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Individual Throttle
Bodies - Part 1
This is the first of a 3 part article discussing Individual Throttle Bodies and my project of fitting a set to my V8 Soarer. Where possible I'll present other options apart from the path I've decided to take to try and shed as much light as possible on the subject. Instead having 1 butterfly controlling the airflow for the whole engine, Individual Throttle Bodies (ITB's) have a separate butterfly for each cylinder. Depending on the design the intake can be made straight and more direct than the stock intake or it can use the lower part of the stock intake manifold and bolt to the top such as these from EFI Hardware in Melbourne.
By having the butterfly much closer to the valves compared to a single throttle body with plenum, throttle response is instantaneous so it's no coincidence that most naturally aspirated race cars use ITB's. The drivability is the big winner here - on their own they won't make a large difference to peak power and really should be a stage 3 modification after cams. Another advantage is that the intake pressure waves that bounce up and down the runners can be tuned by using different length trumpets to maximise efficiency at whatever RPM is desired. For more information about tuning intake runners see my article here. There are a lot of benefits to ITB's however there are naturally some cons to counter the pros. They can be difficult to balance, the tolerances need to be spot on to minimise air leaks and there may not be enough clearance under a low bonnet (hood) to name but a few. It's very important that the machining is of the highest quality and that the operation of the butterflies is smooth and unhindered so they can be closed tight by the return springs. This may sound obvious but with 8 butterflies any little problem or inherent air leak will get multiplied x 8. It should be noted that this is a big job involving wholesale changes to the induction system of the engine. It's not cheap and it is fiddly with a lot of the effort going to the other things needed to make it work, but more on that later.
When undertaking car modifications, just like any other project, you need to have some clear goals of what you're trying to achieve otherwise you're likely to end up with a bunch of mismatching parts designed for opposing purposes. My V8 Soarer has been converted to a 5 speed manual so I don't need lots of low down grunt that you may want for an auto. I generally only drive my car on weekends so while I do sit in Sydney traffic from time to time it's not a big deal so long as I have a reasonable well behaved engine & clutch. I decided a while ago that I wanted to stick with an NA engine which led me to select a W58 gearbox which means I can't go for forced induction without swapping to a stronger box like the R154. I also like track days, so high end power and engine response are both important, plus I have the budget to get a set of cams more suited to producing power over 6000RPM. Throw all that together and fitting a set of ITB's seems like the only natural thing to do... although I now realise that fitting cams first probably would have been a better course.
EFI Hardware
These bolt to the stock lower intake manifold and are available in 40mm or 45mm sizes. I asked Steve Neway from EFI Hardware how to decide which size you need and he said 40mm are for those who want increased throttle response or the look for a show car but aren't aiming for over 200KW. 45's on the other hand are a bit more difficult to set up for low idle with stock cams because of the high vacuum. They are more suited to high-power applications where aggressive cams are installed and the larger diameter is needed for the higher airflow. Information about the ITB's are not on their website but they are very prompt to email and telephone enquiries. The ones I have are almost identical to the ones EFI Hardware sell - in fact they bought the original castings and improved the design - so when I wasn't satisfied with the build quality of the ones I bought (2nd hand) I sent them to EFI Hardware to overhaul them for me. They fitted ball bearings with sealing o-rings around the shaft (instead of nylon bushes which leaked terribly) and butterflies which were individually cut for each bore to get much closer tolerances. The main reason why I chose this style is that with flat tops on the throttle bodies, it would be easy to mount a plate to form the base of a plenum and fit a remote air filter.
Bullet Supercars
I've emailed Bullet a couple of times about the ITB's which appear in their gallery with no response unfortunately. They look like a similar design to the EFI Hardware items in that they use the lower half of the stock intake manifold but they appear to be shorter so would have an easier time of fitting under a low bonnet. Update: Tony from Bullet emailed me to say that in his view the performance gains with stock cams versus the cost of production weren't high enough so they won't be producing a kit.
A1 Turbos (formerly 1uzquadcam.co.nz)
These take a different approach and use 2 sets of modified Toyota 4AGE throttle bodies that bolt to custom cast manifolds. There are a number of advantages to this approach with the 2 main ones being the use of OEM throttle bodies (excellent build quality & operation) and a straight runner directly to the head as opposed to a curved path. Update: Tony emailed me some more photos and dyno graphs showing peak power of 330hp at the wheels with custom cams.
Getting hold of the throttle bodies, and if necessary new manifolds, are only a small part of the picture. Depending on your application you will need to think about how to tackle some or all of these:
I'll outline how I tackled each of these blow but something else to consider is that you really do need the right tools for the job. Without the following I'd probably have never completed it.
The throttle linkages can be fairly complicated and should use rose joints to ensure there is no slack. The smallest throttle movements need to be transmitted to the butterflies in absolute precision otherwise controlling engine speed will be a battle. I bought a full set of linkages from EFI Hardware designed to work with the ITB's that I have. It's called a bell-crank which pushes or pulls in opposite directions when the centre is rotated.
They come with an eccentric throttle pulley which gives you fine control over small throttle openings then increases the rate at which the butterflies open the further you go so the throttle travel isn't too long.
If you're using a piggyback with the stock ECU you should retain the stock TPS and adapt it to fit. It is quite bulky, making it difficult to position but it is a quality unit producing the range of output that the ECU is expecting, plus it has an internal idle switch. Unlike most TPS's, the Toyota one has 4 wires instead of 3 with the 4th wire switching to ground when the throttle is closed. V8 Soarers which don't have this adjusted correctly get all sorts of rough idle and stalling problems so it's something you don't want to ditch unless you're using a full standalone ECU. Initially I tried to use an aftermarket 3 wire TPS and attempted to rig up a micro-switch for idle. Apart from the headache of trying to mount a microswitch which might not even stand up to the temperatures of a running engine, the TPS's output was rubbish and jumped all over the place. Adapting the stock TPS wasn't as difficult as I thought it would be and I would've saved myself a lot of hassle if I decided to use it from the outset. I needed a bracket to hold the TPS to the end of one of the throttlebodies, (making sure it would rotate the correct way) which doesn't need to be super rigid - in fact I used some 1mm aluminium sheet.
To interface the shaft with the TPS I used the attachment from the stock throttlebody. This needed to have the spring stay removed, the prongs that fit inside the TPS shortened and the edges files as it's going to sit further inside the TPS housing. To fit the adapter to the shaft I had to thread the end then file flats on each side once I worked out how it would have to be oriented. The original and new throttlebody shafts are both 8mm which made it easy.
I had to extend the wires back to the loom and there isn't much space where I'm fitting the TPS so I couldn't use the plug unfortunately. When it's all bolted up it's spot on - the shaft rotates freely and the bracket has the necessary strength to hold it firmly in place.
While you can use the trumpet length to tune to boost intake efficiency, practically you'll be limited to what will fit under the bonnet (hood). Of course you could cut a hole in the bonnet and run trumpets straight out the top or you could have the bonnet modified with a "power bulge" to give more clearance. With a standard steel Soarer bonnet you'll probably have to remove a section of the sound-deadening material above the engine but there are strengthening spars behind that may also cause issue. I've replaced my bonnet with one made of 100% Carbon Fibre - it's only 8mm thick in the middle but incredibly strong and only 1/3 the weight of the original. Because it doesn't need any strengthening spars I have a lot more clearance. Even with the increased clearance I need trumpets that are pretty much as short as possible - this introduced issues with how to fit them. The throttlebodies have 4 threaded holes around each bore but with the rolled edge of the trumpet covering these I was a bit stuck. Plus I had to take into account the flat plate which will form the base of the plenum. I decided to bolt the plate to the throttlebodies, then mount the trumpets as pairs in small aluminium adapters which would bolt to the big plate over the throttlebodies. Drilling and countersinking 16 holes in the plate (4 for each throttlebody) plus another 8 to mount the trumpets was a tedious task but made a hell of a lot easier and accurate with the drill-press.
For ITB setups where the trumpets are separated you can get "sock filters" which go over each trumpet and are usually help in place with a cable tie.
Assemblies are also available which will cover 4 trumpets in 1 long rectangular unit which would be more suitable for the EFI hardware or Bullet setups.
If you look for filter setups suitable for Weber carburettors like these from Unifilter you'll be on the right track. While these are fairly easy to set up, they aren't the ideal solution for under-bonnet situations as they draw in hot air which is less dense than the cooler air outside the engine bay. My preferred solution, which I've already alluded to, is to build a plenum around all the trumpets and fit a remote air filter in the stock location where it can get cool air from below the headlight. I'm actually fitting 2 air filters - one behind each headlight as I've already moved the battery to the boot. I prefer the symmetry and with an inlet on each side of the plenum it'll be easier to ensure even air distribution to all cylinders. I haven't had this made yet so I'll be posting an update once the plenum and air filters have been completed.
The standard V8 Soarer measures the load on the engine and determines how much fuel to inject by how much air flows through the airflow meter (AFM). You could retain the AFM if you enclose the intakes and have 1 intake pipe, but that would limit the effectiveness of the system, plus you'd need a piggyback computer to control the fuel. Given that you'd at least need to use a piggyback computer you might as well install one that lets you remove the AFM to keep the intake as open as possible. That leaves 2 methods to determine the amount of air entering the engine - Manifold Absolute Pressure (MAP) or Throttle Position Sensor (TPS). There are pros and cons to both methods which I'll cover in the next installment when it comes to tuning but in a nutshell setting up a MAP sensor based system is difficult to get a good "signal" and you also lose resolution compared to a single throttlebody as it sees less vacuum. A TPS setup is much simpler to set up but some people find it too crude as the main or only load input. The MAP-ECU which I've covered here is a great MAP based fuel computer which imitates the output of the AFM which keeps the stock ECU happy. Another option which I'm going to try for a comparison is the Perfect Power SMT6 which I've ordered from Neil at Rush Imports. The SMT6 is more complicated but it can use MAP or TPS for the load input, plus it can also alter ignition timing where there is more power waiting to be unleashed.
All road cars need vacuum for various functions and this can be a bit difficult with ITB's. These are the items we need to plan for:
The MAP sensor and fuel pressure regulator both need a smooth manifold vacuum signal so it makes sense to link them together, however I found that adding anything else into this circuit made the vacuum signal too weak for the MAP sensor. The brake booster could be connected to just 1 cylinder (I believe some Alfas are set up like this) but I've bought an electric vacuum pump to see how it goes. I bought one designed for electric cars so there are no compromises - the 70/6E from here: http://www.metricmind.com/index1.htm I've also connected the VSV and charcoal canister to the vacuum pump for the time being but I'd like to connect that and the PCV to the intake at a later stage. For now the PCV is connected to an oil catch can.
Next Time The next installment will cover the installation, issues (lots), resolutions (some) and tuning...
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