Selecting a turbocharger for the 300 six

[pmuller9]

One of the first things you often hear is about picking a turbocharger that will spool.
That is not the objective.
The main goal is to pick a turbocharger that is the correct size for the engine and its application.

An engine is an air pump that has a range of airflow from the beginning of its power band to the end of its power band.
The turbocharger's compressor is likewise an air pump that has a flow range from the surge line out to the choke line.

Most of the 300 sixes discussed on this forum are for street use in a truck that works best with a wide power band.
In order to achieve the widest power band with a turbocharger, the flow range of the turbocharger should be matched with the flow range of the engine.
Drag racing is an entirely different story.

The following calculator is the best there is and will be used for the rest of this discussion.

BorgWarner MatchBot

www.borgwarner.com

 

[pmuller9]

Before going any further we need to clarify "Airflow" and also look at "Pressure".

CFM by itself is not a complete measurement of airflow because air can be compressed.
It is CFM at a specific pressure and temperature that is a measurement of the amount of air (Oxygen and Nitrogen) that is being introduced into the engine.
For our purposes we will use the weight of the air per minute in lb/min as an airflow measure.

The engine is a positive displacement pump, so it determines the airflow in CFM.
For an example, a 300 six at 3000 rpm at 85% VE is pumping [(300 x 3000)/2 x .85]/1728 = 221 cfm.

At sea level with an absolute pressure of 14.7 psi and a standard temperature of 59 degrees F, a cubic foot of air weighs .0765 lbs.
The engine airflow by weight at sea level would be 221 cfm x .0765 = 16.9 lb/min

If you double the absolute pressure to the engine with a turbocharger and intercool the air temperature back down to 59 degrees, the airflow by weight would double to 16.9 x 2 = 33.8 lbs/min but the airflow by volume would still be 221 cfm.

Boost pressure is usually stated as a gauge pressure meaning the pressure above atmospheric pressure.
In our example the turbocharger would double the absolute pressure at sea level to 14.7 x 2 = 29.4 psi.
But we would use the gauge pressure and say the boost is at 29.4 - 14.7 or 14.7 psi.
In a different example we might say the boost pressure is 10 psi which is 10 + 14.7 = 24.7 psi absolute pressure at sea level.

A turbocharger is a pressure multiplier.
It takes whatever the atmospheric pressure is at the inlet and multiplies it by its pressure ratio.
If a turbocharger is operating at a pressure ratio of 2 at sea level the outlet pressure will be 14.7 x 2 = 29.4 psi absolute or 29.4 - 14.7 = 14.7psi gauge pressure.
If that same turbocharger is operating at Denver Colorado, the atmospheric pressure may be 12.2 so the outlet pressure at a pressure ratio of 2 = 24.4 psi or 24.4 - 14.7 = 9.7 psi gauge pressure.
The boost gauge will have dropped 5 psi from 14.7 down to 9.7 psi of boost.

In order for the wastegate to restore boost pressure of 14.7 psi, the turbocharger would be forced to operate at a higher pressure ratio which means it will be working harder at a higher rpm.
The new pressure ratio would be (12.2 + 14.7)/12.2 = 2.2

Having clarified Airflow and Pressure along with Pressure Ratios we have what we need to examine a turbochargers compressor map.

 

[pmuller9]

For a first look at a compressor map I chose a 300 six that has a peak torque of 310 ft lbs at 3000 rpm and a peak hp of 230 at 4500 rpm.
This can be done using a ported head with a roller cam with about a 212 degree .050" duration.
The 2000 rpm VE is 80%, the 3000 rpm peak torque VE is 85% and 4500 peak power VE is back down to 80%.

You can see the VE values in the calculator.
You can see the NA torque and power values in the calculator if you set the boost values to zero.

I have the intercooler efficiency set to 60%

If you look at the compressor map you will see the vertical represents the pressure ratio and the horizontal represents the airflow.
The corrected airflow on the map is shown as kg/s but the calculator gives you lb/min, kg/s and kg/hr.

The area to the left of the map is the Surge Zone.
The compressor will not pump if it is in that zone.
The rpm will increase the same as when you cover the end of a shop vac hose.

The area to the right of the compressor map is the Choke Zone where the efficiency is very low and the compressors rpm is greater than what it is designed for.

Just for an example we are going to say that we can have full boost from 2000 rpm to 5000 rpm.
At 10 lbs of boost the calculator shows a pressure ratio of 1.7 at 2000 rpm with a corrected airflow of .118 kg/s.
At 5000 rpm the pressure ratio is 1.74 with a corrected airflow of .277 kg/s
The bottom red load line represents 10 lbs of boost.
The middle load line represents 15 lbs of boost and the top load line for 20 lbs of boost

You will notice that the load lines for each boost level are nicely centered on the compressor map.
If the compressor is larger for this particular engine, the load lines will shift left towards the surge line and if the compressor is smaller the load lines will shift right towards the Choke line.

Take the time to play with the calculator and examine different size compressors along with changing the many other variables.
Click on "View Tutorials" at the bottom of the calculator page for additional help.

The thread is open for comments and questions.

 

[pmuller9]

Here is a good explanation of the turbine housing which is responsible for directing the exhaust gas energy to the turbine blades.

Turbo Tech: Turbine Housings 101

Have you ever asked yourself, “What’s the difference between T3, T4, T6, and V-band turbine housings”? Or maybe, “will a T25 inlet flange work on a T3 manifold”? Or, “what does T3 T4 mean?” If so this article is for you.

www.garrettmotion.com

If you want to spool a 300 six early for low rpm torque, a A/R around .63 is typical
If you want a good midrange to upper you would use an A/R around .83.
For racing where low rpm torque is not a consideration, you would look at an A/R of 1.00 or above.

The smaller A/R has a smaller volute which increases the gas velocity for a low rpm response but acts as a restriction at the upper end of the power band.

 

[pmuller9]

Reserved

 

[Walken100]

Ok, I can't increase pressure to 15 psi at 2000 RPM. The worksheet throws an error (turbine match not possible for point 1). Does this mean that the compressor isn't capable of the pressure at that rpm and is it benign? IE it will make what it makes until rpm increases and you bump up against the waste gate.

 

[jgregg13]

Thanks a bunch for doing this thread. I'm having fun plugging various scenarios into the calculator.

I'm thinking about so many that come here asking or proposing that they want an opinion on how best to get a moderate power gain. Usually the naturally aspirated approach, better intake, headers, cam and big valve head. And may want to go turbo down the road. My thought is if you want about 250 hp you can go with the previously mentioned NA modifications, or you can add a turbo to a basically stock EFI engine. When I say stock I mean stock cam, head, intake, and exhaust manifolds but better pistons and ARP fasteners. From the calculator, it looks like you'll get about 270 hp with 8 psi boost. It looks like the cost is pretty similar going either way. But with the turbo you can increase the boost as much as you dare to for more power. It appears that at 8 psi your getting more torque in the low rpm range than the NA modified engine,

In my calculator inputs, I used 70% VE for the stock EFI engine. Can you tell me what you think the VE would be? And would a stock engine have better VE at 1500 to 2000 rpm?

 

[Bronctopia]

For those wondering about the "topography" lines. They are in dimensionless units of "efficiency".
Why do we care about "efficiency"?
As Paul said, what turbines do is produce pressure.
In a gas (like air), pressure has a strict relationship it must follow.
PV=nRT.
We can rearrange this as:
P=R*T*n/V.
R we can ignore, as it is (mostly) a constant.
So. P=T * n/V.
n/V is air mass divided by volume.
Basically Density.
It is this extra air mass due to density that lets us burn more fuel in the cylinder.

The T is temperature. The more of this we have, the less density we have at any given pressure.
Worse, the more T we have, the closer we are to hitting the "detonation limit" in a spark ignition engine.

But what about aftercoolers? (intercooler is bad slang when you start playing with aero-engineer's charts!)
They can do some good (60% in Paul's example). But the real problem is where that T came from.
It came directly from work done by the turbine wheel. Where did that turbine wheel get the energy to DO that work?
If you guessed engine power, you are partially right. Some comes from the "free" expansion of exhaust gasses during blow down, but later in the stroke, it is coming from crankshaft power.

This becomes what is called a "vicious cycle" real quick, so the less heat-from-work that has to be tossed out the aftercooler, the better the performance.

 

[Walken100]

PV=nRT

I'm having "PiVniRT" flashbacks from school

 

[pmuller9]

Ok, I can't increase pressure to 15 psi at 2000 RPM. The worksheet throws an error (turbine match not possible for point 1). Does this mean that the compressor isn't capable of the pressure at that rpm and is it benign? IE it will make what it makes until rpm increases and you bump up against the waste gate.

This is not a compressor error. It is a turbine error.
It's saying that you do not have the correct turbine housing with the correct expansion ratio selected.

If you look at the 11th line down on the input sheet you will see the line labeled "Turbine Expansion Ratio"
Then look at the last graph labeled "Turbine Sizing Selector"

This turbocharger has a 70mm turbine wheel which is the 6th line up from the bottom on the Turbine Sizing Selector"graph.
Adjust all the turbine expansion inputs until all six dots line up on the 70mm .083 A/R line.

You can collapse all the graphs in between the two views you are working with to make it easier to see the changes as you go.

 

[pmuller9]

In my calculator inputs, I used 70% VE for the stock EFI engine. Can you tell me what you think the VE would be? And would a stock engine have better VE at 1500 to 2000 rpm?

The stock engine with a one barrel carb makes peak torque about 1800 rpm.
The stock EFI engine makes peak torque about 2000 rpm.
The stock shortblock with a 4 barrel carb and headers made peak torque at 2500 rpm.

If you turbocharger a stock engine, what will it have for an intake and exhaust system?
This will determine the base engine.

Using the Power Nation "Eye Popping" video, I went slightly less torque than what they were showing and used
68% @ 1500, 70% @ 2000, 72% @ 2500, 68% @ 3000, 65% @ 3500 and 60% @ 4000
This gave me about 435 ft lbs @ 2500 and 240 hp at 3500 using a 60% efficient intercooler with 12 lbs of boost

It looks like a 49mm turbocharger would cover it.

 

[jgregg13]

If you turbocharger a stock engine, what will it have for an intake and exhaust system?
This will determine the base engine.

Using the Power Nation "Eye Popping" video, I went slightly less torque than what they were showing and used
68% @ 1500, 70% @ 2000, 72% @ 2500, 68% @ 3000, 65% @ 3500 and 60% @ 4000
This gave me about 435 ft lbs @ 2500 and 240 hp at 3500 using a 60% efficient intercooler with 12 lbs of boost

For a "stock" engine, I'm thinking a 4.9 EFI with its original intake and exhaust manifolds. if a single turbo then a 3" down pipe all the way and no muffler. I'm using twin turbos mounted directly to the EFI manifolds with adapter plates and 2-1/2" down pipes with no mufflers. My turbos are KKK K14 units.

Your VE estimates look more reasonable to me. I'm thinking that with the long tube EFI intake the VE will be better in the 2500 rpm range and fall off more at higher rpm. I'm choosing an EFI engine because they're plentiful and cheap. I bought a doner truck that ran fine for $500, and it comes with a lot of what you need for fuel injection. In my case I'm using an Aussie intake drilled for injectors with a 5.0 throttle body, Lightning FJ760 injectors, GM 2bar MAP sensor and Microsqirt.

 

[pmuller9]

Play with the intercooler efficiencies and see how much it affects power.

 

[aussie7mains]

Get a twin screw blower, problem solved!

 

[pmuller9]

Get a twin screw blower, problem solved!

Lets look at that.

A 300 six would require at least a 2.0 liter supercharger.
Here in the USA, you have the following for twin screw superchargers in that range.
Eaton/Magnuson TVS 1900
Whipple/Lysholm W140AX
Kenne Bell 2100

Any one of these units complete with drive snouts are over $3000.
Add the belt drive with pulleys and an intake manifold and you are in the $4000 range.

A 4.9 EFI engine comes with an intake and exhaust system ready for turbocharging for low to medium power applications with boost.

The twin screw supercharger has maximum boost fixed by the pulley drive ratio.
The turbochargers maximum boost can be varied on the fly from 5 to 25 (or more) psi by the wastegate controller.

The supercharger adds extra wear on the front main bearing.

 

[Fingers]

Great thread...

Now my head hurts