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Re: Turbocharging for economy
[Re: gdonovan]
#1085068
10/03/11 06:39 PM
10/03/11 06:39 PM
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Joined: Jan 2003
Posts: 24,562
Brookeville, Md
Mr.Yuck
Not enough dumb comments...yet
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Not enough dumb comments...yet
Joined: Jan 2003
Posts: 24,562
Brookeville, Md
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Quote:
Quote:
boost is boost doesn't matter how it's made.
If I may, you are showing an appalling lack of knowledge regarding turbochargers. Not all boost is created equal, I'm sure several members of the board would be more than happy to point that out.
Superchargers are directly run of the crankshaft, turbochargers are run off exhaust flow. I can hold the throttle at one point and go up a hill and the car would be very happy to go from vacuum to boost just due to the increased load on the engine.
Turbos are NOT superchargers aside from the fact they make positive pressure.
I have owned over a dozen turbocharged vehicles and have worked on thousands of customers cars. Turbo and supercharged.
A s/c will also go into boost up a hill or if you need to mash it to pass. Are turbos not regualted by engine vacuum? They do not always make boost at all rpms. You are right I'm pretty much a novice at this but I'll stand by what I said a 440 turbo'd car is not going to create any boost at highway speeds under zero load...it will not have any effect on the mpg of the vehicle in question. If anything it will make his milage worse because when the boost starts it WILL dump more gas, or it better. And once you go boost it's hard to keep your foot off the go pedal.
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Re: Turbocharging for economy
[Re: Mr.Yuck]
#1085069
10/03/11 07:43 PM
10/03/11 07:43 PM
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Joined: Jun 2008
Posts: 10,847
Oakdale CT
gdonovan
I Live Here
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I Live Here
Joined: Jun 2008
Posts: 10,847
Oakdale CT
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Quote:
You are right I'm pretty much a novice at this but I'll stand by what I said a 440 turbo'd car is not going to create any boost at highway speeds under zero load..
At highway speeds you are going to be under some sort of load short of coasting down a hill.
zero load and highway speeds are mutually exclusive as it takes "x" amount of power to run at speed mph due to mass and frontal area.
My Reliant takes 50 more hp to cut through the air at 140 mph compared to a Charger just due to frontal area alone.
As I already pointed out, some cars will make boost just off idle and gave an example. SRT-4's are notorious for it.
Most turbochargers are regulated by boost pressure- Most waste gates don't open till target boost levels are/almost achieved. Minimum boost on my Daytona was 12 psi, maximum was 30 (all of it setting)
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Re: Turbocharging for economy
[Re: gdonovan]
#1085070
10/04/11 12:05 PM
10/04/11 12:05 PM
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Joined: Nov 2006
Posts: 2,255
IL
furious70
top fuel
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top fuel
Joined: Nov 2006
Posts: 2,255
IL
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trying to tie SC and turbo behavior together is a faulty exercise. Without delving into anything technical to explain it, it can be visibly seen in this example:
Pace a loaded semi up a big hill on the freeway and listen. He won't downshift, maybe won't even move his accelerator pedal or pick up the rpms but as his engine works against the load of the hill and the exhaust temps rise, you'll hear his turbo spool more and more. A SC is never going to do that.
My point is that my experience with my turbos cars (only 1/2 dozen old turbo dodges and now my TT383 in the fury) is that it takes a big hill in order to go into boost. It is pretty easy to get my Fury from cruise @ 20" vac to 'preboost' @10" vac and start to hear the turbos spool up, but I don't go into actual boost unless jab the throttle.
70 Sport Fury
68 Charger
69 Coronet
72 RR
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Re: Turbocharging for economy
[Re: furious70]
#1085071
10/04/11 01:42 PM
10/04/11 01:42 PM
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Joined: Jan 2003
Posts: 24,562
Brookeville, Md
Mr.Yuck
Not enough dumb comments...yet
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Not enough dumb comments...yet
Joined: Jan 2003
Posts: 24,562
Brookeville, Md
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Quote:
trying to tie SC and turbo behavior together is a faulty exercise. Without delving into anything technical to explain it, it can be visibly seen in this example:
Pace a loaded semi up a big hill on the freeway and listen. He won't downshift, maybe won't even move his accelerator pedal or pick up the rpms but as his engine works against the load of the hill and the exhaust temps rise, you'll hear his turbo spool more and more. A SC is never going to do that.
My point is that my experience with my turbos cars (only 1/2 dozen old turbo dodges and now my TT383 in the fury) is that it takes a big hill in order to go into boost. It is pretty easy to get my Fury from cruise @ 20" vac to 'preboost' @10" vac and start to hear the turbos spool up, but I don't go into actual boost unless jab the throttle.
ok so how is that different from what I said? "I don't go into actual boost unless jab the throttle" That's the same thing I said. The car won't go into boost until it's under load. Hearing a turbo "spool up" isn't the same as creating boost. Just as the S/C is pushing air because the pulley is being turned, the air is not pushing into the intake at that time. As one lays into the gas or the engine starts to feel load the boost begins to build.
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Re: Turbocharging for economy
[Re: furious70]
#1085075
10/04/11 07:20 PM
10/04/11 07:20 PM
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Joined: Aug 2011
Posts: 96
Southern USA
TN_Michael
member
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member
Joined: Aug 2011
Posts: 96
Southern USA
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Quote:
Quote:
my CTD gets 24 mpg @ 65 MPH with 2-5 pounds of boost
Don't bring a diesel into the conversation or everyone will get confused 
Diesels do not have a throttle blade and therefore don't pull vacuum. Your CTD will also build boost going downhill with your foot off the accelerator. A gas engine will never do that. Diesels also have a very wide range of operable air to fuel ratios, running as lean as 50:1 at idle.
my bad
my diesel truck gets more milage than my gas truck even with out boost  
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Re: Turbocharging for economy
[Re: TN_Michael]
#1085076
10/04/11 09:57 PM
10/04/11 09:57 PM
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Joined: Jan 2003
Posts: 28,067
Irving, TX
feets
Senior Management
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Senior Management
Joined: Jan 2003
Posts: 28,067
Irving, TX
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Leave the Cummins out of this. Mine behaves the same as yours.
Now, back to gassers...
My hot rod has turbos that most people consider too small for a 440. They will light up and start making boost pretty low. Running 65 mph means pulling 2500 rpm. It does that with 18" of vacuum at 13% throttle according to my EFI datalogs. A slight bit of throttle (opening to 20%) to go around a truck will build 2 to 3 psi boost. At 75 mph the engine is turning about 2800 rpm and is pulling nicely for such a low throttle input.
At cruise, I don't see any boost until I'm over 90 mph. At that point the engine is turning 3500 rpm and is starting to work. It is probably the load on the engine that makes the boost. The engine will hold 3500 rpm without boost in 2nd gear.
I don't remember my 85 or 86 Shelby Chargers running in boost at a cruise unless I was treating the speed limit as a paltry suggestion.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon
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Re: Turbocharging for economy
[Re: feets]
#1085077
10/05/11 05:51 AM
10/05/11 05:51 AM
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Joined: Jun 2008
Posts: 10,847
Oakdale CT
gdonovan
I Live Here
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I Live Here
Joined: Jun 2008
Posts: 10,847
Oakdale CT
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Quote:
It is probably the load on the engine that makes the boost.
Your engine is turning a LOT of rpm at highway speeds and yes, turbos LOVE load just like the top fuelers. I kept lowering the rear transaxle ratio and the car just kept going faster and quicker.
Reliant runs a 2.50 final drive ratio and loafs through the lights at 5200-5300.
Daytona was 3.85 but it had overdrive at cruise, off the top of my fuzzy head, 2500 rpm while going 65 sounds about right.
Feets was your Shelby Charger with stock or near stock exhaust? Chrysler used the cat & exhaust to limit the turbocharger, Daytona had a 3" system.
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Re: Turbocharging for economy
[Re: Twostick]
#1085081
10/06/11 11:55 AM
10/06/11 11:55 AM
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Joined: Jan 2003
Posts: 28,067
Irving, TX
feets
Senior Management
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Senior Management
Joined: Jan 2003
Posts: 28,067
Irving, TX
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I'm very familiar with that. Again, I've been playing with turbos off and on since 1990. I've tinkered with them constantly for the last decade.
You should feel the air moving with a pair of hybrids on a 440. It's a substantial amount of air but the engine still pulls a strong vacuum until it's under load.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon
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Re: Turbocharging for economy
[Re: feets]
#1085082
10/06/11 12:54 PM
10/06/11 12:54 PM
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Joined: Nov 2006
Posts: 2,255
IL
furious70
top fuel
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top fuel
Joined: Nov 2006
Posts: 2,255
IL
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Can we explore that a bit more? Yes, the turbos are spinning and moving the air, but if there is a vacuum that means the engine is still doing the work of sucking the air through the throttle opening and valves. How does one quantify the benefit. 'Ram air' at WOT is one thing, but what you're suggesting is that ram air has a real effect on the engine at partial throttle/vacuum conditions.
70 Sport Fury
68 Charger
69 Coronet
72 RR
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Re: Turbocharging for economy
[Re: furious70]
#1085083
10/06/11 01:10 PM
10/06/11 01:10 PM
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Joined: Jan 2003
Posts: 28,067
Irving, TX
feets
Senior Management
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Senior Management
Joined: Jan 2003
Posts: 28,067
Irving, TX
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The turbos are moving air at idle.
The engine is moving air at idle.
What volume of air each is moving is open for discussion.
Somebody else can do the math on how much air a 440 moves at 900 rpm. I'm a bit busy today.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon
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Re: Turbocharging for economy
[Re: Twostick]
#1085084
10/06/11 11:24 PM
10/06/11 11:24 PM
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Joined: Jan 2005
Posts: 2,540
Milwaukee WI
TRENDZ
master
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master
Joined: Jan 2005
Posts: 2,540
Milwaukee WI
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Quote:
Picture it this way... if the engine is running, the exhaust turbine is turning which means the compressor is also turning. If that is turning, it is moving air. This is the key, the air is ALREADY moving when it comes into the engine. It doesn't have to go into boost to affect efficiency. Anything that will increase velocity even slightly in the manifold can give better fuel distribution cylinder to cylinder which will make the engine more efficient which could equal better mileage.
Kevin
There are so many flaws in this I don't know where to start. First, yes the turbine is spinning. Why? Because of the restriction in the exhaust flow. That in itself is a give and take in fuel economy. The give.....a restriction means less airflow through the engine. Less airflow means less fuel, except,(here's the take) the "in cylinder" mixture gets tainted from the restriction, and weakens the combustion process.
There is also parasitic loss. There is no way to spin anything without expending energy. The energy in this case comes from the fuel.
Turbos and superchargers don't speed up airflow. They increase density. There is a throttle plate between the compressor and the intake manifold on most gas engines. The throttle plate plays a big role in manifold density. At idle and light cruise there is a vacuum in the manifold. The less vacuum, the higher the load on the engine. More load(more air) equals more fuel.
Bottom line is a turbo is an energy exchanger, a machine. You can't convert energy forms without a loss. You wont get more out than you put in.
A turbo can make an engine more powerful, but not without more fuel. The only thing that a turbo is intended to do is add air to an engine. If you add air, you need to add fuel. Adding fuel is not the path to economy.
"use it 'till it breaks, replace as needed"
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Re: Turbocharging for economy
[Re: TRENDZ]
#1085085
10/07/11 03:14 AM
10/07/11 03:14 AM
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Joined: Jan 2003
Posts: 8,180
Detroit, MI
CokeBottleKid
master
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master
Joined: Jan 2003
Posts: 8,180
Detroit, MI
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Quote:
I gotta dis-agree with you, Feets. You will never see bsfc numbers in the .4s with any turbo engine(with the exception of direct injected engines). It's not all that uncommon to see .45 in a well thought out n/a engine.
The myth of economy with a turbo engine comes from, as previously stated, a smaller engine that is capable of making the hp of a larger engine. If you were to use that smaller engine in boost all the time though, you would be no further ahead in economy. It's the time out of boost with a smaller engine that you see your gains in economy.
Listen to this man people, he knows what he's talking about.
There's no such thing as turbocharged economy for spark ignition engines. The only way it pans out is as Trendz mentioned, you match its output to a larger N/A engine and compare BSFC under light loads (4 cylinder turbo to 8 cylinder N/A for example). It only pans out because the larger engines have more friction and pumping losses.
There are a multi-tude of things you get dinged for in efficiency on a turbo engine.
1. You run less compression: we all know compression = power, but it also SIGNIFICANTLY impacts efficiency, in fact it's one of the largest and most well documented players in efficiency. More compression = more efficiency
2. You run less timing: while under light load (vacuum or low boost) the timing is the same-ish as an N/A engine, when under heavy load (high boost) timing is retarded 10-30 degrees easily, obviously having large impact on efficiency.
3. You run way rich: again while not under boost or under low boost maybe at stoich (14.7:1), but under heavy boost EASILY 10 to 11.5:1. You can't burn more fuel than air so that extra fuel is just going out the exhaust.
Plus all the other things Trendz covered such as exhaust restrictions etc.
So in short, if you want to build an economical v8, build a high compression N/A motor with low friction (think smallblock).
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Re: Turbocharging for economy
[Re: TRENDZ]
#1085086
10/07/11 06:22 AM
10/07/11 06:22 AM
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Joined: Jun 2008
Posts: 10,847
Oakdale CT
gdonovan
I Live Here
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I Live Here
Joined: Jun 2008
Posts: 10,847
Oakdale CT
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Quote:
There is no way to spin anything without expending energy. The energy in this case comes from the fuel.
Turbochargers are recovering some of lost heat energy in the exhaust stream, unlike a supercharger which is stealing it off the front of the crank.
One reason why turbos will always make more power than a supercharger.
Top fuel teams were working on turbocharging at one time because the supercharger load was calculated to be as high as 500hp off the front of the crank!
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Re: Turbocharging for economy
[Re: CokeBottleKid]
#1085087
10/07/11 06:42 AM
10/07/11 06:42 AM
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Joined: Jun 2008
Posts: 10,847
Oakdale CT
gdonovan
I Live Here
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I Live Here
Joined: Jun 2008
Posts: 10,847
Oakdale CT
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Quote:
1. You run less compression: we all know compression = power, but it also SIGNIFICANTLY impacts efficiency, in fact it's one of the largest and most well documented players in efficiency. More compression = more efficiency
Actually, filling the cylinders with boost increases the effective compression ratio.
Quote:
2. You run less timing: while under light load (vacuum or low boost) the timing is the same-ish as an N/A engine, when under heavy load (high boost) timing is retarded 10-30 degrees easily, obviously having large impact on efficiency.
If you are actually in high boost your looking to make power and fuel economy is clearly a non-issue at this point. A large naturally aspirated engine at WOT making the same power under the same conditions will also have poor economy too.
Quote:
3. You run way rich: again while not under boost or under low boost maybe at stoich (14.7:1), but under heavy boost EASILY 10 to 11.5:1. You can't burn more fuel than air so that extra fuel is just going out the exhaust.
The same applies to any naturally aspirated engine under WOT.
I have run small engines and big engines, I did what I'm told can't be done (towed with turbo 4 engine for 50,000 miles!) and if I had a choice I'd take a well built small displacement engine that was turbocharged.
Excellent mpg and more power is just the flick of a switch away.
My turbocharged 4 got better mpg while towing a car than my current truck gets empty.
That's real world.
The other thing you have to calculate is, is it worth it?
Slapping a turbo on an existing package isn't going to magically get you better mpg or car makers would be all over it. And how long do you have to drive the thing before you make your money back from the mpg savings to just payoff the turbo setup?
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