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Re: Turbocharging for economy
[Re: gdonovan]
#1085088
10/07/11 09:33 AM
10/07/11 09:33 AM
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Joined: Feb 2003
Posts: 4,953
Houston, Texas
TheOtherDodge
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master
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Posts: 4,953
Houston, Texas
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Talking about a 600 hp application: IMO the biggest benefit in a turbo application is the ability to run a much more numerically lower gear than a N/A motor.  Also, I don't think an N/A motor with a fairly healthy cam is going to be as efficient at lower speeds than a relatively "stock" cam that a turbo uses. Finally, a stock type converter can be used vs a higher stall of an NA application.
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Re: Turbocharging for economy
[Re: CokeBottleKid]
#1085090
10/07/11 09:04 PM
10/07/11 09:04 PM
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Joined: Dec 2006
Posts: 3,533
Indiana
Fury Fan
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master
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Posts: 3,533
Indiana
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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.
Actually, this is not as cut-dry as that. I hope I can explain it accurately...
Ignition advance is required because the mixture does not explode instantaneousy @ spark, but rather as a controlled burn that takes time. As we don't want it burning much after TDC, we must start earlier so that we have complete combustion for the start of the power stroke. More timing is needed as RPM increases becuase there is less time available for the burn event (which still requires about the same amount of time, in comparison).
The flame front travels faster from droplet-to-droplet in a denser or more homogeneous mixture (I believe this is an accurate statement).
So, the more efficient a cylinder head (think turbulence, swirl, quench) or the more boost you have, the less timing is needed, as the mixture is more homogeneous, and gives better flame travel. that does not necessarily mean the burn is less effective.
Excessive timing lead causes pressure to build on the piston while it is travelling upward on the compression stroke - reducing efficiency.
To summarize:
I don't think we can really compare timing #s between NA and boosted engines as relating to efficiency.
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Re: Turbocharging for economy
[Re: Twostick]
#1085093
10/08/11 04:23 PM
10/08/11 04:23 PM
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Joined: Jan 2005
Posts: 2,540
Milwaukee WI
TRENDZ
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Posts: 2,540
Milwaukee WI
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No. An engine's manifold pressure/vacuum indicates load. If you apply the same load, you get the same vacuum, no matter how much pressure is in front of the throttle blade. You're working the equation from the wrong angle. Manifold pressure is resultant. You cruise at say 65mph. At 65mph, your engine may make 12" of vacuum on a flat road, 20" down hill and 4" up a hill. You aren't after a vacuum number, you're after 65mph, and the throttle plate is what you change to achieve that goal. Your example assumes the throttle plate is in a fixed position. If it were, the denser air would pass the throttle plate and speed up the engine. Cruise speed would go up,as would fuel consumption.
"use it 'till it breaks, replace as needed"
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Re: Turbocharging for economy
[Re: TRENDZ]
#1085094
10/08/11 09:30 PM
10/08/11 09:30 PM
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Joined: May 2003
Posts: 6,563
Downtown Roebuck Ont
Twostick
Still wishing...
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Still wishing...
Joined: May 2003
Posts: 6,563
Downtown Roebuck Ont
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I agree with most of your explanation for manifold pressure but I'm pretty sure you have still made my point. (I think  )If the pressure above the blade has no bearing then at our given 65 mph level road load, the blade angle will still be the same as NA or effectively fixed. The denser air will in fact go around the blade but it won't be carrying any more fuel than it would NA because a carb meters fuel based on air volume not air density and the mix will be slightly leaner. Kind of like the difference between 2500' DA and say -500' DA with it jetted for 2500'. Would you agree that if you could cruise steady state at a -500 DA while jetted for a higher DA that there would be the potential for a slight increase in fuel efficiency? And just to be clear, when I say I think a boosted engine can be more fuel efficient than the same engine NA I'm talking single digit % increase. Kevin
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Re: Turbocharging for economy
[Re: Twostick]
#1085095
10/08/11 10:49 PM
10/08/11 10:49 PM
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Joined: Jan 2003
Posts: 8,166
Plymouth, MI
Blusmbl
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Joined: Jan 2003
Posts: 8,166
Plymouth, MI
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Quote:
And just to be clear, when I say I think a boosted engine can be more fuel efficient than the same engine NA I'm talking single digit % increase.
With your version explained you're "cheating" by not having the same tailpipe air/fuel ratio.
It would only potentially make a difference at higher loads, it would definitely not be true from an overall perspective. You could run a speed/load map of an n/a engine and the same engine with a turbo added, and there may be a small number of points where the turbo engine is more efficient because it could make a higher torque value at a given engine speed, but it would most likely be at higher loads, if any at all. Adding the turbo alone is going to decrease fuel economy, between the weight added to the vehicle and the increased pumping losses with the turbo in the exhaust stream.
I would not be adding a turbo to a motor thinking fuel economy would improve. Fun factor, yes. Fuel consumption, no.
'18 Ford Raptor, random motorcycles, 1968 Plymouth Fury III - 11.37 @ 118
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Re: Turbocharging for economy
[Re: TRENDZ]
#1085098
10/09/11 02:23 AM
10/09/11 02:23 AM
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Joined: May 2003
Posts: 6,563
Downtown Roebuck Ont
Twostick
Still wishing...
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Still wishing...
Joined: May 2003
Posts: 6,563
Downtown Roebuck Ont
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Quote:
Quote:
I agree with most of your explanation for manifold pressure but I'm pretty sure you have still made my point. (I think )If the pressure above the blade has no bearing then at our given 65 mph level road load, the blade angle will still be the same as NA or effectively fixed. The denser air will in fact go around the blade but it won't be carrying any more fuel than it would NA because a carb meters fuel based on air volume not air density and the mix will be slightly leaner. Kind of like the difference between 2500' DA and say -500' DA with it jetted for 2500'. Would you agree that if you could cruise steady state at a -500 DA while jetted for a higher DA that there would be the potential for a slight increase in fuel efficiency?
I come from a fuel injected world, where more air in equals more fuel in.
So, you're saying that this hypothetical engine's vacuum changes because it's getting more air, yet your explaination says," A carb meters fuel based on air volume.... My question is, where is the extra air in the engine coming from if a larger volume of air is not going through the carb? Do you think density has no bearing on a venturi? Do you think a carb's throttle angle is directly proportionate to fuel flow? Would you tune your carb to run richer than needed in one spot so you could make it run correct in another and expect a more fuel efficient engine? How about making it run clean everywhere? Your explaination seems to indicate it cant be done.
If density had a bearing on a venturi, you wouldn't have to jet a carb up for "good" air.
With all due respect an EFI setup has very little in common with a carb so to answer your question if I tuned a carb for max cruise fuel mileage it would be a given that it might not perform as well at WOT. That's the beauty of EFI, you can optimize for all loads or throttle positions. With a carb you can get it dead nuts for a VERY narrow range. Anything outside that at best will just be sorta close.
Kevin
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Re: Turbocharging for economy
[Re: Blusmbl]
#1085100
10/09/11 09:15 AM
10/09/11 09:15 AM
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Joined: Jun 2008
Posts: 10,847
Oakdale CT
gdonovan
I Live Here
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I Live Here
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Posts: 10,847
Oakdale CT
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Quote:
Adding the turbo alone is going to decrease fuel economy, between the weight added to the vehicle and the increased pumping losses with the turbo in the exhaust stream.
All one has to do is compare factory engines that are mostly the same aside from turbo setups.
Chrysler had both in 1989- An N/A 2.5 and a turbocharged 2.5.
For all intents and purposes the main differences between the two is a touch more static compression with the N/A motor, the N/A motor has a cam with slightly more overlap. Even though the turbomotor has a far superior intake setup (MPI vs craptastic TBI) the N/A motor was well noted for its better MPG.
21-36 mpg for the N/A motor, 18-26 mpg for the turbo. These numbers are from the Federal MPG website with the same vehicle with manual transmissions.
You are not going to get better mpg slapping on a turbo without reduction of displacement, period.
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Re: Turbocharging for economy
[Re: gdonovan]
#1085101
10/09/11 10:51 AM
10/09/11 10:51 AM
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Joined: Feb 2003
Posts: 4,953
Houston, Texas
TheOtherDodge
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Houston, Texas
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"You are not going to get better mpg slapping on a turbo without reduction of displacement, period." Once again, unless we are talking about a stockish type motor with no stall and 3.23 gearing, I 100% disagree. Less converter, less gearing, = less rpm on the motor. Your example is from 1989 and not only is FI much better today than back then, you are talking about motors making no more than 225 hp. Does anyone ever wonder why all the new high hp production cars are forced induction?
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Re: Turbocharging for economy
[Re: TheOtherDodge]
#1085102
10/09/11 11:28 AM
10/09/11 11:28 AM
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Joined: Jun 2008
Posts: 10,847
Oakdale CT
gdonovan
I Live Here
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I Live Here
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Posts: 10,847
Oakdale CT
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Quote:
Your example is from 1989 and not only is FI much better today than back then, you are talking about motors making no more than 225 hp.
The fuel injection and intake on the 89 turbo motor is SIGNIFICANTLY better than the 89 non-turbo motor.
And yet the N/A motor gets better MPG.
The real world results speak for themselves.
This will only be compounded by modern technology, any improvement that can be applied to a forced inducted engine can be applied to a N/A engine as well.
Rpm isn't necessarily the killer of MPG (I have driven 1.8l Acuras that buzzed down the highway at much higher rates than a typical mopar and get good MPG)
Higher *load* on the motor = more fuel consumption.
Quote:
Does anyone ever wonder why all the new high hp production cars are forced induction?
Doh!
Perhaps because more power can't be extracted by N/A means due to running afoul of federal emissions.
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Re: Turbocharging for economy
[Re: TheOtherDodge]
#1085105
10/09/11 03:56 PM
10/09/11 03:56 PM
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Joined: Feb 2003
Posts: 4,953
Houston, Texas
TheOtherDodge
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Joined: Feb 2003
Posts: 4,953
Houston, Texas
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"Doh! Perhaps because more power can't be extracted by N/A means due to running afoul of federal emissions. " Really? I guess that big inch Viper didn't pass emissions? And you don't think driveability and mpg has no factor in the decision to go with forced induction? Ok. Not going to argue as we all have our own opinions. 
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Re: Turbocharging for economy
[Re: furious70]
#1085107
10/09/11 04:51 PM
10/09/11 04:51 PM
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Joined: May 2003
Posts: 6,563
Downtown Roebuck Ont
Twostick
Still wishing...
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Still wishing...
Joined: May 2003
Posts: 6,563
Downtown Roebuck Ont
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Quote:
Quote:
Well, you got me there. So the basic idea here is add a turbo, and as long as your fuel metering is wrong, you will increase your mileage.
and if we 'stumble' upon this little carb tuning secret, why wouldn't we apply it to the NA engine as well and be back to square 1? If we're gonna run the turbo engine leaner than it should be, why not do the same to the NA?
Been done already. It was called Leanburn. Good idea. Really bad execution.
Kevin
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