With the 350z and G35 becoming cheaper and more popular every year, there are a lot more people interested in the VQ35 than ever before. Over the years Nissans improved upon the original VQ35DE with the RevUp engine and later down the line the heavily revised VQ35HR.
For the most part, it’s pretty clear that the VQ35HR is superior the VQ35DE, but there is a lot of confusion regarding the differences between the two, so let’s dive in and compare the VQ35DE and the VQ35HR.
From the outside looking in, the DE and the HR might appear pretty similar. After all, they’re both apart of the VQ family and they do have a lot of similarities.
They’re both 3.5L V6s, they both have variable valve timing and dual overhead cams, they both use an all-aluminum design, and they both output near 300 horsepower although there is a notable 20HP difference between them.
Underneath it all there are quite a few differences which allow the HR to make more power and have more potential with modifications. Before we get too far into the differences between both engines, I would like to briefly cover the VQ35DE Rev Up engine just so there is no confusion.
The RevUp Variant
In the case of the 350Z, the standard VQ35DE was used from when it was new up until 2005. In 2005, Nissan began offering the Rev Up version of this engine which had its power output increased from 287 horsepower to 300 horsepower.
It’s important to note that for the 350Z in 2005 only the 35th Anniversary with the 6-speed transmission and Track model have the 300hp motor. There is a lot of confusion on the internet that all 2005 6-speed models got the Rev Up engine, but it was just the Anniversary and Track Editions, not the lower models.
It’s very easy to identify the Rev Up because the timing cover will have two big bumps instead of one bump on the standard DE. This is because the Rev Up has variable valve timing on both the intake AND exhaust cams, where the standard DE only has it on the intake side.
The addition of the dual VVT system means the Rev Up also has a different wiring harness and different ECU to control it all. The redline of the Rev Up engine is also higher than the standard DE.
HR Dual VVT System
The dual VVT system is also found on the HR, which is in part what allows it to produce more peak power and offer slightly better efficiency. This VVT system uses hydraulically actuated continuously variable valve timing for the intake cams and an electromagnetically actuated cam phaser on the exhaust side.
The dual VVT system offers a high degree of flexibility in setting valve timing to improve combustion efficiency over a wide engine speed range.
The nice feature of the variable valve timing on the exhaust side is that it helps widen and flatten the torque curve, ultimately making the HR a better engine for street use since it has more usable midrange torque, which means you don’t have to rev out your engine as much.
As one of the ways to minimize friction, Nissan used a hydrogen-free diamond-like carbon coating for the valve lifters. To put it simply, the DLC coating, results in a 40% reduction in friction. At the time the HR came out, it was the first engine to utilize this feature.
Intake System Differences
If you were to visually look at the differences between a DE and HR, the most obvious change would be the intake system. Where the DE uses a very basic intake with one intake tube and one throttle body, the HR uses a dual intake system with two throttle bodies.
The dual-intake system theoretically decreases restriction by up to 18% according to Nissan.
One of the well-documented issues with the DE which was discovered shortly after it came out with a really bad intake plenum design. Unfortunately, the air isn’t perfectly distributed to each cylinder thanks to to the plenum, which can mostly be solved with an intake plenum spacer.
Luckily, by the time Nissan was designing the HR, they were aware of this issue and made sure the HR didn’t have this issue.
Cylinder Block Differences
Looking at the cylinder block, it would appear the DE and the HR use the same block since they both have 3.5L of displacement and both use aluminum construction, but this isn’t the case. Starting with the actual aluminum material, the HR is cast with a harder material.
I think it goes without saying that the harder material makes the HR block stronger, which ultimately means it can handle more peak power with the right modifications. Interestingly enough, the HR block is also slightly taller.
Decreased Connecting Rod Angles
The block height was increased for several reasons, but it was mostly done to decrease the angle of the connecting rod through. By extending the height of the block and extending the length of the connecting rod, the angle of the connecting rod is decreased which reduces piston to wall friction.
All of this ultimately reduces friction and allows the HR to rev slightly higher. Something really interesting which helps reduce friction even further on the HR is the asymmetrical piston skirt, which has a high-pressure side and a low-pressure side.
The reduction in total friction also helps improve efficiency, since there is less drag on moving parts.
Engine Internal Differences
Another difference with the pistons is the increased compression ratio. The VQ35DE has a compression ratio of 10.3:1, but Nissan increased that to 10.6:1 on the HR. The high compression ratio improves efficiency and power output, but it also increases the theoretical likelihood of pre-detonation, especially if you use low-quality fuel.
Compared to today’s engine, the 10.6:1 compression ratio isn’t that high and there are no downsides to the increased compression ratio.
Moving further down the engine we have the crank and crank caps. One of the problems all high-revving engines face is crankshaft deformation, crank walking, and bottom end rigidity.
As RPMs increase, the load on everything which holds the crank in place increases and can ultimately lead to a lot of vibration and premature wear.
When Nissan was designing the HR, they wanted to increase the maximum RPM and also decrease vibration. They did this by adding a ladder frame to the bottom of the HR.
To put it simply, adding a ladder frame to support the crank greatly improves rigidity, decrease vibrations, and greatly reduces friction at high RPM.
Which One is Better?
The question remains, which one is better? Well, I think it’s pretty obvious that the HR is the better engine.
It’s more efficient, makes more power, has dual VVT, a much better intake manifold, dual intakes, and more.
At the end of the day it’s an evolution of the VQ35DE and was designed to be better in every single way with pretty much no comprises.
In total upwards of 80% of the parts were changed. All the changes of the HR ultimately made it more fuel-efficient by upwards of 10% and allowed it to make more power and offer a wider torque band.
The only downside to the HR is that it’s more expensive to buy one-second hand compared to a DE, but that has more to do with perceived value and availability, and it kind of proves that the HR is the more valuable and better engine.
That being said, the DE could be argued as the better engine for forced induction applications because it’s simply cheaper to replace the engine if and when it explodes.