Is it worth me fitting larger that standard wasted stem valves on a high spec LET engine and if so are they still up to the job as none of the larger exhaust valves SBD sell are sodium filled unlike the standard valves. Thanks Rick
provided that the larger stem goes all the way up through guide, I'd say it might be worthwhile - putting more metal just above the head of the valve only though seem a bit pointless as the two paths for heat dissipation are through the valve seat, and valve guide, and unless you increase the contact area of one or both, then it'll get just as hot - or rather, the hotspot will just move up the valve a bit to where the normal 7mm section starts.
the way i read it, sodium is a super conductor, be that for electricity or heat. opening and closing of the valve thrashes the sodium for and aft distributing the intense heat from the face of the valve.
thats my intepretation from alex bells book, and it made sense when i read it.
When i said larger i meant 1mm in overall valve size from SBD and these have a wasted stem on the inlet valves and a 1mm larger head on both the inlet and exhaust valves. I think these ar eht eones they use on there 300NA race engines but i was wondering if they were up to the job on a 450ish bhp LET? Rick
best to ask sbd rather than us really. you would benefit from the larger valve flow area, and benefit from the fact the valves are once piece. couldnt say wether they would take the heat on the exhaust side.
I think it's more a case of the longevity of the exhaust valve seats - sodium valves conduct the heat up and away better than a solid valve, which will naturally shed heat slower, putting more of it into the seat area.
this is all stuff the cossie boys will have come across and either decided it's not a problem, or solved, years ago - maybe get some advice from that direction ? - but do speak to a decent turbo tuner, I think that's the answer.
and I've still not been able to detect exactly what it is about the coscast seats that make them any more suitable for bigger valves than the later GM ones - had a quick measure the other day, couldn't find any obvious difference...
that's what I thought - but a quick measure with the calipers proved otherwise - unless I had a rogue GM head.
I'm not entirely sure that deeper seats would make any odds tbh - unless the metal underneath the actual contact area is deeper or something - but what actual shape the seats are underneath I don't know - it could be something hidden away that you'd not ever see unless you took it out - i.e perhaps the GM head seats are shallower under the bit that would get recut for larger valves.
it's one of those things you always hear about, but finding someone who's actually researched it properely and done it, is another matter.