Anyone run locked out VCT?

[honeybadger]

Howdy all,

As part of my bi-annual engine rebuild, I am exploring all and any options. Given my recent piston to valve contact and the (4) failed VCT plugs/harness issues I've had, I wanted to explore locking VCT out a bit deeper. Here's what I am learning below:

Pros:
-Reduce possible deflection in the phasers (results in mechanical timing not matching what the computer is commanding)
-Reduces weight of the rotating assembly
-Reduces complexity
-Some might say sound

Cons:
-Fairly large TQ loss (am told up to 100ft lbs, but levels out by 5-5.5K RPM)

Some considerations on my end:
-Ultimately, I plan to go with a sequential which would help ensure you're always in the powerband (however, this is a ways down the road)
-Not really looking to break records, but have a fun and reliable car that I can thoroughly thrash at a high level
-Engine sees 4.5-7 track hours a track weekend


Would love to hear thoughts from those with experience and exposure in this area!

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[Angrey]

I would think if anyone can make the pros/cons make sense, it's a dedicated track car like yours where you can live in the powerband.

The VCT is most helpful to driveability and production for those of us who aren't die hard track rats.

Without it as you've pointed out, it eliminates weight, eliminates potential failure points or potential issues, etc. But you basically revert back a step in technology where you have high flowing cam that does poorly in the lower bands but screams like a maniac up top.

One "positive" that's subjective is that without the DCT you could return to a real "ghost cam" tune and actually have real/genuine idle chop

I think outside of blown crazy builds where the tuner/builder is looking to simplify, your use is probably one of the few N/A situations where it makes sense. For everyone else I'd say keep the VCT.

 

[JAJ]

It's fairly easy to find out if you like fixed valve timing - just have a tune made up with the VCT settings locked to a specific set of values and take it for a test drive.

As for things like deflection, there's a sensor and a feedback loop to correct it, so it shouldn't be a problem in a practical sense. Same with the wiring - doesn't FP have phasers for race engines that have a different, more robust, connector on them?

All that said, fewer parts = more reliability, so there are benefits.

 

[honeybadger]

I would think if anyone can make the pros/cons make sense, it's a dedicated track car like yours where you can live in the powerband.

The VCT is most helpful to driveability and production for those of us who aren't die hard track rats.

Without it as you've pointed out, it eliminates weight, eliminates potential failure points or potential issues, etc. But you basically revert back a step in technology where you have high flowing cam that does poorly in the lower bands but screams like a maniac up top.

One "positive" that's subjective is that without the DCT you could return to a real "ghost cam" tune and actually have real/genuine idle chop

I think outside of blown crazy builds where the tuner/builder is looking to simplify, your use is probably one of the few N/A situations where it makes sense. For everyone else I'd say keep the VCT.

I'd love me some idle chop. Not as great as a true big cam, but it's a bit of fun still. I'm leaning towards it, but not 100% sure yet.

It's fairly easy to find out if you like fixed valve timing - just have a tune made up with the VCT settings locked to a specific set of values and take it for a test drive.

As for things like deflection, there's a sensor and a feedback loop to correct it, so it shouldn't be a problem in a practical sense. Same with the wiring - doesn't FP have phasers for race engines that have a different, more robust, connector on them?

All that said, fewer parts = more reliability, so there are benefits.

You have a great idea about the tune, but unfortunately the motor is at the builders. If only I had a second motor

I think I'd rather have Tim degree the cams and then me decide I don't like it and switch back than have me worry about degreeing the same. I need less potentially catastrophic responsibilities with this engine for a while

You can buy a more robust harness that helps solve some of the issues, but it will be a custom job and cost a couple K from what I looked into it last year. I've been waiting until I settle on the right balance of sensors and will probably do it when I switch to an aftermarket ECU.

 

[JAJ]

I'd love me some idle chop. Not as great as a true big cam, but it's a bit of fun still. I'm leaning towards it, but not 100% sure yet.



You have a great idea about the tune, but unfortunately the motor is at the builders. If only I had a second motor

I think I'd rather have Tim degree the cams and then me decide I don't like it and switch back than have me worry about degreeing the same. I need less potentially catastrophic responsibilities with this engine for a while

You can buy a more robust harness that helps solve some of the issues, but it will be a custom job and cost a couple K from what I looked into it last year. I've been waiting until I settle on the right balance of sensors and will probably do it when I switch to an aftermarket ECU.

The easiest way to get a second Voodoo engine for testing is to get a second GT350. Ticks a lot of boxes, actually.

Also, if you're not going to have any bottom end to speak of anyway, then how about a set of these: LM-GT3F-1 Camshaft Kit? In for a penny and all that.

 

[honeybadger]

The easiest way to get a second Voodoo engine for testing is to get a second GT350. Ticks a lot of boxes, actually.

Also, if you're not going to have any bottom end to speak of anyway, then how about a set of these: LM-GT3F-1 Camshaft Kit? In for a penny and all that.

HA. Everyone keeps pushing me to get the cams, but not convinced they're a big enough gain. If I was settled on keeping VCT, it's a no brainer. But if I do a VCT delete and keep it, i'd probably run for a custom grind that has been optimized for it.

 

[Angrey]

HA. Everyone keeps pushing me to get the cams, but not convinced they're a big enough gain. If I was settled on keeping VCT, it's a no brainer. But if I do a VCT delete and keep it, i'd probably run for a custom grind that has more lift.

Absolutely. If you're gonna give up VCT, then it only makes sense to get the benefit of a big cam. .550" is fine if you're a jack of all trades, but if you're gonna be limited to the top end, make the top end big. What do you think is the biggest lift it can handle with the compression and clearance to the piston?

 

[bauern]

Absolutely. If you're gonna give up VCT, then it only makes sense to get the benefit of a big cam. .550" is fine if you're a jack of all trades, but if you're gonna be limited to the top end, make the top end big. What do you think is the biggest lift it can handle with the compression and clearance to the piston?

Max lift doesn't effect PTV clearance, duration does. That's one of the reasons larger duration cams require lockouts.

 

[jmn444]

Max lift doesn't effect PTV clearance, duration does. That's one of the reasons larger duration cams require lockouts.

seems like it would affect it on the exhaust stroke? I mean, even with same duration and just more lift, the valve has to ramp up quicker to achieve higher overall lift right? so wouldn't there still be less clearance when the piston is close to tdc/bdc?

 

[honeybadger]

Max lift doesn't effect PTV clearance, duration does. That's one of the reasons larger duration cams require lockouts.

Do you have any experience with lockouts?

 

[bauern]

seems like it would affect it on the exhaust stroke?

No, that's the duration holding the valve open too far as the piston approaches TDC, or overly retarded ex. cam timing.

 

[bauern]

Do you have any experience with lockouts?

No, sorry. Only that longer duration cams by design would cause the phasers to overadjust.

 

[Angrey]

Max lift doesn't effect PTV clearance, duration does. That's one of the reasons larger duration cams require lockouts.

It does if you plan on holding it long enough. If you're narrowing the duration to the point that the cylinder is bottom dead center, then yeah, lift is theoretically limited by the length of the bore stroke.

I'm talking about duration long enough where there's intersection, what's the maximum lift? I'm assuming it's pretty close to .550."

In the past I've seen dished pistons that would help (but mess with the compression) but it goes without saying if you want to lift higher than the clearance dimension, it's going to come at the cost of duration, which in the case of a DOHC (2 valves) it's not all that detrimental. 4V motors don't have to lift to the moon to get good flow.

The recent heads I just had done by MPR flow 380 CFM at 28" H20 and .550" lift. That's pretty friggin' amazing. I'm wondering how far out we could squeeze that lift (with the same duration) before contact.

 

[honeybadger]

It does if you plan on holding it long enough. If you're narrowing the duration to the point that the cylinder is bottom dead center, then yeah, lift is theoretically limited by the length of the bore stroke.

I'm talking about duration long enough where there's intersection, what's the maximum lift? I'm assuming it's pretty close to .550."

In the past I've seen dished pistons that would help (but mess with the compression) but it goes without saying if you want to lift higher than the clearance dimension, it's going to come at the cost of duration, which in the case of a DOHC (2 valves) it's not all that detrimental. 4V motors don't have to lift to the moon to get good flow.

The recent heads I just had done by MPR flow 380 CFM at 28" H20 and .550" lift. That's pretty friggin' amazing. I'm wondering how far out we could squeeze that lift (with the same duration) before contact.

That's impressive. RGR only got 338.4 CFM at .550 lift on mine

 

[Angrey]

That's impressive. RGR only got 338.4 CFM at .550 lift on mine

Indeed. And it's not even the +1 valve sizes. Tyler indicated they didn't think the +1 was all that beneficial. And I've read/heard it creates shrouding issues, so when he said 380 I was like, yeah, that's more than "enough"

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