What is the difference in the valve stem lengths?
Also, are our valves truly made out of titanium? I've seen a lot of literature suggesting this, if so, are there any aftermarket over sized valves made out of titanium that are off shelf?
I only notice Supertech and Brian Crower making off shelf over sized valves, but they are made out of different grades of stainless steel. This would almost double the mass of the valves it seems like... Seems an odd 'upgrade' to the valve train.
Factory VK56DE valves are stainless or plain old hardend steel just like the OEM buckets, supposedly there was a coating applied on the intake valves of the Flex fuel equipped trucks. The VK45DE had titanium valves and you don't want to go there. That crap is stupid expensive and not needed honestly.
The longer valves were part of a Nissan parts production change over in later VK56DE engines with the upcoming VK56DE, instead of making different intake and exhaust valves, they switched over to utilizing the newer sizes for the VK56VD.
The result is now from Nissan if you buy OEM valves they will be longer than previous year models and also requires a different height bucket lifter.
There isn't a performance gain from this since you're still using stainless valves and NON DLC buckets.
Now, the cool thing is, I ordered some parts from Clark at JWT when I was doing my head build, but that got scrapped because teh heads were garbage, more on that in a minute.
The VK56VD now has sodium filled exhaust valves which is great for nitrous and forced induction, helps with heat transfer and detonation etc.. its a beneficial upgrade for cheap when using OEM valves.
When I was doing my head build and i'm still going to go this route when I start my engine build this january, is i'm going to get with Clark again and purchase VK56VD exhaust valves and OEM intake valves.
No need to go 1mm over size unless changing the piston design, plus you need to be weary when doing this not only of valve to valve contact but also the seats possibly falling out if not machined properly etc.
Granted the valve to valve contact will be delt with when choosing cam profile.
The cylinder heads themselves as far as casting designs from 2004-2015 aren't any different. They all flow the same.
To be honest with you, for natural aspiration and stock displacment with the powerband you'll have utilizing the cams currently offered from JWT, the only thing you will need to do to the heads are as follows:
Valve job (competition type from reputable company, 5523 Motorsports, AHM Performance, MA-Motorsports, etc) that is the meat of the gains right there. You will want to have the bowls and short side radius' blended and clean the casting flash/core shift. Other than that leave them alone, its not about peak CFM flow as it is average flow and velocity is better than volume in this case.
Utilize JWT valve sprigs, intake and exhaust. Might as well while you're in there. Its an extra 120-140 bucks or so.
Get the JWT valve spring compressor tool.
JWT has the cylinder head flowbench data for a lot of VK cylinder heads, but isn't releasing it yet. I can tell you that the VK50VE is the best out of the VK56DE, VK45DE, VK45DD, and new titan VK56VD cylinder heads.
Its like a VQ35HR head with extra chamber/ports. Flows 325+ CFM, that is the VK50VE. That engine was used in the FX50. 390hp 5.0L baddy.
Put it this way, take a look at Coyote 5.0 (truck) stock cylinder heads and you'll get an idea of roughly how well the VK56DE heads flow. Not exact, but very similar.