Cropped Flanges

RX8 Project – Part 12, Turbos #3 – Flanges

This is a step that most people won’t need to do. Or rather there are usually easier alternatives to! When most people build a turbo manifold they simply buy pre-cut flanges for both the inlet and outlet and weld them onto the ends of whatever intricate bit of welded pipework they have devised and all is well. This is fine for the vast majority of turbos currently available but what if we have one that’s a bit more unusual, say one that most people would never even dream of using for a custom setup. For example the custom housing GT15 turbo used on a diesel Rover from about 20 years ago. That would present more of a challenge! Why do I never make these things simple!

So what we need to do is make some flanges, this isn’t a technically complex task but does take a little thought.

The first step is to carefully measure the size of either the fixed studs (or bolt holes). These are commonly M8 and so the bolt OD will be just under 8mm and if the flange has the holes will be more than the bolt size as they tend to be quite generous to aid alignment. M8 clearance hole might well  be as much as 9mm but note these all down.

Next measure the distance between each of the holes/studs, adding half of each hole/stud diameter on these numbers will give you the distance between the centre of each fixing position. This gives the fixing positions and would allow a template for these to be drawn. If doing the job this way you just need to measure the main port diameter and its distance from the centre of each hole/stud position to the centre of the port. In my case one port was handily central in a triangle so I could just measure half way between each pair of stud and draw a line to the third stud and where they cross the port centre goes.

I also tried another approach which involved taking a thing piece of aluminium and physically imprinting it with the studs using a mallet. This can be handy for really irregular patterns but does mean you don’t have a nice dimensioned drawing to keep, but you do get an aluminium template. Basically you take your aluminium, lay it over the studs and tap it with a mallet. This leaves an impression for all the fixing positions. What you’d normally do here is just drill a small pilot hole where the centre of each stud is to use to mark up your steel. in my case I didn’t want to have to remove the studs from the turbo so I drilled them out full size.

Flange Template

At this stage I used the same method to indent the sheet metal for the port which was then drilled with a 3mm hole for later transfer.

The port mark was critical because the port was the largest hole and most likely to go wrong! After marking it up on the 10mm thick steel plate I was going to use as the flange and looking at my pillar drill I decided I needed a substantial clamp for safety! While I could have bought a suitable clamp kit I decided that since I already owned suitable tee nuts for the bed I could make it safely.

Port Drilling

So this was the final drilling arrangement – and yes that is a hole saw! I feel at this point I should point out that not all hole saws are created equal. Most commonly found at DIY shops are only suitable for wood/plastic/plasterboard and maybe aluminium sheet which not unreasonably are the sort of things used in DIY. Proper tool shops will supply hole saws rated for steel but they will cost a little more the set I used was this one. It’s certainly not the most expensive out there and probably won’t last terribly long with this level of use but it’s rare I use them for anything like this and I can replace the individual saws in the set fairly cheaply.

You need to centre punch where the port centre is to locate then mount the plate onto the drill. Put a smallish drill bit (don’t go really small as you risk breaking it, I started at 3mm but you could easily go a little larger as this isn’t really precise work)  into the chuck and carefully align the punched mark on the plate with the tip. Once you are happy with the location tighten the clamps down. Tighten a little each side at a time if you have an arrangement like mine as otherwise the high pressure on one side will tend to make the place slip out of position during tightening.

Next you need to lubricate! This is absolutely critical drilling metals otherwise you will spend a lot of time either sharpening worn drill bits or trying to extract broken ones! There’s a lot of debate on whats best, for most light work I use WD40 but you will get through it quite quickly as it will tend to vaporise with the heat, this is good in that it helps cool the metal and cutting tool but it must be replaced with more. With deeper holes or larger diameters I tend to use 3in1 as it seems to work well. For the hole saw here I actually started using car gearbox oil, this slows the cutting but protects the tool.

Once you have a pilot hole swap the small drill bit out for the hole saw, make sure you have the speed slow, cover everything in lubricant and gently start to cut. This will take a considerable amount of time, be patient and regularly stop the drill and clear the cut debris away from the saw. Try to avoid using your fingers to do this as the edges can be very sharp. An air compressor is great for this but I have found that cans of computer air duster work pretty well.

Once you have your main port drilled remove the plate from the drill and file back any sharp edges then use your template to mark the centres for all the other holes, these will then need to be centre punched as before and drilled out to size in stages, I went 4mm, 6.5mm, 8.5mm from what I remember. The only critical one being the final size with the earlier steps being arbitrary. If smaller increments are used the cuts are normally quicker and easier but it adds more operations and so will likely take longer. Also I drilled all the stages on a single hole and then moved the plate which adds many more drill changes but you could also drill all the holes to one size then change drills but this has the added risk of the alignment being off which increases the chance of the bit chattering and potentially breaking but can be done if you’re careful. For the level of precision we really need it doesn’t really matter.

Rough Cut Flange

By now you should have something a bit like this! At this stage with the new flange seated in place marking the outside edge of the flange becomes much easier – you simply bolt the flange in place and draw (or even better scribe) round it on the mating side. The flange then needs to be removed and trimmed back to the mark. I rough cut the bulk off this with and angle grinder and then tidied the edges back with a bench grinder. Again working 10mm plate takes a little time but it’s not too bad and the outside edge doesn’t need to be perfect just not look silly or clash with anything and still be wide enough to hold a gasket.

Turbo Flanges

Here’s the result, two respectable looking turbo exhaust inlet flanges. The process for the exhaust outlets was exactly the same but the main port was 55mm diameter rather than 36mm diameter making the process take even longer! If you’re in a hurry get them laser/waterjet cut!

In another entry I’ll be looking at the process of making the custom exhaust gaskets I need to match.


4 thoughts on “RX8 Project – Part 12, Turbos #3 – Flanges”

  1. Hey there. I just found your blog while looking for AJ30 lifting eye brackets. I’m at the “both engines on the floor stage too trying to fathom if the V6 will fit and how much of a money pit I’ve started.
    I’ve gone with the ST200 flywheel option and found the same issue with the teeth. I thought the teeth were just really badly worn. I’ve gone for a OEM replacement clutch for the same reason as you have – no point in spending lots of money if it doesn’t work. I haven’t figured out the adapter plate thickness to get the clutch release bearing to spring fingers position to match. Any advice would be much appreciated.

    Good luck with the rest of your project. I’ll be watching with interest for future updates.

    1. Hi, glad you’re finding it interesting!

      Well the first point to address is the money pit. If I’m honest it’s very easy to go totally overboard with it as I’ve alluded to in the blog. This started as a cheapo engine swap and as the amount of custom parts is going on it’s rapidly getting more expensive. The problem being it’s all too tempting to take it as far as I sensibly can while I’m at it! In all seriousness though I think I’m only up to about £2500 so far including the car which isn’t too bad but I’ve yet to do all the pipework so I’m sure it will go up! Stick to stock parts and you will be able to do it cheaper. If it makes you any happier the V6 looks very much like it will fit. The gap between the frame rails in the RX8 is a few CM wider than the factory S-type engine mount brackets so to me It looks like it should be a simple case of bolting a suitable rubber into the mount (Land Rover V8 ones are dirt cheap and fit the S-type brackets) and some basic steel plate for welding to the car. That’s not to say it won’t be a bit cosy but the last time I tried it it looked fine except the front brace in the engine bay was in the way and had to be cut out. The stock S-type sump will not fit though!

      When I started looking at this project no-one I could find offered a sensible adaptor plate for this engine however I’ve recently seen this on ebay which gives mounting locations for a ford (st200 I think) starter on the engine side. I’m not recommending it as I’ve not tried it but it might solve your problem and provide a much easier route than my custom flywheel approach!

      In terms of adjusting the clutch offset you might find that you can either modify the clutch fork with the aid of a welder or modify the fork pivot pin position a little by adding something like a half nut to the back of it. This will of course change the angle of the clutch for a bit but only a hair. Again just to be safe I’ve never done either of these but see no reason it won’t work fine for such a small change.

      Hopefully this will give you some ideas even if it doesn’t give a solution! I’ll be posting more detail as it goes along but in real life the engine has been totally stripped and is having everything balanced ready for rebuild. So there’s plenty more I need to write up, it’s just finding the time!

      1. I was burned buying an adapter plate from P9yco. Took my money and ran. I’m not the only one either. The website has been taken down now. Next time I’m in Wales I might check out the Ebay guy and bring my plywood adapter template with me. If I can work out how thick it needs to be and verify his dimensions it might be money well spent.

        I’m still in the hundreds of pounds at the moment. I broke an S-type “for fun” and the engine, then sold the bits. Made nearly enough to pay for the Jag and the RX8 donors but not the tools and transportation expenses.

        I’ve swapped the X-type sump over already but I’m concerned that the crank pulley may still clash with the steering rack. Have you encountered any clash with the steering rack?

        1. Sorry, had no time recently to keep up to date!

          That’s sad to hear, I looked at buying one from p9yco as well but never got a sensible email reply so decided I’d do it myself. Sounds like it worked out for the best from my point of view but such a shame others got burnt by that.

          Thickness wise I went 10mm but I had to get a little creative because there are two positions on the RX8 gearbox which have location sleeves which protrude 10mm from the bell housing face meaning if you drill the hole in the adaptor you lose anything to put a bolt into. I got round this by drilling the holes out to the right size to locate everything and bolting it all up tight everywhere I could correctly then knocking the location sleeves out. I then custom made some threaded sleeves from some precision ground bar of the right diameter for the hole. These replaced the location sleeves and being a very close fit to both the hole in the adaptor and the sleeve recess in the bell housing once tapped into place I welded them in from the engine side of the adaptor.

          My advice here is go thicker than 10mm!

          From trial fitting I think the pulley will just clear but it will be very close to both the steering and the crossmember. The steering rack can be lowered a little with some relocation plates if absolutely necessary but honestly I think the crossmember will be more of a problem if it is that low!


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