1st Generation (GD 01-08) The one that started it all! Generation specific talk and questions here!

MPG Blues...

  #21  
Old 12-06-2008, 10:39 PM
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Originally Posted by polaski View Post
I think it's a misnomer in this case. Due to the vtec-e design where the second lifter lobe is locked to the first, overall valve timing, lift, and duration are unchanged, just an extra valve opens up in each cylinder. (Technically, that extra valve always opens, most of the time just cracked open enough to keep fuel from pooling up on it.)

It only keeps the engine from starving for air like its 8v i-DSi cousin would be doing above that speed.

Oil pressure is ALWAYS built up otherwise your motor would be dead. A solenoid/valve combo just makes some of it go into the lifter lockers when the ECU says NOW

Guess what, if you're over 3400 rpm (less if you're stepping on the gas) the engine no longer has "swirl" in the cylinders, the valve opening changes it to "tumble" (like a somersault) and is part of the cause for the lower fuel efficiency above that speed. When below that speed and half the intake valves closed, the higher port velocity coupled with better-retained gas velocity through the compression stroke (both of which maintain fuel vaporization), coupled with the more uniform fuel mix at time of ignition, allows lower timing under higher compression with complete combustion, and that increases power transferred thus allowing less throttle.

I bet the OP was speeding, or in stop-go traffic, or drives as if he has no idea when his engine is changing modes of operation
I think thats wrong.
Suzuki pioneered the TSCC head in 1978 and used in well into the 80's.
The TSCC head (Twin Swirl Combustion Chamber) made more power above 3000 rpm to redline. This was THE engine that launched a million drag racing careers.
"swirl" or lack thereof is not dependent on RPM.
Cylinder scavenging is more of a problem at higher RPM but the engineers at Suzuki (then Honda and Kawasaki) nailed it flat with their hemi head motors that not only improved combustion at higher RPM but also scavenging.
 

Last edited by ricohman; 12-06-2008 at 11:10 PM.
  #22  
Old 12-06-2008, 10:42 PM
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Do you guys get winter blend fuel?
In Saskatchewan we get winter blend which can cause at least a 10% hit in economy.
 
  #23  
Old 12-06-2008, 11:35 PM
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Ahh must be nice to get 30+mpg, only experienced it once so far in my 8500 miles. Last tank was 25mpg.
 
  #24  
Old 12-06-2008, 11:38 PM
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Originally Posted by dick29662 View Post
Tire pressure has a large impact on your mileage. Under-inflated tires will do exactly what you experienced. The OE tires I have leak down. In three months mine will lose 5-6 psi. After that get the alignment checked. Maybe momma hit the curb at a bad angle. Also try to keep away from alcohol diluted gasoline. It hurts my gas mileage around 5-10%

All the Best! Dick W
I keep my tire pressure at 35psi and check it with every car wash. I guess I never realized how passenger weight can affect gas mileage.
 
  #25  
Old 12-07-2008, 12:07 AM
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Originally Posted by ricohman View Post
I think thats wrong.
Suzuki pioneered the TSCC head in 1978 and used in well into the 80's.
The TSCC head (Twin Swirl Combustion Chamber) made more power above 3000 rpm to redline. This was THE engine that launched a million drag racing careers.
"swirl" or lack thereof is not dependent on RPM.
Cylinder scavenging is more of a problem at higher RPM but the engineers at Suzuki (then Honda and Kawasaki) nailed it flat with their hemi head motors that not only improved combustion at higher RPM but also scavenging.
No, I'm right. It's the same concept on the y5 engine. When the one intake valve is closed, all the air passes into the combustion chamber on the same side, causing it to rotate for the most part on a vertical axis. This would be even more true on the L15 due to the much shallower valve angle. When both valves are open, the axis of rotation changes to something closer to horizontal. I'd imagine the port divider is offset somewhat so it's not a true horizontal tumble like the old Hondas but it still would be the dominant tendency.

The benefit of the one valve being closed is the stratified charge. When rotation is on a vertical axis at the top of the compression stroke the richest air/fuel mix is concentrated at the spark plug. This reduces the fuel required to run stoich as well as giving a certain detonation resistance when employing the proper quench. Biggest reason the y5 can run 17:1 and higher a/f without destroying bearings.

We're stuck with a more stoich fuel ratio because of NOx emissions but still it does help.
 

Last edited by polaski; 12-07-2008 at 12:11 AM.
  #26  
Old 12-07-2008, 10:39 AM
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Originally Posted by polaski View Post
No, I'm right. It's the same concept on the y5 engine. When the one intake valve is closed, all the air passes into the combustion chamber on the same side, causing it to rotate for the most part on a vertical axis. This would be even more true on the L15 due to the much shallower valve angle. When both valves are open, the axis of rotation changes to something closer to horizontal. I'd imagine the port divider is offset somewhat so it's not a true horizontal tumble like the old Hondas but it still would be the dominant tendency.

The benefit of the one valve being closed is the stratified charge. When rotation is on a vertical axis at the top of the compression stroke the richest air/fuel mix is concentrated at the spark plug. This reduces the fuel required to run stoich as well as giving a certain detonation resistance when employing the proper quench. Biggest reason the y5 can run 17:1 and higher a/f without destroying bearings.

We're stuck with a more stoich fuel ratio because of NOx emissions but still it does help.
Two smaller valves will flow better at lower rpm than two big valves or 4 small valves.
But a 4 valve head will flow better at higher RPM, swirl included if that's important to you.
Its been around forever.
I'm just debating the "swirl loss" at higher RPM. And that is simply not the case with all heads.

From a patent.
A cylinder head for a four-cycle internal combustion engine with improved intake port and combustion chamber configuration. The physical shape of the intake port and combustion chamber directs the flow of the incoming air/fuel mixture in a swirl path, which is directed toward the spark plug. In particular, the intake port has a fin at its terminal opening into the combustion chamber. The fin creates a swirling motion in the incoming gasses and also directs the flow of the gasses toward the spark plug. As a result, a greater percentage of the intake charge is in close proximity to the center of the combustion chamber and the spark plug, and hence combustion occurs faster and more completely. In a preferred embodiment of the invention, the portion of the cylinder head that forms the upper surface of the combustion chamber, includes a shear ledge that further acts to direct the flow of the incoming gasses toward the sparkplug. The shear ledge acts as a secondary boundary for the gasses that go past the intake port fin, directing that portion of the charge that goes past the intake port fin toward the center of the cylinder and closer to the spark plug. As a result, the engine runs more efficiently, has cleaner exhaust emissions, runs at lower temperatures and has increased torque and horsepower.


Kevin Cameron, the guru of all things mechanical has written some outstanding articles on this.
Sportbike Performance Handbook - Google Book Search
 
  #27  
Old 12-07-2008, 12:28 PM
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Originally Posted by Rod2Rice View Post
Ahh must be nice to get 30+mpg, only experienced it once so far in my 8500 miles. Last tank was 25mpg.
That's about what I get, never gotten above 27 mpg and that was a week with lots of highway driving. I think for us, it's the corn in the gas that's causing the drop in mileage. And there is not a thing we can do about it right now - hopefully some smart person in Congress will get that situation changed back and we can get the crap out of our tanks and back into starving people's hands for food.

 
  #28  
Old 12-07-2008, 12:53 PM
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Originally Posted by Juliane View Post
That's about what I get, never gotten above 27 mpg and that was a week with lots of highway driving. I think for us, it's the corn in the gas that's causing the drop in mileage. And there is not a thing we can do about it right now - hopefully some smart person in Congress will get that situation changed back and we can get the crap out of our tanks and back into starving people's hands for food.

Well, the ethanol is better to use than the MTBE that was previously used.

Ethanol vs MTBE
 
  #29  
Old 12-07-2008, 01:02 PM
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I've been getting about 30-36 combined mileage for the 7 months I've owned my Fit. But for some reason my last tank I got 41 mpg with a lead foot!?! Surprised the hell out of me.
 
  #30  
Old 12-07-2008, 05:02 PM
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Originally Posted by ricohman View Post
Two smaller valves will flow better at lower rpm than two big valves or 4 small valves.
But a 4 valve head will flow better at higher RPM, swirl included if that's important to you.
Its been around forever.
I'm just debating the "swirl loss" at higher RPM. And that is simply not the case with all heads.

From a patent.
A cylinder head for a four-cycle internal combustion engine with improved intake port and combustion chamber configuration. The physical shape of the intake port and combustion chamber directs the flow of the incoming air/fuel mixture in a swirl path, which is directed toward the spark plug. In particular, the intake port has a fin at its terminal opening into the combustion chamber. The fin creates a swirling motion in the incoming gasses and also directs the flow of the gasses toward the spark plug. As a result, a greater percentage of the intake charge is in close proximity to the center of the combustion chamber and the spark plug, and hence combustion occurs faster and more completely. In a preferred embodiment of the invention, the portion of the cylinder head that forms the upper surface of the combustion chamber, includes a shear ledge that further acts to direct the flow of the incoming gasses toward the sparkplug. The shear ledge acts as a secondary boundary for the gasses that go past the intake port fin, directing that portion of the charge that goes past the intake port fin toward the center of the cylinder and closer to the spark plug. As a result, the engine runs more efficiently, has cleaner exhaust emissions, runs at lower temperatures and has increased torque and horsepower.


Kevin Cameron, the guru of all things mechanical has written some outstanding articles on this.
Sportbike Performance Handbook - Google Book Search
You're 100% right, and so am I.

I'm referring to cruise conditions only. With just 1 intake valve opening the gaseous velocity will always be higher and prevent fuel condensation during compression stroke better.

A rotation parallel to the axis of the cylinder wall retains more momentum than one that isn't, and it's this airspeed that keeps vapor pressure low and fuel vaporized. It's when this speed goes down too far that microscopic droplets reform and reduce burning efficiency.

There's a reason the d15b8 only had 8 valves, each offset to the side of cylinder center, to reach near 50 mpg.
 
  #31  
Old 12-07-2008, 08:42 PM
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Originally Posted by polaski View Post
You're 100% right, and so am I.

I'm referring to cruise conditions only. With just 1 intake valve opening the gaseous velocity will always be higher and prevent fuel condensation during compression stroke better.

A rotation parallel to the axis of the cylinder wall retains more momentum than one that isn't, and it's this airspeed that keeps vapor pressure low and fuel vaporized. It's when this speed goes down too far that microscopic droplets reform and reduce burning efficiency.

There's a reason the d15b8 only had 8 valves, each offset to the side of cylinder center, to reach near 50 mpg.
True. But remember that the main accelerator (besides pressure) in fuel vaporization isn't necessarily velocity but the heat of the admission suface at low RPM. This is why you get poor vaporization when the engine is cold. Hot intake valves can go a long way in keeping the mix in vapor at low RPM.
Deflagration varies as in any fuel there is a significant difference in the light end and heavy end molecules in gas that occurs pretty much at random in distillation.
Sometimes you get a good tank and sometimes not!
 
  #32  
Old 12-09-2008, 10:45 PM
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Technique people, Technique is key.

Accelerate slow
Shift at 2K
Drive the speed limit or less
P&G
DWL
DWB
FAS

70mpg is possible with all the above.

50mpg is possible without turning the motor off.
 
  #33  
Old 12-09-2008, 11:17 PM
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Originally Posted by pb and h View Post
Technique people, Technique is key.

Accelerate slow
Shift at 2K
Drive the speed limit or less
P&G
DWL
DWB
FAS

70mpg is possible with all the above.

50mpg is possible without turning the motor off.
i'm sorry but do that in my town and you will be run over. i get 25-28 mpg city no matter what i do i think some fits have a gas mileage problem. ive had 3 of them 2 07's and a 08 one of the 07's got over 33 city but the other 2 have never gotten above 28 city. and no lead foot and no jack rabbit starts i had a 92 civic dx hatch that got 33-38 city no matter how hard i drove it i just don't get why my fit doesn't do this. the 92 hatch only weighed 100 pounds less my wifes 98 escort wagon gets 31-34 city and it weighs more and has the same hp and torque. thats why i say Technique hasn't helped me at all and yes my fit is auto and i think thats why it gets shity mileage.
 
  #34  
Old 12-09-2008, 11:20 PM
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fuel economy isnt about anything but the driver
 
  #35  
Old 12-10-2008, 12:04 AM
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mpg can be affected by alot of things not just the driver..
 
  #36  
Old 12-10-2008, 12:07 AM
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but the BIGGEST factor is the driver
 
  #37  
Old 12-10-2008, 12:35 AM
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Originally Posted by Juliane View Post
That's about what I get, never gotten above 27 mpg and that was a week with lots of highway driving. I think for us, it's the corn in the gas that's causing the drop in mileage. And there is not a thing we can do about it right now - hopefully some smart person in Congress will get that situation changed back and we can get the crap out of our tanks and back into starving people's hands for food.

Yup that corn certainly isnt helping. We have 10% all year round here, have for quite a few years as well.

I just filled up tonight, 22mpg.
 
  #38  
Old 12-12-2008, 04:58 AM
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08 AT Base, I never have to go over 3k to get up to speed in town and I'm usually off the line faster than most of the people. Interstate speeds I keep it around 65-75mph and get around 33-35mpg average. This is traveling with myself (300lb+) and prolly 100lb or more of music gear. On average I try to keep it from engaging vtec unless I really need to get up to speed. Even with the occasional romp around town with 3 other people in the fit I never see under 30mpg.

As far as gas goes I usually stick to shell.
 
  #39  
Old 12-12-2008, 06:18 AM
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I have an 08 AT. My mileage has gone down recently. I had been getting 39-40 going 75 mph on a hilly freeway, with 25% city driving. It has gone down to 36. The best I recieved was 48 MPG going 50 in a 55 mph zone. Automatics can get good mileage.
 
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