[s346k]

Originally Posted by 6spdhyperblue

...at most I landed on a end goal of ported heads and oe LT5 cam

funny you mention this. once i tracked down the LT5 cam specs i was sold on this idea. i wonder how the curve will act without vvt mushing it along over 6k.

[NA18CamaroSS]

Has anybody tested the LT5 camshaft against the GM hotcam?

[KingLT1]

The LT5 cam is the same spec cam as the LT1 minus the AFM lobes. So you would have to delete AFM to run it. I also believe the LT5 has a different fuel lobe. You can get them from Scoggin Dickey for less then 200.00 bucks. Might be a good option for those that want to delete AFM and keep the stock cam profile. There were some companies that had "AFM delete" kits for the Gen 4 LS engines with AFM but I haven't seen anything yet for the LT1.

LT5- 200/207 .551/.524 116.5 Non AFM.

LT1- 200/207 .551/.524 116.5 AFM

[KingLT1]

Originally Posted by cmitchell17

So I know what you're saying about deleting things. I feel the same way and I would love to be able to keep cam phasing on my cammed LT1, but like s346k was saying its more trouble than its worth. So I believe the issue with trying to retain VVT with bigger cams is supposedly the phaser can become unstable and not command the right position. Now this is just all what I hear, I have never tried using and experimenting with my VVT with my bigger than stock cam and valve springs, but most of the big shop all came out with "VVT optimized" cams when VVT first came out on the GEN V LT1 and some of the truck GEN IVs. I think the issue is that with bigger cams you need stiffer springs and I think this supposedly makes it more difficult for the phasing mechanism to do its job from the increased spring pressure and therefore, increased friction. I am having a hard time logically concluding this though.

I would love to see a lot better and more hard data on the subject like logs and dyno runs comparing advancing and retarding a bigger cam. The stock tune if I remember correctly sits at the fully advanced position and is retarded by the phaser about 9-11 degrees at WOT starting at about 4000 rpms or so. I have heard people comment that they weren't able to get any better power numbers than the factory gets with the 9-11 degrees.

I think the main reason for the VVT phasing from the OEM side is it provides a built in EGR functionality. Like others were saying it kicks on at cursing speed and retards the camshaft by about 30 or 40 degrees if I remember correctly. The intent here is to try to leave the exhaust valve open way too long and have some exhaust sucked back into the cylinder. EGR is mainly for emissions, but it can increase efficiency by effectively diluting the air charge. It basically displaces some of the fresh air with "used up" air. So by doing this it has to open the throttle more to keep the same torque output. Opening the throttle as much as you can helps reduce pumping loses and increase efficiency.

That being said the difference and gain in efficiency for any of this stuff we are talking about is so negligible and small it is not noticeable and I would be willing to bet it is well within the uncertainty range of what you can calculate your fuel mileage.

I see the potential in using the VVT to try to make bigger cams behave better at idle although I haven't really thought it through but it seems like control reversion with big overlap numbers, which is similar to what I was describing above.

The point of VVT is the ability to advance the cam timing at lower RPM to gain low end torque and then be able to retard it for better top end. It doesn't have anything to do with EGR. The problem with VVT and higher lift and duration camshafts is the loss of Piston to Valve clearance. This is why the limiter kits were initially introduced to keep valves from hitting pistons. However several shops found out that locking it out all together didn't really sacrifice much at all in the midrange for better top end. Yes there is a torque loss from idle-3k rpm but most don't seem to mind that trade off.

http://www.superchevy.com/how-to/eng...n-iv-v-engine/

[6spdhyperblue]

Would be better if they were lt2 spec w/o afm but hey if we’re going there, Chevy performance, make an aluminum l8t 400ci crate with that cam and ported heads

[ShiftingSS]

Appreciate everyone’s input, and thinking lt2 and a ported tb with e85 and test pipes is probably the way to go.

As far as vvt, afm, and reliability goes, some of the advice around here is simply crazy, nothing else to say. Everything has a trade off.

[6spdhyperblue]

What’s the trade off with deleting afm hardware? It’s not enabled on m6 cars from the factory? Just dumping the hardware theoretically should improve performance and reliability.

[s346k]

Originally Posted by ShiftingSS

Appreciate everyone’s input, and thinking lt2 and a ported tb with e85 and test pipes is probably the way to go.

As far as vvt, afm, and reliability goes, some of the advice around here is simply crazy, nothing else to say. Everything has a trade off.

have you ever seen an afm lifter? as well as the cam phasing hardware...? one look at those things and you'll change your mind.

[cmitchell17]

Originally Posted by KingLT1

The point of VVT is the ability to advance the cam timing at lower RPM to gain low end torque and then be able to retard it for better top end. It doesn't have anything to do with EGR. The problem with VVT and higher lift and duration camshafts is the loss of Piston to Valve clearance. This is why the limiter kits were initially introduced to keep valves from hitting pistons. However several shops found out that locking it out all together didn't really sacrifice much at all in the midrange for better top end. Yes there is a torque loss from idle-3k rpm but most don't seem to mind that trade off.

http://www.superchevy.com/how-to/eng...n-iv-v-engine/

Why wouldn't they just ensure adequate PTV through changing the calibration? Are you saying stability is not an issue? I wish it wasn't but I've never actually tested it out myself with a bigger cam and springs since I put a zero lockout in mine.

[KingLT1]

Originally Posted by cmitchell17

Why wouldn't they just ensure adequate PTV through changing the calibration? Are you saying stability is not an issue? I wish it wasn't but I've never actually tested it out myself with a bigger cam and springs since I put a zero lockout in mine.

Because there isn't enough PTV to swing the cam timing around very much...it has to be limited to maintain enough PTV. Yes stability is a issue as The limited phaser starts to fluctuate mechanically at higher RPM 6700+... so that is why many shops started locking it out. If you build the combination correctly you won't lose a ton of low speed torque with it locked anyway. The key is to increase compression to make up for the loss of DC from the larger cam.

[6spdhyperblue]

That’s why the 0-4* limiter is the way to go...the phaser is strong enough to work as a switch. When in this configuration it will hold 0* and 4*..closed and open. This way the phaser accuracy is not needed except for holding 0* which it can, then when commanding 4* it will land and stay up against the limiter plate. No fluctuating

This would give you that advance to get some early and then open to 4* to carry up top. Just make sure to go with a cam that’s specd to have ptv clearance with the 4* swing..cam motion

[KingLT1]

GPI found that they make more power up top with the phaser locked opposed to the 4 degree limiter. The phaser becomes flaky mechanically with limiter kit up top. Pray even seen the same thing in his testing. The info is out there or well it use to be. I wish these guys would go back to posting this stuff on forums instead of Social Media platforms so it's easier to search and find again for future use.

[6spdhyperblue]

For sure, if I cammed I’d go pray stage 2, locked. Hands down. To me that one gets the most out of it and beyond that is diminishing returns(unless you cut the hood)

I was just saying if you were compelled to use vvt, that’s the best you can do...and at least were the results from cam motion on their stg 1
If going this route pick a stg1 cam with the mildest lobes u can and look to maximize idle stability, off idle torque and carry the power. I was planning on going down this road but ended up deciding to keep the oe stick

Agreed on fb

[ShiftingSS]

Originally Posted by s346k

have you ever seen an afm lifter? as well as the cam phasing hardware...? one look at those things and you'll change your mind.

Saw the bulletin and you have a point, just mean it’s hard to measure overall mix of responsiveness + power + efficiency, and locking the cam back dates this engine by about 20 years when it comes to a mix of those factors, that’s all. Different strokes 👍