4 cylinder vs 6 cylinder

[bobc455]

Everyone seems to be overlooking one key point: that V6 motors can run much slower than 4-cylinder motors, which gives back a LOT of the losses described above.

I've been quite disheartened lately - my wife just picked up a 1998 Buick Park Avenue with a 3.8 6-cylinder (the best motors Detroit ever produced IMO). For years I've been quite proud of my little saturn tooling along, but now her "monster" park avenue gets nearly the same MPG (31 MPG highway, compared to about 32 on my saturn) and is much bigger and luxurious to boot.

One of the key differences is that my Saturn will rev at 3000+ RPM, while her 3.8 revs at 1800 - 2000 or so RPM. I'm sure there are other differences as well, but that 3.8 motor is just a fantastic design.

-BC

Edit: On my 455 Buick, I have a 2.56 rearend in there now. I run about 2200 RPM at interstate speeds. However if I had the financial resources to put in a GearVendors overdrive unit, which would bring RPMs down 1750 RPM or so, the motor would be quite happy (and I could probably hit my 20 MPG goal)

[theholycow]

Originally Posted by bobc455

Everyone seems to be overlooking one key point: that V6 motors can run much slower than 4-cylinder motors, which gives back a LOT of the losses described above.

Would that still be true when comparing engines of equivalent displacement?

[Snax]

I don't think so. Just take a look at the 650 rpm idle speed of single cylinder dual sport bike. (Mine topped out at 5400 rpm too.) If you go liter for liter with the same bore to stroke ratio, you are not going to see much difference in the kind of rpm required at any given speed.

[Sludgy]

There are a lot of things that contribute to economy, not just the number of cylinders:

Air / fuel ratio (leaner is better)
Bore / stroke ratio (long stroke engines are better than short stroke engines)
Compression ratio (higher cr is better for emission controlled engines)
Cam timing (a cam timed for low rpm torque is usually better)
Exhaust gas recirculation (high egr gives better mileage)

BUT, the number of cylinders does have an impact.

I wish someone would make a twin cylinder compact p/u truck. Subaru has a flat four that they could cut in half to make a big 1.25 boxer liter engine. Stick that in a 2000 pound body, and I'd have my 30 mpg 4wd truck. Hell, they could probably get 25 with the boxer 4.

[GasSavers_RoadWarrior]

When you come right down to it, the same amount of fuel makes more or less the same amount of power, in the engine's most efficient range. So it's down to whether or not the size and weight of the vehicle suits the motor and gearing. There was the case of the last generation Taurus released to the public without a 4cyl option.. but the fleet buyers insisted on a 4 cyl... result... a dog that gets worse FE than the 6 cylinder. Then at typical highway traffic speeds, 4 cylinder versions of minivans rarely get any better than the 6 cylinder ones, due to higher loading that tops them out of the peak BSFC island and uses a throttle angle that makes them likely to keep popping in and out of lockup if the driver isn't very smooth.

Large 4 cylinder motors usually suffer extra drag from balance shafts installed for NVH and smoothness reasons, so probably don't have much advantage over a 6 of similar capacity.

[R.I.D.E.]

http://www.innas.com/Assets/files/Hydrid%20brochure.pdf

Here is the solution.

regards
gary

[GasSavers_Scott]

Odd engine combos, I got 34 mpg out of a 1600 Corolla Auto, and 34 mpg out of 1300 auto Festiva. The MGBGT with a 2000 six, Chevy's Cavalier/Cobalt 2.2 four, that can get into the high 30's with half a demensional V8. Mazda's MX3 2 litre V6 and even the lowly Ford Tempo V6 limited option. Then theres the new Tiburon V6.

Main bearings, VW air cooled 3 mains, the V4 Saab Ford 2 litre from the 60's ralley years, they had 3 mains. Subaru and Porsche boxer 6, thats 4 mains. Take a 4 cylinder, thats 5 mains and a straight modern 6 like the BMW 2.5 six and you got 7 mains. Now I have heard some great mileage number from 325 series with its lower revver and we can forget the VW 10 degree single cylinder head 2.8 and 3.4 Siamese V6 with 4 main bearings.

My 93 Ford Explorer with a 4 litre 6 and auto could knock out 26 and that was a flying brick in the air, but the trans in OD was running at 1500 rpm on the highway.

The Solstice gets better mpg at 65 than 55, it barly pulls 2000 at 55 and is sluggish and boggy, but 65 its closer to 2400 and its mileage computer jumps into the 30's.

I mean with the 6's extra connecting rods, pistons, valves, all that stuff add's up to rotational mass, but then theres the torque that replaces a 4 cylinders rpm's. I think with careful balancing a V6 can be very economical. My self I love the sound of a 6, be it a V or straight, the left-right-left-right firing order does something, its like a musical note, not the rassberries most 4 cylinders make, unless you talk about motorcycles, a 600 four sounds like an F1 engine. The Jag 6, Dino 6, BMW 6, and the Mitsubishi 3000 six are just beautifully exotic sounding.

The hybrid idea I think is wonderfull, it is 2009 and hybrid's work, Toyota and Honda proved they can be economically produced, eventhough the price used is kept artificially high. I was watching Prius prices for years expecting last year for a used generation 2 Prius to fall below 10,000, instead it went up. The technology is simple, batteries, controller, electric motor/generator, its not rocket science.

I think V6's are still viable and with the right packaging economical and dare I say a V8, what about the latest generation Corvettes getting into the 30's.

[R.I.D.E.]

My recently purchased Toyota Echo manual has been pulling a 50 MPG average without radical driving techniques. $3300 for an 01 with 71.5 k miles.

It's light at 2020 pounds and has a 1.5 liter engine with 10.5 compression and a long stroke for grunt but uses regular fuel. Pulls fine from 25 MPH in 5th gear.

I do wish it was taller geared. 2100 at 60 would be nice instead of 2500. Frontal area is a little large but this is a fairly tall car with headroom for a 6'4" male driver in a very small package. Carrying close to max load yesterday it still had plenty of power for me.

Coil overs, no distributor. Beam rear axle and struts on the front, so alignment is only a toe adjustment. Compared the the Insight the simplicity and ease of maintenance is very appealing to me. Some may not like the body style, but with a CD of .29 and the nice vertical seating where my butt isn't dragging the ground like the Honda, I thinks its a better combination for an old man like myself.

regards
gary

[GasSavers_Pete]

Originally Posted by guest001

But if you where to look at it from the point of view of just the Engine management, and not look at frictional loses or weight of the vehicle.

On a sort of related note:

I have had two cars both with the GM 3.8 90 degree V6 engine.
The first with the Buick variant was a manual 5 speed , weighed 1350 kgs and had no air conditioning or power seats or windows.

The second with the Chevrolet version has the 4L60E automatic fitted , air power seats and windows and weighs about 1600 kgs.

Logically you would expect the first car to be more fuel efficient but this is not so.

The first car averaged around 10.0 l/100 kms and the second around 7.5.

The second would be a little more aerodynamic but it is also larger and heavier so I think one offsets the other.

The main reason I can find is in the engine management system used and the fifteen years of development and refinement between the two systems.
The first is an earlier version of the second.

Cheers , Pete.

[theholycow]

GM 3.8 with a 5 speed manual and a lightweight car? You Australians get all the cool cars. What Buick model was offered there with that configuration?