Gxp 5300 v8

[tblake]

Just curious,

Displacement on demand?

So at cruising it is a 4 or 6 cylinder? And when power is needed is all 8 cylinders are used?

Is it a reliable configuration? I know cadillac did DOD a while back and had issues, so the technology didn't hang around.

Is it a standard GM Pushrod type motor? So, when in 4 cylinder mode, Does it cancel fuel injectors and drag the valves along? Or are the valves actually cancelled somehow?

Just wondering....

[CrazyHorst]

Decent read here.

http://en.wikipedia.org/wiki/Active_Fuel_Management

The basic problem with allowing the valves to run while just simply shutting off fuel is that the O2 signals would go absolutely wacky due to the "free oxygen" in the mixture. Allowing the fueling to compensate would lead to the catalyst to turn cherry red (actually purple due to the insulation in the case) but you get the idea.

When you visualize the cylinder layout, the front and rear cylinders on the RH bank (2, 8) are active while the (3, 5) center cylinders on the LH bank are still active.

A possibly simpler alternative would be to allow open loop speed/density fueling of the active cylinders while the other cylinders would continue to pump air with the valves fully functional. The O2 signal is ignored in open loop since it's pegged anyway - however overfueling could not be allowed due to the catalyst temp effect above. However, running open loop for reasons other than (startup, power enrichment, piston, catalyst, or engine cooling protection) I believe are prohibited by EPA. Some of those overfueling events have also been threatened to be taken away as well leading to new engineering problems.

[tblake]

Very interesting, Thanks!

So the GXP 5300 is not a pushrod motor, (or is it), and how does it keep the intake and exhaust valves from opening when cruising with 4 cylinders?

[CrazyHorst]

More info here: "active fuel management" is a key phrase

http://www.gminsidenews.com/forums/f...agement-50389/

The Gen 4 base engine is close to the Gen 3 - small block V8 (derived from the Gen 1 and Gen 2 "classic" 350cid/5.7L iron block/iron head). The Gen 3 family (4.8, 5.3, 6.0) was used in similar displacement in trucks starting in MY 1999, mostly directed for the MY2000 GMT800 truck & utility production. Gen 4 (in truck form) is iron block aluminum head pushrod.

Just so we stay on-topic here, a couple features piloted in the SII 3800 "lives on" in the Gen 3 & Gen 4 V8. The investment cast roller rocker arms is one such component. The crank-driven gerotor oil pump in the front cover is another -- vastly superior in performance to the old spur-gear oil pumps attached to the rear main bearing cap if you ask little old me.

[CrazyHorst]

Here's a basic picture of how the valve(s) are deactivated. Basically a hydraulic system with an electrical signal controlling a solenoid valve that makes the lifter rigid or soft...although it is using engine oil as the hydraulic fluid....which is subject to chemical "change", contamination, and aeration. Those last 3 make the application more challenging than a typical industrial hydraulic system.

[BNaylor]

Originally Posted by tblake

So at cruising it is a 4 or 6 cylinder?

Its a V4.

The Active Fuel Management System aka DOD cylinders used are 1, 4, 6, 7. Obviously it is a reliable setup, however, GM did some improvements on the LS4 engine for the 2009 GM cars that have it.

[tblake]

Interesting....

When the oil is not applied to the lifters, and valves are cancelled, does the collapsed lifter make knocking noises?

[troy1]

From my understanding oil is always applied to the lifter its just that when DOD is active the lifter has a controlled leak and can not overcome the spring rate of the valve springs which make the valves stay shut. Because there is no real gap between push rod and lifter there is no noise.

[BNaylor]

Originally Posted by tblake

Interesting....

When the oil is not applied to the lifters, and valves are cancelled, does the collapsed lifter make knocking noises?

No! Tim, all you feel or hear is the smooth operation of an excellent V8 engine.

[tblake]

Hmmm, good to know. Sorry for all the stupid questions Bob.

[richtazz]

my aunt just picked up an '09 Impala SS, and it gets 34 mpg (at 73 mph with the cruise control set) on a highway trip from Flint, Mi to their cabin in Cadillac, MI while in 4cyl cruise mode. It will also break the tires loose on a 30 mph rolling punch with the trac control disabled. I'd say best of both worlds there! I'd have one or a GXP Grand Prix if funds would allow.

[BNaylor]

Originally Posted by richtazz

It will also break the tires loose on a 30 mph rolling punch with the trac control disabled. I'd say best of both worlds there! I'd have one or a GXP Grand Prix if funds would allow.

Rich, it is even better with TapShift which the Impala SS doesn't have.

I can make the tires sing going from 1-2 and 2-3 gear.

The best part is when AFM gets disabled when you put it pedal to the metal. The broad power and torque curve on this engine is amazing.

[grandprixgtx00]

Originally Posted by BNaylor

Rich, it is even better with TapShift which the Impala SS doesn't have.

one thing the Impala SS also does not have is different size tires, so when i DO break the tires loose at 30MPH, i can rotate them

but in all seriousness, i think i would rather have a GXP. Still love my SS though.

[BNaylor]

Originally Posted by grandprixgtx00

one thing the Impala SS also does not have is different size tires........ i can rotate them

235/50-18 versus 255/45-18. Nothing a spare set of front wheels and tires won't cure. I purchased two a few months ago.

Now the bicycle air pump I have in the trunk is a trip.

BTW - Whats with the shift indicator in the Impala SS or lack of any markings on the shifter?

[grandprixgtx00]

Originally Posted by BNaylor

BTW - Whats with the shift indicator in the Impala SS or lack of any markings on the shifter?

Funny you should bring that up, because thats one of the first things i noticed when test driving my SS. It only shows up on the dash cluster.