3.9L LZ9 engine internal upgrade & performance?

[SappySE107]

Non VVT cams don't fit without the TCE cam bearing spacers, which were supposedly discontinued. You can PM CNCGuy about it if you want to investigate that option.

[paramount]

Well I have talked to a lot of L99 and LY6 guys on lS1 tech and some of the engineers there say that you can get gains just from tuning the cam phaser. Here is a quote "Make sure to tune cam phasing table
I have been tuning VVT vehicles for 3 years with EFI Live and I can tell you that there is tons to be gained from playing with cam phasing whether you choose to keep the stock VVT cam or go with an aftermarket cam.

In stock form, GM will retard the cam timing 20-30 degrees in the cruising rpm/load range in order to pick up some fuel economy. Basically, they are trying to make the motor act smaller and the EGR that is created dilutes the incoming air charge. In my testing, this practice AT BEST, increases fuel economy up to 1 mpg, but the loss in torque means that the vehicles are gutless when cruising and will often have to downshift from 6th to 5th or even 4th gear just to climb a slight grade.

In my tuning, I will advance the cam when it benefits the engine and retard it where it makes sense. With the stock cam, I've actually gained torque by retarding the stock cam some at 1200-1600 rpm in order to run more ignition timing. You see, the engine makes best power when peak cylinder pressure occurs at 13 degrees after TDC. If the cam is advanced too much at lower rpm, you have to retard ignition timing too much to stay out of knock. As a result, you make peak cylinder pressure well past 13 degrees ATDC. This reduces torque.

Basically, you need to balance ignition timing with cam phasing. They both go hand in hand. EFI Live has dozens of VVT tables that address cam phasing and ignition events that happen only with cam phasing.

With aftermarket cams, they benefit from more advance at lower rpm because of the EGR and lower dynamic compression they produce. For what it's worth, the GM software only retards the cam so you need to spec your aftermarket cam with the maximum amount of advance that you expect your engine to see (while keeping a careful eye on P to V clearance). I like the TSP VVT cams more than the MAST VVT cams because they don't run an excessively large exhaust event. Running too big an exhaust event hurts torque down low (when you advance the cam) and gets P to V clearance really tight (when you retard the cam). Most of my VVT cams have smaller splits between intake and exhaust.

[paramount]

In other words I have decided to stay with VVT because even though it has difficulties, I think the advantages outweigh the challenge

[NateD4]

I'm going the other route (keeping VVT but using a custom cam). I'll post once I see how well it works or doesn't work.

[gectek]

There is very little to be gained from the VVT that Gm uses. I have tried to tune them. Most of the people see gains just from the TM delete and normal spark advance and AFR correction and fuel trim correction. You want to see what a maggie L99 dyno graph looks like?

Tell me if anything looks funny. Now guess what happened to that car? That one even has a custom grind VVT camshaft in it.

[paramount]

There is very little to be gained from the VVT that Gm uses. I have tried to tune them. Most of the people see gains just from the TM delete and normal spark advance and AFR correction and fuel trim correction. You want to see what a maggie L99 dyno graph looks like? [ATTACH=CONFIG]6809[/ATTACH]

Tell me if anything looks funny. Now guess what happened to that car? That one even has a custom grind VVT camshaft in it.

False statement. TSP makes cams for the V8's and their stage 3 cam has dyno proven at least 70 more horsepower at the wheels. Maybe the custom grind cam tech
didn't know what they were doing or maybe the tuner wasn't experienced with VVT.

[gectek]

That was a TSP cam and they worked with them on the cam tuning and dyno like they do to all of them. Maybe you are not listening, I have first hand results of all of this as i was there and am working in the LS industry every day. Not a false statement at all. How is it a false statement that they do not work as well as a normal cam? They have LS3 cams out now that make 500 RWHP. You cannot do that with a vvt cam. Sorry. I will try and find a dyno graph, but I guess you just dont get it. GMs VVT system is flawed and the tuners are not using it like it could be, but even if they did, it would still make no difference. The standard cam will make more power. I have about 3 dynos to prove that, but I guess proof isnt good enough?

[NateD4]

I'm not sold that GMs VVT is flawed (useless). I will agree that a true variable overlap and variable duration would yield better results. However I think VVT has some gains to offer. I'll find out when I get my new VVT DOD cam for the LZG. But by all means post some dyno numbers. It would be interesting to see.

[1988GTU]

VVT is in my opinion not worth the hassle due to it creating more parts to manage for. I would only leave VVT in place for emission purposes only, which is what it's main purpose in existence is for.

[Z26-T]

VVT is in my opinion not worth the hassle due to it creating more parts to manage for. I would only leave VVT in place for emission purposes only, which is what it's main purpose in existence is for.

X2
VVT is great for removing the need for an EGR.

[gectek]

I am sure that is not the reason. At all. If it were, all the original LS6 engines would have VVT. Cam design will produce its own "egr" action with overlap.

[NateD4]

That won't happen unless you plumb in the exhaust into the intake.

the overlap will help with scavenging from the cylinders.

[ericjon262]

I am sure that is not the reason. At all. If it were, all the original LS6 engines would have VVT. Cam design will produce its own "egr" action with overlap.

overlap doesn't change on the high value engine's VVT, so this wouldn't be the cause, now changing valve events could give an EGR action, but it's not overlap.

[gectek]

Does anyone understand what egr does? And I did not say the VVT engines had the ability to change overlap in the ohv engines. Now it def will on the DOHC ones.

[NateD4]

EGR, exhaust gas recirculation... does exactly that... pipes some exhaust back into the engine and burns some of the unburnt mixture/oil.

I don't think the LZ series have EGR. I found no indications of it when I tore down the 3.9L