Mike Kojima posted on May 25, 2009 09:19
Since the exhaust side of the engine uses conventional camshafts, a normal high performance camshaft can be used. There are a few unique twists to the VQ37VHR engine’s exhaust side though. The exhaust cam is offset to the outside of the engine’s V by 4mm. We think this was done so the VQ37VHR can use the same cam drive chain and other parts as the older versions of the VQ engine. Due to the offset, the exhaust cam needs to have an asymmetrical profile to get symmetrical valve opening and closing motion. The odd things is that the exhaust cams centerline is offset 4mm to the inside for both heads but the cam grind is identical for both banks. This means that the exhaust valve motion is different and opposite for each bank of cylinders. We are not sure why, perhaps this is a Nissan engineering oversight? This issue is not harmful as it does not affect wear or durability but it probably leaves some performance potential on the table.
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| The VQ37VHR engines exhaust cam is offset toward the outside of the engine by 4mm. Look at the relationship of the cam center to the center of the exhaust valve stem. Unfortunately this makes the cam follower effectively smaller, reducing the possible increases in lift and duration a performance cam can be made to have |
The other performance hampering issue caused by the offset exhaust cam is that it effectively makes the cam followers on one bank of the engine 4mm smaller in diameter. This limits how big in lift and duration the exhaust cam can be made without the cam lobe running off the edge of the cam follower. Because of this, a performance exhaust cam for the VQ37VHR engine must be potentially milder than the normal VQ engine. Despite this, Jim Wolf Technology is currently investigating the possibility of making a larger exhaust cam for the VHR. In the meanwhile, due to the difficulty in modifying the valvetrain, forced induction will probably be the easiest way for the tuning community to extract larger amounts of power from this engine.
There are other important changes to the VQ37VHR head that help improve performance over the VQ35DE. The first change involves the intake and exhaust ports. On the intake port, the port splitter is moved by all the way to the valve bowl. This follows a trend in other ultra high performance 4 stroke heads like purpose built race engines and motorcycle engines. Moving the splitter back probably increases the ports cross sectional area for more flow without reducing gas column velocity. The short side radius of the intake port is also more gradual for less turbulence inducing flow separation in the critical turn into the valve pocket. This helps improve flow, especially at low valve lifts. The exhaust port also has a flow improving change to the contour of the short side radius.
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| The VQ35DE's intake port has the port splitter between the intake valves quite a bit forward of the valve pocket. The transition from the port wall to the valve seat is pretty abrupt which hurts flow especially at low lifts |
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| The 370Z's VQ37VHR's intake port has the port splitter moved way back into the valve bowl area, a trend seen in other high output engine designs like racing engines and motorcycles. This helps flow. It also helps reduce the ports fuel wetted area helping with emissions. Note the smooth transition from the port wall to the valve seat. This really helps flow |
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| The sharp flow inhibiting transition from the valve seat to the port is easily seen in this cut away for the VQ35DE head |
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| The exhaust port of the Nissan 370Z's VQ37VHR engine is much smoother, especially in the transition from the valve seat to the exhaust port |