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Sedans Saturn Aura Saturn Aura vs. Honda Accord
326 messages, Last post on Dec 19, 2007 at 5:48 AM
You are in the Saturn Aura Forum. Your Hosts are pat & karens
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Replying to: phaetondriver (Nov 27, 2007 9:26 am) |
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Replying to: robertsmx (Nov 27, 2007 9:21 am) I still believe, that a piston on a compression stroke and valves closed, causes more resistance to the engine than one with valves open. Maybe with all valves closed, there is so little air in the cylinder that the resistance becomes insignificant. Haven't given much thought to all valves closed all the time. Might just work> Thanks again for the detailed reply Phaeton Driver
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Replying to: phaetondriver (Nov 27, 2007 9:38 am) I see another advantage. A typical approach (without VCM) to get better fuel economy on highway would be to use as tall gearing as possible in the top gear. But there are downsides to it. Go too tall, and with increased loads, the car may not be able to hold the top gear. And even if it could, the cruising rpm will be lower. I will demonstrate this using numbers. IIRC, Accord V6 has a 2.63:1 overall drive ratio in the top gear. That would be relatively short for the V6 but not while operating in V4 mode (2050 rpm at 60 mph). This looks like a recipe for fuel economy in mid-30s at about 60 mph, if not better. In oversimplified terms, had Honda not used VCM but a tall top gear using a 6AT, for similar throttle opening, the V6 would have required an overall drive ratio of 1.75:1 and that would be way too tall to be practical (about 1400 rpm at 60 mph). In fact, this overall drive ratio will also hurt lower gears as they will have to be taller as well (hence poorer off the line performance). The advantage doesn’t stop there. When the car is cruising at 60 mph, with the revs at 2050 rpm, for the same throttle opening, it would have more horsepower on tap (even with two cylinders out) than if it were revving at 1400 rpm with all six cylinders firing. If the car now encounters mild acceleration or a minor hill, with VCM there is an instantaneous engagement of all six cylinders, at 2050 rpm and 2.63:1 overall drive ratio. The responsiveness will be unmatched by non-VCM version which was cruising at 1400 rpm and 1.75:1 ratio for same throttle opening. So, even if a gear shift isn’t warranted to meet the need for acceleration for the VCM version (which would be the case, if demand for power is higher), the non-VCM version will definitely need help. When Accord’s gear ratios were released by Honda, I wasn’t very happy about them. And still am not, but only with the lower ratios. The top gear ratio really makes sense. Too bad I can’t find an Accord V6 to rent and see its fuel economy potential over a tank of gas. One of the biggest surprises I have had from owning the TL was its fuel economy. I was expecting 21-22 mpg in mixed driving, but getting 25-26 mpg. I was expecting 28-29 mpg on highway at 75 mph, but get 32 mpg. I can only imagine the Accord V6 being capable of beating it.
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Replying to: robertsmx (Nov 27, 2007 9:21 am) 
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Replying to: chrono (Nov 27, 2007 1:52 pm) That's one place I was let down sitting in the Aura Hybrid. The steering wheel felt like it belonged in a car costing half the price, with a really rough, hard grain plastic.
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Replying to: thegraduate (Nov 27, 2007 2:00 pm)
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Replying to: chrono (Nov 27, 2007 2:14 pm)
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Replying to: phaetondriver (Nov 27, 2007 2:27 pm) |
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Replying to: robertsmx (Nov 27, 2007 10:12 am) Sixth 0.74 Final drive ratio 2.77 I know I see right about 1750 RPM at 70 MPH and very close to 2000 at 80. Does this equate with the ratios, give the 18inch 50 series tires? I hope so. With these numbers on a relatively level highway the MPG is quite good for a 4000 pound car. I say 4000 pounds as when I made my last trip I had a lot of stuff in the car plus a passenger. As I posted on the real world MPH forum I got 30 MPG over a 910 mile trip with about 85-90% at 80 MPH. The CD (coefficient of drag), tire inflation, and weight, affect MPG and how well a car pulls in any given gear, so finding the best final gear ratio is a complicated process of all of these factors and probably trial and error. Maybe your feelings for the final gear and trans ratios in the new Accord are somewhat based on your knowledge and understanding of the real world factors which result in actual MPG. Car companies often have to disregard these to get the EPA numbers they need.
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Replying to: chrono (Nov 27, 2007 1:52 pm) The leather steering wheel on my Aura XR is very nice. Haven't seen non-leather versions. |
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