Until Cosworth or a similar big gun steps forward this is probably one of the better if not the best head gasket you can buy for the QG18DE. The stock headgasket is probably good for 170hp and maybe 200hp with conservative tuning but elevate the power output way beyond that it will not reliably hold the power in the long run. You can read about why Ajusa in the B15U forum.
The other competitor would be the Fel-Pro Permatorque MLS. I did contact another popular head gasket manufacturer - Cometic but they told me they did not have the CAD files and at most would only be able to come up with a copper head gasket. The Fel-Pro Permatorque MLS is only available in one bore size - 80.5mm bore hence my piston overbore would be limited to 80.5mm or less. I decided to settle for the Ajusa as it comes with a 81mm bore size.
As I could not find this head gasket from the States I decided to contact the Ajusa head office in Spain. Typically large corporations could not be bothered to answer to small customers like myself but surprisingly Ajusa did. Even better still there is a Malaysian distributor located in the Klang Valley - O.E.M Conti-Parts Sdn. Bhd. (telephone: +60378779963)
A couple emails and phone calls later I placed an order for two units of the Ajusa head gasket. Three months later these arrived via a container ship. If you do not want to wait three months and want to utilize air freight be prepared to double the price. Bro Jack helped me to collect the head gasket. Picture of my head gaskets below. All pictures courtesy of Jack too. Thanks Bro! Part number is 10145400. Part number for QR25DE engine is 10145500.
Close up. The gasket is three layer hence the MLS (multi layer steel) acronym. Per B15U forum the top and bottom layers are steel while the middle layer is aluminium.
Hopefully with my ARP head studs this will hold the power and be reliable.