3.9L LZ9 engine internal upgrade & performance?

[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.

[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.

[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.

[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?

[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]

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.

[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.

[paramount]

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

[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.

[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]

So go with a non VVT cam and tune out the VVT?

[gectek]

Answers in red.

When you say retarded, do you literally mean they are retarded compared to centerline of the crank. Or are you saying they aren't good? I meant they are horrible for any type of camshaft honestly.

Also I thought the whole reason for VVT on pushrod engines was to adjust the RPM range where peak torque happens (as much as you can with fixed duration). I know you can manually advance or retard most cams with a variety of aftermarket items (offset bushings, pulleys etc..). I've never heard that the effects aren't worth it before. I usually hear it provides some shifting of peak torque. The whole reason is to try and use advancing and retarding a camshaft while in motion to provide more torque down low when needed. Honestly the VVT system shuts off at like 3k or somewhere of the like unless otherwise tuned. So it is used to try and promote lower end power and possibly raise fuel economy by making more power available sooner without going to a larger camshaft for OE vehicles. On every VVT application that I have put a regular camshaft in, I have gained fuel economy. And I tuned the vehicles before with VVT but to less avail on the MPG than putting in a straight cam and tuning it. This is in LS of course, but you get the point. Those cams you are referencing and the idea behind them are normally race inspired and would have no actual application in a DD world. Normally now, the advance is ground in (or retard ground in) so there is no need to advance or retard the cam, and in some instances you cannnot. They are normally to help promote power pickup in the lower RPMS due to building cylinder pressure. only being able to advance a camshaft by (honestly) a small amount, or retard it the same way, will not make any more power in the upper RPM, because the engines are limited to air flow in those upper RPMS anyway. Since the duration is fixed, it would not make any more power up there anyway honestly. Changing the LSA is where most of that comes in. The only real application that a normal person would see with this is the Gen 4 STR-10 vipers. They have an intake lobe phaser that changes the LSA of the cam and is more beneficial than any fixed VVT cam or controller.


I also though the OEMs use VVT to help flatten the torque curve out and to also allow them to get better economy. They do, but it does a piss poor job of it, as well as active fuel management. Every truck I have tuned, I turn it off and they pick up at least 3-4 MPG everywhere and some alot more than that. I can tell you the torque curve does not change at all and is mostly helped due to the availability to lock in more spark advance in the lower RPMS without it building so much cyl pressure.

When you say the longer runner fails, do you mean it produces not appreciable torque gains throughout the RPM band? Just curious. I mean the longer runner does not do its job as theorized and help make more torque early on in the RPM range. I will link those graphs in just a moment.

With that said are you saying runner length and plenum volume have no effect on power? Or just that the difference between the long and short runners are negligible? I am not saying plenum volume hurts anything, but the long runners of both the truck intakes and the 3.5/3.9L engines will kill any power that would be ideally promoted in the upper RPMS by say that tuning valve. That thing is ridiculous. The 660s already have a good length runner on them, there is no need to make it 9 times longer. Plus the 3.9L already has built in torque by displacement alone. More attention should be spent on porting and correct cam selection, which Ben addresses, and less on theorizing what better way to use the VVT cam honestly. Get rid of that Dual plane UIM also and go with the reg 3.5l one. That is worth power alone.


Sorry had to ask this is contrary to everything I've ever read or heard about cam timing and VVT. I know on DOHC engines they are able to alter the lobe separation angles.

[NateD4]

There was really only one company that was focusing their time on the VVT custom cams as Comp Cams shelf grinds are retarded, but they have since stopped that venture as they ran into issues with it not delivering as promised and the cost of parts was more than just using non vvt stuff. Honestly I have NEVER seen a power increase on any LS VVT system with a custom VVT camshaft over a non VVT design and I have been in the business for quite some time. It is just like the LS truck intakes with the longer runner supposedly promoting more tq in the lower rpms than the car intakes, again that myth was busted also. The LS VVT system is used primarily in the truck applications, where the longer runner intake is supposed to help them, but again, it fails horribly.

Just put a reg camshaft in it and be done with it. Changing the ICL is not that huge of a deal on the fly to even worry about. The biggest factor would be to being able to change the amount of duration the lobe is lifting and setting down the valve, but with the weak ramp rates of the cams, it does not make that big of a difference anyway and that is not the angle that people approach it from. They only see it as advancing or retarding the ICL and ECL, which is does as well, but the events happen so fast, its really a lose situation honestly.

When you say retarded, do you literally mean they are retarded compared to centerline of the crank. Or are you saying they aren't good?

Also I thought the whole reason for VVT on pushrod engines was to adjust the RPM range where peak torque happens (as much as you can with fixed duration). I know you can manually advance or retard most cams with a variety of aftermarket items (offset bushings, pulleys etc..). I've never heard that the effects aren't worth it before. I usually hear it provides some shifting of peak torque.


I also though the OEMs use VVT to help flatten the torque curve out and to also allow them to get better economy.

When you say the longer runner fails, do you mean it produces not appreciable torque gains throughout the RPM band? Just curious.

With that said are you saying runner length and plenum volume have no effect on power? Or just that the difference between the long and short runners are negligible?


Sorry had to ask this is contrary to everything I've ever read or heard about cam timing and VVT. I know on DOHC engines they are able to alter the lobe separation angles.

[NateD4]

What kind of engineer are you?

Aerospace.

[gectek]

There was really only one company that was focusing their time on the VVT custom cams as Comp Cams shelf grinds are retarded, but they have since stopped that venture as they ran into issues with it not delivering as promised and the cost of parts was more than just using non vvt stuff. Honestly I have NEVER seen a power increase on any LS VVT system with a custom VVT camshaft over a non VVT design and I have been in the business for quite some time. It is just like the LS truck intakes with the longer runner supposedly promoting more tq in the lower rpms than the car intakes, again that myth was busted also. The LS VVT system is used primarily in the truck applications, where the longer runner intake is supposed to help them, but again, it fails horribly.

Just put a reg camshaft in it and be done with it. Changing the ICL is not that huge of a deal on the fly to even worry about. The biggest factor would be to being able to change the amount of duration the lobe is lifting and setting down the valve, but with the weak ramp rates of the cams, it does not make that big of a difference anyway and that is not the angle that people approach it from. They only see it as advancing or retarding the ICL and ECL, which is does as well, but the events happen so fast, its really a lose situation honestly.