Single Throttle Bodies
Almost every car made since the 1970s, when manufacturers switched from carbureted engines to electronic fuel injection (EFI), is of the single throttle body design. One single butterfly valve controlled by the gas pedal determines how much fresh air flows to all of the cylinders in an engine via the intake. This is a simple setup and it works well for everyday cars.
Some more exotic cars, such as the Ferrari 458, have two two throttle bodies each feeding one bank of the V8 engine. This is somewhat unusual and even in this case, there’s still a linkage between the two intake plenums to allow crossover of air.
The case for regular road cars using single throttle bodies is pretty straightforward. They’re cheap to make because there’s only of them per car. They’re easy to tune because all the cylinders draw from a common air volume in the intake plenum. That in turn makes engines with single throttle bodies predictable and easy to mass produce on a production line. They also make throttle response very gentle and somewhat delayed, because a momentary vacuum occurs in the intake when a cylinder tries to draw air. Portions of this can be tuned out of an engine, but the lag will always be there.
For all these reasons, single throttle bodies are much better for the everyday and inexperienced driver.
Individual Throttle Bodies
As the name suggests, this means that there’s not one throttle body for all cylinders, but a throttle body for each individual cylinder. This is a common motorsports setup on naturally aspirated engines, but also exists on some performance road cars and most motorbikes. Most notably, the 1978 BMW M1, 1985 BMW M3 and 1989 Nissan Skyline have had this as OEM stock equipment.
Unlike single throttle bodies, air flow is basically unrestricted and there’s no vacuum in an intake that air needs to be pulled from. The air also does not have to make twists an turns to reach a cylinder. With ITBs, air has a straight path into a cylinder. Also, like equal length headers on an exhaust, ITBs also ensure that the distance air has to travel into a cylinder is the same across all cylinders. In single throttle body setups, this is not possible, making air speed/volume and fuel flow potentially very different from one cylinder to the next.
This means that throttle response is instantaneous. Because air flow is highly unrestricted, this allows an engine builder to also run very high lift cams or high levels of boost.
Why do it if it doesn’t get you more power? Well, it does get you more power, though you have to be smart about the rest of your engine. For some, it’s a bolt-on to stock components whereas for others, it’s the icing on top of the cake of other mods. For the example, the Nissan 350Z in this article had some very aggressive cams installed, but was maxed out on air flow. With the Nissan 350Z 3.5L ITB setup from Jenvey, the final goal of 100 whp per cylinder was reached.
Racing and hot rod looks
Looks are also a big part of adding an ITB setup to your engine. Here is a long and very detailed article from Driftworks on their DW86 drift car build which includes and install of the Jenvey LS3 kit
with carbon fiber airboxes. Compare the look of such an ITB engine vs. a stock LS3 crate motor:
You be the judge.
There’s also a really cool build thread of an ITB setup going into a 3.2 liter Porsche Carrera (1984-1989) at this link. How about these before and after shots:
You can learn more about the Jenvey 3.2 liter Porsche setup here.
Simply put, ITBs have a huge wow factor and will make your engine compartment look awesome.
EFI replacement that looks like classic carbs
There’s also a much more objective reason to go with ITBs. For carbureted cars or even the first generation of clunky EFI systems, this is a great way to maintain a classic look, yet have all the benefits of modern EFI.
Taking classic Porsches as an example, though this applies to many other cars, the 2.7 and 3.0 liter Porsche’s from the 1970s had an EFI system known as Bosch CIS. At this point, parts for this are all rebuilt, not new and debugging these systems has become a major paint point for owners. The parts are around 40 years old at this point!
ITBs therefore offer an excellent solution for this parts sourcing issue, including carbureted cars. The setup is quite simple and with hotrodding these kinds of cars becoming very popular, this is an excellent addition to any car. It gets you the right style with modern technology, yet maintains that old school looks.
Some more applications
Since I know you came not just to learn more, but to also see more, here’s a collection of threads of various other ITB setups being run:
- Want to see an LS7 in action? Here’s a video of an HKE-built engine using this Jenvey kit for LS7 engines. Naturally, there’s also an LS3 kit available, like the Driftworks engine mentioned above uses along with the really stunning carbon fiber air boxes.
- Here a video of the Driftworks car on the dyno.
- 3.4 liter Porsche build using this Jenvey Porsche 48 mm kit.
- A thread on Honda S2000 ITBs. We carry the Jenvey S2000 set here.
- Video of a Miata with ITBs doing WOT pull to 8500: http://vimeo.com/11190533. We carry a variety of Jenvey Dynamics setup for Miata 1.6 liter, NA 1.8 liter and NB 1.8 liter engines.
There are of course many more, but that’s a few.