the twin charging engine project


Wrench Pro
I'm looking at hooking my G2.5-550 turbo on a tiny supercharged engine which makes 80-105 ft-lbs 1000-5500rpm by itself. I want my final result to be 433whp with torque not exceeding 250ft-lbs through the very wide power band. The supercharger pipes directly into the intake manifold so some check valve pressure regulation seems like the solution. Ideally, I want to blend the S/C and T/C for only 3000rpm, then shut out the S/C. Anyone here have experience with doing a twin charge?
Sounds like an awesome project. I've no experience on twincharging the G2.5. I guess you have to watch the compression ratio and fuelling, and I do know the mapping is very important. Were you going the aftermarket ECU route on that?

Are you doing a parallel twin charge or sequential? Are you putting the supercharger first? What sort of supercharger are you using (roots/screw...?)

Personally I'd use the supercharger at low end and have the turbo cutting in and boost up power from around 2000rpm.

Intercooling is important as this setup creates a lot of heat.
Yes, the supercharger is the lead in, the turbo mixes in around 2500rpm but doesn't come full on until 6,000 and the S/C starts disengaging at ~5,000. The S/C alone peaks torque at 4400rpm with 105ft-lbs, falling off rapidly to 88ft-lbs at 5600rpm. The Audi 1.4L TDI inspired me to give this a shot. I'm still planning it so I don't know how I'll be connecting them yet. The tiny 3 cylinder Nissan HR12DDR has the same S/C and I think it's a roots type. Haven't got any of the parts yet so lots of speculation at this stage. Could use the feedback on which ECU to choose but the Nissan stock ECUs are pretty comprehensive. Rather than use one big ass intercooler, I'm leaning toward a three stage design with smaller ICs. Lots of advantages to this strategy on paper, we'll see what it does in real life.
Nissan aftermarket ECU's if required cos stock ones can be mapped quite extensively include the

Apex i power FC, Nistune or even Link (all are cheap, easy and work well if your tuner knows them)
Haltech E8
Motec is about the best according to most of the Nissan guys I deal with.

I'm curious to know your thoughts on the benefits of multiple intercoolers - to my mind it will just have lots of pipe joins and impeded some air flow.
Thanks for the tips, it saved me some time. Stage intercooling has many benefits and the additional pipe itself is one of them, especially when the pipe is heatsinked and in the airflow. Additionally, the added via gives the pressurized air more time to settle and cool. Think about a shop compressor and you'll understand what I mean. The standing pressure evenutally cools the air in the tank. This is why some builds employ an airbox/buffer. Another thing is the amount of heat exchanged with high speed airflow through smaller IC's compared to the larger flow matrix of a bigger one. In the latter case, more of the heat slips through the middle stream in the pipe where in the former case, those heatstreams are cooled by the following stages.
Aussie mads MOTEC is the choice of our WTA champ as well as our V8 supercars. Haltec is another highly regarded make.
Norris designs has a twin charged tvs [iirc] + turbo [mitsubishi evo] . sc cuts out like a/c once turbo is on. kit is available @ ? 7-8 k gbp.
Here is the planned torque output for S/C=5psi and adjacent T/C=36psi:
RPM torque
1500 80ft-lbs
2500 95ft-lbs
3500 120ft-lbs
4500 200ft-lbs
5500 220ft-lbs
6500 220ft-lbs
7500 225ft-lbs
8500 225ft-lbs
9500 225ft-lbs
10500 216ft-lbs
For those following along, plot these number out on graph paper and submit your thoughts on the resulting curve. Depending on how I mix the two chargers, I can get more total torque but it won't be as nice as smooth as the one above.
Smooth n/a style with a nice bump at 3.5k. Lots of boost for low numbers. Small cc engine?
Yes, a puny 77 cubic inch displacement. The ramp up at 3500 should be exhilirating and depending on the gearbox, it can happen right at 50kph in 4th and 85kph in 5th; exactly where you want it on the street.
Certainly an intriging project which I do hope goes well but Im afraid you will struggle to get a 1270cc motor to spin enough air to get 430+whp
.I think adding a turbo to a superharged engine has a lot more issues than the other way around.
With the second you have the power just filling the lag with a supercharger , this doesnt mean major engine changes. You are plugging a gap and this wont affect the top end so the engine will be strong enough
the norris example used earlier was a turbo car to start with

Fitting a turbo to a supercharged engine is different -Doubling the power top end means you will get far more heat (not a good thing) , You may need to lower the compression ratio and or strenghten the engine.
Also I dont know the engine but will the head actually flow more than twice the air as at present because a turbo physically needs the aiflow to spool up before producing power - If it wont/cant do this Im afraid the idea wont physically work.

So I would suggestyou will need bigger valves , different cams and maybe a forged motor ( if yours is alraedy forged then that is sorted) And a completely programable ECU - LInk ,haltech motc etc.

Ps this post is meant to be constructive .
@Dr. Acula
I've tried looking up interviews with Abarth and Martini to hear what they did in the S4 but found little useful information. What source do you have that would help me?

As you correctly point out, the heads will be restrictive but I think I can overcome that with an airbox/buffer and pressure regulation. It's a direct injection engine so I will have good ignition control. I have an innovative way to intercool that might also keep the air temps down and air density high. The stock aluminum engine block should be able to handle the 250ft-lbs of max torque and because it's so small it'll be easier to cool. The S/C will create the airflow to start the turbo in the low revs and fade out just as the T/C ramps up. The critical area is in the 2500-5000 band where both chargers are boosting. If I can sort that out the rest should be pie. Like I stated earlier, it looks good on paper but all the best plans of mice and men...

The DIG-T-R managed to get 283ft-lbs out of this block with a larger bore, does anyone know what they did in the head?
Last edited:
i cant fault your optomism which is great,
The principle is fine but few cars successfuly sort twin charging - the ones that do are usually either built from scratch with twin charging in mind or are turbocharged cars already producing the power.
This is why fitting a turbo to any engine often requires a fair amount of engine work This will still be the case.
Twin charging by adding a turbo also means you are restricted by the engines physical constraints - in this case the small capacity and a restricted head (for the new power you are aiming for)
If these are not sorted you cant flow the air you need regardless of what else you do with intercoolers and induction.
But good luck.
Nothing worth doing is without challenges 8^)
An interesting tidbit about the HR12DDR, it uses variable expansion. This will add anothe level of complexity to this project but will also provide more options in tuning the engine. As per your comments about the max head flow, I'm sure you are well aware that the force of air pressure increases flow. I'm planning on 36 lbs of pressure from an airbox/buffer, what size aperture will I need to make 450hp?

Similar threads

Please watch this on my YouTube channel & Subscribe.