Shoot Holes in My Idea

Okay so let's pretend you're an OEM with no established image or a bad image. Say, Mitsubishi, Scion, GM Europe or Suzuki.

You want to start from the ground up to make a car that will return your company to profitability, build an image and allow for the easy incorporation of new technologies. This is what you know:

1. The vehicle will need to be efficient to deal with CAFE and similar regulations. This means 9000 rpm redlines and V12s are probably out of the question. You'll probably also want large quench areas and a pretty long stroke to maximize efficiency and to provide room for things like Direct Injection nozzles.

2. The vehicle will need to be modular to provide maximum efficiencies of scale. Preferably this would apply to the engine, suspension and basic chassis along with other things like fuel systems and basic electronic architecture.

3. The vehicle will need to be safe. Passenger impact rules mean it will probably need either a big nose, a boxer engine, or a rear mounted engine.

4. The vehicle must be versatile. Niche cars don't make money. We need something that can stretch from station wagon to sporty car to econo box to entry level luxury.

So here's my idea.

Start with a large displacement flat four engine. Something in the neighborhood of 3.0 liters. Redline it at something modest, say 6000 rpm, and run a SOHC 2 or 3 valve cylinder head for large quench area and minimal valvetrain friction. This will also minimize the engine's thickness, a consideration that will become important later. With conventional injection and a compression ratio in the neighborhood of 10:1, this should make for a very low stressed base engine with 180-ish hp/ 180 is lb-ft torque. This would probably get mid 30s fuel economy in a Civic or Sentra sized vehicle.

This would be the base engine for the US market and the Australian market, and the plus one engine for the Asian and European markets. For the Asian and European markets, the base engine could be the same thing simply cut in half to make a 1.5L flat twin. Run a little bit more cam and call it 110 hp. The reasons for this are tax related. In most European and Asian countries, engines under 1.6 liters (1.5 in Asia) get favorable tax rates. This should be well over 40 mpg in a Fit or Yaris sized vehicle.

For a plus one American version, or a plus two Euro/Asian variant, add VVT and Direct Injection for a still low stressed 210 hp/200 lb torque. I don't see why this couldn't be a 40 mpg type engine in a Sentra sized vehicle.

For the plus two American version, plus three Asian version, put a turbo on top of the VVT, Direct Injection variant and get a still low stressed 300 hp/320 lb ft. Call it high twenties fuel economy.

Now we need to solve the versatility and safety problems. For the sake of giving pedestrians a soft surface to bounce off of and for giving the engineers the biggest, least compromised crumple zones possible, I would mount the engine behind the rear axle. This would also help with aerodynamics because you could make the nose much lower.

Because we have a boxer style engine, and because we're using this chassis as the basis for several types of vehicle (sedan, hatch, wagon, sporty-coupe), we can put the engine under the trunk floor with minimal loss of storage space in the back. We'd also have a large new "trunk" in the front.

Because a rear engine car is probably not going to struggle with front end grip, we can get away with a cheap strut design. We can even compromise it quite a bit for packaging and storage space because, again, rear engined cars don't ask a lot of the front axle. On base level cars, or on the sporty coupe, we could probably ditch power steering as well.

The performance benefits to this layout are obvious.

So...basically VW in the 60s?

Sounds like a great plan, cant wait to take delivery of my new car...oh wait, carmakers dont give a steaming e36m3 about what car buyers want. They foist garbage upon us and tell us to be happy with it.

ReverendDexter wrote: So...basically VW in the 60s?

Corvair, Beetle, 914, 911...

I have idea, but apparently, I'm not an enthusiest anymore.

4cylndrfury wrote: Sounds like a great plan, cant wait to take delivery of my new car...oh wait, carmakers dont give a steaming e36m3 about what car buyers want. They foist garbage upon us and tell us to be happy with it.

Not quite true. Carmakers don't give a steaming E36 M3 about what car enthusiasts want. Carmakers do, however, care very much about what your average brain-dead appliance shopper wants; it's just that shoppers outnumber us 10 to 1 or more. And the government really doesn't care what car enthusiasts want; they just mandate whatever they think brain-dead appliance drivers need to keep them from making themselves all the way dead.

Isn't a compression ratio of 10:1 a little high for a mass production vehicle?

DoctorBlade wrote: Isn't a compression ratio of 10:1 a little high for a mass production vehicle?

Nope... quite a few 12:1 and higher cars out there. There's even turbo 10:1 mass production cars out there.

You'll find that four cylinders run out of displacement around 2.5L for balance reasons - nothing more to add than that.

tuna55 wrote: You'll find that four cylinders run out of displacement around 2.5L for balance reasons - nothing more to add than that.

Inline fours, yes. Boxers are different, I think.

Hello there.

92CelicaHalfTrac wrote:

DoctorBlade wrote: Isn't a compression ratio of 10:1 a little high for a mass production vehicle?

Nope... quite a few 12:1 and higher cars out there. There's even turbo 10:1 mass production cars out there.

Ah. All I know is that the LS engines seem to do fine with sub 10:1. I'm still learning.

New Mazda skyactive gas engines are running 14:1 compression.

Speed 3 runs 9.5:1 with 16-17psi.

In reply to z31maniac:

but requires premium. i think the highest oem C/R with port injection on regular gas is around 9:1

supposedly DI can reliably run higher compression, but i think alfadriver disputed that at some point

Strizzo wrote: In reply to z31maniac: but requires premium. i think the highest oem C/R with port injection on regular gas is around 9:1 supposedly DI can reliably run higher compression, but i think alfadriver disputed that at some point

My 07 magnum 3.5 is 10.something:1 on 87 octane gas

In reply to Strizzo:

If I did, I was wrong. DI gives you the ability to run 1-2 ratios higher.

I have a hard time imagining the 3.0 liter flat four that delivers 30+ mpg and 180 hp. Not saying you're wrong or that it's impossible, just that I don't see that sort of efficiency on the market.

Then again, I'm no engineer.

make is a S/C flat 4 diesel.........

More use around the world for diesel fueled cars. Significant torque advantage, and potential for high mileage.

Oh... and as far as diesel "performance" ask Audi and Peugeot about their diesel racing cars

ReverendDexter wrote: So...basically VW in the 60s?

Not far off, except for double the displacement and design the body to be on this side of awful for space efficiency.

Tom Heath wrote: I have a hard time imagining the 3.0 liter flat four that delivers 30+ mpg and 180 hp. Not saying you're wrong or that it's impossible, just that I don't see that sort of efficiency on the market. Then again, I'm no engineer.

Maybe I'm wrong, but I thought cylinder count did a lot more to hurt efficiency than displacement.

When I dreamed up this scenario I was sort of thinking about what makes an LS powered Corvette a 28 mpg car (low revs, few valves, lots of quench) crossed with what made the 944s such good all rounders.

Am I wrong in supposing a 180 hp, 3 liter engine would be pretty mild on cam profiles?

Duke wrote:

4cylndrfury wrote: Sounds like a great plan, cant wait to take delivery of my new car...oh wait, carmakers dont give a steaming e36m3 about what car buyers want. They foist garbage upon us and tell us to be happy with it.

Not quite true. Carmakers don't give a steaming E36 M3 about what car *enthusiasts* want. Carmakers do, however, care very much about what your average brain-dead appliance shopper wants; it's just that shoppers outnumber us 10 to 1 or more. And the government *really* doesn't care what car enthusiasts want; they just mandate whatever they think brain-dead appliance drivers need to keep them from making themselves all the way dead.

This was actually the idea behind my concept. Really versatile white bread that pleases the regulators and can be made into something cool alah this

for marketing purposes and positive buzz.

Actually, not far off the concept for the original air cooled VWs.

I recently measured the height of my flat-four Subaru engine. EJ205. Even without figuring in things like the intercooler and turbo, the overall height was within an inch of my "tall" I-4 Miata engine. The intake manifold plumbing required to reach those two heads without sharp kinks results in quite a tall apparatus.

My WAG is that older carb'd cars were able to get away with a lot less intake manifold and were thus "flatter" and more accommodating to under-floor packaging.