Lightning Lexuses

A 4-valve hemispherical means that there is less room for the valves to move than in a 4-valve pent-roofed. A true hemispherical shape with 4 valves does not make much sense to me: there needs to be two valves open at a time, and in a hemispherical design any two valves that would be open at the same time would collide. That means costly repairs if you start your engine -- or the valves need to be very small, eating up all the inherent benefits of a

4 valve design.

Cadillac Northstar V8 uses Peugeots 1912 design, pent-roof combustion chambers.

The pent-roof combustion chamber can achieve stable operation over a wide mixture range providing good economy and good power in a single package.

The power of the engine depends on three factors: volumetric efficiency, thermal efficiency and turbulence.

When compared with a hemi, I believe that volumetric efficiency is better in the pent-roofed design. Thermal efficiency and turbulence are probably either equal or slightly better with the hemi, but overall the pent-roofed design is better -- though a bit more expensive.

What comes to chamber volume and rising compressions: My guess is no. The design of the piston crown can compensate for the volume of almost any design.

Jaguar did some work for rising the compressions for getting higher efficiency from their V12 engines. They got to the point of 14:1 compressions with their Fireball chamber (designed by a swiss engineer Michael May). Most likely the efficiency gains produced huge amounts of NOx and the ratios were lowered to 12.5:1 to the production version and subsequently to even lower ratios.

I believe the pent-roof design of the cylinder head is mostly about the volumetric efficiency, i.e., the flow of gases is more free with the 4-valves in a pent-roof design than with anything else designed so far.

BTW, as far as I know, there are no penthouse combustion chambers although I have to admit that that would probably sell better in some consumer classes -- "complete with the softest pink interior and all the essential lowrider options"

How are you spec'ing out a GS to make it $70,000? They go for mid $40's around here.

I'm wrong on two counts:

1. I was thinking of the LS
2. Even the LS isn't ,000

I stand corrected. I was being sarcastic, by the way.

I was a little sloppy with my math, but no one questioned the superiority of the HEMI power now did they? Maybe Chrysler will drop in the 500 hp Viper engine like they did in the big Dodge truck!

Time to watch Monster Garage where they will be working on a HEMI Dodge station wagon. I cannot wait :)

PS... I heard that MTV is doing a "Pimp my Ride" Lexus series.

I have been trying to explain that there is nothing inherently superior with the hemispherical design. The highest kw per liter is found in engines with pent-roof combustion chambers, not hemispherical. The only superiority is in marketing.

Latest V8 hemispherical

- Pushrod-operated overhead valves, 16 valves

- hydraulic lifters with roller followers

- Sequential, multi-port, electronic, returnless fuel injection

- Cast iron block, aluminum alloy heads, hemispherical combustion chambers, 90 degree V

- Compression Ratio: 9.6:1

- 257 kW / 5,654 l = 45.45 kW per liter

Respective ratios for some of the latest 4-valve pent-roof designs:

Honda Accord 2002: 114 kW / 2.0 l = 57.0 kW/l Honda Accord 2002: 140 kW / 2.4 l = 58.3 kW/l BMW 545i 2004: 245 kW / 4.398 l = 55.7 kW/l BMW 525i 2004: 141 kW / 2.494 l = 56.5 kW/l VW Phaeton W12: 309 kW / 5.998 l = 51.5 kW/l VW Golf 1.6 FSI: 85 kW / 1.6 l = 53.1 kW/l VW Passat 2.8 V6: 142 kW / 2.8 l = 50.7 kW/l Cadillac XLR 4.6: 235 kW / 4.6 l = 51.1 kW/l Lexus LS430 2004: 213 kW / 4.3 l = 49.5 kW/l Toyota MR2 2004: 103 kW / 1.794 l = 57.4 kW/l Corolla 1.6 2004: 81 kW / 1.6 l = 50.6 kW/l Saab 9-3i: 90 kW / 1.8 l = 50.0 kW/l Renault Megane: 83 kW / 1.6 l = 51.9 kW/l Mazda6 2.3: 122 kW / 2.261 l = 54.0 kW/l Mazda RX-5: 107 kW / 1.839 l = 58.2 kW/l

It seems difficult to find lower power to displacement ratios than what hemi is offering - actually I was able to find two engines, but those were really not performance oriented at all. Some sports engines offer even more embarrasing ratios, but I am not 100% sure that these are still naturally aspired:

Ferrari Enzo: 492 kW / 5.988 l = 82.2 kW/l BMW M: 252 kW / 3.246 l = 77.6 kW/l

The Japanese are setting the benchmark for the reasonable family cars category in the range of 58 kW/l. The latest HEMI is about

30 years behind this with its 45 kW/l ratio.

HEMI is a registered trademark of DaimlerChrysler Corporation. A lot of money is poured in to make people believe it is a fine piece of technology. However, it has more image value than technical value. The biggest gains are in cheaper production, not in power or economy. Of course a company will spend a lot of money that (saved in engineering and manufacturing) to make people believe that they are getting the best.

If you like the sounds, have been brainwashed by DaimlerChryslers long-term marketing campaign, or just cannot afford more advanced technology, you might as well buy a push-rod HEMI. I like my car silent and powerful, not noisy and powerless.

MTV? Everyone in my town is pimping their used Lexi.