this is purely theory at this point but i have been thinking of a turbo 8v for a while, So here are my thoughts, standard 2l 8v GTI engine has a CR of 10:1 the chamber in the head is 30cc per cylinder, the dish in the piston is 16cc? so with my maths that means the HG is about 3.5cc? heres how i got there 1984cc / 4 cylinders = 496cc per cylinder, the chamber = 30cc the piston & gasket must equal 19.5cc so 496cc / 49.5cc = 10.02 to 1 am i right so far?
now a 2042 8v engine requires 1.35mm machining of the top of the piston, now a friendly welsh man did mine and he machined the bowl but not as much a the higher parts of the piston crown, giving a higher than standard CR. anyway ignoring the dish and assumining that 1.35mm was taken off entire piston crown. 2042cc / 4 cylinders = 510.51cc per cylinder, the chamber = 30cc the piston & gasket must equal 19.5cc so 510.51cc / 49.5cc = 10.31 to 1 now including the dish that has been machined as much as the rest of the piston crown. my pistons were machined to give the engine a calculated CR of 10.8 to 1 on a std head, to get 10.8 to 1 the cylinder = 510.51cc the chamber =30cc so the piston & gasket = 17.25cc so 510.51cc / 47.25cc = 10.8 to 1 the head has been skimmed so the chamber is now 29.5cc, work done by the man in the shed. the cylinder = 510.51cc the chamber =29.5cc so the piston & gasket = 17.25cc so 510.51cc / 46.75cc = 10.92 to 1 So my engine has a CR of 10.92 to 1 Still ok?
however, if i wanted to lower the compression ratio for turbo purposes, i could and this is whne i really start rambling, fit the original 2l crank reducing the stroke by the 1.35mm. so the maths now looks like this. 510.51cc - 496cc per cylinder = 14.51cc the chamber = 29.5cc the piston & gasket = 17.25cc + the 14.51cc so 496cc / 61.26cc = 8.1 to 1 so that would give a place to start from, a bit low mind but it would work?? now a couple of questions am i right so far? if the gasket is only worth 3.5cc then the gasket must get squashed to less than 0.1 of a mm?? anyone have any ideas what the metal HG is worth in cc's?
Aren't the 2.0's all 10.5:1? I reckon the gasket is about 5cc, but we're fairly close. CR = (Swept Volume+Combustion Chamber) / Combustion Chamber. So in this case = (496+49.5) / 49.5 = 11.02 I think your measurements might be slightly out, but you're not far off.
so you can lower the compression by added a gasket is that right?? Also why do forced cars need lower compression?
I see yr thinking, but doing it that way would open up the squish zone by 50 tho and be likely to cause detonation problems. Even with low compression ratio's, squish is important. Opening out the chambers in the head & pistons are the correct way to do it. What's the dish size in a G60 piston ?
Dish is big on a g60. I don't know the numbers but having seen 1 then you can certainly tell the difference between a g60 and a std. 8v. Heads are basically the same as an 8b pb even if the part numbers are different.
Yeah, the G60 heads have bigger exhaust ports, but I think that's about it. Later VW service PB heads have the bigger ports too.
Units are out... 0.1 CM not MM for example, using an 83mm bore Area = 4.15x4.15 CM x3.142 (or whatever Pi is) = 54.1 x height 0.1 CM (assuming the gasket compresses to 1mm) = 5.4cc. Forgot to mention... Stop fannying about and get the car on the road
I know I know, Im working on it a bit more now, now the kart is up and running and the job around the house have been sorted. you sound like the wife!
I hope not... you seem to have a new plan for that lump every time you post. Better off getting the car on the road and enjoying it. This is a thread you should be posting on... http://www.clubgti.com/forum/showthread.php?p=1583103#post1583103
