This is where the fun really starts. In my wisdom I have decided to fit a Rotrex supercharger to my Duratec engine.
I am certainly not the first person to do this, but am in a minority at the moment. Caterham did it with the X330 (aptly named as it had 330bhp) which was fitted with a 2.3 Duratec and Omex have done it on a Westy demonstrator.
If you are thinking of any supefcharging project then I would throughly recommend a book called 'Supercharged!' by Corky Bell which is basically the s/c bible. Plain english advice from a guy with years of experience.
As usual, click on the pics for a bigger view.
Engine modifications
This is a matter of personal preference. There are several companies running 11psi on completely standard engines (cast pistons etc) without any reported problems. This is fine as long as you dont feel the need to push the limits of what is possible. Any detonation will eventually break piston ring grooves and it will be an expensive rebuild in this case.
I will be fitting forged 10:1 compression ratio pistons imported from the states. Rods are a nice to have (if only for safetys sake) so I will be installing a set of those too. (£249 delivered from the US). Although the engine isn't going to be seeing silly revs (limit set at 7000rpm) forged rods give that added security especially as they are a weak point of the standard Duratec.
Other than that the engine will be as shown on the other page. GSXR 750 throttle bodies, 440cc/min injectors, wet sump etc.
The Supercharger
I have gone for a Rotrex C30-94 supercharger. This is perfectly sized for the engine and has proven itself in many installs around the world. It is a centrifugal superchager, basically a gearbox attached to the compressor part of a turbo. They have several advantages over the Rootes or GM superchargers, and also some drawbacks.
The supercharger kit consists of the charger, oil cooler, oil tank, oil filter, a bottle of oil and all the relevant oil line fittings (most of which is in the left hand pic above)
I intend to run around 1 bar (14.7psi) of boost with forged 10:1 compressio ratio pistons. Centrifugal chargers work well with high static compression ratio engines, this is also good for you as a driver as it means you keep the snappy low down performance and economy. The reason is that they don't build full boost until much higher up the RPM than a postive displacement supercharger (e.g. Rootes/GM) meaning you are less likely to get problems with detonation and pre-igntion.
This level of boost should see somewhere around 320-330bhp in theory. This should be more than enough, and I will probably struggle to put the power down on the road anyway!
I am planning to mount the supercharger on the exhaust side of the engine as shown in the right hand pic above. I may have some problems with clearance to the steering column, but this can be moved is absolutely necessary. Everything is certainly going to be tight. The reason for putting it here is 2 fold, it means the air pipes can go from the charger to the intercooler down one side of the car, then back to the plenum down the other, keeping it neat. And secondly that it would make the engine even wider if it were installed on the intake side, which isn't a great thing, then the alternator would have to be mounted in the charger position, so either way I can't win really!
Radiator and Intercooler
It is debatable if you need an intercooler at 1 bar of boost, but I am installing one just for safetys sake. It can only help by lowering intake charge temps, which increases its density and allows you to get more power with less boost essentially!
Due to the tight space I am going to be having a custom intercooler and radiator made. The radiator is based on the polo one but is a twin core and 70mm thick. The intercooler is a 50mm core and 60mm thick overall. Both will be supplied as a single unit (though they will be seperable should it be required later). The cost here is rather steep (£680 for the pair) but it will be necessary in order to keep everything cool.
Pics will follow when it arrives (late Jan 2010!)
Dump valve
This is a standard recirc valve from a VAG car. Readily available on ebay or in the scrap yard. I may use this or an aftermarket one, depends on cash flow at the time and if one comes up at the right price. With a Rotrex type supercharger they are best venting boost to atmosphere rather than recycling it, so even if I use this valve it will be vented to atmosphere.
The purpose of the dump valve is to vent excess boost when the throttle is closed quickly, otherwise the boosted air has nowhere to go and can eventually cause damage to the supercharger or other parts.
Above is the dump valve I will be using on my car. It is a twin piston one made by Forge Motorsport, RRP £70. I dont specifically need a twin piston (only required if an airflow meter - MAF - is installed) but it was cheap and came along at the right time.
Forged eye candy
I decided to take the plunge and order the forged pistons and rods from the US due to the extortionate cost of the same parts over here.
The pistons are made by Wiseco, one of the big names in the USA in forged engine parts. They are 10:1 compression ratio, which is 0.8 lower than the standard UK spec Duratec. This didnt really bother me due to the supercharger. They also make high compression (12:1) pistons as well at the same price (£300). They came complete with rings and pins. Even have moly coated skirts with the rather snazzy Wiseco logo on the side.
The rods are made by K1, who are part of the Carillo group. They are billet rods, which means they have been machined from a solid forged lump of metal rather than forged to shape then finish machined. There are advantages and disadvantages of both. The fact of the matter is the rods arent really going to see much more stress than in a std engine as the rev limit is staying at 7000rpm. But I thought I would install a set for piece of mind more than anything. Theoretically the weak link in the bottom end is the crank now which is rated to 9000rpm....
The pistons and rods were assembled relatively easily. There's a knack to fitting spirolock clips which involves locating one end in the groove, oiling it all up then giving it a sharp push with a piece of dowel. The clip will then spring into place nice and easily without damaging anything. The rings were gapped to check they weren't going to jam up and then fitted to the pistons, then each assembly slid into the block using a piston ring compressor. All in all a nice clean and easy job and it was rather rewarding to see the shiney new pistons in their new home!
The rest of the rebuild
ARP main studs have been fitted into the block, again not because I intend to rev the engine to 9k but more for piece of mind. The crank, pulley and sprocket were taken down to Scholar Engines in Suffolk to have the keyway cut. They come highly recommended and at £50+vat for the work it was a bargain too. Everything was cleaned down and the crank refitted to the block. The main studs torqued to 60lbft in sequence and then the ARP rod bolts torqued as well.
I modified the timing chain cover by cutting off the FWD engine mounting. Time consuming job, but a big angle grinder really speeds it up. There is plenty of material around the mount, but a little thought is required to avoid breaking through.
While the head was off I took the opportunity to clean up all the ports. Nothing major, just removed the casting marks in the ports and blended any sharp edges out. Probably worth a few BHP at the end of the day. The valves were then lapped in. The whole head was then washed out with the hose pipe, then blown out with compressed air to eliminate any swarf particles and lapping paste. New stem seals were fitted for the valves then the valves refitted to the head. Uprated Kent VS60 springs were fitted as the standard ones are a little weak and 1 bar of boost pushing on them will probably be a bit too much. The benefit is if I decide to upgrade to a cam with higher lift then I can do it without lifting the head.
The ARP head studs were then lubed up, the new head gasket fitted and then the head slid on. Studs were torqued as recommended in 20lbft increments up to 60lbft. The cams were then fitted and the valve clearances checked. I need 7 new buckets, which is another expense I could do without, however needs must. Whilst I am waiting for these to arrive I will continue with the brackets for the supercharger.
The new sump was also fitted. The sealant used is the Ford recommened Loctite 5900, its around £25 for a tube which is more than enough to do half a dozen engines. It is available in smaller quantities too, but speak to your local engineering place and see what they have. I think it looks rather good, if I do say so myself, and my friends dad made a stunning job of TIG welding it for me.
Supercharger Mouting
The supercharger mount is now finished. Its since had the ends of the tube capped and a coat of paint since the pics were taken. I had a laser cut plate for the supercharger mount made from 6mm steel. The rest of the bracket is a mixture of 20x20 box section and 6mm steel plate. This might sound a little excessive, but the supercharger could be pulling a considerable amount of power at full boost. All of the bolt holes through the box have crush tubes welded in, allowing the bolts to be done up nice and tight without distorting the box section.
An alignment jig was made from box section as shown in the first photo. Great care was taken to make sure the pulleys are perfectly aligned. Gates list the shaft parallelism tolerance for poly v belts as 0.25 degrees, so there isn't much room for error. I am happy to say that the jig was a success. The bracket distorted slightly during welding, but a 0.7mm shim behind the front bolt on the lower bracket brought everything back into alignment.
There is approx 30mm clearance to the exhaust to the back edge of the supercharger. The exhaust will be double wrapped and an aluminium heat sheild fitted to keep away any radiated heat. This should be enough to keep the supercharger body and the incoming air nice and cool.
Now I just hope that everything will fit under the bonnet as I plan. I know that I am going to have to move the steering column downlink, but how much I dont know until the engine has been test fitted to the chassis.
The next job is to make 3 idler pulleys to get better wrap of the belt around the supercharger and crank pulleys.
The techy spreadsheet
OK, here is the techy Duratec spredsheet for you all.
CLICKY
It contains a load of useful info on the Duratec, and specifically on my install. May be of use to someone.
Costs
Here is the tally of all the costs.
Supercharger kit and pulley = £980
Dump valve = £30
Plugs = £8
Forged rods = £249 (US)
ARP Head studs = £70 (US)
Intercooler and rad = £680
Forged pistons = £300 (US)
Kent valve springs = £120
Crank keyway mod = £50
New valve buckets = £75
Total supercharger install (to date) = £2,562
