We have been asked recently about the effects of the Motordyne Engineering 5/16” intake manifold plenum spacer along with our single turbo kit and a few months ago we conducted a test on our 2005 non-revup Nissan 350Z. Previous tests that had been done with the SOHO single turbo kit were with the stock exhaust manifolds and no intake manifold plenum spacer, thus providing 392 hp and 406 ft-lbs of torque at a boost level of 8.58 psi. Nissan Engineers have done a phenomenal job designing the VQ35DE engine but as most of us know the stock plenum was not designed to its full potential. The plenum that comes on this vehicle from the factory was not designed particularly to aid in airflow in a forced induction system let alone any performance additions, meaning that that space inside the plenum is restrictive and detrimental to making horsepower.
Motordyne Engineering has done an excellent job of research and development on theri own in regards to the airflow restriction and benefits that can be achieved inside the VQ’s plenum. With the addition of the 5/16 inch plenum spacer adding volume, the initial pressure drop that is inside the plenum is reduced by a factor of 9, thus increasing the overall airflow inside the plenum. With increased airflow comes an increase in the horsepower capabality. In previous tuning sessions with customer cars on NA setups along with plenum spacers we have seen good increases in horsepower numbers as high as 10-15+ rwhp. When we decided to add the spacer to our 350Z with stock manifolds and our turbo kit we were expecting good results and the goal was to see how low of boost we could run to make the same near 400 numbers that are common on daily driven setups in an effort to strain the motor even less than the very minimal amount it already does. As you can see in Figure 1 below, the two graph lines represent the SOHO turbo kit with no plenum spacer at boost levels of 5.82 (red) psi and 8.58 psi (blue).
As you can see in Figure 1, in order for a 10% increase in horsepower and torque there is a 32% increase in boost pressure that is required, thus more stress on the engine internals. After installing the Motordyne Engineering 5/16″ plenum spacer and some quick tuning of the stock computer with the aid of UpRev Osiris, we saw a drastic increase in power and a drop in necessary boost pressure to achieve almost the same power levels at nearly half the boost. In Figure 2 below, these were the horsepower and torque values that we achieved with only the addition of the 5/16” plenum spacer, and in Figure 3 you can see the comparison of horsepower numbers against the dynamometer pull at a boost pressure of 8.58psi.
There was around a 9 rwhp and 14 ft-lbs difference between the two dynamometer pulls at SAE but there was a 45% difference in boost pressure to achieve these values. The plenum spacer definitely allowed the engine to breathe much easier and thus aided in creating incredible power at such a low boost pressure. This is a great discovery that we found on the dynamometer because it takes a substantial amount of stress off of the engine internals and allows the engine to operate at a more efficient level. With the addition of the plenum spacer we were able to achieve an incredible 26.21 horsepower per pound of boost and 32.26 ft-lbs of torque per pound of boost, making this turbo kit even more so one of the most efficient kits in the market in terms of power and torque per pound of boost.
As a comparison for sake of argument, a few months ago we had a 2003 Nissan non-revup 350Z with stock exhaust manifolds that we installed a Motordyne Engineering 5/16” plenum spacer along with a comparable single turbo kit. In Figure 4 below you can see the comparison between the SOHO Single Turbo Kit (blue) vs the Momentum Single Turbo kit (red) on identical vehicle setups on the same Dynojet dynamometer and at SAE.
The comparable single turbo kit, which can be seen in Run 11 (red), made great safe power for a stock daily driven block but required around 42% more boost pressure to make the same power as the SOHO Turbo Kit (blue). Many people may say that the turbo that we have chosen is the main reason as to why we make these values, which is a large factor, but the overall design of the turbo kit along with the Garrett GTX35R turbo that we have chosen is why we make such great power at such low boost. Be sure to visit our online store and our turbo kit section for more information and contact us to place an order for your single turbo kit!