niugnep

From service manual for LMG 5.3L, 2007. They ARE different.

Bill Reid

iTrader: (14)

... and someone will need to determine if the new fancy lifters are lift sensitive... seeing is how they still ride on the cam while oil pressure prevents pushrod actuation. I think it would be cool if an aftermarket cam can be installed yet still retain the newly engineered fuel economy.

Bill

nighthawk08

the way I see it at some point they could no longer collapse enough to stop the pushrod actuation. Its just a matter of determining at what lift that will occure.

interesting to see the cam lobe specs. I wonder why they have more lift. What purpose does that serve?

eallanboggs

iTrader: (1)

I read as much information I could get my hands on about AFM and VVT. I still have those articles and I'll quote them directly or provide a link. I'd like to be able to do a cam swap on a NEW Silveado as much as the next guy, but finding out what I had to contend with in regards to AFM and VVT I gave up on the idea. I had a cam ready to go and even some Comp Rs to go with it, but AFM killed that idea. At least I have a set of Comp 1.85 Pro Mags and Comp Hi Tech hardened pushrods to go with the rollers. Maybe higher ratio rockers will be the way to go for people who want to increase lift and duration some if they can't do a cam swap. That's the route I'm going to take anyway because I already have the parts sitting on the shelf in my garage. The information I've read on VVT is even less clear than on AFM. The articles used the word "phasing" which to me implies that it both advances and retards which I don't think VVT does. I believe it only retards the timing and if I remember correct the intent was to retard the exhaust. That's all well and good, but it's pretty hard to retard the exhaust without also retarding the intake as well on a single cam system. VVT has to be a clutch system of some sort. Either hydraulic or electromechanical. If it's hydraulic then that means an additional solenoid to control the oil flow. I wish GM would have left this engine alone. VVT and AFM shows where GMs priorties are and it certainly isn't towards the high performance aftermarket. The increases from VVT and AFM would have to gargantuan to compensate for the inability to do a cam swap they create. Stop and think about how many of the sponsor on this site or LS1Tech that are offering aftermarket cams for the 07 Silverado with AFM and VVT. I can't think of a single one.

nighthawk08

I still want to know why you couldn't put an aftermarket cam in an AFM engine? There may be a reason or two that you can't, but I'd like to know where the limitations are. You stated that it can't be done but didn't provide a reason. I'll leave VVT out of this because 99% of the trucks have 5.3L in them which don't have VVT.

2006 8.1

I don't think any 5.3's have VVT. Just the Active Fuel Management. Which, by the way, in 5,000 miles, I can't tell any difference in economy from my 05 with 4.10 gears and my all aluminum flex fuel 2007 with 3.73 gears. They both get 15.5 on the I-state at 80mph. Had I known that, I would have stuck with the 4.10s

nighthawk08

correct.

the afm settings prevent it from coming on very much, tuning the AFM settings may be able to get you some more mileage....but thats still up in the air also.

eallanboggs

iTrader: (1)

After having reread the article it appears you might be able to install an aftermarket cam if one were available, but I don't believe it is. Keep in mind that the reluctor wheel has to be moved up to the front from the back where it currently resides. Now let's say for the sake of argument you could put your hands on a cam like this which you install along with a set of old style lifters. You've also removed the LOMA assembly because you don't need that anymore. My biggest concern are the oil passages that lead to the LOMA(which has now been thrown in the junk pile) as well as the oil passages that lead from the LOMA to the "special" lifters which we are no longer using. These oil passages have to be blocked off in such a way that oil flow in the rest of the oil gallery is not inhibited in any way. This last task to me appears to be the most difficult. And what about the lifter trays that the old style lifters use. I doubt this new block uses them. If it doesn't will the lifter trays fit into the new style block and has the block been driiled and tapped for the bolt that holds the lifter trays in place? These are just a few of the questions that need to be answered. Now that I think about it a first time cam swap on this engine isn't going to be a walk in the park as we currently think of it. On this motor the heads and intake are going to have to come off so you can get to those "special" lifters. That sucks. Well maybe not. I was going to pull the heads off anyway to install my StageII Patriots. Now all I need is the cam because I already have a set of the old style Comp Rs. I will have to pop for 4 lifter trays, but heck those are only about 5 bucks each. Anyone know who sells this aftermarket cam?

nighthawk08

I'm sure it can be done by eliminating all the AFM stuff...

But I'd also like to know what would happen if you left it in, and active? What would happen with a larger camshaft?

Also, any GenIV cam will work in the new motors, there are plenty of people running cammed LS2's which are essentially the same thing with more displacement and no AFM (although the provisions are in the engine for AFM).

niugnep

I thought it was interesting that the afm cylinders have more lift...must be to have a better lobe profile for engaging and dis-engaging?? I think in a little bit the aftermarket will have cams for this engine, nothing special really other than the diff lobes which may or may not be required.

I have some info on VVT, one pdf is attached, the other is too large (its the actual take apart and description). PM me with e-mail and I'll send it.

I think these engines will be just as capable once these things are sorted out. Its just new is all.

And on my RCSB I am getting pretty good mileage around town (20 US mpg), highway anything over about 65 mph its in V8 all the time, but still knocking down about 23 US mpg @70-75mph, truck is still new (1200 miles) with the 5.3, 20's,3.73's and full load. It helps in town for sure, not so much on the highway unless you want to drive at 60mph everywhere....

One other thing, the manual says if the cam must be changed then the lifters must be changed. Not sure if they are assuming lobe damage which would (of course) require lifter replacement..the only reason GM would replace a cam is if it went flat or broke, so changing the cam for the sake of performance not sure if they can be lifted up like the Gen III, the parts pics appear the same but we'll have to wait until some brave person tries it I guess. Lifter replacement requires head removal.