Definitive answer to variable cam timing on e78... retard, advance, or both?

Good morning, all. I have a very simple question, but have gotten many, many conflicting responses from my research just need to know the answer to this question(s):

The E78 ECM in a Cruze 1.4t. Variable cam timing, WOT tables. Is the following correct?

Intake, WOT table:
0 = parked (6.5-8.5 degrees BTDC) (I have seen varying numbers, the idea being that they are parked in that range before top dead center)
+1 = X degrees of retard in camshaft rotation
n > 0* = retard (or rather, camshaft degrees of retard from the parked position, which is 0)

Exhaust, WOT table:
0 = parked (6.5-8.5 degrees BTDC) (I have seen varying numbers, the idea being that they are parked in that range before top dead center)
+1 = X degrees of retard in camshaft rotation
n > 0* = retard (or rather, camshaft degrees of retard from the parked position, which is 0)


The rest I am asking, if because I have see conflicting info; some say that both cams can ONLY retard from their parked position. Others have stated that the intake can ONLY advanced from parked, and exhaust can ONLY retard from parked.

The stock tune on the E78 for the cruze 14t has the intake cam starting at low numbers and gradually ramping up, while the exhaust cam essentially dives down and STAYS down around 1* in those tables (which when logged, shows it chillin around 9-.95*, which I have to assume is retard, keeping the exhaust valve closed earlier, allowing the turbo to force more air into the cylinders).

Basically, what I am asking is this: On BOTH cams, are the BOTH retarded from parked (regardless of the number) or is the intake ONLY Advancing, and exhaust is only retarding (as positive numbers from from 0, or their parked position.).

I would greatly appreciate anyone that has some definitive insight on this, as for v8 and v6 applications, there is a lot of info, but it varies from platform and gen to platform and gen. I just need to know what the tables I have to work with actually do.

Also note that I am not talking about the low/me/high tables. PURELY the WOT tables for the intake and exhaust VVT tables.


Thanks for any info you can give me on this that is vetted and proven. I don't have access to a dyno, and WOT run kill gas hard and the cops don't much care for the noise and such. ;)

Really? Nobody knows at all? Not the admins? Employees? Other tuners?

I was not surprised you did not get an answer. Very few know, and not many of those that know are going to share at this time.
Good luck and keep asking. I'll keep watching.

ZZP has a 400 HP Sonic. Maybe they know.

So, I have found that the following is true pretty much across the board for GM VVT setups:

Intake advances
Exhaust retards

Both, at least on the LUV, park at 8 degrees of camshaft rotation BTDC (Intake)/ATDC (Exhaust).

The same rules for boosted engines apply for cam timing, and you just really need the think about LSA to where you want to position power. I spent a few months digging into this, and like, 100 flashes later. Probably not kidding. I would seriously sit there, log, run WOT, change a little bit, repeat, over and over for a few hours almost every damn day, and have found what these engines tend to like. Of course, I am sure there are others that are much better at this stuff than I am, but I know this platform very, very well, as I have been screwing with it every day up until recently for 2 years. Still some kinks to work out, but yeah. Long story short, she will do at least 140. ;)

And I am sure they do, but I seriously doubt they are going to share that, which I feel somewhat the same about, as the way I have my cam timing set up for my particular vehicle, I can give tips, but I likely won't be giving exact numbers any time soon.

Will update if I learn anything about it. Currently I like running as much on the exhaust as I can ~23? but cant seem to delete the intake cam. Seems to pin at ~20 at idle even if I zero out all the tables available. Might search in a hex editor for more tables if I'm not missing something obvious...

I am very much interested in this, too. Here's the stock angles for the Opel Corsa 2016 and Opel Corsa 2019 (A14NET) 1.4T engines running E78 and E78A ECU respectively.

Attachment 122124

And a short log of an experiment i did. At WOT i locked the intake at 28 deg, and the exhaust at 2 deg up to about 4000 RPM. The result was 250 kPa desired MAP, but the car barely boosted to 150 kPa (absolute values).
From 4000 to redline i did the reverse, so 2 deg intake and 28 deg exhaust. The boost was basically instant at that point.

Attachment 122125

These engines, compared to the rest of the GM DOHC VVT engines use a unique phasing strategy. Both cams are mechanically fully advanced when in their parked (0*) position. From a mechanical timing perspective, the exhaust cam opens VERY early, so the only time you see the commanded angle less than around 8-10* is under light load / economy situations where pumping losses can be reduced. Under these same circumstances, intake valve timing is fully retarded to reduce pumping losses during intake / compression.

For spool-up, the exhaust cam is fully retarded (around 30*), and the intake cam is fully advanced (0*) to provide maximum amount of overlap. Once spool is achieved, both cams settle in the 14* range or so.

I'm glad this was resurrected because there is virtually no info on VVT timing. Before VVT most engines pretty much liked the same lobe centerline for a given rpm. Surely there is a chart somewhere that shows typical ideal centerlines for VVT?
As for the turbo, I don't know what timing it prefers. tunerpro mentioned max Ex retard for spool up and max adv Int. Are you saying that is ideal or just what the mfg of that eng did? Mine eng is a twin turbo Mercedes V8 and it's numbering system and timing are different than GM, but once deciphered to lobe centerlines I'd imagine we want pretty much the same thing?

I understand the advanced Int for low rpm to net more gas to exhaust, but I'd assume any actual overlap will kill that, especially in a turbo. I'd assume a turbo will always want zero overlap, but rather than thinking about overlap, or lack of it, I'd think when the Ex opens and where its centerline is mattes most.

Regardless of what the Int is doing I'd assume there is an ideal Ex the turbo wants for each rpm and I'd assume at low rpm the Ex should be advanced to spool sooner? It seems it would be a better blast of hotter Ex under more pressure but there are a lot of factors between the Ex valve and the turbine so I'm likely missing something? Maybe the second half of the time it's open ends up killing the advantages? Or maybe we're not talking lower rpm? Whatever the case/rpm, how would ideal Ex timing differ from a NA engine, which I do understand?

I have small turbos so they spool up too fast at lower rpm and overboost, so I'd like to reduce that <3k. Then after 4k my boost drops fast, so any help there would be nice. So far my tinkering to increase >4k has done nothing >:| Probably just at my limit thanks to Ex flow after the Tbo but I was hoping...

https://www.youtube.com/watch?v=bnIsNwdKnCw

This might be of help to some people.


So i installed a bigger turbo on my 1.4 engine last week, this is the boost curve at the stock intake and exhaust cam angles.
200 kPa MAP at about 4200 RPM. There is 10 degrees of freedom in both directions on the intake cam with the stock configuration (see above).
I will try advancing/retarding by 5 degrees some time in the next two weeks and then post the results. Every other parameter will be identical. Wastegate DC will be fixed at 95% and only the turbo lag/spool RPM will be measured.

Attachment 122500

Any updates with this test? I saw some people advancing the exhaust cam to provide early spool (advanced exhaust provides hotter exhaust gases helping the spool)

https://www.enginelabs.com/news/spoo...ing-for-boost/

Quote:

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Originally Posted by vitorsegnini

Any updates with this test? I saw some people advancing the exhaust cam to provide early spool (advanced exhaust provides hotter exhaust gases helping the spool)

https://www.enginelabs.com/news/spoo...ing-for-boost/

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Disclamer: not trying to prove which way advances or which way retards which camshaft. And honestly when you're testing that kind of stuff for yourself, it's irrelevant. Just what's the best combination for the 1.4T engine with any kind of turbocharger.



It's VERY complicated doing this on the road, you can't fix the RPM in place and simulate different kinds of loads with the throttle like you can on the dyno. And honestly you could spool a 1000 hp turbo with a 1.0 liter if you try hard enough with VVT and proper tuning.

The stock VVT tables are exactly perfect for the stock turbocharger fastest spool time in the RPM range where it was designed to spool the best it can, from 1000 to 2000 RPM which turns out to be 25 degrees exhaust cam. Here's some screenshots. These pulls were done back-to-back on the same stretch of road and the timing was fixed using the controls in the VCM Scanner.



Attachment 124460

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And here's what turbocharger surge looks like, it's the kind that you do NOT want to see or hear. Wide open throttle and going stutututu, this creates the most stress on the shaft connecting the compressor and turbine.
The kind that goes stututu after you release throttle is harmless mostly as there's no more exhaust pressure creating forces of opposite direction on the turbo components.

Attachment 124464

This is 10 degree intake and 25 degree exhaust combo. This will keep spooling the turbo as much as it can irrelevant of the RPM, it will just take quite some time. It's great if you have a huge ass turbo that can't spool under wide open throttle, but you want to drive on low RPM and basically high load uphill. And even some highway driving with some hills.
Obviously not great for this turbo as it surges, this is a stock 270-300 hp unit from a 2.0 Turbo engine from the Astra H OPC/VXR and it manages full boost at about 2800 rpm on that engine.

This is a perfect situation where performance camshafts will help, it will swallow more mass airflow under the same boost pressure. Which means it moves the point of operation to the right on the compressor map and away from the surge line, which means even more boost, woooooo! (and more power)


Attachment 124465

Here's the stock turbocharger with 28 degree intake and 2 degree exhaust - don't do this, the turbo doesn't want to spool AT ALL. But 2 degree intake and 28 degree exhaust works just fine.

All logs attached below

Attachment 124466
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Attachment 124470 - the one with the surge
Attachment 124471



From my limited testing today - intake makes little difference, higher degree exhaust makes most of the difference. To make it more effective - lean out the fuel as much as you can and retard the timing as much as you can.
You want the hot HOT exhaust gasses expanding in the exhaust manifold to make the turbo spool as soon as it can. When you're up to the required boost, the situation is a bit different. Any combination will keep the boost just fine, after that the task is to make the most power you can.
This brings me to a good hardware modification - you want the exhaust header wrapped. Same mass of exhaust gasses - but hotter, because you're not wasting heat and keeping it trapped inside - create more pressure in the limited volume of the exhaust header which means it makes the turbo do its thing faster.

Another great experiment are intake cam angles, you want to keep it at just the right spot to make the most power for a given intake manifold pressure. Advancing as you go up in the RPM range.
You CAN do that without the dyno, but it involves a bit of math, basically measuring and taking the fastest acceleration between two points across the RPM range, and in the end merging to get the final intake angle curve.

Also i just noticed... when you hover over the WOT Desired Angle Base button, in the lower right corner it mentions a range of expected numbers inside.

Stock manual transmission cruze tune. WOT desired angle for intake AND exhaust mentions a range from 0 to +32 degrees.
This is what the numbers and the 2D curve look like.

Attachment 124605

Attachment 124606


Stock manual transmission opel tune, 2019 year car, newer E72 ecu. WOT desired angle for intake and exhaust range is -64 to +64 degrees.

Attachment 124607

Attachment 124608

The desired angle range is 0 to 128 degrees on both.


On the opel, the WOT angles for both intake and exhaust match the last row in the desired angles tables.
Both seem to be a single 1 byte number, gonna try figuring out a formula to convert between the two. This leads me to believe one of them might be misrepresented.

EDIT:
The formula to convert between the two is like this

CHEVY = OPEL * 0.25
OPEL = CHEVY * 4

Basically copy paste between the two and either multiply by 4 or 0.25 to get the correct scale

I think the chevrolet one isn't represented properly in the vcm editor, i wonder what the cam angle logs show when driving the car.

1.4 uses the same sprocket on intake and exhaust cams. Both are locked fully advanced by default. What is you see in VCM editor and the scanner are both retard.

When you start the car you can watch the VVT solenoid duty cycles and cam position. You will see the intake cam unlock and slowly retard towards 24 degrees.

This is actually not true. The intake is parked at 8? before top dead center and the exhaust is parked eight degrees after top dead center or what it considers one in vcm suite or zero essentially so as you start to advance the intake or retard the exhaust and for the record from what I've seen you can only go from parked and advance the intake and you can only go from parked and retard the exhaust. Do you can't go negative then what it's parked at. So intake always advances exhaust always retards. The there really isn't a point to retarding the intake because advancing the intake is what allows for more power. You'll never see a variable cam timing system that retards the cam to gain power. Unless it's doing something with the exhaust Cam and tangent to increase overlap in those areas where naturally aspirated vehicle would require it. But from what I've read they work the same way as every other VCT system that GM has intake advances exhaust retards they're both parked at 8? before and after top dead center respectively and they only move one way I mean of course you can retard back to your part position but you can't retard less than your parked position. That's been my understanding and I've actually used that successfully to gain a surprisingly a lot of power right where it's needed in the cruise. I'd say between my variable cam timing setup and my flex fuel conversion and running 80% ethanol and of course up in the power and advancing the timing a bunch which is only capable of doing that because of the flex fuel conversion those two things right there gave me more power than every other mod that I put on my car it gave me more power than my intercooler more power than my cat lives down pipe and more power than anything all put together was just playing with the cam timing and advancing the spark with the aid of the 80% ethanol that I was running.

What I said is 100 percent correct. They are the same sprocket and park in the fully advanced position. You cannot advance it any more than the parked position. Everything is in degrees of retard.

0 degrees is parked, any other number is degrees of retard.

Attachment 125764
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In the above post I added some general info about how VVT works.

Here is a picture of the exact sprocket on this engine. You can see the large spring that returns the cam to the parked(advanced) position.

Attachment 125766

Well, good news is my ZZP camshaft arrived and i'll post tuning results and numbers as soon as we get it installed and put on the dyno.

Here's something else, in the meantime. As this whole cam thing is very interesting.

Attachment 125770

These are the cam angles from an Opel Astra K 1.6 SIDI engine. Engine codes A16SHT/B16SHT. Developed by Opel, using the E80A ECU.
Got the stock file for that if anybody wants, but i digress.

The cam angles seem to be fixed under wide open throttle


Attachment 125771

And here's a comparison between the 1.4T engine (left) and the 1.6T SIDI engine (right).
Numbers aren't the same but the general outline and shape seems to be very similar.

Now why would they have fixed angles for WOT?