Since the BNR32/33/34 Skyline GT-Rs were only really available in Japan and a couple other parts of the world, previously you only really had the JDM engine parts to choose from. Now that I work at Cosworth, I hope to change that. Although we are buried with all kinds of other work, I try to squeak out RB26 parts when I can. So far I’ve managed to help crank out new con rods, bearings, head gaskets, and now valve springs (more coming soon!). It takes a bit to convincing to get the OK to design RB26 parts. The RB26 is now an old engine and we are only designing parts for the RB because it has such a huge following worldwide.
Having measured and analyzed nearly every Japanese cam grind currently available to mankind, we were able to design a valve spring that could control valve motion with just about all of the Japanese cams. Many of the Japanese cam lobe designs aren’t really that aggressive when compared to real deal race engines so we were able to design a spring with relative ease. Many of the JDM manufacturers offer type A, B, or C or Step 1, 2, 3 cams. The Cosworth springs you see pictured below cover the A, B, 1, 2 range all in one spring. In reality they cover the type C/step 3’s also, but only under certain conditions.
What sets these springs apart from the rest is that they are designed for use with high lift cams up to 8500rpm and 12.0mm of lift. You’ll notice that many of the JDM valve springs that can handle high lift cams are designed for 10,000 rpm so they have very high open pressures (and not nearly enough seat pressure for some reason). This is important to keep valves from floating at high rpms, but sucks up horsepower and can increase cam lobe and tappet bucket wear. It seems that tuners all over the world are now using long duration high lift cams for applications UNDER 8500 rpm. There is no need for a spring with super high open pressures (relatively speaking) at only 8500 rpm. On the other hand, many of the JDM springs with lower open pressures cannot handle high valve lift. If you look carefully at their specifications, many of them cannot handle more than 10.3mm or 10.8mm lift. The Cosworth High RPM valve springs are the answer for any cam that ranges from short duration (250-270°) and low lift (~10.3mm) for up to 9000rpm and long duration (270-304°) and high lift (~12.0mm) for under 8500 rpm.
We can thank Mine’s and the HKS 2530 turbos for creating the whole big cam, medium sized turbo, sub 8500 rpm style of engine tuning. If you think the Mine’s car is running their off the shelf cams, you should hear it idle. If it has a pair of their off the shelf 250° cams, then I’m black. The car can BARELY idle. In America, I’ll have to pat myself on the back for creating the trend with Kim Johnson’s BNR34 and pretty much smoking the shit out of nearly everybody at just about every competition we attended with a daily driven street car. I was influenced by rally engines that used long duration high lift cams with medium sized turbochargers and had insanely wide powerbands and flat torque curves. To this day I still get emails from Skyline owners that say, “What did you use for xxxx part on Kim’s car? I’m trying to build a clone.” In reality, to build a clone you’ll need about $35K and a trip to XS Engineering, but I guess it doesn’t hurt to ask. I give advice, but not secrets.