[Muscle Master]

Originally Posted by Allpar

I thought I read that the HEMI's cylinder walls are not as strong as LS-engines. I know the first LS1s were pretty thin and later ones would accept a little larger honing, but I thought I remembered seeing that the 6.1s were thin. I think a lot of what's been posted is obvious regarding power and such so I won't beat a dead horse there. It's aluminum instead of heavier iron. I'm not sure of all the options for the HEMI, but you can get to 427 c.i. on an LS3 without resleeving (I've only seen sleeving options to get 426 on the HEMI, but again, I'm sure there are other options.) I believe the HEMI is more complex, at least in the ignition department. It's my understanding HEMIs needed double spark plugs in the past in order to burn off more the unburnt fuel in order to get past emissions; again, I don't know how reliable this is. LS-engines don't require this.As a MOPAR guy I'm sure you could give me insite there too I know that LS-engines have pretty good rods and cranks but the early rod bolts were a liability. I've read about many LSXs (not the block, just generic for LS1, 2, 6, etc.) running 800 RWHP with stock cranks and a lot running with 600 RWHP with stock crank and rods and the LS3 has, largely, components from earlier LSX engines.

I think it's hard to argue, from the standpoint of what past posts already have, that the LS3 is just plain superior from the factory. When you start modding it, that might change, but I don't know enough about the HEMI to argue that...

I don't have time to answer your ? but this should answer your qustion

Originally Posted by Allpar

Each cylinder has an ignition coil pack over one spark plug, and a regular plug wire connected to the other spark plug. Further, the coil pack also has a plug wire attached to it that extends to the opposite cylinder bank. It appears that each cylinder shares a coil pack with another cylinder. Each of the two plugs on a given cylinder is fired by a separate coil. One plug has a coil directly attached, and the other is fired via an ignition wire connected to a coil located on another cylinder on the opposite bank. The benefits would be one-half the number of coils (8 vs. 16) compared to each plug having its own coil, and of course less weight.”
“Cryptojoe” wrote: “Being the good Motech Graduate I am, I can say that the extra plug fires during the power stroke to more fully burn the hydrocarbons. Unlike the Japanese systems of the late 1970s and early 1980s, which avoided the use of catalytic converters, the second ignition allows additional power in the down stroke while lowering the need for restrictive catalyst plates in the converter. This increases breathing, adding to horsepower output as well.
“As you may recall, in the 1980s Japanese manufacturers reduced unburned hydrocarbons by placing spark plugs either in the exhaust pipe (which fired with every piston ignition) or in the exhaust manifold (which fired each time their corresponding cylinder fired). Chrysler morphed this idea to include dual fired plugs on each cylinder, which allows the firing to take place closer to top dead center, and then again when the piston is on the back side of the power stroke.”
Patrick added: “This [also reduces] NOx and O3 (ozone) emissions. Full combustion results in heat, water, and carbon dioxide. While a very small amount of NOx emissions are produced, they are only significant during incomplete or partial combustion, due to the lack of available oxygen, high temperatures, and various chemical reactions. That's why catalytic converters have been standard on cars for the past 3 decades. The extra set of spark plugs on the HEMI and on previous engines are designed to reduce emissions BEFORE a catalyst is needed. They add some horsepower, but not very much. The only exception to this rule is on top-fuel dragsters that almost literally 'pour' gas down the venturis. A single plug can't burn that much gas, regardless of the ignition’s power output

Dual spark plugs are used to speed fuel combustion, making the engine more powerful and efficient while decreasing emissions (though not down to ULEV levels). A cylinder deactivation system, which does not appear to be related to systems used by Mercedes, was originally designed into the engine to prevent fuel from being wasted when the engine is under light loads. We don't know whether this was continued, because it is not mentioned in any of Dodge's current publicity materials. (Thanks, Troy Kleffman.)

And

Originally Posted by Allpar

The basic, deep-skirted engine block structure was redesigned with reinforced bulkheads to handle higher loads.
To get more air in and out of the cylinders, SRT engineers bored out the diameter of each cylinder by approximately 3.5 millimeters in order to increase the total displacement from 5.7 liters to 6.1 liters. Cylinders are honed with torque plates to ensure a truer bore, to reduce friction and increase power.
Oil squirters, aimed at the underside of each piston, are added to aid piston cooling for engine durability. A special oil pump pressure relief valve is added to accommodate the squirter oil flow.
The oil pan and windage tray are modified to manage oil return to the pan sump at high engine speeds and improve power.
Larger-diameter, flat-top pistons with high-load capability are specified to handle the SRT 6.1-liter HEMI’s compression ratio, which was increased to 10.3:1 from 9.6:1. Connecting rods are redesigned and make use of higher-strength powder metal material. New floating piston pins are introduced to handle higher loads.
The SRT 6.1-liter HEMI’s crankshaft is forged from micro-alloy steel and rotates in tri-metal main bearings for high-load capability. The crankshaft damper is retuned for higher engine speeds.
The SRT 6.1-liter HEMI features cylinder head ports designed with larger cross-sectional area. This allows 11 percent higher flow in the intake ports, and 13 percent higher flow in the exhaust ports.
A billet steel, high-strength camshaft features more overlap and lift for better performance.
Intake valves feature hollow stems and 2 mm larger heads compared to the 5.7L engine, allowing more air flow. The hollow exhaust valve stems are filled with sodium to dissipate heat efficiently. Premium valve springs with external dampers enhance the SRT 6.1-liter HEMI’s valvetrain and enable higher engine speed operation to 6,400 rpm. The valvetrain system enhancements allow the peak output engine speed to increase to 6,000 rpm from 5,000 rpm — a 20 percent increase.
Engine breathing is improved with specially designed intake and exhaust manifolds.
The cast aluminum intake manifold is designed with shorter, larger-diameter and tapered runners for high-speed tuning. Internal runners are core-dipped to smooth the runner finish and improve air flow.
Fuel injector flow capacity is also increased by 14 percent over the 5.7-liter engine. Electronic throttle control is shared with the 5.7-liter HEMI, but breathes through a revised high-flow air cleaner box outfitted with a tuned resonator delivering a deep performance sound character (and good for an extra eight horsepower).
Exhaust headers on the SRT 6.1-liter HEMI are individual tubes encased in a stainless steel shell. Exhaust runners allow increased gas flow while maintaining fast catalyst light-off, while adding 12 horsepower over the 5.7-liter engine’s cast manifolds.
To control the combustion process, SRT engineers fine-tuned the engine management system using dual knock sensors with premium fuel.
So why aren't these items used in the stock Hemi? Well, in some cases, they demand premium fuel, a tradeoff many drivers aren't willing to make - 340 horses move nicely, and many won't spend an extra 20 cents a gallon for another 20 or so horses that will be hard for most people to feel. In other cases, it's gas mileage - the 6.1 is a performance motor and gas mileage was not the primary concern. In most cases, though, it's a matter of money; the standard Hemi does an incredible job of producing high power at low cost, especially compared with, say, similarly powered Volkswagen or Mercedes V8s.

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