Throttle Modification

15 July 2009

So as shown on the previous page, I have a problem whereby the throttle cable is in the middle of the pedal box. I can't move the pedal box, so something has to change with the throttle.

Options I can think of are:

1: Move the throttle.

Easy enough, but any move will increase the throttled volume (amount of air in the intake system behind the throttle), which is bad for throttle response. So I'm a bit loath to do this.

2: Turn the throttle upside-down.

This will put the throttle cable gubbins on the side away from the pedal box:

Unfortunately, it doesn't fit properly that way around (although that could be solved with a bit of grinding), but also is too high and the pipes you can see on the top of the throttle body will be sticking out of the bonnet.

3: Make the throttle rotate clockwise

It currently rotates anti-clockwise (to open the throttle):

If it were to rotate the other way, the cable attachement bracket would be away from the pedal box, and the cam shouldn't foul the pedals anymore.

Out of these, I preferred the idea of option 3 the most. Turning it upside-down isn't really a goer, and I can always resort to moving it as a fallback. Changing the rotation shuoldn't have any adverse performance effects that I can think of. It is harder, of course, but then that's normal.

So I started by dismantling the throttle butterfly to see if it would actually work backwards. Should have been easy enough, but one of the screws holding the butterfly plate in wouldn't budge, so I had to (very carefully) drill it out. That done it all comes apart easily:

A quick fiddle confirmed that it would indeed work turning the other way. Offering it up to the engine, the large plastic cam is still rather too big however, and will still foul the pedals. It has an unused cable guide on it, which I guess must have been for something like a kickdown cable for automatics? Anyway, there's a lot of fat which can be trimmed from it. I considered cutting it away, but I'm not sure how well the plastic will stand up to that, and it probably will end up looking a mess. So I've ordered some 6mm ally plate, and will make a new, smaller cam using the plastic one as a guide to get the shape right. I'll also need to make a new cable attachment bracket, or modify the existing one.

26 July 2009

Haven't had a lot of time on the car (summer DIY jobs calling on my time), but I have managed to order some seats, which should be with me in a couple of weeks, as well as managing to make up a new throttle cam out of alluminium. Well, two actually, because I snapped a drill off in the first one, rendering several hours of work wasted at a stroke. But anyway...

Everything fitted, and it was starting to look quite workable...until I remembered the throttle position sensor. This will of course not "just work" the other way around. In order to keep it rotating the right way, it have to be moved to the other side of the throttle...the same side as the cam. After much looking and muttering, I unfortunately came to the conclusion that my option 3 wasn't going to work. Bloody new fangled electrickery.

So, back to the drawing board...or whiteboard in my case. A very useful addition to the garage, for gathering thoughts, measurements and rude doodles by your mates. After while, I had a few more ideas to try out:

4: Move the intakes to the other side of the engine

I decided I'd take the plenum and intakes off, just to see if they could be fitted to the other head; this would mean that the throttle was at the front, which wouldn't work, but if the intakes fitted, it might be possible to chop the front and back of the plenum off and reverse everything. If that was possible, the throttle would be on the passenger side of the car, avoiding the whole problem of clearance.

Didn't work though - the heads are handed and the plenum won't fit on the other side, without vast amounts of work. The intake pipes would have fitted fine though...

5: Independant throttle bodies

That would do it. Apart from the cost though (which is quite considerable), I'd have to build a plenum from scratch if I still wanted to use a supercharger, and probably a filter box even if I didn't. It would mean that the bit poking through the bonnet was central, so I could fit a standard bonent scoop, however.

6: Custom Plenum

As above, making a plenum to sit between the V would solve the problem, but is pretty drastic and would be work I'd have to get done by someone else. Or one could be made as a mirror of the current one, to sit on the other head. Would work in theory, but there would be a very sharp bend in the air intake line, as it is going to have to run down the left hand side of the engine to get to the front (steering column etc is on the right hand side, so it can't go there)

7: Use a bottom-mount pedal box

Some kits use a pedal box mounted in the bottom of the footwell - Rally Design do one specifically for 7-style kits. That would avoid the problem, however a quick peruse of the catalogue later, I was pretty sure that it wouldn't fit - there's a good reason dax mount the pedals from the top, and that is because the footwells themselves are so small.

8: Find a TPS with the same specification that works in the opposite direction

If I had a throttle sensor which worked opposite to this one, my original idea would still work. I'm not sure I can be bothered researching Bosch part numbers from the early 90s though.

So I think I've gone through most of the possibilities now. Should have, I've been staring at the thing for long enough. Out of all of these, the most feasable / least work / least hacking about of the engine looks to be the one I thought of first...move the throttle.

Cue a mock-up using some old brake pipes and various cardboard templates:


Looks like it'll work. Not going to be ideal for airflow, but as mentioned above, the trunking will have to turn 180 degrees to go back down the side of the engine anyway, so probably not making it any worse than it has to be. Current thinking is to buy a aluminium pipe with 45 degree bend, cut out the bit I need, and get it TIG welded onto a square flange at each end. The flanges and pipe I can do myself, the welding will require a professional though I think.

04 August 2009

So I bought an "intercooler bend" from ebay, with a 45 degree bend. I then made up the two flanges, using the 6mm ally plate I'd bought previously. First up, I drilled the four bolt holes, bolted them to the throttle, and marked out the central hole. This I made on the lathe. I mounted the piece on the faceplate (which required some clamps to be made up out of some M12 bolts and angle ally), cut a large hole out using the parting-off tool, then took it out to the finished size using a booring tool. Once that was done, I filed the edges square by hand. Actually, the one which mounts on the throttle is square, whereas the end of the plenum is all over the place. I've made the flange match as I think it will look better if the join isn't sticking out, bringing attention to the wonky-ness:

   Cutting the central hole on the lathe, and the finished cut alongside the intercooler bend. Outside edges not shaped at this point.
   The two flanges roughly finished, alongside the cut-down pipe, ready for welding up. And yes, the right hand one is very wonky, and yes, the end of the plenum really is that shape. On the right, showing how it will fit. Room for the clutch and everything!

So now it's "just" a case of welding it all up. I've been experimenting with welding ally with the MIG, and I'm encouraged by my efforts so far. It's quite different to welding steel, and there are a few youtube videos which have helped a lot. I've run out of gas at the mo, but I'm going to do a few more trial pieces using the offcut bits of tube and plate, then if I feel up to it, will do it myself. I'm confident I can stick it all together, the question is whether it'll be neat enough! If I can get the hang of it to a reasonable standard, it should be a great help when it comes to doing the various bits of odd shaped panelling I need.

And in other news, my seats arrived from JK Composites. They're a special size made specifically for the Rush, (the model number is N4042), so fit perfectly. Really pleased with them, they weigh nothing, look fantastic, and feel great to sit in. And on top of that, they're about half the price of Cobra sevens or Intatrims. JK are a small company who are great to deal with, definately recommended.

13 August 2009

Over the last week, I've been doing lots of welding practice. Got through a couple of mini bottles of argon, and made a lot of bits of scrap ally. For the final few tests, I used the offcuts from the intercooler tube, and the remainder of the 6mm ally I'd made the flanges from. This meant I could get the welder set up exactly right for doing the real thing.

I basically ended up on full power, with a bonkers feed rate (nearly twice that of steel), which from my reading is normal. I found that keeping the tip fairly close (<10mm), nearly at right angles to the work, and using a reverse "c" motion worked best. Oh, and moving fast! It all happens a lot faster than steel. That said, I was able to do some fairly neat welds. So tonight, I decided to have a last practice and try the real thing.

So how did it go, I hear you ask? Well, on the whole, pretty good. Obviously the neatest bits are underneath, with the messiest bits right where you'll see them. And I did run out of gas part way through (note to self - always start a new gas cannister for the actual job, because running out sucks!). So I had to grind that bit back and re-do it. But I think I'm pretty pleased with it - or will be, assuming it's airtight! Still needs polishing up and finishing off, of course.


No shot of it in place yet, I'll try to get one up later. And of course, I need to rebuild the throttle itself.


Here's the extension in place, with the throttle attached. Loads of room around the pedal box now!

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