So I've just had news today that I need to replace all the valves in my heads due to excessive wear, so I'm now looking at the aftermarket options that are available. While I'm sure others exist, the two most popular options are SuperTech 0.5mm oversize and Ferrea 1mm oversize.

 

Between the two I'm currently unsure which direction to take. Initial thoughts are to go for the bigger Ferrea's as they will obviously allow more air into each compression cycle. However, some basic research has revealed that going bigger also moves the power band further up the Rev range (which is something I'm not particularly keen in doing). Is my research correct (not specifically 300zx research) or are Z heads "under valved" and could really do with bigger valves anyway?

 

Which brings me to the SuperTechs. Sounds to me like the ideal option in that they're big enough to allow more air into the combustion cycle, slightly cheaper, and should have less immediate draw backs, but maybe not as future proof if I decide to add cams in the future?

 

Further to that, another concern I have is around use of the stock retainers. Can the stock retainers be used with either of these valves? Or am I now looking at having to upgrade my springs and retainers to match the valves? (I cannot see any desire or need of me to have the ability of running higher rpms in the future) I also intend to stay on stock cams for the foreseeable (I have other higher priority mods I want to sort first)

 

So who has experience with these valves and what feedback can you give in relation to how they perform and any figment issues that you came across.

 

Cheers in advance

 

P.s machining costs do not come into the equation, choice of these valves won't effect any of the other machining work I'm having completed

Bump

My personal opinion would be that if your valves really need replacing then a good set of used low mileage heads would be the best way to go if you have no huge future power goals.

 

In reality I'm sure that all that really needs doing would be a new set of valve guides and the seats re cutting. A 5 angle valve job would give more benefits than bigger valves and should cost less.

 

If the valves are worn enough to need replacing surly other things such as the cams, followers and cam bearings will also be past their best, hence my suggestion just to pick up some used heads.

 

Are you using a zed specialist?

Have you used the search function about this on 300zxclub.com? Lots more information of this type there than here. Purely because there are so many more high powered zeds.

My personal opinion would be that if your valves really need replacing then a good set of used low mileage heads would be the best way to go if you have no huge future power goals.

 

In reality I'm sure that all that really needs doing would be a new set of valve guides and the seats re cutting. A 5 angle valve job would give more benefits than bigger valves and should cost less.

If the valves are worn enough to need replacing surly other things such as the cams, followers and cam bearings will also be past their best, hence my suggestion just to pick up some used heads.

 

Are you using a zed specialist?

 

Bar the guides which are also past their best and the cause of my oil usage, everything has been checked and perfectly within tolerance.

 

5 angle is old tech now, I'm having a full profile cnc valve seat and throat job on my heads. As above, valve guides are already being replaced.

 

No, not using a z specialist, rebuilding myself.

 

Stephen, as mine is a '95 series 4, it has 48p heads. Try finding a set of those second hand!!

I have started to look on 3zc but the problem over there is the big power guys are aiming for top rpm power to suit the strip rather than a balanced spread that I'm looking for

 

- - - Updated - - -

 

Sorry Stephen, bloody curser jumped, so the second hand heads thing isn't directed at you lol

speak to mark derby, he did that which you are talking about

I did wonder lol. I have a set of 10Y heads here which are the same essentially just without the tt valves. I'm not parting with them though.

 

I found this for you, you may have already read it;

 

http://www.300zxclub.com/showthread.php?t=225271&highlight=Oversize+valves

Nice, where did you find them?!? (Aren't they out of a J30?)

Well I've just pinged an email to Greg Dupree to find out his opinion. It goes without saying that it is specific to my engine spec (currently 575 at the fly for those who don't know) but I think the answer will be relevant to those of us running the smaller end of the updated turbo spectrum with the vast majority of the breather mods fitted (piping, intercoolers etc)

If you get an answer I have no doubt it will be very interesting. My heads are from as far as I can tell a late spec NA.

Yeah I'll post it up here for future reference for other people considering changing their valve sizes

Out of interest who is machining the valve seats for you?

http://www.rolandalsop.com/index.php?option=com_content&view=article&id=24&Itemid=28

 

If you want some bed time reading, read up on the Newer Bb contour cnc valve seat machine, the results are effin impressive to say the least

They're doing all my machining work:

 

Rebore to 88mm

Diamond plateau honing

Decking block

Dynamically balancing entire bottom end

Clean and deburring oil galleys and waterways

Head skim

Disassemble and inspection of valve train

New guides

Cnc valve seats

Clean and deburring of oil and waterways

Reassembly of valve train with new valves

Cheers bud, il have a read.

So I've heard from the Z guru himself, Greg Dupree @ SZ...

 

"Hi Nick,

 

In short the .5mm oversize work the best with a 88mm bore size.

 

The larger valves allow more air to move, this increases the whole powerband and allows the turbo to spool quicker.

 

Going to a full mm oversize causes flow issues with a 88mm bore as the combustion chamber cannot be opened enough to get the addition flow around the outside of the valve without further increasing the bore.

 

Cheers

Greg"

 

There we have it. If your running 88's, 0.5mm oversize valves is the way to go!

That was concise and informative. Both good things.