Steve Morris Posted January 30 Report Posted January 30 (edited) I’m getting a US head skimmed to UK spec and wondered if there was a consensus around 3.4” as the standard? (Head depth, that is). Edited January 30 by Steve Morris Quote
trchris Posted January 30 Report Posted January 30 Hi Steve according to the guys across the pond they skim the head to 3.4 to give approximately 9.5 compression ratio , check out the triumph experience website or do a Google search hope this helps Chris Quote
Kenrow Posted January 30 Report Posted January 30 This is from one of our vendors here in the States specializing in high performance: Good Parts TR6 CR Quote
Steve Morris Posted January 31 Author Report Posted January 31 Thanks chaps. Will shoot for 3.416” according to the chart. Quote
BRENDA1 Posted January 31 Report Posted January 31 If you have YouTube have a look at Elin Yakov’s Rust Beauties he is doing a TR 6 US head skim at the moment. Mike Red Rose Group Quote
Steve Morris Posted January 31 Author Report Posted January 31 Really helpful video, thanks Mike Quote
JohnC Posted February 1 Report Posted February 1 On 1/31/2026 at 5:44 PM, Steve Morris said: Thanks chaps. Will shoot for 3.416” according to the chart. It's not just about head thickness. You should measure the volume of each cylinder head to work out what skim you need, if any. Then get your machinist to make all cylinder head volumes equal before skimming. JC Quote
michaeldavis39 Posted February 1 Report Posted February 1 John C - and how would a machinist make all cylinder head volumes equal? Quote
JohnC Posted February 3 Report Posted February 3 On 2/1/2026 at 11:32 PM, michaeldavis39 said: John C - and how would a machinist make all cylinder head volumes equal? Dunno, but mine did. I assume with careful use of some kind of grinding tool. FWIW I measured the volumes with a pipette when I got the head back and all were within my measurement error of each other. Cheers, JC Quote
john.r.davies Posted February 3 Report Posted February 3 That is the problem with saying that a blanket 3.4" of head height is Golden. More performance is achieved not just by increasing CR, but improving flow as well. There are known mods to the inlet/exhaust ducts and the chamber itself, which would be done with an die grinder and burr, by hand, so that there will be small differences in the result, and different chamber volumes. So 'buretting' the chamber sizes to compare them is an essential part of the process, followed by further removal of metal to equalise them all. Then how much to skim may be calculated to achieve the CR that you want. May I refer you to my article on Sideways? "How to raise the compression ratio safely and effectively" at https://sideways-technologies.co.uk/forums/index.php?/topic/7551-how-to-raise-the-compression-ratio-safely-and-effectively/#comment-99739 John Quote
JohnC Posted February 3 Report Posted February 3 Sorry, you're right. I used a burette, not a pipette . And it was indeed after the head had been flowed (mainly exhaust ducts IIRC). JC Quote
JohnC Posted February 3 Report Posted February 3 10 hours ago, john.r.davies said: May I refer you to my article on Sideways? "How to raise the compression ratio safely and effectively" at https://sideways-technologies.co.uk/forums/index.php?/topic/7551-how-to-raise-the-compression-ratio-safely-and-effectively/#comment-99739 I get a message saying "This account has been suspended" Quote
john.r.davies Posted February 3 Report Posted February 3 Yes, Sideways is, unaccountably offline! No idea why. Enquiries continue. John Quote
Kenrow Posted February 4 Report Posted February 4 How far do you want to go? See chapter 6... Vizard - Tuning Standard Triumphs Quote
Kenrow Posted February 4 Report Posted February 4 Of course, if you just skimming to get the head away from the anemic US values you could just pick a number based on the chart and go from there. For a streetcar you would not notice if each chamber were off a little? And if a streetcar, if you shoot for a head thickness to give you say 9.55 or so, are you going to notice a big difference if you end up with 9.5 or 9.6? There was no way Triumph matched all the champers. Quote
john.r.davies Posted February 4 Report Posted February 4 9 hours ago, Kenrow said: How far do you want to go? See chapter 6... Vizard - Tuning Standard Triumphs Yes, I would have linked to that site and that diagram, if you hadn't done it already! I follow Vizard when I rebuild an engine. And yes, Kenrow, Triumph OE chambers are not identical - I've buretted them - but within what I'd call acceptable tolerance. It's when you start to remould them a la Vizard, and by hand that intolerances creep in. John Quote
john.r.davies Posted February 4 Report Posted February 4 12 hours ago, JohnC said: I get a message saying "This account has been suspended" Back online! From Sideways' volunteer Webmaster, "a rogue website scraper bot in Seattle USA was hammering the site (22,000+ hits in an hour)" so the host provider took it offline to protect others. Our Webmaster has blocked the rogue site, and Sideways is up again. Thank you, Craig! So "How to raise the compression ratio safely and effectively" at https://sideways-technologies.co.uk/forums/index.php?/topic/7551-how-to-raise-the-compression-ratio-safely-and-effectively/#comment-99739 is now available for you to read. John Quote
Kenrow Posted February 4 Report Posted February 4 12 hours ago, john.r.davies said: And yes, Kenrow, Triumph OE chambers are not identical - I've buretted them - but within what I'd call acceptable tolerance. It's when you start to remould them a la Vizard, and by hand that intolerances creep in. John Totally agree! Quote
JohnC Posted February 5 Report Posted February 5 On 2/4/2026 at 11:14 AM, Kenrow said: How far do you want to go? See chapter 6... Vizard - Tuning Standard Triumphs That's what made me choose the guy who did my head - he had a copy on the shelf. A very dogeared and grubby one Quote
JohnC Posted February 5 Report Posted February 5 21 hours ago, john.r.davies said: So "How to raise the compression ratio safely and effectively" at https://sideways-technologies.co.uk/forums/index.php?/topic/7551-how-to-raise-the-compression-ratio-safely-and-effectively/#comment-99739 is now available for you to read. I think that was one of the first articles I read before deciding to have a little head work done. Thanks John - really well written and clear. JC Quote
Kenrow Posted yesterday at 12:18 AM Report Posted yesterday at 12:18 AM Thanks John, I had not seen your Compression Article in Sideways before.... Quote
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