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Old 09-29-2016, 09:21 AM   #1 (permalink)
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Default Honda should have used 3 cylinder engine in Insight G2

Seeing the Mirage, Focus and Fusion cars with 3-cylinder engines (and driving just fine) I wish Honda had put their original 3 cylinder in the G2. It would have scored over 55mpg on the EPA Highway cycle (and Honda could brag about beating prius).

That was a missed opportunity. At the least they could have made it an option: 4 cylinder or 3 cylinder... I of course would have picked the 3, because I love the 3 cylinder in the G1 and the Ford Focus. Small and efficient.
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Old 09-29-2016, 09:58 AM   #2 (permalink)
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The number of cylinders doesn't mean anything, except maybe packaging. Maybe internal efficiency, but that's way over my head. It's the displacement and tuning that matters. Our engine can barely pull our cars. It wouldn't work in a car that's 900 lbs (about 50%) heavier. Honda increased the displacement from 1.0 to 1.3. For whatever reason they decided to do this with four cylinders instead of three. I've never driven a G2, but I bet it is not overpowered.

The Focus is turbocharged and makes about twice the HP as the G2. It's mileage is lower.

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Old 09-29-2016, 02:01 PM   #3 (permalink)
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The original G2 gets 41 mpg on the EPA cycle.
I don't think dropping one cylinder would make it 35% more efficient to get to 55 mpg. It would have less internal friction, but have to work harder for the same power.
Bigger cylinders or a turbo would reduce the gain even further.
A long geared manual gearbox would allow for more control and hypermiling techniques; that should do more than dropping a cylinder.

Four cylinders make for slightly smoother running on low revs. And that's where my revs are pretty much all the time; 1100 rpm in the city, 1600-1800 on the highway.

I do get over 60 mpg per tank in summer weather. My lifetime average (all season) beats 55 mpg. But my driving style does not resemble EPAs.

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Old 09-29-2016, 02:14 PM   #4 (permalink)
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Although Ford 3 cylinder engine tend to do well in NEDC and EPA tests, sites tracking real world fuel consumption tell a different story.

Check out the RealMPG register on www.honestjohn.co.uk. Where a Ford 1.0 turbo 3 cylinder and a 1.6 NA 4 cylinder are installed in the same car real fuel consumption is usually very close.

It's usually close enough that the difference can be accounted for simply in that the 3 cylinder version has a start-stop system. Or maybe it's just the way we drive in the UK...
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Old 09-30-2016, 08:37 PM   #5 (permalink)
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While it's generally true that smaller displacement results in higher economy, after a certain point it starts to move the other way. Here's why:

Let's say you need to make 20HP to cruise at 65mph in the G2. If the 3-cylinder delivers 20HP at 3500rpm and the 4 cylinder delivers it at 2500rpm, the 4 cylinder would probably get better fuel economy, because you're having to rev up the smaller engine, getting it outside of its most efficient operating range (which is ~1750-2250rpm btw). The 3 cylinder can probably more efficiently make 15HP, but you'd need to improve aero and/or reduce weight to get the power needs down.

G1 3 cylinder BSFC (efficiency chart):




A larger engine does have some things working against it, such as more friction at the same RPM and, if you don't have tall enough gearing, it will run at lower load and be less efficient. However, there's an ideal engine size for producing a given amount of power most efficiently, and smaller is not always better.

Food for thought: The C7 Corvette has a 6.2L V8 that can deliver 650HP, and PopularMechanic found it delivered close to 40mpg when cruising on the highway at 55mph. It does this because in top gear, it's spinning at 1100rpm at 55mph. My old Civic was running about 3500rpm at that same speed due to the silly-short B16 transmission, and it never delivered more than 35-38mpg at these speeds.

EDIT: I should add that speed is a big variable here too, because power needs vary with speed. A 4 cylinder engine might actually have been more efficient in the G1 for cruising speeds above... let's say 70mph, because you could bring the revs down, but the G1's 3 cylinder would probably be more efficient in the G2 than its own 4 cylinder at lower speeds, I'd guess anything below 45-50mph.

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Old 09-30-2016, 09:04 PM   #6 (permalink)
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You still have to include the "weight" as a contributing factor also.
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Old 09-30-2016, 09:08 PM   #7 (permalink)
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Quote:
Originally Posted by Willie Williford View Post
You still have to include the "weight" as a contributing factor also.
Sortof. Weight adds to rolling resistance, but in terms of cruising economy, the impact is not large. If you're looking to maintain a specific acceleration rate / 0-60 time, you could pair a larger electric motor with the 3-cylinder.
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Old 10-06-2016, 12:37 PM   #8 (permalink)
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Going from an I4 to I3 engine is 25% less reciprocating mass (pistons, rods, etc), 25% less oil resistance/splash losses, and therefore a measureable savings energy wise. A Ford Fiesta I3 gets 19% over the I4 version (36 highway to 43 highway), and I would expect a similar increase if the Insight G2 had the original I3. So the 2010 Insight scored 43 highway. +19% by switching to I3 option == 51 mpg highway

I think they should have used the I3 in the Civic Hybrid too. IMHO the four-cylinder in my HCH is overpowered & wasting gas.
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Originally Posted by RedDevil View Post
The original G2 gets 41 mpg on the EPA cycle. I don't think dropping one cylinder would make it 35% more efficient to get to 55 mpg.
Perhaps I was over-optimistic, but you are mixing numbers. You are quoting combined cycle, where in my original post, I was using the HIGHWAY test. (IMHO the city test is fundamentally flawed & inaccurate & should be ignored.)
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Old 10-06-2016, 12:41 PM   #9 (permalink)
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Those savings go away if you need to rev the engine 33% higher. I guarantee the Insight's i3 could not keep an HCH1 going down the highway at 70mph with the gearing it has in the Insight, and if you geared it shorter, you'd be out of its optimal RPM range and BSFC will rise, so you might actually end up with worse economy.
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Old 10-06-2016, 12:51 PM   #10 (permalink)
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You're putting way too much emphasis on the number of cylinders and skipping way too much stuff in the middle. Don't you think Honda Engineers thought of this stuff and made calculations? You're mainly forgetting the required horsepower to move a certain weight. You're forgetting gearing. You're forgetting tuning. An engine that can barely move a G1 isn't going to be able to pull a heavier G2 or a Civic. The HVH1 is already underpowered worse than the G1, even with a bigger engine.

You're also ignoring the fact that the Fiesta 3 cyl doesn't do nearly as well in real life as it does for the EPA tests. Manufacturers often tune their cars to do well for the EPA and ignore real life so they can post big (fake) numbers to fool people like you. VW even tuned theirs to do well in emission tests.....

My old Ford tractor had 3 cylinders. It got terrible mileage. I wonder what Ford did wrong?

Sam
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