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Advice for oversize valves on an overbored 1.8

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Hi all,

I've recently restarted my rebuild of a "quick" engine for my cabby to replace its very tired EX. The new engine has a DX block bored out to 83mm (1870cc), forged rods/crank/pistons and a 270° Piper cam up top. The head is from one of the carb models (casting number 026 103 373Q, without injector holes but with the inlet manifold coolant passage) and currently fitted with 40mm inlet valves and 33 exhausts - so the same spec as the DX head. The inlet and exhaust manifolds have been ported as well as the head and it came with a nearly new Weber 32/34 DMTL.

The engine's been sat for over ten years prior to my ownership so I'm basically going through it replacing all the seals and bearings. I haven't had the crank, intermediate shaft or distributor off as they looked fine but everything else has been apart.

I've just started stripping the head so I can send it off for refurbishment - at a minimum new guides, decoke, skim and the valves and seats recut. Since they'll be setting it up anyway it got me thinking about getting some new valves for it…

A bit of internet research suggests that going 0.5mm oversize is possible on the stock seats but going to 40/35 (i.e. TSR's Pack C head) also gets a lot of good reviews - with new exhaust valve seats obviously! Has anybody any experience of fitting oversized valves who could recommend me what to go for? It's going to be a weekend driver so I just want something punchy which won't run out of steam too quickly. Cost isn't a huge priority as I'd rather do it right the first time and never have to touch it again! I've been struggling to find any UK suppliers for anything which isn't helping :)

Are there any OEM valves from other models which will fit? Is it worth swapping to 7mm conversion guides or tapered guides? Is it better to go slightly oversize on both, more inlet while leaving the exhaust or go for the mad 42/35 combo? Should I just leave well alone? I've really no idea and the more I read the more indecisive it makes me! :lol:

Thanks in advance,

Stone

"Klaus": 1987 Clipper Cabrio, LA7Y, 1.8 Weber (auto)
1995 Corrado VR6, LK4Z: RIP
2003 Golf R32, LB5R

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Figured I would "just do it" so ordered some REC806 exhaust valves (35mm head, 8mm stem triple grooved for OEM collets) from G&S Valves - very reasonable at £19ea. They look great so hopefully my machinist can work some magic with them once the new seats are installed!

"Klaus": 1987 Clipper Cabrio, LA7Y, 1.8 Weber (auto)
1995 Corrado VR6, LK4Z: RIP
2003 Golf R32, LB5R

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I never replied to this as I have no experience tuning the 8v engine, always thought the 16 valvers offered more for less. However from things I remember reading back in the day I think over size valves do offer something.

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The 16v engines definitely have great potential - there's a turboed one in a Mk2 making over 1200hp! - but I wanted to keep things fairly original in the theme of tuning it using parts that would have been available to the original owner.

Also I got the replacement engine very cheaply!

The plan is to get it all reassembled, bribe my mechanic to swap it for the old unit and then head over to Crazy Quiffs for a manual conversion with a GTi 5-speed box. Then I can sort out the upholstery and it'll be all done :)

"Klaus": 1987 Clipper Cabrio, LA7Y, 1.8 Weber (auto)
1995 Corrado VR6, LK4Z: RIP
2003 Golf R32, LB5R
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