Nivlek2525 Posted November 30, 2020 Share Posted November 30, 2020 (edited) Hello all, Not sure if this should go here or in the engine section. Please let me know if it should be somewhere else. I've been struggling with a standard, non-unleaded cylinder head. I've got one valve I just can't get a 100% seal on. With a 100psi in the cylinder I can hear it passing slightly. I'd decided to wait for a later unleaded head but in the meantime I've been doing a lot of reading on here and on the OpelGt forum. Anyway, I have a 2.4 head with bigger valves and high ports and I understand it is possibly better flowing. However the larger combustion chamber lowers the CR when stock So I've measured the combustion volume on both (see pictures) and I get GTE volume 50cc and 2.4 volume as 53cc. This is quite crude as I can only measure to the nearest cc. First question is can anyone confirm or offer better/factory figures? Secondly I've estimate the CSA of the combustion area tracing it with graph paper and counting up the squares. I get 51.6cm² Second question, can anyone provide a better value? I calculate that to lower the volume of the 2.4 by 3cc I need to take 0.58mm off the head or 23 thou. Would anyone like to check my maths? I spoke to the machine shop today and he didn't see any problems physically removing this much. Q3 Since I need to deal with cam timing would anyone suggest removing any more? Is a CR of 9.4 about right? Finally, the Cam gear has an effective radius of 58.5mm which means a skim of 0.58mm will retard the timing by 0.57 degrees...I think. Rallybob has a number of posts suggesting that advancing the timing a little is a good thing on these engines. About 3 deg is mentioned. Therefore retarding the timing at all doesn't sound good. He had a great post about drilling out the locating hole on the cam gear and using offset bushings as a DIY friendly way of advancing the timing, so that's the plan. As always, any thoughts or experience appreciated. Head is booked in for Friday to be skimmed and for 40 quid I think I'll give it a go as a little project. The worst that can happen is I'm out £40 but I could end up with a big valve unleaded head and learn a few things along the way. Photos and calcs https://photos.app.goo.gl/3nafT3pqwjwVMsPS8 DIY adjustable cam. https://www.opelgt.com/threads/source-for-cam-vernier-sprocket.26749/page-3 Offset bushings https://www.ebay.co.uk/itm/281727256845 cheers all K Edited November 30, 2020 by Nivlek2525 Lots of typos 1 Quote Link to comment Share on other sites More sharing options...
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