Team America World Time Attack – ARK Design’s BNR32 Skyline GT-R Part 8


cutting VQ35 cylinder head

We didn't have a complete CAD model of the VQ35DE engine so Tyler could do a valve to piston clearance check in CAD. Rather we had to do a physical mock up. What a bitch. I know builders have been doing it manually for years, but when you add DUAL variable cams, that's quite a few measurement points. You get spoiled with CAD…anyhow, I wanted to physically check valve to valve contact too so I decided to section a cylinder head and take physical measurements. Yes, I could have done it with a boroscope and dial indicators, but it's just not quite the same as seeing it. Plus I had found a spare casting to sacrifice.

vq35 valve to piston measurement

I cut cylinder 5 in half so I could take physical measurements. Actually I got super busy and Magnus actually did it for me when he was in between builds (thanks, buddy). The cams are a grind that was developed for the Cosworth VQ35 Top Shop engine. Kevin at Kelford Cams in New Zealand was able to crank these out for me pretty damn quick. I was able to get a custom ground cam from Kelford all the way in New Zealand faster than I could at a local grinder here in California! 

vq35 valve to piston clearance measurement

It's a bit of work to build a mock up VQ since there are so many chains, tensioners, pulleys, covers, etc. but it's a necessary evil when using big cams, big valves, and domed pistons with dual variable cams. If I remember correctly (I don't have my notes in front of me), the intake cams are 300°-12.5mm lift and the exhaust cams are 296°-12.3mm lift.

vq35 sectioned cylinder head

Valve to valve contact! The solution was for Steve, the master cylinder head dude, to cut down the Cosworth +1mm valves by 0.5mm making them actually +0.5mm over stock. It did not totally prevent valve to valve contact, but we gained some more variable cam range by reducing the valve diameters. We kept the +1mm valve job to keep the flow advantage of the larger valve diameter's valve job with the sacrifice of there being a smaller area where the valve seals against the seat, but this should be fine for a race engine. The V to V contact occurs at full intake cam advance and full exhaust cam retard. But now that I have the exact crank degrees where this occurs, I'm in good shape. Here's where the Pectel ECU's referencing crank degrees for the variable cam control actually works to an advantage. While most ECUs use an offset value (e.g. -20), Pectel uses actual crank degrees (e.g. 107°) for the intake cam position and a crank degree reference for the exhaust cam position. Now I can set the min/max range in the software and never have valve to valve contact.

VQ35 cam trigger machining

Kelford accidentally sent me non-variable exhaust cams. They sent out replacements right away, but we needed the cams ASAP. It was partially my bad for not checking immediately after receiving the cams. Mike, the machinist at Cosworth, helped me to set this rig up. It's nice to have a complete machine shop full tooling and an experienced machinist.

vq35 cam trigger machining

It was a simple cut once we measured up a factory cam and had it all set up. I even brought some cams from home for another VQ powered project I have coming up and machined those too should I decide to run dual variable cam.

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