when larger valves are fitted and combustion chambers enlarged by grinding, as all cylinders must have the same size combustion chambers.

[con67]

Think its -5ccs each to get to 18:1 on an xud, where do you take it from though?

[daddyfixit]

either ;
1. grinding away the cylinder head combustion chamber, checking with liquid as described.
2. fitting a thicker head gasket (some manufacturers used to fit 2 x gaskets to get u.k spec cars to run on unleaded in the late 80,s-----reduced comp.ratio)
3. machine crown of pistons down, reducing thickness of the crown though !!!!

[con67]

Theres a toyota patent floating about the net about the chamber design they have a groove in the centre of the cloverleaf, Ive seen the pistons in real life, the peugeot sort of has the same design imo it should be deepened. I dont like the hg or skimming the whole piston ideas. I always wanted to try this with ceramics, still got the pistons and rods but no car to put them in

[con67]

ffs double post noob moment

[Dave]

Theres a toyota patent floating about the net about the chamber design they have a groove in the centre of the cloverleaf, Ive seen the pistons in real life, the peugeot sort of has the same design imo it should be deepened. I dont like the hg or skimming the whole piston ideas. I always wanted to try this with ceramics, still got the pistons and rods but no car to put them in

Yeh I thought of doing that, take a drill to the cloverleaf, that way can also know exactly how much volume your taking out... keeps the sweep to the pre-cup too...