Interesting read about turbo power requirements

[Frank I]

Originally Posted by Dave@ddmworks Everyone once in awhile we get asked about how much power the supercharger takes to operate vs. the "free energy" that a turbo uses. So, we came across this article that described the engine losses because of the turbo and how to estimate them. This is not "supercharger propoganda" and I am not knocking turbos here, as we like them also , just wanted to throw out some information for everyone. "Myth 1: The energy it takes to spin a turbocharger is free. I love turbochargers as much as anybody, but if I had a nickel for every person that incorrectly claims the energy to drive a turbocharger is "free" I would be a rich man. The turbocharger's drive system is more mechanically efficient than the belt on a supercharger but it's not free. The most basic laws of physics say that nothing is free. Some people have changed the terminology to say that the turbo is driven by "wasted energy". That's more nonsense. The energy needed to expel the exhaust from the combustion chamber is not wasted, in fact it's rather essential. Many makers of Turbo kits phrase it another clever way. They say that the energy needed to drive the turbo is "not taken directly from the crankshaft like it is with a belt driven supercharger". Ok, well at least that's basically true although somewhat misleading. It may not be taken "directly from the crankshaft" but it is taken from the engine. So how is the energy taken, and how much is used? Here are the facts as reported in many N.A.C.A. reports. Exhaust drives the turbocharger and that causes exhaust backpressure robbing power as surely as if the compressor section was connected to a belt. It may not rob as much (it's possible under some conditions it will rob more) but it does rob power. Here is a quote from N.A.C.A. " When an exhaust turbosupercharger is used, the net engine power is the total engine power supercharged less the reduction in power due to increased exhaust back pressure." So there you have it, turbos cause exhaust back pressure taking power away from the motor. The report goes on to say just how much the loss from exhaust back pressure is going to cost and I assure you it's not free. If it was, then all the efforts made in the performance industry to reduce backpressure via special mufflers, headers etc. would be wasted. So just how much power will the turbo consume? They compiled a ton of data on that. It will vary somewhat from motor to motor, even between two theoretically identical motors. The number they came up with is 6.2% of total engine horsepower when using 10 pounds of boost. That's assuming exhaust pressure in the manifold between the combustion chamber and the turbine is equal to intake manifold pressure. It's imporant to understand, that's a best case scenario. A turbo car will need very good unrestrictive equal length exhaust manifolds and a perfectly sized turbocharger to achieve this. I suspect the best manifolds made for race cars by masters like Jim Steck or the mad South Africans are good enough to get these results. In practice when limited by engine compartment space, strength requirements and other factors it's not likely you will find a manifold this good on a street Alfa. Many turbo cars have double the intake pressure in the exhaust manifold prior to the turbine. At 10 pounds of boost that would cost about 15.3% of the engine's horsepower using N.A.C.A.'s formula. Time to plug in some real world numbers. A MP62 supercharger providing 10 pounds of boost on an Alfa 2.5 will use about 27 horsepower. It could potentially use less with optimal piping, but on my car it uses 27 horsepower so that's real world data. My car has about 250 flywheel horsepower so using N.A.C.A.'s formula a very efficient turbo set up would need 15.5 horsepower to drive the turbo. While there is no doubt that 15.5 is less than 27, it's a factor that's small enough to be offset in other areas. Now using the same formula a turbo with a restrictive type of exhaust manifold will use 38.25 horsepower. My point here is not to say that belt driven superchargers are better or worse. The point is that according to the best engineers in the U.S. at the time working with a nearly unlimited wartime budget determined that the energy to spin a turbocharger is not free. I am sure the brainwashed free energy crowd will state that these reports are old and turbos have come a long way. Of course if free energy was used to spin a turbo then it wouldn't matter how much they improved in this regard. An improvement of any percentage times zero is still zero. In other words if they are free now because they are twice as efficient as the older units the math says the older units must have been free to. " This is quoted from : Supercharger Kit Thanks! Dave

Dave:

Very good thread and I understand and agree with what you are saying.

However in all fairness, both forms of forced induction, supercharges and turbochargers are good but after extensive engineering and thermodynamic studies conducted over the past 70 years it all boils down to AN AIR PUMP ALWAYS HEATS AIR IT COMPRESSES. That is a thermodynamic law.

Air pumps are made of various different designs and will heat air at different amounts for the same flow rates and pressure ratios. The differences are due to the different efficiencies of various types of pumps. Roots-type superchargers are normally rated at about 50% efficiency and turbos normally are rated at about 75% efficiency.

As you know the higher the efficiency, the less the heating effect on the air. Efficiency is the key to real power since heat in the intake charge is the enemy of performance.

As you also know, the density of an intake charge is less as the temperature rises so an engine consumes less air at the higher temperature even if the pressures are the same. The other problem of course is the higher the temperature, the more likely the engine will eventually detonate. The one killer of forced induction engines is the thermal and pressure shocks of detonation.

As for your statement most people believe turbochargers give free power, well that is of course wishful thinking, turbochargers do draw power from the engine. However when comparing turbochargers to superchargers, you must keep in mind that the power output potential of any supercharger is measured by the amount of airflow the device creates after factoring out the power required to drive it and the extent to which it heats up the air while creating the flow and pressure. In most supercharger applications a belt is used to extract energy from the crank to operate the supercharger which usually run around 50% efficiency (as I stated above) while on a turbocharger heat and airflow are forced through the turbine section of the turbocharger which reduce the flow areas which create back pressure.

What most inexperienced novices do not comprehend is the smaller the turbocharger, the more power loss there is due to the smaller size which creates more back pressure. On the other hand, the larger turbos create less back pressure and therefore have less of a power loss.

What this basically boils down to is a turbocharger has an inherent design advantage over a supercharger that is belt driven. A turbocharger has less of a power loss and therefore is more efficient. However, it is not free power and is only around 75% efficient verses 50% for most of the better belt driven superchargers.

In either case, forced induction of either type is good, especially today with advancements in metallurgy, 5 axis CNC machining capability and electronics to control engine pressures, temperatures and speeds.

In closing, let me just say I had the opportunity to drive one of your supercharged cars and I was very impressed with the smoothness. You guys know your stuff and do excellent work but from an engineering and thermodynamic perspective, a turbocharger is more efficient and therefore is the reason it is used today by more manufacturers and more race teams when forced induction is allowed. Just my

Frank I

[elff]

Two atoms walk into a bar
The one turns to the other and says, "I think I lost an electron"
the other says "Are you sure?"
The first replies "I'm Positive"

[solsticeclampe]

Good read and a good sales tool too! given the fact that the Turbo takes a tinney bit more time to spool up giving me S/C fever even worse. I'm about to run out of warranty
and was trying to have all my ducks in a row & even fuel prices are cooperating. Boom!!
Thursday driving along-- Ext. Cab Loaded Silverado 102,000 miles Like New----Boom I loose Overdive. The rpm's went from 1.1 K to 3,000 @ 65 mph. I was nearly home so I was trying not to stop. I hit a couple lights and realized I had 1st gear which after hitting
high rpms would shift right to 3rd with no advance to 4th. Got home fine, but after parking, I realized I had no Reverse either. I new what it was but hooked up an OBDII
and the laptop to scan the PCM, I already had resolve though, No DTC's in the PCM or the ECU! Would have rather bought a new PCM/ECU from PCMforless, Thank you very much Revmann, ya I do enjoy what they did to my ECU. you were right, but that's just a taste!
Yes Ladies and gentlemen, Tuesday or Wednesday I'll be 1,999.00 poorer as the planetary for (all 3 gear location) reverse, 2nd and overdrive snapped like a twig.
4L60E w/overdrive. Amyway I'll regroup. I'm having the transmission bullet proofed
as I love my truck and it's the only thing I've ever had break on it.

[duckSol]

Originally Posted by Chemist Carnot's ... Now, I think turbochargers are great. I went with the supercharger that DDM offers becaus it had the _amount_ of power it had. The turbo systems provide a bit more than I am comfortable with. The S/C is for me, to quote Goldilocks, "just right."

To quote Sgt. Schultz, I know nothing, NOTHING!"

[carlintexas]

EVEN with the Custom Turbo System that DDM built for me - and let me tell you the dyno graph is nearly a straight line from 0 to 310whp.......no 'hard' turbo kick or lag.

Thank you to Dave and Randy for selecting the perfect equipment to make this happen!

There is still a difference in the 'Butt DYNO' between the turbo and the supercharger.

I don't know if a turbo @ 8 lbs boost produces more whp than a S/C at the same boost.....

I don't know if the air temp at the throttle body is less with one vs the other......

But I do know that at 0 to 60 an S/C will spank a turbo with equal whp (I would even say you could give the turbo an additional 25whp and the S/C would still cross the line first).

I would like to see the 0 to 60 times of two automatic transmission Sols - one S/C and the other a turbo with both producing 250whp (regardless of the lbs boost)!

I would be glad to bet on the S/C!

[Critterman]

And yet Carl, you drive a turbo, even though you had your chance

[bradyb]

lOl, nice obscure article from an Alfa Romeo forum?

I remember a 20% horsepower increase between a turbo bolt on kit and a bolt on supercharger kit running the same PSI.

Check this out, here's a quick comparison on a SS Trailblazer:
Magnacharger Radix Intercooled Supercharger running Seven PSI gains 120 HP/120'Ib Trq
STS Turbo Intercooled running Five PSI gains 150 HP/167' Ib Trq.

That is a fairly regular comparison, turbo makes more power running less PSI. A supercharger needs to run 3-4 PSI just to make up for the power it robs from the motor, a turbo is about 2 PSI. That 2 PSI power gain over the supercharger is where the turbo makes more power simply put.

Here's an old STS chart (STS Vs Magnuson, ProCharger)



An easy comparison, compare a 2.4L Supercharged vs a 2.4L turboed?

[Mr. Stone]

I don't need an article from DDM or an argument with anybody about turbos versus superchargers to justify my purchase. I got exactly what I wanted. There is more to a car and its performance than peak hp numbers.

[RevmanII]

Originally Posted by Mr. Stone I don't need an article from DDM or an argument with anybody about turbos versus superchargers to justify my purchase. I got exactly what I wanted. There is more to a car and its performance than peak hp numbers.

Amen ....

[duckSol]

Originally Posted by Mr. Stone I don't need an article from DDM or an argument with anybody about turbos versus superchargers to justify my purchase. I got exactly what I wanted. There is more to a car and its performance than peak hp numbers.

Originally Posted by RevmanII Amen ....

Hp is no good if the car can't be held on the road.
Some of us came from that era of "...where the rubber meets the road..."

[Chemist]

I am secure in my supercharg-ed-ness and am not threatened by those who prefer the turbo. The goals and the methods of S/C and turbo differ, so do opinions.

In this new era of American politics, can't we just be tolerant of others' preferences for forced induction?

[Dave@ddmworks]

Originally Posted by bradyb lOl, nice obscure article from an Alfa Romeo forum? I remember a 20% horsepower increase between a turbo bolt on kit and a bolt on supercharger kit running the same PSI. Check this out, here's a quick comparison on a SS Trailblazer: Magnacharger Radix Intercooled Supercharger running Seven PSI gains 120 HP/120'Ib Trq STS Turbo Intercooled running Five PSI gains 150 HP/167' Ib Trq. That is a fairly regular comparison, turbo makes more power running less PSI. A supercharger needs to run 3-4 PSI just to make up for the power it robs from the motor, a turbo is about 2 PSI. That 2 PSI power gain over the supercharger is where the turbo makes more power simply put. Here's an old STS chart (STS Vs Magnuson, ProCharger) An easy comparison, compare a 2.4L Supercharged vs a 2.4L turboed?

Once again, I do want to reiterate that this was not started as a Turbo vs. Supercharger thread, just to point out that there is no "Free energy" or such thing as "wasted energy" that is used to spin up a turbo. Although BTF is right that if you have a large enough turbo and a great manifold design you can get that exhaust restriction to be pretty low, kind of like the old Porsches. However with such a design low end response is drastically reduced.

The fact is that there is still a restriction on the exhaust side of the engine with a turbo that will never allow the engine to evacuate the cylinders as well as it could if the turbo was not there. A supercharged or naturally aspirated engine with proper headers will always do a better job.

As for supercharged vs. turbo 2.4L Ecotecs at the same pressure ratios, we have done that already - Hahn's turbo kit at 8psi according to their dyno on their website at STD correction and smoothing of 5 makes 245HP and 250 ft/lbs of torque, Our supercharger kit at 8psi with STD correction and 5 smoothing makes 245 HP and 254 ft/lbs of torque. This is the real happy area for our supercharger for adiabatic efficiency, as we see much better (up to 66%) than the "50%" number that the old superchargers used to have. Even the turbo in Hahn's kit is not that much better peaking at 71% adiabatic efficiency according to Mitsubishi's own chart and it falls below 60% efficiency also. The difference in temperature rise, pre-intercooler at 71% vs. 66% is 4 degrees. The difference post intercooler depends on the efficiency of the intercooler, and so far we have the best intercooler available

However, peak horsepower numbers are not the best comparison as far as what is better for your particular driving style and this is where people usually choose if they want a turbo or a supercharger. As we have seen our non-intercooled supercharger kits that put 195HP at the wheels run with factory GXP cars that are putting out 220 HP at the wheels run the same time at the drag strip over and over. Power under the curve is also important. Turbos can usually push higher pressure ratios more efficiently and so if you are looking at making more than 12psi, the turbos are a better choice (right now), at the cost of throttle response. Positive displacement superchargers will usually have the best throttle response and more power under the curve, at the cost of not being able to push high pressure ratios (ultimate power).

To summarize: Both systems take power to compress the air. One takes it from the belt, one takes it from the exhaust, the only similarity is that both set-ups are more fun than stock

[duckSol]

My back hurts, I need to stick to riding a Big Wheel instead of a BEEEUICK!

[oldskool]

Just my two cents here, but if you choose the correct turbo for the horsepower goal you have in mind (or for the supercharged comparison you wish to make), the turbo should rob less horsepower than the s/c. Anyone who believes in "free energy" is naive at best and retarded at worst.

You cannot compare boost pressures on two different turbos, much less on a turbo vs supercharger. The supercharger will vary boost with a temperature change because of how it works (fixed airflow per pulley diameter), while the turbo will maintain a constant psi as per the wastegate or MBC setting. To make a more scientifically sound comparion, two of the same engine at the same horsepower level need to be compared, not the same boost pressure.

That said, BOOST ROCKS!! Who cares how you get it or where you get it, JUST GET IT

[solsticeclampe]

Originally Posted by carlintexas EVEN with the Custom Turbo System that DDM built for me - and let me tell you the dyno graph is nearly a straight line from 0 to 310whp.......no 'hard' turbo kick or lag. Thank you to Dave and Randy for selecting the perfect equipment to make this happen! There is still a difference in the 'Butt DYNO' between the turbo and the supercharger. I don't know if a turbo @ 8 lbs boost produces more whp than a S/C at the same boost..... I don't know if the air temp at the throttle body is less with one vs the other...... But I do know that at 0 to 60 an S/C will spank a turbo with equal whp (I would even say you could give the turbo an additional 25whp and the S/C would still cross the line first). I would like to see the 0 to 60 times of two automatic transmission Sols - one S/C and the other a turbo with both producing 250whp (regardless of the lbs boost)! I would be glad to bet on the S/C!

I'ts gonna be a DDM S/C for me! Thanks for that highly informative narritive, though I must say your engine compartment is Wicked Awesome!