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More info on the 6.1 Hemi

This info is lifted off the allpar.com site (great resource). Required reading before you think of modding your SRT-8:

What makes the SRT version different

The SRT version produces another 85 horsepower and 30 lb-ft of torque than the 5.7 liter Hemi, and only some of that comes from the extra .4 liters of displacement. The Hemi produces more power per liter than any past Chrysler V8, including the 1966 Street Hemi, though with the technology available today, that's not surprising. Changes to the 5.7 include:

• 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.