ZZP Intake Manifold Insert Testing

Upper Manifold Insert Discussion

The stock intake insert has the runners extended from the aluminum lower intake manifold up and wrapping half way around the upper curvature at the top of the upper intake plenum. The pictures below show the stock upper intake manifold insert in position and pulled out. The additional runner length provided by the stock intake insert is ideal for low RPM running, but sacrifices upper RPM power. Furthermore, the runner on cylinder #6 partially blocks the main intake passage entering the plenum from the throttle body. This situation likely reduces the ultimate air flow possible at high RPMs. All of these factors lead one to believe removing or modifying the upper intake runner configuration should benefit higher RPM performance. The trick is to do this without sacrificing too much lower end power.

Intake Insert in Upper Manifold

Intake Insert in Upper Manifold

Intake Insert pulled out

Intake Insert Pulled out

ZZPerformance HV Insert Solution

ZZPerformance has developed an upper intake manifold insert to replace the stock intake runner insert. This is their solution to removing the stock intake runner and removing the performance restrictions that are suspected. This ZZP HV insert is to replace the stock insert with an intake insert of their own design (see picture below). Their solution increases the lower intake manifold runners by an additional 1/2". This insert also has the entrances to each runner rounded to improve entrance flows into each runner. Another feature of the ZZP HV Intake Insert is the ports for passing engine coolant to the throttle body were not drilled. This means the ZZP HV insert serves the same purpose as the EPP TB Coolant Plug. Thus, the same gains from the coolant plug should be made by the ZZP HV insert. Lastly, this intake insert leaves the inlet opening from the throttle body completely unobstructed. All of these design features should provide great improvements to the upper RPM power potential of the L36 engine. The questions to be answered are: By how much does it improve the upper RPM performance? How much low RPM performance is sacrificed, if any? How much of the L36's power band is reshapened by this insert?

Test Setup

To resolve these questions revolving around the potential benefits of ZZPerformance's HV Intake Insert, I obtained a test vehicle (Pontiac Grand Prix GT, L36 engine) and a HV Intake Insert from Zooomer at ZZPerformance. The test GT had various modifications that could be considered recommended complements to the HV Intake Insert. These included ZZP ER High Ratio Rockers, ZZP Stage 1 HV Throttle Body, an EPP Cold Air Induction, U-Bend removed from exhaust system, a 2 1/4" off-road downpipe and a 180ºF Thermostat. While all of these modifications are not required, they do enable the L36 to run at higher RPM with the stock camshaft. Without these modifications, the true potential of the ZZP HV insert would likely not be fully realized. If an aftermarket camshaft were used, equal or greater gains may be possible with the ZZP HV insert over the stock setup.

Testing Procedure

Prior to the installation, I collected performance data to baseline the car's performance. After this data was collected, I installed the insert and left it to sit overnight for the sealant adhesive to cure. On the following day, I repeated the performance tests. The weather conditions for the day were warm and humid. During baseline testing, the temperature was 63ºF, Humidity of 72% and a barometer of 29.35"of Hg. The engine was brought up to a stable operating temperature of 182ºF by the PCM's Engine Coolant Temperature readings. A total of 18 passes were used to collect all the performance data, with 6 replications for any one parameter. The results for replicated runs of each parameter were averaged together in the final analysis. On the day following the insert installation, the test conditions were very similar with the temperature at 56ºF, Humidity of 76% and a barometer of 29.05 "of Hg. The GT was running on 93 octane, had ~14,000 miles on the engine.


The affects on the performance curves were not totally surprising. What was surprising is the magnitude of the affects and the dramatic characteristic changes to the power curve. As can be seen in the charts, the gains in peak HP and Torque were ~9.1 WHP and 2.0 ft-lbs respectively. While these improvements to the peak HP and torque values are impressive, what is more impressive is the increases made to these parameters in the upper RPM range, i.e. 5,000 RPM and beyond. The improvements above 5,000 RPM are remarkable to say the least. If you were to look at the torque curve above 5K RPM, the engine no longer hits a wall and suffers a fall off of torque. Since HP is the multiplication of RPM and torque, the engine can now produce vastly more HP above 5K RPM than with the stock insert. When comparing the before and after HP values at 5,800 RPM, the insert boasts an improvement of nearly 30 WHP (~135 vs ~165 WHP). This alone has more significance to tapping the potential of the 3800 V6 than does raising the peak values alone. When comparing the power curves to the air flow data curves, the results are substantiated. The mass air flow curves indicate the same dramatic improvement to air flow through the engine above 5,000 RPM. The peak volumetric efficiency is not improved because this is more characteristic of the camshaft. Keeping in mind the peak efficiency point of the stock camshaft is ~4,700 RPM, the HV insert does not impact the efficiency curve at that point. All of the improvements to the volumetric efficiency curve exists above 5,000 RPM. Again, this correlates with the HP and torque curve improvements.

Looking at the affects to the lower RPM range by the HV insert is also interesting. One would expect to loose quite a bit of low end performance due to the intake runners being shortened by such a great amount. However, the improved flow characteristics of the unobstructed plenum inlet and the contouring of the runner entrances tend to minimize or prevent these losses. From the flow and power curves, the loss in performance below peak values is very minor and most likely negligible. My conclusion is this modification is very beneficial for L36 engines that have been modified to operate at higher RPM ranges and produce significantly greater horsepower. This ZZP HV Intake Insert essentially unleashes a great number of ponies corraled in the high RPM band. Once these ponies are set free, the engine really comes alive!

Air Flow Measurement Results ¹:

Mass Air Flow
(Lbs. per min.)
Volumetric Eff.²
Test Conditions
OEM intake manifold setup.
ZZP Intake Manifold Insert installed.

Air flow data interpretation:

  • Installing the HV insert increased peak mass air flow from 22.8 #/min to 24.4 #/min. This translates to an overall increase in mass air flow by 7% over the OEM setup. Keep in mind that these improvements are strictly found in the upper RPM range.
  • Volumetric Efficiency (VE) of the L36 Naturally Aspirated engine was not increased any with the using the HV insert. The VE was increased significantly above 5,000 RPM. Noteworthy is the ~6% increase in VE at 6,000 RPM.
  • These improvements support the ambition of having the L36 engine breathing significanlty better at high RPM.
  • This HV insert extends the usable operating range of the test engine configuration well into the 6,000 RPM regime. A reprogrammed PCM would be required to take full advantage of this additional power available there.

Stock Setup Volumetric Chart

ZZP Intake Insert Installed Volumetric Chart

Power Measurement Results:

Peak Horsepower
Peak Torque
Test Conditions
180.7 $a$t$ 5100 RPM
193.3 $a$t$ 4700 RPM
OEM intake manifold setup.
189.8 $a$t$ 5300 RPM
195.3 $a$t$ 4900 RPM
ZZP Intake Manifold Insert installed.
High RPM Torque
Test Conditions
~135 $a$t$ 5800 RPM
~125 $a$t$ 5800 RPM
OEM intake manifold setup.
~165 $a$t$ 5800 RPM
~150 $a$t$ 5800 RPM
ZZP Intake Manifold Insert installed.

Power data interpretation:

The collected data was analyzed to determine the horsepower and torque at the wheels. This data was completely independent of the volumetric data, but proved out very similar results.

  • Installing the HV insert increased peak horsepower from 180.7 WHP to 189.8 WHP to yield an increase of 9.1 WHP. This translates to an overall peak power increase of 5.0% over the OEM setup. These results match well with the gains measured by the volumetric data.
  • What is more amazing is the horsepower that is unleashed above 5,000 RPM and peak horsepower. The insert produces an additional 30 WHP at 5,800 RPM compared to the stock intake insert (~135 vs ~165 WHP). This improvement is not only see but also felt as well when driven.
  • The peak torque produced by the L36 Naturally Aspirated engine was increased from 193.3 ft-lbs to 195.3 ft-lbs to yield a gain of 2.0 ft-lbs of torque. This is a gain of 1.0% with the use of the HV insert. What is more notable is the ever increasing gains to the torque curve above 5,000 RPM. At 5,800 RPM, approximately 25 ft-lbs of additional torque is produced. This alone is a huge difference.
  • What is also important to observe in these power and torque curves is the very minor loss in lower RPM performance. These are well offset by the gains made in the upper RPM range. Those gains make the minor low end sacrifice easy to overlook.
  • The changes to the performance characteristics of the L36 engine are dramatic, when combined with the other engine modifications listed. This HV insert unleashes the L36 to truly operate well above 6,000 RPM and produce a great amount of power there too.

Stock Setup Horsepower & Torque Chart

ZZP Manifold Insert Installed Horsepower & Torque Chart

º All testing performed on a GM 3800 Series II (L36) Naturally Aspirated Engine in a late model Grand Prix. The engine was brought up to stable operating temperature and conditions for all test data collected. Engine coolant temperatures were held within a few degrees of 182°F.

¹ Mass Air Flow measurement data was obtained using a OBD-II Scan Tool. Mass Air Flow values were read from the MAF sensor via the Powertrain Control Module (PCM).

² Volumetric Efficiency is a quantitative measurement of the engine's ability to breath (pull air into the combustion cylinders through the induction system and push it out through the exhaust system). Volumetric efficiency measures the standard volume of air entering the engine and divides this value by the theoretical volume of air the engine should be displacing based on its total, physical displacement. Volumetric efficiency is closely correlated to the torque an engine can produce and thus the horsepower than can be made.