Engine Development in Modern Automotives

Manufacturers are waking up and taking the route of more hp per liter. Keeps weight down, improving performance and fuel economy.
But it seems nobody has informed Dodge that the 8.3L in the Viper is a pile of garbage.

 

What about the 7.0 liter LS7 Corvette motor? 505hp and 26mpg. Who cares how much it displaces? All that matters is the inputs. Cost, mpg, and hp. HP per liter is often quoted by the loser.

 

I read something of interest in either R&T or C&D last night...

Tech column claimed that a high compression naturally aspirated engine will be more efficient than a smaller turbocharged engine.

The reader challenged it, saying that the turbo effectively raises the compression ratio by pre-compressing the charge before intake...the editor writes back and said that it did not really change the effective compression ratio.

Therefore, a turbo is just a low-compression engine which has more charge forced into the cylinder on intake cycle. The real compression ratio is volume BDC / TDC and is determined mechanically. The work extracted from the fuel/air mixture is enhanced in efficiency by this mechanical ratio, not the total volume. So, again - the turbo motor operates as an analog of a larger, low-compression naturally aspirated motor.

So, thinking along these lines, perhaps the route Ferrari is hinting at (low-displacement V8 Turbos to replace the NA V12 in their top cars) could perhaps be subject to a little thought analysis? Maybe higher compression, TDI, advanced materials, careful choice of displacement, etc. could keep the classic 12 cylinder viable for a time longer?

BTW - doesn't this kind of need to be in the Technical Column?

 

In a naturally aspirated engine exhaust is waste energy.

If you can turn some of that energy with a turbine into useful work ie to increase air flow on the intake side, then you have increased the overall efficiency of the entire engine.

 

True, Simon - but remember - that "recovered" energy is not directly being used to turn the crankshaft; it is being used to drive a supercharger that just crams more air and fuel back into the engine. What my source was talking about was the efficiency of extracting as much work as possible from whatever amount of air/fuel charge you have in the engine to work with - hence the mechanical compression argument.

Thus, a turbo should be viewed as a more efficient way to drive a supercharger than using a pulley on the crankshaft - but it only increases power at the cost of spraying in more fuel.

(There were, in fact, some Aeromotive attempts to directly couple an exhaust turbo to the output shaft of the engine - the big radials in the old B-36 bomber were made like this. They gave a lot of trouble in service, and did not result in any significant gain from what I have read)

James - just doing my part to act a Superdelegate for the V12...

 

That's not entirely true. The turbine creates a lot of backpressure and that makes the engine less efficient. Turbos make great power, but they hurt cruising mileage. If they were truely using waste energy they'd be on many more cars. Who doesn't want free power?

I wonder if an oversized wastegate could be used as a bypass for the turbo at cruisnig loads to alleviate the back pressure?

 

Good point James. That explains why they are not good for mileage.

 

But, if you dump the turbo drive gasses when cruising, then you are back to an unboosted low-compression engine.

Not to nitpick, but the trubo does also heat up the intake air, such that in many cases an intercooler is needed to keep the engine from detonating itself to pieces.

Now, somebody needs to bring up the old dream of variable-compression engines, maybe also turbocharged?

 

To be expected from a Corvette guy. Chevy needs 7 liters just to make 500hp? Even Hyundai can do that. Ignoring HP/liter is often done by those that need to justify a crappy motor.

 

Disadvantages are normally outweighed by the advantages.

And it's not free. The big disadvantages of Turbochargers on small cheap engines is that they are relatively expensive.
They are a complicated application on todays electronic engines with their associated emmisions equipment (higher development costs).

Basically, for a given power you can use a smaller TC engine (with the associated better fuel consumption) than naturally aspirated engine.

Waste gating totally negates any benefit a turbine will bring.

 

Very true. I was thinking that as I typed but I didn't include it for some reason.

A direct injected turdbo motor should be able to have decent compression though. I bet we see some more of those in the medium term future.

 

Define "crappy"

Costs less is "crappy"?

Gets vastly higher mileage is "crappy"?

Less complicated is "crappy"?

I want to know why more or less HP per liter is important.

Chevy doesn't need 7 liters to make 500hp. They do it that way because it is the most cost and fuel efficient.

 

All true to a point. There are lots of bigger NA motors that get the same mileage as a simlilar power TC engine so there is an obvious penalty for turbocharging. There is no benefit to a turbo at cruising speeds so wastegating around it would only help.

 

I still remember two points that old Smokey made about the simple pushrod American V8 -

a). He said that 4 valves/DOHC would not prove to be of much benefit to a large V8 road engine. Our V8s are operated at such low RPMs that this kind of breathing is not very useful to them. This is proven by an honest assesment of my 1995 ZR-1 engine compared to my 2004 Z06 engine. Both make 405 hp, the Z06 has the advantage by 15 ft/lb of torque, and will do the quarter mile maybe a tenth faster. The ZR-1 will rev 1000 more RPM and has a much higher top speed. Both return about 25-26 mpg on the highway, due to the high overdrive 6th.

b). He said that in stock-car racing, the ultimate high HP reading on a dyno at high RPM was meaningless. Races were won and lost by the torque/HP curve in the acceleration range well under the HP peak. This gives you power to pass, outdrag other drivers after a caution, pull out of a draft from a following car before he can jump you, etc.

So, you do have to give the big block pushrod Corvette engines pretty high marks for performance & efficiency - especially compared to their smaller displacement turbocharged competition.

What I was suggesting above was that maybe there is room for Ferrari to take up part of the big-inch, torquey, and efficient philosophy like GM with their traditional 12 cylinder designs. My Testarossa, after all, really works more on torque than raw RPM - it really will do everything I normally need between 2000 and 4000 RPM - and most TR owners praise the torque just as much as anything else about the car. Wonder if it could be made to turn 26 MPG with light weight, better modern FI or DFI, higher compression, and suitable gearing (maybe a 6th?)?

 

I believe the large displacement engine is going to become rare due to increasing mileage requirements. We will get increased mileage by making cars lighter, recycling energy and making the engine more efficient. Turbos help towards this end by recycling exhaust energy and by providing power on an as need basis.

Stay out of the throttle and you stay out of boost and your mileage will be pretty good, although maybe not as good as the NA engine in cruise; it is a tradeoff between usable power and mileage. Brake regeneration and systems like that help engine efficiency by shutting down unneeded systems during throttle/braking so the motor can focus on moving the vehicle.

We will also see advancements in diesel and this is where the biggest bang for the buck is. There is new technology out there called HCCI or Homogenous Charge Compression Ignition. This is the new generation diesel. Unlike conventional diesel, where gas and air get compressed until detonation, in HCCI the fuel is squirted at the last second at the top of the piston stroke. There are technical challenges with HCCI but most agree that it will be very, very efficient. Turbo HCCI is where it’s at.

 

Why is it garbage?

 

V-10 balance issues - too big & heavy - horrible exaust note (many say it sounds just like a UPS truck)...

I guess some people do like these things, but I will never understand why.