Slant Six Forum :: Turbo or Blown???

A certifical supercharger takes as much power to turn wither it is exhaust driven or belt driven.
More or less true, but the parasitic loss of the centrifugal is always less than the turbo because of the turbo's pumping loss from exhaust pressure.

Quote:

I don't know the answer, but I would not believe that statement as gospel, without numbers to back it up. There is HP lost due to back perssure, with the turbo, but it takes HP to turn a belt/chain/gear drive centifiical supercharger. There ain't no free lunch.

Mitch, I was impressed by the article you wrote and thanks for posting. I am confused about one thing though. I was under the impression that Turbos were driven by exhaust FLOW (and pressure), not HEAT. Heat is just a by-product of the flow process. And the temperature drop after the turbine? Where does all that heat go? This makes no sense. Are we pumping this heat into the engine? What is causing the turbine to give up it's heat?

Quote:

Just looking at it from the perspective of simple physics it's obvious that there is a pressure differential across the turbine propellers. The gasses on the engine side are under pressure but the pressure is relieved on the outlet side; lower pressure results in lower temperature. There is actually a formula for it but I don't remember what it is.

Author:	valiantfreak [ Thu Mar 23, 2006 4:09 am ]
Post subject:	Turbo or Blown???
So tell me guys, which is the way to go for big HP gains.....Turbo or Blown? Money is no object.....

Author:	Dart270 [ Thu Mar 23, 2006 4:22 am ]
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Turbo will get you more ultimate HP. A few people are making over 500HP with 12-17psi boost. Most likely Cameron Tilley will make over 600 crank HP with a few upgrades to his motor. Super might be easier to fab though, and there is apparently a kit available for around $3500 that includes all parts and brackets for a centrifugal blower system. Search recent "engine" posts for "supercharger". Lou

Author:	kesteb [ Fri Mar 24, 2006 8:31 pm ]
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Boost is boost. The engine dosen't care what is making that boost. A certifical supercharger takes as much power to turn wither it is exhaust driven or belt driven. A roots style supercharger takes more power to turn, but make its power in the lower rpm ranges. What are you trying to accomplish?

Author:	panic [ Sat Mar 25, 2006 9:15 am ]
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The engine dosen't care what is making that boost. No, the turbo backpressure (about 2 psi per 1 psi of manifold boost) has a major effect on breathing, cam design, etc. A certifical supercharger takes as much power to turn wither it is exhaust driven or belt driven. More or less true, but the parasitic loss of the centrifugal is always less than the turbo because of the turbo's pumping loss from exhaust pressure.

Author:	panic [ Sat Mar 25, 2006 9:17 am ]
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Money is no object? If you want serious attention paid to your question don't say things like that. If it's true, why are you asking us? Have your entire car air-freighted to Gale Banks along with $50,000.

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Author:	Charrlie_S [ Sat Mar 25, 2006 9:46 am ]
Post subject:
Quote: A certifical supercharger takes as much power to turn wither it is exhaust driven or belt driven. More or less true, but the parasitic loss of the centrifugal is always less than the turbo because of the turbo's pumping loss from exhaust pressure. I don't know the answer, but I would not believe that statement as gospel, without numbers to back it up. There is HP lost due to back perssure, with the turbo, but it takes HP to turn a belt/chain/gear drive centifiical supercharger. There ain't no free lunch.

Author:	valiantfreak [ Sat Mar 25, 2006 6:04 pm ]
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Money is no object? If you want serious attention paid to your question don't say things like that. If it's true, why are you asking us? Have your entire car air-freighted to Gale Banks along with $50,000. -Panic, I do want my question taken seriously. And I will make statements like that. What you can't take seriously is your silly statement about shiping my car to Gale Banks with $50,000. What I meant by that is that I am considering building a wicked slant with some type of forced induction. Money doesn't scare me, so my focus is impressive HP that will spank those idiotic Mustangs and Cameros, all done with 1/2 a Hemi. I think everyone on this site would love to see that. Sure you could go with a supercharged big block and get 1000 HP. That's not what I want.....I want a head turner and something fun. The whoel thing that sparked my post was that I recently saw an ad for a blower kit for the slant, and wondered which was better. Hope this clears some things up....And thanks to everyone for giving their 2 cents!

Author:	kesteb [ Sat Mar 25, 2006 7:28 pm ]
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Quote: A certifical supercharger takes as much power to turn wither it is exhaust driven or belt driven. More or less true, but the parasitic loss of the centrifugal is always less than the turbo because of the turbo's pumping loss from exhaust pressure. Maybe, I have read the studies made during the '30s and '40s when the NCSA was testing supercharged engines for military airplanes. Those studies showed that how the certifigual supercharger was turned didn't make any differance. Peak power, rate of climb, etc, was the same wither the supercharger was turned by the crank or by exhaust pressure. The conclusion was it didn't matter which was used, what mattered was the packaging for a given airframe.

Author:	MitchB [ Sat Mar 25, 2006 10:04 pm ]
Post subject:
Quote: Quote: A certifical supercharger takes as much power to turn wither it is exhaust driven or belt driven. More or less true, but the parasitic loss of the centrifugal is always less than the turbo because of the turbo's pumping loss from exhaust pressure. I don't know the answer, but I would not believe that statement as gospel, without numbers to back it up. There is HP lost due to back perssure, with the turbo, but it takes HP to turn a belt/chain/gear drive centifiical supercharger. There ain't no free lunch. I have seen many, many board discussions about turbo systems and there is a lot of misleading information swimming around on the net. With regard to forced induction, any crank driven supercharger will draw a huge amount of power to move air into an engine. I have spoken with engineers who have done research in this area. Let's use the Ford 5.0 as a model. In stock form, it takea approximately 80 crankshaft horsepower to make 500 rear wheel horse power. Factoring in drivetrain losses, let's say you have make 575 crank HP in order to see 500 at the wheels. What this really means is you must make 575 + 80 or 655 crankshaft HP to see 500 at the wheels. You don't see the power consumed by a supercharger. You only see the what the dyno tells you. But you DO see this when you look at things like brake specific HP - which is a function of how much fuel you are putting into the engine. Let's look at turbocharging. There are many ways to build a turbo system. The key point you MUST remember is a turbocharger uses heat energy to do work. A well designed turbo system will place the turbo as close to the exhaust ports as possible. This is where the maximum amount of heat is available. Measure the temperature right before and after the turbine. You will see a 300 - 400 temperature drop. Turbos are driven by heat energy. This is in a well designed system. Most aftermarket systems run a lot of plumbing between the heads and the turbo(s) due mainly to the difficulty in designing and casting manifolds that will fit in the car and not cost a fortune in a limited production run. What happens as you move the turbos away from the exhaust ports? You use more and more of the engine's pumping action to drive the turbos. When you do this, you kill the turbo's efficiency because it takes proportionately more power to drive a turbo via pumping losses as compared to driving it with heat. Going back to our Ford model, with a stock 5.0 running 10 lbs of manifold pressure running two correctly sized turbos hung right off the heads making 500 RWHP, the exhaust backpressure between the port and the turbine should be no higher than a few psi. Run a setup that places a single turbo mounted remotely with a ton of plumbing between it and the heads and you will have very high exhaust backpressures. Spool speeds will be lower, BSFC will be much lower and the engine will make less power. To crutch such designs that do not use heat efficiently and use excessive backpressure, you have to run wierd camshaft designs with much greater intake duration compared to exhaust. The key is to design a system that puts maximum heat into the turbos. The way to do this is is with a system that uses the shortest possible path from the exhaust port. Many years ago when the were in the preliminary stages of design for their street turbo systems, Porche ran tests to measure the parasitic loss in their turbo systems. This was corroborated with turbo manufacturers. Their data indicated that the system design they were testing at the time had an efficiency in the range of 82 percent. Compare this to the Ford that uses 80 HP to make roughly 250 HP. That gives an efficiency of 30 to 40 percent at best. One engineer I spoke with working for a well known turbochager manufacturer actually used an electric motor to measure how much power was required to drive a commonly used supercharger at power levels needed to move a measured amount of air at boost levels typically seen on Ford 5.0s. At 700 HP, on average you will consume 175 HP to drive a centrifugal supercharger. Mitch

Author:	valiantfreak [ Sun Mar 26, 2006 1:04 am ]
Post subject:
Mitch, I was impressed by the article you wrote and thanks for posting. I am confused about one thing though. I was under the impression that Turbos were driven by exhaust FLOW (and pressure), not HEAT. Heat is just a by-product of the flow process. And the temperature drop after the turbine? Where does all that heat go? This makes no sense. Are we pumping this heat into the engine? What is causing the turbine to give up it's heat?

Author:	grthigpen [ Sun Mar 26, 2006 4:53 am ]
Post subject:
good writeup

Author:	dakight [ Sun Mar 26, 2006 5:28 am ]
Post subject:
Quote: Mitch, I was impressed by the article you wrote and thanks for posting. I am confused about one thing though. I was under the impression that Turbos were driven by exhaust FLOW (and pressure), not HEAT. Heat is just a by-product of the flow process. And the temperature drop after the turbine? Where does all that heat go? This makes no sense. Are we pumping this heat into the engine? What is causing the turbine to give up it's heat? Just looking at it from the perspective of simple physics it's obvious that there is a pressure differential across the turbine propellers. The gasses on the engine side are under pressure but the pressure is relieved on the outlet side; lower pressure results in lower temperature. There is actually a formula for it but I don't remember what it is.

Author:	MitchB [ Sun Mar 26, 2006 6:23 am ]
Post subject:
Quote: Mitch, I was impressed by the article you wrote and thanks for posting. I am confused about one thing though. I was under the impression that Turbos were driven by exhaust FLOW (and pressure), not HEAT. Heat is just a by-product of the flow process. And the temperature drop after the turbine? Where does all that heat go? This makes no sense. Are we pumping this heat into the engine? What is causing the turbine to give up it's heat? Heat is a form of energy. Turbos use the heat energy in the exhaust to perform the work of compressing air. The temperature drop across the turbine is a measure of how much heat the turbo is using to convert to work. Some heat is transferred into the air the turbo is compressing into the engine, but this is incidental. Most of the heat energy is converted into work. Mitch

Author:	MitchB [ Sun Mar 26, 2006 6:32 am ]
Post subject:
Quote: Quote: Mitch, I was impressed by the article you wrote and thanks for posting. I am confused about one thing though. I was under the impression that Turbos were driven by exhaust FLOW (and pressure), not HEAT. Heat is just a by-product of the flow process. And the temperature drop after the turbine? Where does all that heat go? This makes no sense. Are we pumping this heat into the engine? What is causing the turbine to give up it's heat? Just looking at it from the perspective of simple physics it's obvious that there is a pressure differential across the turbine propellers. The gasses on the engine side are under pressure but the pressure is relieved on the outlet side; lower pressure results in lower temperature. There is actually a formula for it but I don't remember what it is. This does not account for the amount of work performed by a turbo. Heat is a form of energy. A turbo uses this energy to perform the work of compressing air into the engine. In a well designed system, most of the energy used by a turbo comes from the heat in the exhaust, not by the pressure differential caused by the pumping action of the engine. In fact, the pressure differential accross the turbine should be minimal. As you compromise the system design, the pumping action becomes more of a factor. When you start using pumping action, turbo efficiency starts to go way down. Mitch

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Author:	panic [ Sun Mar 26, 2006 2:38 pm ]
Post subject:
Yes, the amount of power used off the crank to turn a Vortech is wasted and exceeds the power loss in pumping effort by a turbo. My point was that a turbo is not "free power". Sorry if your fantasy is dampened by my adverse reaction to "Money is no object", but no, I don't take anyone seriously who says things like that. After 40+ years doing this, the source of such a comment is generally someone who: 1. has no money 2. never spent any money 3. this is their first project 4. has no idea whatever what things cost You can say anything you want, just without my interest.