Compression Ratios

rabidh

I've got a ported head at home, which hopefully I'll fit over winter with some piper cams. I was wondering about getting the head skimmed to raise the compression ratio though... Has anyone looked into this or done it on a Z22SE? (I haven't found it from a search...)

On MarkV's site he reckons the Z22SE is 10:1 compression, and I think Vocky was saying at some point that the old red top was 11.5:1. I get the impression it should make the engine develop a bit more power, and possibly even be a bit more efficient. It definitely worked on the old Ford Pinto engine we did it for.

http://en.wikipedia.org/wiki/Compression_ratio
Wikipedia reckons that some engines with knock sensors (which ours have?) can get as high as 13:1, and my dad's 20 year old Lotus manages 12.5:1 with no knock sensor I think, so 11.5:1 seems like a pretty safe bet, and would probably let me run on decent quality non-premium fuel (Shell?).

What are the valve clearances like with normal cams and with the Piper regrounds in? Is it close enough that I probably shouldn't try this, or have they left enough space that I could take a bit off the head?

alanoo

Raising the comp ratio is of course a very good idea, BUT it is simply impossible with the stock ECU without getting knock. Many people tried this in the US with major problems.

Of course, if you go with a standalone, it is simply a must have.

Wiseco can do specific pistons at least upto 12.5:1 ! add ₁₈₀$ per piston from the info I got.

rabidh

Ok, I've just done some calculations from that wikipedia formula using:
Stock CR = 10.0:1
bore = 86mm
stroke = 94.6mm
disclaimer: these may be total bollocks 🙂

The chamber volume is 61.06cc
The required chamber volume for 11.5 ratio is 52.33cc
The cylinder area is 5809mm²

So the amount i'd have to take off the head is 1.5mm!! cryb..

Seems like a lot really. To be honest skimming the head would be a mile cheaper and less hassle than new pistons though. Also it ensures I have a perfectly flat head to go on my block. Worst case if it fails I can buy a thick head gasket and put that on.

The US ECU is different to the European one though? Do you have any links to the threads where they found the issues? Do you know what codes the ECU was throwing? I'd imagine a higher compression ratio would look to the ECU as if the fuel was a lower octane level than it should be.

slimvince

iirc american z22se:s have 10:1 CR, but european ones (as in my Speedster) has a CR 10.5:1 (or was it even higher?).
However - whatever you find out regarding the possibilities of raising it without an ECU-swap is great to know about.
One possible way (that I have not investigated) is to add a piggy-back to the ECU (instead of doing a complete swap which introduces questions about drive-by-wire, speedo and abs-integration etc...).
Some people think you need a better head to cope with the raised CR (like the SAAB ones), not sure about this myself.

rabidh

Argh. I misread and did 10.5:1 first. For that, you need to take off 0.948mm.

It'd be good to know what the compression really is as I got the info from Mark's site http://www.verboom.net/projects/speedster/engine/index.html

I'll try and find out how much it is to skim my head. If its reasonable I might take 1mm off and see.
Does anyone know about the valve clearances?

edit: just looked here http://www.speedsterclub.nl/bibliotheek/technische%20documentatie/tis/Standard%20Information/Engine%20and%20Engine%20Aggregates/00031316-Engine%20Identification.pdf
And it would seem the 'S' in 'Z22SE' means 9.5-10 CR

edit: edit:
full info here http://www.modifiyem.com/forum/archive/index.php/t-46954.html

alanoo

Comp ratio is 10:1

EDIT : comp ratio is 10:1 in European Z22SE AND in US ones (post 2004), only the first US ecotec got a 9.5 comp ratio
http://www.speedsterclub.nl/bibliotheek ... a%20(Z22SE.pdf

baldie87

yes our z22se is 10:1

to skim the head on ours is a waste of time becuase of the chain. if you look at the american web sites they dont recommend raising the compression this way due to the chain. it would be better raising it with pistions at 11:1 for an N/A and maybe some more if you go the forced way

rabidh

Good point about the chain, I hadn't considered that...

Is it because the chain goes a bit slack and the tensioner can't take it up reliably, or is it timing? (although I doubt 1mm of timing change would be too awful - its about 1 degree if the sprockets are 10cm dia).

JohnnyN

I'm sure my cylinder head was skimmed when I had the Schrick cams fitted. Not sure what amount was removed though?

notsure.gif

markv

Saw that vmax do a raised compression tuning step on the z22se:

http://www.vmax.de/html/z22se.html

(press cancel if you get a popup).

So for the evo190 they seem to raise compression to 11.0:1 and raise the fuel pressure with 1 bar 🙂 They seem to change over to larger injectors when going to the evo230 stage.

Mark

alanoo

baldie87 said:
yes our z22se is 10:1

to skim the head on ours is a waste of time becuase of the chain. if you look at the american web sites they dont recommend raising the compression this way due to the chain. it would be better raising it with pistions at 11:1 for an N/A and maybe some more if you go the forced way

Hum, have you got some links about that ?

With the Schrick cams we have approx 3.5mm of piston/valve clearance at TDC, which is simply stupid; we are looking at skimming the head but we need a confirmation of the eventual issues