K24 Intake Manifold Testing

Purpose: 

With Honda K series engine swaps continuing to grow and grow in popularity, we wanted to start putting together a library of information to help everyone make informed decisions when selecting parts. 

From the factory, the Honda K series engine is extremely efficient, and can perform even better with simple upgrades like the manifolds we’ve testing today. While some people will reach for the largest or “highest flowing“ parts right off the rip, we wanted to test different manifold configurations back to back to have clean and easy to understand data.

One thing to remember before we dive into this test, is that we are using a K24A (2.4L Vtec) engine, and a different displacement engine may react differently depending on your application. 

Intentional Starting Variables:

• Test 1: Skunk 2 Pro Series Intake Manifold w/ 74mm TB
• Test 2: Skunk 2 Ultra Street Intake Manifold w/ 74mm TB
• Test 3: Skunk 2 Ultra Race Intake Manifold w/ 90mm TB
• Test 4: Skunk 2 Ultra Race Intake Manifold + 2 Liter Plenum Spacer w/ 90mm TB

Constants:

• Engine: 2.4L K24A (RBB-2 JDM Engine) Stock Internals
• Header: Skunk 2 Alpha Swap Header
• Fuel: Gasoline 93 octane
• Lambda Target: .88
• Dyno:  Superflow SF-Powermark
• Engine Acceleration Rate:  500rpm/sec
• Start RPM:  2,500rpm

Unintentional Starting Variables:

• Engine Coolant Temperature: [T1: 171°F, T2: 176°F, T3: 179°F, T4: 182°F]
• Engine Oil Temperature: [T1: 191°F, T2: 186°F, T3: 185°F, T4: 194°F]
• Ambient Air Temperature: [T1: 86.8°F, T2: 90.5°F, T3: 93°F, T4: 96.4°F]
• Density Altitude: [T1: 2153ft, T2: 2434ft, T3: 2677ft, T4: 2920ft]

Test 1: Skunk 2 Pro Series Intake Manifold w/ 74mm TB

Results:

• Peak Horsepower: 239.1hp @ 7000rpm
• Peak Torque: 195.9tq @ 5400rpm

This manifold is most similar to Honda’s OEM “RBC” manifold, and being their most affordable option makes it very popular for those swapping K series engines into their chassis. Due to that fact, we started our baseline testing with Skunk 2’s Pro Series Manifold and their matching 74mm Throttle Body. 

Now that the baseline has been established and the data has been collected, we can start comparing our next tests to this run.  For the next test, we are stepping up to Skunk 2’s Ultra Street manifold.

Test 2: Skunk 2 Ultra Street Intake Manifold w/ 74mm TB

Results:

• Peak Horsepower: 248.5hp @ 7400rpm (↑ 3.93% from test one)
• Peak Torque: 195.5tq @ 5500rpm (↓ 0.20% from test one)

We let out engine cool down and switched over to Skunk 2’s Ultra Street Manifold. This manifold does have a removable plenum that allows you to add spacers if you choose to do so. The neat thing you’ll find with this manifold is you’re still able to use an OEM bolt pattern style throttle body. We kept the same 74mm throttle body for this test. For this manifold and the rest of them moving forward, we need to run an additional coolant port off to the front right of the head. This is so that we can run this "K20" style intake manifold. 

We immediately see how we picked up peak horsepower and almost matched peak torque with this swap alone across the whole powerband. Below, you'll notice we highlighted the areas where this Ultra Street manifold out performs the Pro Series manifold and clearly shows the better of the two. 

Test 3: Skunk 2 Ultra Race Intake Manifold w/ 90mm TB

Results:

• Peak Horsepower: 251.7hp @ 7800rpm (↑ 5.27% from test one)
• Peak Torque: 195.0tq @ 5400rpm (↓ 0.46% from test one)

This next test was with Skunk 2’s Ultra Race Manifold. This is the largest in their fleet, and like the previous manifold, also allows for plenum spacers to be added. For this third test, we did not use any plenum spacers, and since this larger manifold uses the “Ford Style” 4 bolt throttle body flange, we bolted on Skunk 2’s 90mm throttle body. 

On the previous two manifolds we had noticed the horsepower started to taper down before 8000rpm. With this configuration, we saw that the engine power didn’t drop off as hard at that higher RPM so we increased the redline to 8100, where we then saw the power curve flatten out. We saw some loss in the mid range as expected, but to our surprise the lower rpm range looked very similar to the previous manifolds. The area where we did pick up power was at the very top of the run, after 6700rpm. The window where we increased power is pretty small with this manifold.

Test 4: Skunk 2 Ultra Race Intake Manifold + 2 Liter Plenum Spacer w/ 90mm TB

Results:

• Peak Horsepower: 254.6hp @ 7900rpm (↑ 6.48% from test one)
• Peak Torque: 192.5tq @ 5200rpm (↓ 1.73% from test one)

This last test was with the same Ultra Race Manifold and 90mm throttle body, but we also added one of their plenum spacers, increasing the manifold’s internal volume by 2 liters. 

We once again increased the peak horsepower but lost out on the peak torque. In this last dyno graph you can see that there are sections where the non spaced plenum does better, and then some sections where the manifold with the spacer does better. There wasn’t a defined superior combo until 7300rpm where the Ultra Race with the plenum spacer clearly makes more horsepower and more torque. In this last pull, we also increased the redline by another 100rpm. 

In Conclusion:

What did we learn here? The brief takeaway from this test procedure is that the different manifolds all reacted differently depending on where in the RPM you’re looking at. The Pro Series manifold made the most peak torque, but not the best torque all around. The same can be said about peak horsepower in the last test with the Ultra Race w/ 2 Liter plenum spacer making the most peak horsepower but not the best overall power band. 

Given thats the case, it’s important for us to look at the dyno graphs as a whole instead of just the recorded peaks. Doing so, we see the average winner of all these combos being the Ultra Street manifold. 

The Ultra Street nearly made the most peak torque, and was only off by .20% compared to the Pro Series, but carried much better overall performance. Against the Ultra Race manifolds, the Ultra Street was ahead everywhere until 6700rpm where both Ultra Race configurations started to win. Given that the window from 6700rpm - redline is much smaller than the rest of the usable powerband below it, the Ultra Street wins on average for this test.

You may still be interested in the smaller of the three manifolds, the Pro Series, if you’re looking to still have an OEM style, compact manifold that doesn’t require an additional coolant adapter on the cylinder head. The cheaper price point of the Pro Series also makes it easier to afford and can be a deciding factor for you. 

We also cannot ignore the fact that the Ultra Race Manifold combos did in fact make some additional horsepower and torque at that higher RPM section. Although a small window, if the type of racing you’re doing will have you live in that small RPM range, the Ultra Race may be for you. Given that this test was performed on a completely stock longblock, and you wouldn’t want this engine constantly having to live only at that higher RPM, we’d still reach for the Ultra Street Manifold.

What did you find most interesting about this test, and what would you like to see us do next? Reach out to us and we’ll make it happen.

Thanks for reading along, and we hope this information was helpful to you!