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Twincharge WRX

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I have been working on this baby for a few years. I don't have a lot of time as I do 14 hr shifts at work.

Ej 257 sleeved block with CP pistons , BC rods, ACL bearings, ported heads, bc 272 cams,gtx3076r, ID1000 injectors with a haltech PS1000. IO expander, closed loop fuel and an J and S interceptor for closed loop knock control and monitoring.

The bit I have been working on for the last 3 months or so is manufacturing better pipe work for the twin charge setup and wiring to suit.

I have a switch in the cabin that when I switch it on turns on the compressor, closes the supercharger bypass, arms the water methanol injection and selects the correct fuel, ignition and boost maps. It should be running again this weekend.

I had a fairly rough setup running without the water meth and without optimised timing and I was fairly happy with the results.

With the new setup I will still maintain good fuel efficiency whilst cruising, but she should be a monster with the supercharger turned on.

Also I have been part of HPA for over a year and I would not have the knowledge to complete this project without what I have learned here from Andre and reading the forums with everyone sharing their knowledge. Thankyou

Look forward to seeing pictures man sounds like a crazy setup

Sounds like a great project! Please post up some photos :)

I had plans back in my uni days of twincharging a Toyota 4AGZE fitted to a KP60 Starlet. in the end the project kind of got abandoned which I still regret as I would have loved to have got the project up and running.

What are you running for a supercharger?

That sounds amazing, you need to get some photos and videos up of this

Yeah, I definitely want to see that too !

The first thing that popped into my mind reading this your setup:

"interceptor" "switch" "turns on the compressor"

The supercharger is not as large on the Interceptor sadly.

Space to fit things has been the largest issue.

The battery has been relocated into the boot and the thermofans have been replaced with low profile units between the front mount and the AC condenser.

I am currently running an SC 14 which is being over driven somewhat.

For a cheap compressor it makes 7 psi the moment I open the throttle and the compound is making 30 psi gauge pressure below 3000rpm.

I don't think the SC14 will last long at these sorts of pressures, but I am yet to find something as compact.

Any suggestions on a better supercharger would be helpful. Total length including the pulley can not be over 30cm.

I have made the pipework out mild steel tubing mainly as a prototype and a pattern as it is cheap and I could do it myself.

These will be powdercoated after a tidy up but in the end I would to like to make the whole thing out of welded poly for less heat soak and cooler AIT.

Please excuse the welds as I am no boilermaker.

Attached Files

I have mounted the sprayer for the water\meth prior to the air temp sensor as I am hoping to build some safety into the setup by having an ignition strategy based on air temp. Theoretically if the water tank empties, the IAT should go up and I can pull timing out to avoid det.

You could look at something like a Sprintex. I think they are manufactured in Perth somewhere.

is there any way you can put a bypass valve in place? so once the manifold pressure raises beyond the 7psi it removes the supercharger from the system?

I have a bypass valve that I could use for this purpose but I won't be doing that for some good reasons

There is an advantage to be had running the supercharger all of the time and it relates to turbine back pressure and scavenging

Basically the theory is that with the compounding you have a higher intake pressure in relation to turbine backpressure than you would have with a standard turbo set up which results in better scavenging and less residual gases I'm your cylinder which in turn allows you to run more timing and consequently more power.

The supercharger is never a restriction as it moves the same fixed volume of air, regardless of the density, per rotation

I am only using the bypass valve for cruising

Very interested in this thread. I am considering twin charging my 3SGTE. With a larger than standard turbo it's lacking oomph out of corners on track.

We've worked out the placement of the parts, but haven't bought anything yet. What I can't work out is how to size the supercharger. I need it to be producing good boost between 2 and 4k rpm, at which point the turbo will be going well.

Does anyone have any tips on calculating the right size?

Google a guy by the name of warpspeed. He is on the Automotive engineers website and has a lot of experience on these setups and is quite happy to explain indepth .

Basically though, if you have a 2litre engine that moves 1 litre of air per 360 degree revolution and you get a 1500 cc supercharger you have 500cc of air extra per revolution which being half of its capacity gives you about 7 psi or half a bar of boost before the turbo is involved.

He also suggests that you go way larger on the turbo than you normally would for said engine and go the largest possible turbine for that turbo mainly to help reduce exhaust backpressure at higher rpm.

If the turbo would normally see full boost at 4000rpm expect to see that at 2000rpm and lower.

My 2.5litre with the 3076r with the 80ar exhaust housing normally would not even start to make any real pressure below 4000rpm.

With the slightly overdriven 1.4l supercharger I see 7psi the moment the throttle opens and the recirc valve closes and I am seeing 30psi at 2000rpm and could probably get much higher if I let it.

The previous setup was pretty rough as I just wanted to get a feel for how it worked before I sunk all of my time into it. I was blowing boost hoses of flat out and even splitting silicone hose. I hadn't had it over 4500rpm and then my liners dropped, so I pulled it all apart and started plumbing it up properly.


Thanks for the tips there bikeboysam. Some good advise there, although technically taking some time to digest!

I also happened across one of Andre's old posts: http://www.speedhunters.com/2015/04/knowledge-boost-selecting-a-supercharger/

So seems that selecting the right charger isn't as simple as I thought! I originally thought centrifugal was right, however it seems it's a bit like my turbo charger. If we want the supercharger to provide low end grunt and to spool the turbo, then maybe an alternative is needed.

More research needed - and perhaps I should start another thread on just this topic.

"Google a guy by the name of warpspeed. He is on the Automotive engineers website and has a lot of experience on these setups and is quite happy to explain indepth ."

Warpspeed (Tony) can be found in various places. Speedtalk is one and the other is the PTS Flowbench forum.


I tried a centrifigul type before I did any research on the subject, and you are correct in that it is too similar to a turbo.

It did not work well at all. Constant displacement I the go.

I would aim for a supercharger that gives you 7psi. It is amazing how fast the turbo spools up with that driving it.


Do you know him?

Hi bikeboy, thanks for the tip. From what I've read it does seem that constant displacement is the way forward.

In your application, where did you put the supercharger? From what I'm reading (warpspeed etc) people don't like putting it inbetween the air intake and turbo (with bypass) as I have planned, but I can't find someone who has done it.

I don't personally know Warpspeed (Tony) but I have read alot of his online postings in the two forums we are both a member of. He has been a help to me on the PTS forum with information about flowbench motors etc. He is a very knowledgeable person and from what I have seen is willing to assist people online when he can.


Mine goes Filter, turbo, intercooler, supercharger and then throttle body and plenum.

Ideally you would have another heat exchanger(intercooler) between the supercharger and the throttle body.

Also having the supercharger after the throttle body simplifies things a lot as you don't need an unloading valve when off throttle, though you lose the option of bypassing the supercharger when cruising. Some would argue that it is unnecessary anyway.

The setup that you are toying with is possible, but are are you planning on it being a compound setup or do you want to run them individually and switch from the supercharger to the turbo after the turbo is spooled? That is how the TDI golf's go about it but from what I hear it is very hard to blend the transition and if you look into compounding you will find that it is a no brainer as the benefits are huge and that your setup would be just as if not more complex to manufacture .

Post a pic of your engine bay and I may be able to suggest some ideas.

Hi Bikeboy. Will try to get a pic - car is at the garage at the moment. Should be plenty of space though as were planning to use the space above the engine for accessibility, for the parts which we can't fit alongside.

The reason for the supercharger was to reduce / eliminate lag. The car is for circuit racing and I struggle with current setup out of corners. We're making some big changes to the car now due to cooling on long runs so there's the opportunity to do something different too. The idea fo the SC was to run up to about 4000 rpm then cut out, with turbo then pulling air via diverted channel. I have read a lot about the blending issue, but did get the inspiration from the VW cars.

If the SC is after the turbo then it'll have to be running all the time, so won't I still experience some "lag" for when the turbo eventually cuts in and compounds with the SC. Presumably with that setup though, I'd get away with a smaller turbo.

On your setup with the SC before the throttle body, how do you stop the SC from producing boost against the "closed door" when off throttle?

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