KA24 Throttle Body
Why?[edit]
I've noticed that a lot of people recommend upgrading the standard RB30 throttle body to the larger KA24 item. You might wonder why? Why not use the XF throttle body, it has a much larger diameter? There's a couple of reasons quite a few people recommend this mod as oppose to the XF conversion.
If you've read the XF throttle body article, you've seen the messing around that goes with fitting it. Messing around with the throttle position sensor, new intake plumbing, modifying the bolt holes to match the plenum, etc. So what makes the KA24 TB upgrade a good alternative?
Basically, the KA24 throttle body has none of these problems. The TPS is compatible with the RB30 TPS. It bolts straight to the plenum, with no modifications aside from porting the plenum itself. The standard intake piping fits as well, which is another plus. Another good thing about the the KA24 TB is that you don't need to upgrade other parts of your intake to take full advantage of it, as the next largest restriction is the AFM, which is still larger than what the TB is. With with the XF item, the AFM restricts flow meaning you can't take full advantage of how large the TB is. The KA24 throttle body is 60mm internal diameter while the RB30 throttle body is 54mm ID. You'd be surprised at what difference 6mm can make.
Well, if it's so easy, why write a how to on it? Because there's still a couple of things you will have to do to make it work.
Where?[edit]
You'll find a KA24 throttle body on a KA24 engine surprisingly enough. U12 Pintara's use these engines, so they're your best bet. I'm not sure if other cars used them as well. At this point I'd like to suggest trying to find a throttle body without cruise control, it will make things a bit easier a bit later on. I payed $44 for my throttle body from U-Pull It. Maybe more from other wreckers, or cheaper if you reckon you can fit it down your dacks.
How?[edit]
I'm going to assume you know how to remove the standard throttle body from the plenum.
Removing throttle linkage from RB30 throttle body[edit]
To make this easiest for yourself, clamp the throttle body in a vice, or just clamp it somewhere so it can't move around much. Start by un-doing this nut, it's a 12mm (to save you looking for the right size)
After you've undone the nut, get a flathead screwdriver and use it to pry the small arm of the spring off this metal bit (the above picture doesn't show it tensioned because I only put the whole linkage on for the sake of the photo). Wriggle this metal bit off, where the throttle cable clips into. Release the pressure on the spring and slowly turn it back around once.
After this, take the small whiteish plastic ring off.
At this point, I'll say make sure you don't lose any pieces, because it's hard to improvise with these, and buying another throttle body simply for parts is less than ideal.
There are two springs, an outer spring and a inner spring. They both have "hoops" I'll call them for lack of a better work which are connected to a small bar below the main butterfly bar. Get a flathead screwdriver, whatever size you see fit, and pry them off
After you've done this, grab the whole lot, and slowly wriggle it off the bar. It can take a little bit of patience, I found mine got stuck a bit, but persist with it.
It should all hold itself together when you take it off. Once you've got the whole lot off, you don't have to worry about the RB30 throttle body anymore.
If you haven't already remove the throttle linkage stuff off the KA24 throttle body, following basically the same procedure as above.
Fitting the RB30 throttle linkage to the KA24 throttle body[edit]
Now, depending on whether the engine you got your throttle body from had cruise control or not, this might differ slightly for you. My throttle body had cruise control, so it had a longer bar from the butterfly, and a longer bar below it for the "hooks". Because of this, I had to saw the smaller bar to a shorter length so that the metal piece of the linkage that the cable clips onto didn't foul on it, as you can see in my pictures.
Anyway, fitting the linkage is basically the opposite of removing it from the RB30 TB.
Push the spring section on first. You may need to twist and turn it so it goes on, because the holes in the linkage need to line up with the ones on the butterfly bar obviously, and there is one or two internal ones you can't line up by eye, so just turn it around and push until you get it on.
Make sure you put these back on when you push the linkage on.
After you've done all this, grab your flathead screwdriver again, and turn the outer spring's arm back around to pre-tension it (this is so the throttle body closes tight, otherwise your car will idle high and you'll have an incredibly light accelerator pedal)
Once you've turned it around, place the plastic ring back in place,
And put the throttle cable holder thing back in place.
The arm is supposed to sit like this, with a bit of maneuvering with the screwdriver it shouldn't be hard to get it in place.
Now, because I had the throttle body from a cruise control model, I needed a couple of washers so I could tighten my linkage properly. I used I couple I found in the shed, use whatever you can find really.
Don't do it up too tight, I fucked the thread on part of my butterfly bar from doing that, so I had to use a larger washer to space it out to a part with good thread.
Coolant hoses, etc.[edit]
The only real stuff around with this, is that the coolant hoses come out at different angles on the RB30 TB compared to the KA24 TB, so you'll need to make your own basically. I took my old hose down to Auto Pro and got some 3/8 heater hose and some new hose clamps.
You might be alright with the original hose from the firewall side of the plenum to the TB, but mine needed to be replaced so I did that one as well, but the hose from the radiator side of the plenum needs to be changed. 3/8 hose will JUST fit over the plenum connection, it was an incredibly tight fit, but it goes on, and goes onto the KA24 TB connection nicely.
You could also cut the coolant pipes off the KA24 throttle body and bypass it with a single hose from the front of the plenum to the rear of the plenum. The coolant flow is only used to prevent icing of the throttle body in cold temperatures. It'll stay a heap cooler without coolant flowing through it and heating it up unnecessarily.
The TPS works without any mods, and the standard intake piping will fit fine as well, so you don't need to worry about any of this.
Results[edit]
After fitting the new TB, there was a definite improvement in response, and a slight increase in power. The engine revved up a bit quicker than before.
Contributors[edit]
- Lupes
- Brad M