: New 04" 4.6 vs previous 3 less MPG?



MichSTS
03-18-04, 11:54 PM
I was told that the new 4.6 has been totally redesigned with 80% of the components being different or redesigned. I also noticed on the stickers at the dealer lots, that they are rating the vechilces with 3 less MPG. Makes no sence. Can any one explain why the milage has slipped & what are the major changes.

Thanks in advance John

LymanSS
03-19-04, 01:17 AM
The redesigned northstar is the one that shows up int he XLR and the SRX. It has variable valve timing which results in more power and torque. It is also designed to be longitudinally mounted in a rear drive car nstead of the transverse setup in the front drive seville and deville. To the best of my knowledge the 2004 devilles and sevilles sill have basically the same engines they had before.

Scott



I was told that the new 4.6 has been totally redesigned with 80% of the components being different or redesigned. I also noticed on the stickers at the dealer lots, that they are rating the vechilces with 3 less MPG. Makes no sence. Can any one explain why the milage has slipped & what are the major changes.

Thanks in advance John

BeelzeBob
03-19-04, 11:41 AM
Several things changed with the Northstar engine for the 04 model year.


First, the transverse front wheel drive version of the engine is basically unchanged. Some internal parts changed slightly but, for the most part, the engine is carryover from previous years. The TFWD engine does get the polymer coated pistons and the forged steel crank in 04 but, functionally, that doesn't affect the operation of the engine.

The RWD version in the XLR, SRX and recently released STS is significantly changed. That is the one you are referencing that is "80% new". Several design changes had to be made to the engine to mount it longitudinally in the new RWD vehicles and changes had to be made for RWD and AWD applications. Fundamentally, the cooling system for the engine had to be completely revamped as the FWD engine had the water pump at the rear of the engine and all the water plumbing and such at the rear. With the RWD engine the water pump and plumbing is at the front necessitating changes to the accessory drive, block and head casting changes, water passage changes, etc. The RWD engines get variable valve timing on both the intake and exhaust cams. To control the 4 cam phasers the lube system had to be significantly modified as well as oil plumbing in the heads. Lots of new hardware in there. The VVT gives a slight power increase and a MUCH broader torque band. The VVT also allows the elimination of the external EGR system which simplifies the engine control system significantly...although the VVT control is adds a great deal of complexity and sophistication.

As far as the fuel economy ratings....much there is controlled or influenced by the car the engine is in, the mass of the car, the AWD applications (more mass, more friction, more rolling resistence, etc...), how the engine was certified and tested for the official fuel economy label...i.e...which engine/car represents the major engine family for certification. There is usually only one fuel economy label for an engine family regardless of carline or engine power output so the rating may seem "low" or to have "changed" from previous years when in reality the engine is exactly the same fuel economy/efficiency but the number may decrease due to the production mix of cars, volumes of cars produced and the recertification required to get the EPA fuel economy number for the new mix. All manufacturers will try to use their best fuel economy player to get the official EPA fuel economy rating....but sometimes there is no high fuel economy package for a particular car line to fall back on....

If your concern is that the engine is "less efficient" then you can rest assured that the new RWD Northstar version is much more powerful and efficient than the previous generations (due primarily to the VVT system...as well as better flowing ports in the heads and larger valve sizes...) but the official fuel economy ratings may appear lower than in the past due to model mix and application changes.

Some things to consider are that the RWD Northstar only goes into the performance versions of the cars it is in. With the FWD cars the LD8 engine with the 3.14 final drive ratio and skinny, hard fuel economy tires was the volume leader and the fuel economy "pick" for EPA. Tires make a HUGE difference in the fuel economy rating on the EPA test due to the rolling resistence. On the XLR, for example, the only version of the car has large, performance tires and an agressive axle ratio....not the best for the EPA number but good for what the customer wants. Similar on the SRX and STS....the Northstar is in the lower volume, performance package with the large tires...the V6 is the fuel economy leader for that package with the lower rolling resistence, all weather tires.

Bottom line, the EPA fuel economy rating is to be taken with a large grain of salt..... It is about the last thing to judge the engine or powertrain technology or absolute efficiency by...