I have recently had my cylinder head on my 2wd sapph skimmed and it measure's to be 138.50. I now its under the reccomended limit, But i heard about a saver shim for the cosworth that i can get hold of. what im wanting to know is are they a good under all that pressure and do they work properly with no hassle. Does anyone reccomend them or use them and has had any problems. cheers