Hi

What is the difference between natural aspirated and supercharged versions of the AJ16 intake valves

NA valve part number EBC3953
SC valve part number NBC2533AA

based on the service manual the dimensions are the same? But the must be difference because the part numbers are different. Is the difference in material or shape ?

background is that I have spare head assembly (not sure is this NA or SC head) that is under some work, and we found out that two intake valves are bent.

NA valves are easier to find...

 

Well seems not like much. Some photos for those that are interested below
Dimensions and weights are seemingly the same, only difference is the colouring but that might be just cosmetic, seems not to be any coating.



NA intake valve



SC intake valve



NA valve weight



SC intake valve




SC on left NA on right


There might or might not be difference in the neck machining.

 

I wonder of one is regular steel and the other sodium filled?

 

The SC engines had higher spec valve materials, because the peak combustion temperatures were higher. Inlet valves are not sodium filled. This technology is only used on exhaust valves, but after 20 years I can't remember if it was even used on the SC engines.

 

Firstly I am not saying that Andy would be wrong when saying that the material spec is higher on the SC intake valves but based on just the pricing of the valves it might not be the case or then the higher spec material is not too special. It would also be easier to understand that the higher spec material would be on exhaust side (higher EGTs).

Intake valves ; SC version (PART NO. NBC2533AA) was cheaper than NA version when I bought them from Dave Manners. Now when I checked they have change pricing so that the NA versions are bit cheaper (~ 4 GBP per pcs) so this might be just due availability and not because of material differencies?
Based on Jaguar Classic parts catalogue part numbers and pricing:

Exhaust side; There was stellite ( https://en.wikipedia.org/wiki/Stellite) version of the exhaust valve on XJR until engine version until engine (167860), part number EBC8633 (https://www.jaguarclassicparts.com/uk/part/EBC8633) price with out VAT GBP 45,83. From engine 167861 onwards it was replaced with NBD2532AA with price of £5.64 (w/o VAT).

Stellite version (same part number EBC8633) is offered also to the natural aspirated version and is the only version available.



Sodium filling; if there would be sodium filling there would be weight difference as there is quite big difference in the densities (Sodium 968 kg/m³ vs Steel 7800 kg/m3)