m http://www.rossmachineracing.com/3sbucket.html (http://www.rossmachineracing.com/3sbucket.html) m
Happened across this rather by accident, quite interesting nonetheless. I appreciate for the average joe it won't make much difference, but I was just wondering how "lightening the valvetrain weight allows higher RPM limits."
Is this to do with the Shim? Whats Shim? Never heard that term before! s:?: :?: s:?:
simple, the less mass you have to shift, the easier you can do it, hence less stress on everything involved when reving hgher.
Now aas to if theres any benefit to reving higher?
Quote from: "MRMike"I was just wondering how "lightening the valvetrain weight allows higher RPM limits."
As Mark said - it makes things lighter.. lighter things take less energy to move, and you can move them faster as they take less energy to stop moving..
Primarily, when it comes to valves - if you start to move the stock setup too fast (I've no idea what that speed is on the MRS) then everything starts to contain so much kinetic energy that the valve springs can't stop the movement anymore, and you start to get valve bounce (the valves will bounce open & closed a little after they open & shut, rather than smoothly opening and closing).
You can get over that by fitting stronger springs (quite common with lairy cams) or lightening the valvetrain (specifically valves & lifters/tappets)
QuoteWhats Shim? Never heard that term before! s:?: :?: s:?:
A shim is just a thin piece of material used to alter the thickness of another thing.. a bit of cardboard under a wobbly table leg is a shim, but in this case it's a thin disc of metal of a specified thickness that effectively alters how thick the hydraulic lifter (tappet) that pushes the valve up and down is..
Thing is, you rely on this shim and the lifter acting as one entity - which they will do in the stock setup.. but with very high lift cams in place, the lifter could rise so high that the shim actually gets so high it can pop out of the tunnel that the lifter & shim sit in.. which would be quite bad.. or catastrophic actually I should imagine.
The shims are used to adjust valve clearances due to manufacturing tolerances & differences, or due to wear & tear in an engine rebuild.. hence the reason that you need to buy lifters that have a specific depth if you replace shimmed lifters with shimless ones..
Hope that all makes sense s:) :) s:)
Aaron
Quote from: "aaronjb"Primarily, when it comes to valves - if you start to move the stock setup too fast (I've no idea what that speed is on the MRS)
MWR has mentioned that 7400rpm should be very safe and they have revved their shopcar higher "forever"...surely more than any NA 1ZZ-FE has any use. Except maybe some heavily modified ones...
Quote from: "Tem"MWR has mentioned that 7400rpm should be very safe and they have revved their shopcar higher "forever"...surely more than any NA 1ZZ-FE has any use. Except maybe some heavily modified ones...
Indeed - you'd need to be shifting a lot of air to need more revs than that, and an awful lot of modding.. and then you might as well turbo it or stick a 2ZZ in as a new base-point.. s;) ;) s;)
Worth noting that the article in question was (as I read it) talking about lightening the 3S-GTE valvetrain with 1ZZ-FE parts s;) ;) s;) and the 3S is, as you and I both know, a generation older, and judging by those figures, quite lardy in the valve-train-weight stakes.. s:) :) s:)
Though from what I remember, either of those figures make the valvetrain of my VG30DETT 300ZX positively super-heavyweight s:shock: :shock: s:shock:
Although getting the tappets out with a big magnet was fun.. s:twisted: :twisted: s:twisted: (We were replacing them.. never did sort out the godawful start-up tappet knock though.. That was $250 down the tubes!)
A friend of mine did this on his 3SGTE MkII MR2-T and said it made a nice difference. He actually took some of the shimless buckets off of one of my spare 1zzs since he ended up ordering the wrong thickness on one of them. It's too bad none of that article is applicable to the Spyder.
Quote from: "markiii"simple, the less mass you have to shift, the easier you can do it, hence less stress on everything involved when reving hgher.
Now aas to if theres any benefit to reving higher?
I thought along those lines, but surely that makes it quicker to shift, it doesn't 'raise' the ability to rev though alone does it?
EDIT: Just realised it said "allows higher RPM" not "will give higher RPM" Doh ! Your Quite correct Mark
it makes it safer to rev higher, to actually do so you need an ecu fiddle to get past the rev limiter
Many Mk1 MR2 owners with 4A-GE are also doing this. They are using Yaris buckets though...