Would it be stupid to twin charge a skyline? Would that be possible/practical to do on an rb engine?

[RA708]

I know nothing about car mechanics or anything I'm just curious. My simple monkey brain wants to hear a stutututututu and weeeeeeeeeee on the same thing. Some people on other forums have said it's pointless and to just use a twin turbo setup which is definitely a thing in skylines.

 

Could someone explain to me the benefit of having something twin charged vs twin turbo-ed?

[MBS206]

If you want the screaming "weeeee" sound, just let the gasket between the exhaust manifold and the turbo break a little. It'll go "weeeeeeeeeeeeeeeeeeeeeee" everytime its on boost...

[RA708]

28 minutes ago, MBS206 said:

If you want the screaming "weeeee" sound, just let the gasket between the exhaust manifold and the turbo break a little. It'll go "weeeeeeeeeeeeeeeeeeeeeee" everytime its on boost...

Looked it up. It sounds so expensive lmao

I'd rather not. Awwwww but I just love that sound

[GTSBoy]

Yes, it is entirely possible to twincharge a Skyline. It is not....without problems though.

There was a guy did it to an SOHC RB30 (and I think maybe it became or already was a 25/30) in a VL Commode. It was a monster. The idea is that you can run both compressors at relatively low pressure ratios, yet still end up with a quite large total pressure ratio because they multiply, not add, boost levels. So, if the blower is spun to give a 1.4:1 PR (ie, it would make ~40 kPa of boost on its own) and the turbo is set up to give a 1.4:1 PR also, then you don't get 40+40 = 80 kPa of boost, you get 1.4*1.4, which is pretty close to 100 kPa of boost. It's free real estate! This only gets better as the PRs increase. If both are set up to yield about 1.7 PR, which is only about 70 kPa or 10ish psi of boost each, you actually end up with about 1.9 bar of boost!

So, inevitably it was a bit of a monster. The blower is set up as the 2nd compressor, closest to the motor, because it is a positive displacement unit, so to get the benefit of putting it in series with another compressor, it has to go second. If you put it first, it has to be bigger, because it will be breathing air at atmospheric pressure. The turbo's compressor ends up needing to be a lot larger than you'd expect, and optimised to be efficient at large mass flows and low PRs. The turbo's exhaust side needs to be quite relaxed, because it's not trying to provide the power to produce all the boost, and it has to handle ALL the exhaust flow. I think you need a much bigger wastegate than you might expect. Certainly bigger than for an engine just making the same power level turbo only.

The blower effectively multiplies the base engine size. So if you put a 1.7 PR blower on a 2.5L Skyline, it's like turboing a 4.2L engine. Easy to make massive power.

Plus, because the engine is blown, the blower makes boost before the turbo can even think about making boost, so it's like having that 4.2L engine all the way from idle. Fattens the torque delivery up massively.

But, there are downsides. The first is trying to work out how to size the turbo according to the above.

The second is that you pretty much have to give up on aircon. There's not enough space to mount everything you need. You might be able to go elec power steering pump, hidden away somewhere. but it would still be a struggle to get both the AC and the blower on the same side of the engine.

Then, you have to ponder whether you want to truly intercool the thing. Ideally you would put a cooler between the turbo and the blower, so as to drop the heat out of it and gain even more benefit from the blower's positive displacement nature. But that would really need to be a water to air core, because you're never going to find enough room to run 2 sets of boost pipes out to air to air cores in the front of the car. But you still need to aftercool after the blower, because both these compressors will add a lot of heat, and you wil have the same temperature (more or less) as if you produced all that boost with a single stage, and no one in their right mind would try to run a petrol engine on high boost without a cooler (unless not using petrol, which we shall ignore for the moment).

I'm of the opinnion that 2x water to air cores in the bay and 2x HXs out the front is probably the only sensible way to avoid wasting a lot of room trying to fit in long runs of boost pipe. But the struggle to locate everything in the limited space available would still be a pretty bad optimisation problem. If it was an OEM, they'd throw 20 engineers at it for a year and let them test out 30 ideas before deciding on the best layout. And they'd have the freedom to develop bespoke castings and the like, for manifolds, housings, connecting pipes to/from compressors and cores. A single person in a garage can either have one shot at it and live with the result, or spend 5 years trying to get it right.

[RA708]

25 minutes ago, GTSBoy said:

A single person in a garage can either have one shot at it and live with the result, or spend 5 years trying to get it right.

So it's a ginormous undertaking that will be a massive headache but will be sorta cool if pulled off right. And also expensive. I'm sure it'll be as expensive as buying the car itself. I don't think you could just do this build without upgrading other things to take the extra power. Probably lots of custom stuff as well.

All this assuming the person has mechanical knowledge. I'm stupid enough to try it but smart enough to realize there's gonna be mistakes even with an experienced mechanic. I'm a young bloke on minimum wage that gets dopamine from air being moved around and got his knowledge from a Donut video on how engines work.]

 

Thanks for the response though super informative!

[MBS206]

1 hour ago, RA708 said:

So it's a ginormous undertaking that will be a massive headache but will be sorta cool if pulled off right. And also expensive. I'm sure it'll be as expensive as buying the car itself. I don't think you could just do this build without upgrading other things to take the extra power. Probably lots of custom stuff as well.

All this assuming the person has mechanical knowledge. I'm stupid enough to try it but smart enough to realize there's gonna be mistakes even with an experienced mechanic. I'm a young bloke on minimum wage that gets dopamine from air being moved around and got his knowledge from a Donut video on how engines work.]

 

Thanks for the response though super informative!

Getting the setup right, is likely to cost multiples of the purchase price of the vehicle.

[RA708]

58 minutes ago, MBS206 said:

Getting the setup right, is likely to cost multiples of the purchase price of the vehicle.

Yep super expensive, awesome. It would be a cool passion project if I had the money.

[joshuaho96]

3 hours ago, RA708 said:

Yep super expensive, awesome. It would be a cool passion project if I had the money.

It's a fun daydream but personally just looking at OEM implementations of twincharged engines like the recent Volvo engines it makes my head hurt. So, so much complexity compared to even other GDI turbo inline 4s. 

[RA708]

6 hours ago, joshuaho96 said:

It's a fun daydream but personally just looking at OEM implementations of twincharged engines like the recent Volvo engines it makes my head hurt. So, so much complexity compared to even other GDI turbo inline 4s. 

Another thing I would do if I was studying mechanical engineering

 

Eh if I won the lotto I’d do it. Otherwise yeah just a day dream.

[RA708]

On 4/5/2025 at 6:52 PM, GTSBoy said:

Yes, it is entirely possible to twincharge a Skyline. It is not....without problems though.

Here’s a follow up question, what if you add a super charger to an already turned engine like a rb25det or something. Would the systems in place (inter coolers and exhaust manifold) be a good way to lessen time and head ache? Or would it be more annoying to add a supercharger to the turbo-ed system then designing a new system entirely?

[GTSBoy]

21 minutes ago, RA708 said:

Here’s a follow up question, what if you add a super charger to an already turned engine like a rb25det or something. Would the systems in place (inter coolers and exhaust manifold) be a good way to lessen time and head ache? Or would it be more annoying to add a supercharger to the turbo-ed system then designing a new system entirely?

There is no difference. The existing turbo and intercooler would very most likely not be suitable for reuse. The existing tune would be meaningless. The issues with fitting things in are exactly the same.

[Dose Pipe Sutututu]

23 hours ago, RA708 said:

Eh if I won the lotto I’d buy a 911 GT3 RS, a  RS6 and a M5

I would too.

[MBS206]

1 hour ago, Dose Pipe Sutututu said:

I would too.

AMG GT R, and R8 is what I'd replace RS6 and M5 with.

[Ozdavroz]

Twincharging to me is either for Xtreme car builders who want to make something unique, or for manufacturers who want to keep the service and spare parts sides of their businesses profitable. 

My lotto dream car garage is to buy 2 of every 90's japanese performance car, keep one stock and tune the other one. Probably need a bigger backyard too

[Dose Pipe Sutututu]

And probably your own distillery to make ethanol lol.

[GTSBoy]

1 hour ago, Ozdavroz said:

buy 2 of every 90's japanese performance car

Yeah. A long time ago someone hassled me to buy a raffle ticket where first prize was a Mitsu 3000GT. He was most up[set when I asked if 2nd prize was 2 of them.

[MBS206]

7 hours ago, Dose Pipe Sutututu said:

And probably your own distillery to make ethanol lol.

You totally couldn't have that many cars running on Ethanol. You'd be employing two full time mechanics just to keep going through the vehicles, flushing old fuel out, and possibly changing anything the ethanol has eaten between the months it would be between drives.

[Ozdavroz]

9 hours ago, Dose Pipe Sutututu said:

And probably your own distillery to make ethanol

more like convert my house into a facility to produce methamphetamines, to pay for all the over night parts from Japan I'll need to maintain them. Saturday night lotto only pays out so much for division 1