biggest impacts on fuel consumption?
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biggest impacts on fuel consumption?
i know we're not too concerned with milage in our cars, especially those who spend more time at the track
but i'm interested what are the main characteristics that effect fuel consumption during part throttle/low rpm for a domestic engine
is it primarily displacement, port size, or (im guessing) valve overlap, or to a lesser extent the 'area under the curve' for valve events
if you're getting bad milage does that mean you're blowing lots of gas out the exhuast, or burning it very innificiently? seems to me if you're burning it then it should be making you go.... so i'm interested in what wastes it in hi-po cars
i find it interesting that some people here with freakish super stockers have similar highway milage to 2.0 four-bangers, and are able to get up and over th e 30mpg mark with ls1s
but i'm interested what are the main characteristics that effect fuel consumption during part throttle/low rpm for a domestic engine
is it primarily displacement, port size, or (im guessing) valve overlap, or to a lesser extent the 'area under the curve' for valve events
if you're getting bad milage does that mean you're blowing lots of gas out the exhuast, or burning it very innificiently? seems to me if you're burning it then it should be making you go.... so i'm interested in what wastes it in hi-po cars
i find it interesting that some people here with freakish super stockers have similar highway milage to 2.0 four-bangers, and are able to get up and over th e 30mpg mark with ls1s
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Joined: Jun 2003
Posts: 741
From: Orlando, FL
that depends on what speed i had to take na rental car back to florida one time and i drove my car 94 t/a stockand the camry 4 cylinder rental was driven by my friend i drove from ft stewart ga to daytona which is 225 miles we were driving 90 prettty much the whole way. i made it there and still has 1/4 tank left the camry we had to fill up once about 40 miles from daytona both have the same size tank also. the reason for this is because for that 4 cylinder to do 90 you have to give it gas probably at least half throttle but for the t/a to maintain that speed i just rested my foot on the gas. so to a certain point more power will give you better gas mileage on the highway than the 4bangers but not in the city.
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Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Re: biggest impacts on fuel consumption?
Originally posted by Jimmy17
i know we're not too concerned with milage in our cars, especially those who spend more time at the track
but i'm interested what are the main characteristics that effect fuel consumption during part throttle/low rpm for a domestic engine
is it primarily displacement, port size, or (im guessing) valve overlap, or to a lesser extent the 'area under the curve' for valve events
It's efficiency, or how much hp the engine gets from each bit of fuel at the rpm and throttle opening required to run a constant speed. BSFC (brake specific fuel consumption), usually measured in lbs of fuel per hp per hour, is usually spoken of for max power, but it's important for part throttle also.
Gearing is a biggie. If an M6 LS1 is only turning 1800 @70 mph, and an engine half the size needs to turn 3000 @ 70, the fuel used might not be all that different. The hp required in a given car doesn't change with what engine's up front.
On a long trip, Bret's '00SS M6 beats my Corvette A4 with 3.15 gear by a mile per gallon or so, mainly because his engine is turning about 350-400 rpm slower at 75-80 mph even though the Vette has less aero drag.
if you're getting bad milage does that mean you're blowing lots of gas out the exhuast, or burning it very innificiently? seems to me if you're burning it then it should be making you go.... so i'm interested in what wastes it in hi-po cars
i find it interesting that some people here with freakish super stockers have similar highway milage to 2.0 four-bangers, and are able to get up and over th e 30mpg mark with ls1s
It's low efficiency, as you said. Another good pointis that to pass someone with your big, torquey LS1 or LT1, you just nudge the throttle and you have about doubled the torque output. With the little 2L, you have to geve it a yard of pedal or even downshift to get enough grunt to pass. That sucks up fuel.
Big engines loafing along can be very fuel efficient, compared to little engies working their lungs out.
The part I like is when you want to go, downshift 2 or 3 gears, hit it and wave bye-bye to the 2L s-box. Yeah, there are some street driven 2L boxes that will take the LS1 SS, but not all that many around here.
My $.02
i know we're not too concerned with milage in our cars, especially those who spend more time at the track
but i'm interested what are the main characteristics that effect fuel consumption during part throttle/low rpm for a domestic engine
is it primarily displacement, port size, or (im guessing) valve overlap, or to a lesser extent the 'area under the curve' for valve events
It's efficiency, or how much hp the engine gets from each bit of fuel at the rpm and throttle opening required to run a constant speed. BSFC (brake specific fuel consumption), usually measured in lbs of fuel per hp per hour, is usually spoken of for max power, but it's important for part throttle also.
Gearing is a biggie. If an M6 LS1 is only turning 1800 @70 mph, and an engine half the size needs to turn 3000 @ 70, the fuel used might not be all that different. The hp required in a given car doesn't change with what engine's up front.
On a long trip, Bret's '00SS M6 beats my Corvette A4 with 3.15 gear by a mile per gallon or so, mainly because his engine is turning about 350-400 rpm slower at 75-80 mph even though the Vette has less aero drag.
if you're getting bad milage does that mean you're blowing lots of gas out the exhuast, or burning it very innificiently? seems to me if you're burning it then it should be making you go.... so i'm interested in what wastes it in hi-po cars
i find it interesting that some people here with freakish super stockers have similar highway milage to 2.0 four-bangers, and are able to get up and over th e 30mpg mark with ls1s
It's low efficiency, as you said. Another good pointis that to pass someone with your big, torquey LS1 or LT1, you just nudge the throttle and you have about doubled the torque output. With the little 2L, you have to geve it a yard of pedal or even downshift to get enough grunt to pass. That sucks up fuel.
Big engines loafing along can be very fuel efficient, compared to little engies working their lungs out.
The part I like is when you want to go, downshift 2 or 3 gears, hit it and wave bye-bye to the 2L s-box. Yeah, there are some street driven 2L boxes that will take the LS1 SS, but not all that many around here.
My $.02
Thread Starter
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Joined: Oct 2002
Posts: 116
i'm well aware of the rpm and right foot impact
i guess maybe an example of what i'm after is... a stock ls1/ls6 might just eek out 30mpg on the highway in a manual car
a wildly modded street/strip car wont get nearly that at same rpm's and same displacement.... why?
i guess maybe an example of what i'm after is... a stock ls1/ls6 might just eek out 30mpg on the highway in a manual car
a wildly modded street/strip car wont get nearly that at same rpm's and same displacement.... why?
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Originally posted by Jimmy17
i guess maybe an example of what i'm after is... a stock ls1/ls6 might just eek out 30mpg on the highway in a manual car
a wildly modded street/strip car wont get nearly that at same rpm's and same displacement.... why?
i guess maybe an example of what i'm after is... a stock ls1/ls6 might just eek out 30mpg on the highway in a manual car
a wildly modded street/strip car wont get nearly that at same rpm's and same displacement.... why?
There are ways to get lots more power without killing the mileage completely . The 500 hp Magnuson supercharger package for the LS1 is fairly efficient, but then it doesn't involve a wild cam.
FWIW: Designing an OEM engine like the LS6 is way more of a challenge than modding one. GM directed that Vette mileage, as tested by EPA standards, not be a "gas guzzler" so the buyer would have to pay an extra tax. It has to meet emission standards for 50,000 or maybe it's 100,000 miles, even when driven by idiots or little old ladies. It is also relatively cheap to build, compared to many other 400 hp production engines.
Last edited by OldSStroker; Aug 15, 2003 at 06:36 AM.
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Joined: Feb 2003
Posts: 641
From: St. Charles, Il
OldSStroker, mabye you can answer a similar question for me.
Along time ago when I was planning on building my motor I was doing the calculation for my fuel injector size and somone gave me a table to determine my BSFC. IT was somthing like this
9.0:1 compression = .55
10.0:1 = .50
11.0:1 = .45
First of all I cant see how compression is the only variable, second of all, I was going to use .45 because im running 11.1:1 compression but he said using .50 would be more accurate for a LT-4 (so he basicly confused the hell out of me)
Along time ago when I was planning on building my motor I was doing the calculation for my fuel injector size and somone gave me a table to determine my BSFC. IT was somthing like this
9.0:1 compression = .55
10.0:1 = .50
11.0:1 = .45
First of all I cant see how compression is the only variable, second of all, I was going to use .45 because im running 11.1:1 compression but he said using .50 would be more accurate for a LT-4 (so he basicly confused the hell out of me)
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Joined: Mar 2003
Posts: 433
From: Athens, GA
Originally posted by OldSStroker
There are ways to get lots more power without killing the completely mileage. The 500 hp Magnason supercharger package for the LS1 is fairly efficient, but then it doesn't involve a wild cam.
There are ways to get lots more power without killing the completely mileage. The 500 hp Magnason supercharger package for the LS1 is fairly efficient, but then it doesn't involve a wild cam.
another car we did was an ATI blown 03 vette. it did 447/396 at the wheels. he said gas milage wasnt affected really. then again he only had the car about 1200 miles before we put the prochager on it. it only has a corsa muffler system to complament the sc.
just giving known examples of great power and gas milage as well as drivability as both these cars are capable of daily chores as is. trey
oh and my heads/cam 403 TA gets about 16 mpg on the open road with the AC blowing. gotta love 2.73 rear gears.
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Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Originally posted by Dave Feerst
OldSStroker, mabye you can answer a similar question for me.
Along time ago when I was planning on building my motor I was doing the calculation for my fuel injector size and somone gave me a table to determine my BSFC. IT was somthing like this
9.0:1 compression = .55
10.0:1 = .50
11.0:1 = .45
First of all I cant see how compression is the only variable, second of all, I was going to use .45 because im running 11.1:1 compression but he said using .50 would be more accurate for a LT-4 (so he basicly confused the hell out of me)
OldSStroker, mabye you can answer a similar question for me.
Along time ago when I was planning on building my motor I was doing the calculation for my fuel injector size and somone gave me a table to determine my BSFC. IT was somthing like this
9.0:1 compression = .55
10.0:1 = .50
11.0:1 = .45
First of all I cant see how compression is the only variable, second of all, I was going to use .45 because im running 11.1:1 compression but he said using .50 would be more accurate for a LT-4 (so he basicly confused the hell out of me)
You might ask a couple of other guys how they chose injector size.
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Joined: Apr 2000
Posts: 1,614
From: Charlotte, NC
Last year I decided to try to improve my car's power and effeicientcy.
With gas prices on the rise, pollution out of control, and with our country at the mercy of OPEC I really wanted to change the way i'm going to make power.
So what I've done is used a Eaton supercharger with high effecientcy bypass (supposively less than 1hp loss at high way speeds)
I coupled that with a tight camshaft 210ish/220 duration with a 114 LSA. Little overlap and lots of lift to hopefully build torque and Low RPM effeciency.
I went to a moderate piston (9:1) for a blower car. Again to keep low RPM effeciency a little higher.
I've also used a higher gear than most (3.23). The torque from the roots blower more than makes up for really long legged gears.
I'm hopeing to put down 450rwhp with a very useable streetable torque and hp power band and get 27ish MPG.. Or what it did from the factory.
With the old motor and blower, (133k miles, hotcammed, eaton at 9psi) the car averaged about 18 50/50 city hwy and 23ish on the freeway (55mph). I definately think 27 is attainable at a 65mph cruze
With gas prices on the rise, pollution out of control, and with our country at the mercy of OPEC I really wanted to change the way i'm going to make power.
So what I've done is used a Eaton supercharger with high effecientcy bypass (supposively less than 1hp loss at high way speeds)
I coupled that with a tight camshaft 210ish/220 duration with a 114 LSA. Little overlap and lots of lift to hopefully build torque and Low RPM effeciency.
I went to a moderate piston (9:1) for a blower car. Again to keep low RPM effeciency a little higher.
I've also used a higher gear than most (3.23). The torque from the roots blower more than makes up for really long legged gears.
I'm hopeing to put down 450rwhp with a very useable streetable torque and hp power band and get 27ish MPG.. Or what it did from the factory.
With the old motor and blower, (133k miles, hotcammed, eaton at 9psi) the car averaged about 18 50/50 city hwy and 23ish on the freeway (55mph). I definately think 27 is attainable at a 65mph cruze
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Joined: Feb 2003
Posts: 641
From: St. Charles, Il
Originally posted by OldSStroker
I think you are correct; there are lots of variables. If what you are doing is just determining injector size, you don't want to be too small, so using the .50 or .55 is safer. If your engine actually gets a .40 BSFC and you have injectors which will support .55, you have about 37% excess.
You might ask a couple of other guys how they chose injector size.
I think you are correct; there are lots of variables. If what you are doing is just determining injector size, you don't want to be too small, so using the .50 or .55 is safer. If your engine actually gets a .40 BSFC and you have injectors which will support .55, you have about 37% excess.
You might ask a couple of other guys how they chose injector size.
the motor is already built and running. Im just looking to figure out how the fomula works....
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Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Originally posted by Dave Feerst
the motor is already built and running. Im just looking to figure out how the fomula works....
the motor is already built and running. Im just looking to figure out how the fomula works....
If you have 500 fwhp and use .50 BSFC, (when running at max power),
500 * .50 = 250 lbs/hr total
250/8 cylinders = 31.25 lbs/hr/injector.
I'm not sure about the max duty cycle you should choose, but at about 87%, 31.25/.87 = about 36 #/hr
Using .45 BSFC and 87% it's about 32 #/hr.
FWIW, if you were running at 180 mph and 250 lbs/hr (~40 gal/hr), your fuel economy would be about 4.5 mph, which I guess is just about where Winston Cup cars are on long, unrestricted tracks like Michigan. They are running a tad faster and with more hp, but lower BSFC's..probably in the 3's.
If they run 45 laps on a tank on Sunday we'll see.
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