Home made GSXR throttle body conversion

[dynofiend]

The reason IRTBs can help with power is that a single plenum equipped car can suffer from charge robbing, which is where the intake 'pull' from one cylinder 'steals' some of the air from a cylinder which is about to suck in its own air (a bit over simplified but thats it). Also they tend to offer better filling of the cylinders from laminar air flow. Watch someone hold a cigarette in still air. The smoke first rises upwards in a straight line quite quickly, after which it begins to tumble and slow down. The straight section is where the smoke is in a laminar flow, and as you can imagine, this is desirable for airflow. All of these things become even more of an issue if you decide to use a more agressive cam with larger overlaps. Retaining a plenum and maf sensor whilst using IRTBs removes much of the benefit.

There is no need to worry too much about a cold air supply. This is a particularly overrated part of 'tuning' as most cars engine bays tend to be around ambient temps once the car is moving, and even then, a 10C drop in intake temps only provides something like 1bhp extra, which is undetectable.

As has been said, most IRTB setups dont use a map sensor (there is some confusion in this thread already in the difference between map and maf, but i wont go into that here, suffice to say the mx5 uses a maf not map as standard) due to a flucuating vacuum signal. You can run all four intakes into one, and use something like a fuel filter to dampen the signal if you wish. I will be running the car initially on whats called alpha N, which is using a combination of the TPS and air temp (ill be using a GM open element air temp sensor). Ill connect up a map and monitor its signals before deciding whether to incorporate that.

Running injectors further away from the head can help the mix, but this is really only relevant at high rpms, usually above what the car can rev to as standard. My setup will be using the stock injector positions as that way I can retain the OE fuel rail.

The FPR shouldnt be an issue, as ill just disconnect the vacuum reference which will mean itll have a constant pressure, and (if my brain is working) it will default to the 'higher' pressure when I do this.

IRTBs will never be able to compete with a turbo set up for power or speed. Those who have or want IRTBs are fully aware of this, and tend to hold power delivery, and in particular the noise, as a higher priority

The ECU i settled on is a Megasquirt, which is a DIY job. No doubt ill have many frustrating nights ahead of me, and then hopefully one or two sweet sweet eureka moments

Once i have the ECU running, ill be using a spare head I have to play with, perhaps trying to modify the ports and raise compression, maybe some exhaust modifications, remove the cat etc. But thats something to think about later. One step at a time...

[dynofiend]

Oops, I had forgtten to attach the latest 'finished' picture of the ITB setup. Ive had to lose another inch of the trumpets which is a shame, but I always add this back by extending the blue tubes. Ive found that bunnings sells 40mm rubber hose connectors very cheaply, and they come with two jubilee clips each too


First problem was the old injector holes in the TBs which were redundant. I wanted to make them into vacuum attachments to power the brake servo, but my first attempt didnt go so well using small lengths of tube and 'liquid metal'. The liquid metal stuff cracked and was actually quite brittle, so I started again. First off I had some left over 'poppers' from when I made the windblocker. I also had the ariel from the mx5 which I had removed as it was broken. First I cut 4 small lengths of the arial to make tubes, and then took one part of the popper kit and widened the hole in it so that the tubes sat tight over the resulting lip, so tight that they actually required tapping home with a small hammer.





Then I soldered the tubes to their new bases, the solder filled the 'moat' around the tubes and these are shown pre-soldering.



Next I superglued the tubes into place and filled the first 'chamber' with traditional 2 part epoxy putty.



Then I took four more of the popper buttons, widened the holes even more than previously and pushed them over the tubes so they were about 1cm further up the tubes. This provides good lateral support for the tubes and stops the epoxy putty from taking the brunt of any sideways movement that might be imparted on the tubes from vibration. I dont have a pic of this stage, but I made this to show what I mean. Blue stuff is epoxy.



Finished outside.



So this is what the business end looks like. No chance of anything being sucked into the inlet should any part of the fixing fail.



And on to the finished article, including the newly created vacuum lines. One large one for the servo, and two smaller ones which can feed anything else which needs them (Im not actually sure how many I need)

Also note the trumpets which I have modified so that they sit tight inside the the throttle bodies, neatly blocking off the holes which the secondary butterfly spindle used to run through at the same time. I then used some more 40mm hosing over the top to hold everything in place. The finished article is really strong and everything has been a good tight friction fit into everything else all the way through the build. This is mainly because of the amount of time ive spent thinking about what to use, and how to use it.