Why The Gen-V LT Outshines The LS

[j91z28d1]

yeah, I'm 99% sure I don't agree with any of that. vvt ls and non vvt ls both have no egr valve. egr was removed from the ls engine when the ecm got good enough to make them pass the epa limits without egr valves. somewhere around 2001-2003 I believe, depending on the car and long before vvt. there's not really a way to run exhaust back into the intake manifold using the cam. especially a single cam in block push rod engine just by advanceing and retarding the cam. this is been used for 50 years manually to move power band around. that's all it is.


as for afm, you're forgetting that both valves are left closed when 4 cyl is active. which means there's no air pulled into the cyl. so nothing to compress. you don't have pumping losses on those 4 cyl. so you're not only saving fuel burn from closed injectors, you're saving the tq needed to compress air/fuel. it 100% makes a difference but do the benefit out weight the down side of it breaking. not at all. it's junk because it fails. it would be just fine if worked for 300k without fail.


as for aftermarket vvt cams. this has also 100% been done. tx speed has spent a lot of time developing cams and they will supply a vvt tune for it. the 5 or 6th Gen camaros have vvt in the automatic cars and non vvt on the manuals. they get like 15ft lb of tq better with a correctly tuned vvt aftermarket cam. and it does show up on dynos and track. the liming factory is again the single cam in block. you gotta limit the amount of movement to such a small amount the bigger the cam gets so the valves don't hit the pistons., it almost isn't worth it. now a double over head cam with control of both individually. 100% worth it.

 

[RET423]

To get EGR doesn't require a seperate EGR system if you have VVT, the exhaust valve can be left slightly open at the start of the intake stroke & exhaust will be drawn into the the cylinder whenever the VVT wants it

The EGR effect is using inert exhaust gasses to pollute the air/fuel mixture enough to slow/cool its burn rate, how & when they get that exhaust to return to the combustion chamber is the EGR system

The old EGR system was replaced with VVT but EGR wasn't done away with

 

[RET423]

As for the AFM, having both valves disabled in the closed position increases load on the engine, GM designed it that way.

Take any syringe & place the plunger in any position you like, then put your finger over the end to simulate closed valves & try to move that plunger in & out; it will have vacuum resistance when you try to pull & pressure resistance when you try to push

This is how GM eliminated rattling when in V4 mode, but utilizing the resistance of trapped air to absorb the slack

If one of the valves was left open this resistance would be greatly reduced but it would still exist as a parasitic loss

But the parasitic loss even if removed wouldn't make V4 mode more efficient, the same power is needed to move the same weight at the same speed in the same conditions whether you create that energy with 4 or 8 cylinders; it's just physics

AFM is a gimmick that delivers less efficiency and increases engine maintenance costs & production costs

 

[j91z28d1]

I would disagree with basically all of that. if you have vvt control of dual over head cams you could in theory suck some exhaust back in the cyl. but even those cars have egr valves. it's not a good way to do it and with single cam push rod engine, you could never retard or advance a cam enough to do that without the valves hitting the pistons. there's a limit as how fast vvt can move a cam, and it's not per cycle. it's slowly a few deg over a rpm band. also many non vvt ls engine do not have egr valves. it was simply not needed to pass the epa limits with better ecm's. my yukon is ls hybrid 6.0 with a Miller cycle cam shaft grind. it's a one off late intake valve closing grind to let more fresh air/fuel out thru the exhaust to get a cleaner more efficient charge to compress, it requires more static compression since it's losing dynamic compression by doing that. no way it's sucking dirty air back into the cycle. it's specifically designed to do the exact opposite. and it doesn't have a egr valve.



as for afm pumping losses, do your experiment with the finger over the tip, yes it creates a vacuum and is harder to pull back, but let go and what happens? the vacuum pulls the piston back up. there's almost no actual loss. next time you have you valve cover off, pop the 2 rocker arms off, do a compression test and watch what happens. Basically nothing. you'll always have friction but that's about it.

 

[donjetman]

AFM is a gimmick that delivers less efficiency and increases engine maintenance costs & production costs

Its a transfer of wealth

 

[RET423]

EPA standards escalate, when tuning was able to hit the mark with greatly reduced EGR the factory eliminated the EGR system and ground the cam to allow a very slight EGR effect all of the time; this was sufficient to meet the EPA standard until they increased enough to once again require more EGR; by then VVT coupled with the cam grind was how they increased the EGR instead of reintroducing a stand alone system

Overhead cams are not necessary to create EGR, it can be done statically with a fixed cam grind or dynamicly with VVT or a combination of the 2 which GM has done