Theoretical turbo question

I have a question about turbos that I never found an answer I was satisfied with. We used to have an old fiat that was just a junker used for general hooning purposes. I told my uncle who is a heavy truck mechanic that I would like to install a turbo from a diesel pickup on it. He said the little 2.0 liter would never move enough air to spool it up. I said that a 2.0 at 6000 rpm should move the same amount of air as a 6.0 liter at 2000 rpm(which is where a diesel lives), he said it wouldn't work. I understand there are variables like volumetric effiency, but theoretically I think my hypothesis about the airflow should be correct. What do you guys think?

a 1000cc sportbike that revs to 11,000 rpm will max out a gt2552 before a 1.6L Miata will. Compression ratio still needs to be accounted for in either case, turbo diesels do run a much higher compression then their gas counterparts and sport bikes run quite high compression for NA gas motors

Yes, with 100% VE, a 2.0L at 6K moves the same air as a 6.0L at 2K. 2K is probably only 2/3 of the way to redline on that diesel, though, whereas I suspect the Fiat would be close to topped out, if so then it's still too big. The diesel is also likely operating it at a higher pressure ratio than you would want to run it on a gas engine.

I'd recommend reading up on compressor maps, Garrett has a reasonable introduction on their site.

http://www.turbobygarrett.com/turbobygarrett/compressor_maps

captdownshift wrote: a 1000cc sportbike that revs to 11,000 rpm will max out a gt2552 before a 1.6L Miata will. Compression ratio still needs to be accounted for in either case, turbo diesels do run a much higher compression then their gas counterparts and sport bikes run quite high compression for NA gas motors

Yep, IDK how it works exactly either, but all I know is the turbo on the 998cc raptor is pretty big. I don't start building boost until 7-8k rpms and tops out low boost at 7psi around 11k. Redline is 14500rpm on it with a 12.7:1 compression ratio.

I just like to say "doesn't matter, made boost"

Swank Force could probably answer this question though. IDK of many diesels that are building much boost at 2k rpms though...

My 6.0 powerstroke can make 20psi at 2k rpms.

yamaha wrote:

captdownshift wrote: a 1000cc sportbike that revs to 11,000 rpm will max out a gt2552 before a 1.6L Miata will. Compression ratio still needs to be accounted for in either case, turbo diesels do run a much higher compression then their gas counterparts and sport bikes run quite high compression for NA gas motors

Yep, IDK how it works exactly either, but all I know is the turbo on the 998cc raptor is pretty big. I don't start building boost until 7-8k rpms and tops out low boost at 7psi around 11k. Redline is 14500rpm on it with a 12.7:1 compression ratio. I just like to say "doesn't matter, made boost" Swank Force could probably answer this question though. IDK of many diesels that are building much boost at 2k rpms though...

Besides like.. all of them? You slippin, Paul?

To keep this sickeningly simple, it's all about flow. OP could probably use his equation as a real rough rule of thumb.

The 2554 on a bike vs. 1.6 miata thing... depends on what you mean by "maxed out." The turbo will only flow so much (power), doesn't matter what motor it's on. It'll max out that flow number with lower pressure though. Because bike motor.

Fun fact: I run a MKiii Supra Turbo on the MX6. I run twice the pressure that's safe for the turbo on a 7mgte, because my motor doesn't flow worth a damn. HOWEVER, i also spool it way harder and earlier than a 7mgte does as well, despite being less displacement.

gearheadmb wrote: I have a question about turbos that I never found an answer I was satisfied with. We used to have an old fiat that was just a junker used for general hooning purposes. I told my uncle who is a heavy truck mechanic that I would like to install a turbo from a diesel pickup on it. He said the little 2.0 liter would never move enough air to spool it up. I said that a 2.0 at 6000 rpm should move the same amount of air as a 6.0 liter at 2000 rpm(which is where a diesel lives), he said it wouldn't work. I understand there are variables like volumetric effiency, but theoretically I think my hypothesis about the airflow should be correct. What do you guys think?

Sound guideline rule, but the big issue will be driveability. Thats where a better comp and turbine map come into play.

DaveEstey wrote: My 6.0 powerstroke can make 20psi at 2k rpms.

That is true, I was referencing steady state like an idiot....DOH

For what it's worth my 2.0L 4g63 Turbo engine makes about 550whp on a Holset HX35 turbo. This is the turbo pushing 32psi at peak. So short answer is yes, a 2.0L can move plenty of air to spool a turbo... even a big one.

Main advantage with a diesel turbo (like my holset) is diesel exhaust is less dense than gasoline exhaust. As a result diesel turbos are designed for with a more aggressive (i.e. faster spooling) impeller. Now move that turbo on a gasoline engine and you have one hell of a combination.

On another note I am building currently a 1.6L triumph engine with a small GT17 on it. Im pretty sure you can turbo charge anything...

550whp dyno video: https://www.youtube.com/watch?v=jdPleq23pws -sorry for the poor quality.

There are a lot of smart people on this board. Thanks guys.

The Holset example is pretty much picture perfect for the question you asked. Dodge put Holset turbos on 5.9L diesels for 15+ years and the internet is LOADED with examples of people putting those turbos on ~2.0L engines. Caveat: they can't spool them before 4k rpm. Most of them rev to 7+, though.

Eh, we spool hx35s pretty quick. But... that's a diesel based engine so.... I dunno?

F2t s are not powered ny logic. Theyre powered by the shattered dreams of ricers

The more displacement and the earlier the VE peak, the faster it will spool a turbo. An F2T would probably spool an HX35 earlier than something like an f20 even if it went on to make half the power.

Turbos initial spin comes from the movement of air. The power comes from the enthalpy, which is not only gas velocity but the heat energy in the exhaust as well. Your air velocity equation theory is correct, but you are leaving out the heat in the exhaust. If the heat isn't there, the turbo won't produce the boost you are looking for.

How and why does the compression ratio of the engine and exhaust heat effect the output of the turbo?

Ok, here. The greater the displacement and the better the low rpm VE, the more fuel the engine will be able to turn into heat at low rpms.

Honestly, this is a rabbit hole i'd rather not go down because i think even formally trained engineers have a pretty E36 M3ty average when it comes down to explaining how turbos work. When it comes down to it, the only thing that will cause air movement is pressure differential. You can have movement without heat and still spin a turbo. You cannot have heat without movement and still spin a turbo. The engine runs off heat. You could say the turbo runs off heat because it runs off the engine, but that would be misleading. The turbo runs off air movement generated by heat.

More heat = more energy = more magic = more spinny spinny = more go faster

Swank Force One wrote: More heat = more energy = more magic = more spinny spinny = more go faster

WHOA WHOA WHOA, take it easy on the technical jargon there Bill Nye. ;)

http://130.83.195.220/publications/paper_110914_SAE_COMVEC_2011-01-2214_nakhjiri.pdf That paper explains all the different losses etc inside a turbo.

Just remember they are just a pump and work on flow not pressure. Pressure is a bi product of moving flow through a small space. (think finger over the end of a garden hose).

Also, Because they are driven off a common shaft, whatever work you put into the turbine you MUST get out of the compressor.

Vigo wrote: Ok, here. The greater the displacement and the better the low rpm VE, the more fuel the engine will be able to turn into heat at low rpms. Honestly, this is a rabbit hole i'd rather not go down because i think even formally trained engineers have a pretty E36 M3ty average when it comes down to explaining how turbos work. When it comes down to it, the only thing that will cause air movement is pressure differential. You can have movement without heat and still spin a turbo. You cannot have heat without movement and still spin a turbo. The engine runs off heat. You could say the turbo runs off heat because it runs off the engine, but that would be misleading. The turbo runs off air movement generated by heat.

The easy, and perhaps technically incorrect, anwser is a turbocharger is more efficient the hotter it is in that the conservation of heat energy is greater.

There are a million variables when it comes to turbocharging and without discussing a specific engine we will circle around ad infinitum.

I would recommend finding a good explanation on AR ratios and the different kinds of turbos. You really can turbocharge anything.

Also, a note on the Holset. The damn things are indestructible. The turbos were designed to go 300,000+ miles on a diesel truck. They also are only oil cooled which eliminates the need for coolant lines (Some people run Garrett style turbos without coolant lines, but that is a whole different story). There are also slightly smaller Holset turbos in the family like the HX30 and the H1C which if you are doing a smaller engine might be a better choice.

In regard to my build, I see positive boost pressure by 3000 rpms and full boost (32psi) by 3900 rpms. Pretty amazing for a turbo that size. Not to mention the lack of power down low (Still 200+ Hp) is not a concern because I would prefer not to rebuild my transmission and drive line every year...

This was always clear to me:

First Law of Thermodynamics

The first law of thermodynamics states that, as a system undergoes a change of state, energy may cross the boundary as either heat or work, and each may be positive or negative. The net change in the energy of the system will be equal to the net energy that crosses the boundary of the system, which may change in the form of internal energy, kinetic energy, or potential energy. The first law of thermodynamics can be summarized in the equation:

is the change in internal energy (This is enthalpy)

is the change in kinetic energy (this is velocity of the air, with the exception of a smaller inlet than the outlet, this stays close to the same as the inlet speed, with the exception of a small amount of compression between the compressor wheel and the engine. This is why there is more lag in rear bumper mounted turbos and why turbos like no mufflers. This is very close to zero.)

is the change in potential energy (it ain't getting ready to jump off a cliff so this is zero)

is the work done by the system during the process (This is the side that compresses the intake side)

All that being said, what does the work? Enthalpy. So that equation boils down to.

=

It's the heat, not the movement of the air, where the turbo makes most it's power.

This is also why turbos get so hot. It really is cool when you think about it.

NordicSaab wrote: ... On another note I am building currently a 1.6L triumph engine with a small GT17 on it. Im pretty sure you can turbo charge anything... ...

Can you post more details ?

Lots of people put diesel turbos in their cars. It's just that it might be super laggy on an old 2.0l.

Like a SR20DET with it's more modern design with a turbo has a lot less lag than an older 2.0.

If it's like a HX35 putting that on a 2.0l would be lag city. That would probably work well with like a 300ZX engine though.

erohslc wrote:

NordicSaab wrote: ... On another note I am building currently a 1.6L triumph engine with a small GT17 on it. Im pretty sure you can turbo charge anything... ...

Can you post more details ?

I posted this on the challenge thread but I can post it here too.

http://www.youtube.com/watch?v=ac0GvY2FVWs

It is 1 of the twin turbos from a 3000gt vr4. Nothing crazy. Welded to stock exhaust. Hacked up volvo turbo charge pipe. No intercooler. I sounds like a cat in a blender. Come see it at the challenge.