Dreaded Fist writes about Nissans and about modifying cars for high performance.
RB20 Intake Manifolds
The topic of RB20 intake manifolds is a hot one. As the price of used Nissan RB20DET engines continues to tumble, more people are viewing them as a viable option to their current engine. The RB20 itself is a marvel, with a sturdy iron block and thick cylinder walls (thanks to a small 78mm, or 3.07") bore, the block itself can handle untold amounts of power. The 1.743-rod ratio, too, is desirable for motorsports style applications. With a laughably short 69.7mm (2.744") stroke, the RB20 is an engine that was build to rev, and rev hard. So hard, in fact, that even a stock RB20DET will struggle below 3000rpm as if it has been caught in some type of chasm. The true benefit, however, is that once you surpass 3000rpm, things start happening. The lovable whoosh through the filter, the familiar howl of the 20 starts to sing, and the smile on the drivers face increases ten-fold.
So what does any of that have to do with RB20 intake manifolds, you ask? Quite a lot, actually. There are numerous designs that have been tested, redesigned and tested again. The end result is that both size, shape and capacity all have dramatic effects on how your RB20 will behave. If you're interested in making as much mid-range power as possible, you're going to want longer intake runners. Likewise, if you're all about top end monstrous power, you will probably be happier with a shorter runner design. At the end of the day, most people switch not for the (potential) significant performance benefit, but rather the cleaner look and reduced intake piping heat soak. Below is a stand RB20 intake manifold and piping arrangement.
Stock RB20 Intake Manifold
There is nothing inherently wrong with the OEM intake manifold design, with the exception of the relatively convoluted intake piping setup that it creates. At stock and increased power levels, the OEM setup is fine, if a bit unattractive. Despite the adequate performance, the OEM setup suffers from heat soak, as does the factory crossover pipe and side mount intercooler piping. With increased heat soak comes increased intake temperatures. Higher intake temperatures can lead to increased likelihood of engine destroying detonation.
The OEM RB20 intake manifold setup does offer some benefits. The OEM design is two pieces, with an upper (the one you can see) and a lower portion. The lower portion consists of the intake runners, which are nice and long. As was mentioned earlier, longer runners typically translate to improved low to mid-range power production. Something Nissan felt the RB20 needed plenty of, due to the more high-rpm-oriented design of the engine. When switching to a shorter intake manifold runner setup, you may well notice a decrease in low and mid rpm performance.
The OEM plenum design offers mostly equal distribution of air to each of the engine's six cylinders and was designed with that (as well as production costs) in mind. And that right there is why the OEM intake manifold setup ruffles so many feathers. The unit itself is cast aluminum, with a rough (some would say ugly) texture, that was designed for functionally before all else. For some, it's simply not shiny enough. Scroll to the bottom of this article to read a more clear list of the pros and cons of the stock RB20 intake manifold.
The Aftermarket Solution
Fortunately, the RB20 has a significant aftermarket from both foreign and domestic countries (depending on where you live, of course). The automotive aftermarket offers countless styles, designs, and price points to work from. There are very high-quality designs, with welds that will make a grown man weak in the knees, and there are lower quality "eBay" brands that will work, albeit with a little bit of time and effort.
When considering an aftermarket RB20 intake plenum, you'll need to consider various other possible issues that may arise during the upgrade. Below is a compiled list of what to look out for.
- Can the stock throttle body be reused, or will an adapter be required?
- Can you reuse the OEM throttle cable, or will a modified cable or new setup be needed?
- Will you need to extend the wiring for the stock throttle position sensor?
- Will the new throttle body position require a smaller and/or relocated battery?
- Does the plenum supply adequate air to the first and last cylinders?
- Are there appropriate vacuum ports, or will they need to be added?
- Does the manifold allow you to retain the OEM idle air control valve?
- Do the welds look like they will hold up to the movement and vibration created by the engine?
- Does the plenum replace both the upper and lower manifold, or only the upper?
- How long are the runners? Shorter runners will provide high rpm power gains while sacrificing lower RPM power output.
- Do the runners line up with the stock ports on the cylinder head?
- Will the welds on the runners hold up to movement/heat/vibrations?
Where possible, use only the highest quality gaskets available for the application. This shouldn't be too much of an issue with a high-quality name brand intake manifold but could present trouble with an off-brand Ebay sourced item. When in doubt, always acquire and use OEM gaskets for reliability.
Plazmaman RB20DET Intake Manifold
Plazmaman, based out of New South Wales, Australia, is known for producing absolutely beautiful intake manifolds for various makes and models. They also happen to make this beautiful RB20 intake manifold, which is designed to utilize the OEM lower plenum, allowing you to retain the longer intake runners for better mid-range torque production. By eliminating the OEM cross over pipe, the Plazmaman manifold dramatically reduces the amount of intake piping when used in conjunction with a front mount intercooler. The Plazmaman RB20 intake manifold bolts directly to the OEM lower runners, and utilizes the OEM throttle body, idle air control valve (IACV) and throttle cable. The plenum measures in at 5 litres of capacity.
In testing, Plazmaman saw gains as high as 19HP at the wheels on standard boost pressure (possibly slightly increased due to easier breathing). Their test engine would have had, at the bare minimum, a front mounted intercooler, as would be required with the throttle body placement. No further information is available about other modifications made to their test car.
Available Options, Prices in Australian Dollars
- Mirror polishing - $965.00
- Black - $895.00
- Raw billet - $865.00
- Silver - $995.00
- Oversized throttle body (66mm or 72mm available) - $495.00
- 38mm recirculating blow off valve - $299.00
- 38mm non-recirculating blow-off valve - $249.00
- Manifold to intercooler pipe - $195.00
NOZZS RB20DET Intake Manifold
NOZZS RB20DET intake manifolds feature a proven aluminum construction and have been tested up to the 600hp level. In testing, NOZZS claims their RB20 plenum will hold 3bar (or 43.5psi) reliably and without failure. Based purely on the picture, it is apparent that the design is quite similar to the Greddy RB25 intake plenum, with runners and ports suited to the RB20. The manifold features a sloping design towards the sixth cylinder, which is said to aid in the proper distribution of air between all cylinders.
The welding on the NOZZS manifold is very well done, with a very clean and professional look. The plenum features pre-drilled and tapped vacuum ports, which will allow you to connect up to 5 items to a vacuum source directly off the plenum itself. For more information regarding the NOZZS intake manifold, it is recommended to contact them directly to ensure accurate information. The link to their website is available on the right, below the images of their RB20 intake manifold. As of publishing, information regarding reuse of the stock throttle body, idle air control valve or OEM throttle cable is unavailable.
Features and Pricing in American Dollars
- 5 pre-drilled vacuum ports on plenum
- Clears water outlet neck
- Clean and professional welds
- Current pricing: $640.00 (polished finish)
GodSpeed RB20 Intake Manifold
The Godspeed RB20 intake manifold is, as you've probably guessed, a near replica of the Plazmaman plenum featured above. I was apprehensive about featuring the Godspeed plenum along with the Plazmaman; however not everyone can afford to drop $1,000+ on a part for their car, and I'm trying to be impartial.
The Godspeed manifold has provisions for the idle air control valve, however, it is anyone's guess as to whether the face is straight or not. At any rate, with a manifold such as this, it would be wise to have a professional metal worker give it a look over for you. This will add to the total cost, even more so if work is required to get the manifold up to spec. You may end up having to spend some extra cash to have the faces decked, and welds cleaned up.
The Godspeed manifold is great for those who are welding and/or metallurgy inclined, who want shorter intake piping and cleaner setup. For those who can't weld or who aren't comfortable with modifying the plenum should it be required, the Plazmaman RB20 intake manifold may be a better choice.
Features and Pricing
- Retains OEM lower intake manifold
- Should bolt on without to many hassles.
- Inexpensive alternative to the Plazmaman RB20 intake manifold setup.
- Current pricing: Varies from $230 to $350 depending on the eBay seller.
PNT Performance Intake Manifold
Both the plenum and runners on the PnT Performance RB20DET intake manifold are made of cast aluminum. The intake manifold fits well for an aftermarket part, with clean professional welds and a tried and true design. Stock vacuum hosing, idle air control valve and fuel rails are compatible with the PnT intake manifold. Unlike most other "eBay" manifolds, the PnT manifolds feature internal velocity stacks on each runner, which improves airflow into the engine by creating a Venturi effect. There are various "stages" or "versions" of the manifold available, ranging in price from $649.00 to $1,000. The less expensive of the two does not come with a throttle body. When you opt for the second stage, you receive the plenum as well as a 90mm throttle body and a fuel rail to suit.
The PnT Performance RB20 intake manifolds perform well in cold and warm weather environments and are a sure fire way to improve power production in the higher RPM range.
Features and Pricing
- Includes water lines
- Works with OEM idle air control valve, fuel rail, and throttle body.
- Current pricing: $649.00 to $1,000
OEM RB20 Manifold Pros and Cons
While many people chose to replace their RB20 intake manifold with an aftermarket front facing design, there are the select few who chose to stay with the OEM cross over style design. There are a few reasons, one of which is air distribution between cylinders. When you look at the old Gibson GTS-r race cars of the 1980s, which were powered by the early RB20 engine, you will see that they stuck with the OEM intake manifold design. Pictured is the Gibson GTS-r, which features the OEM intake manifold, albeit with a modified piping design that gets rid of the OEM cross over pipe. This style of piping would help reduce heat soak, as well as eliminate a few extreme 90 degree bends that most piping styles are required to make in front mount intercooler setups.
Due to "lag", many people opt to upgrade to a front facing intake manifold in an attempt to reduce that lag sensation. By opting to use a front facing intake manifold, several feet worth of intake piping can be eliminated, thereby decreasing the amount of lag in between gear shifts and when getting on and off the throttle. It could be argued that utilizing a front facing intake manifold, in addition to a phenolic intake gasket, that heat soak is reduced by significant amounts.
It is worth noting that the RB20 intake manifold has been proven up to 400+ horsepower in both motorsports and in street cars. The likelihood of the OEM intake manifold reducing your power output is highly unlikely unless you are making a significant amount of horsepower and/or running copious amounts of boost.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.