1000HP Z06 Build with some issues. Mechanical and tuning related.

[JASON11WS6]

So the car is a C7 Z06 with a Magnuson 2650, big cam ported heads and about 21psi. I rebuilt the engine after the oil pump froze up on me during a pull. Clearances were good, everything went together fine.

First issue we had was the head was leaking coolant (ported hit a water jacket). Swapped that out and once we put the 5" intake and 112mm throttle body the idle seemed to go to hell. I updated the tune and when it's warmed up the car drives excellent. But while it's warming up if you try to put it in gear the car starts to backfire. Timing goes straight negative and it's like the car is going into boost at idle. I suspect it has something to do with not enough vacuum with the big intake and tb. Anyone else have any issues with the big intakes and tbs? Pretty sure the vacuum drops and the bypass opens open and it's a run away effect.

On the mechanical side the oil pressure started dropping. After just rebuilding the motor I'm fairly concerned. At start up its around 40 but if you let it sit and get warm it'll drop to 15 psi. Also, it'll overflow a little coolant too if you let it idle long enough or take it for a drive on a hotter day. I wonder if the head surface (it's been off a lot) needs to be decked again? Would a bad head gasket cause enough issues to lower the oil pressure before the oil really has a chance to get heated?

Just trying to get this car sorted out before I lose my mind. Any help is appreciated.

JUICEDZ.2650.2023.005.VTT.hptJUICEDZ.2650.2023.IDLE.hplJUICEDZ.2650.2023.003.hpl

[TriPinTaZ]

What happens if you increase the MAF value by 10% in the low RPM range and decrease the VVE in the same area by 15-20%?

[Joshinator99]

I ditched the vacuum bypass and went with a Smoothboost electronic boost controller. Completely fixed the low vacuum issue at idle.

[1scls1z]

What happens if you increase the MAF value by 10% in the low RPM range and decrease the VVE in the same area by 15-20%?

Agree...This is what I would try.

[Alvin]

What happens if you increase the MAF value by 10% in the low RPM range and decrease the VVE in the same area by 15-20%?

Curious if you think you'd get the same result failing the MAF and doing VVE? I've been experimenting lately with this and the last pretty good sized cammed cars have all been completely straight with a hammered out VVE and almost none to none VT changes.

As things evolve its always nice to see what we can get away with not doing that in the beginning we used to think was required.

[JASON11WS6]

Your advice is usually spot on with the idle stuff. I'll give this a shot.

[JASON11WS6]

I ditched the vacuum bypass and went with a Smoothboost electronic boost controller. Completely fixed the low vacuum issue at idle.

I'll look into this. Sounds like a good option although it's a little pricey.

[GHuggins]

Problem is the torque model on the idle part. Airmass side is probably still too high or being ramped wrong and map side too low causing the throttle to open. I've even gone in behind some tuners that had the off idle torque models too high causing them to build boost during normal light throttle input. You either have to learn how to tune the models or don't mess with them. I've never seen one idle right with a stock model after being heavily modified even with the VE and everything dialed in perfectly. You've completely changed the motor and then you lowered the map torque model with the VE corrections whilst raising the airmass side of the model with the MAF corrections, so there's no mathematical way that they can still be the same after the fact.....

[TriPinTaZ]

Curious if you think you'd get the same result failing the MAF and doing VVE? I've been experimenting lately with this and the last pretty good sized cammed cars have all been completely straight with a hammered out VVE and almost none to none VT changes.

As things evolve its always nice to see what we can get away with not doing that in the beginning we used to think was required.

Failing the MAF is the old way. I don't do this anymore. But as Greg said, its all a mix. Airmass, VVE, and Virtual Torque. They have to be close enough for each one to make sense in Dynamic Air Calcs or you get weird behavior.

[Alvin]

Yeah, but my point is that old way gives different results.. I think superior IMHO. which seem to work out a lot down the line too. It's worth a shot.

I mean to be perfectly honest.. the car I did last week started off with me backing out VVE. Timing was negative or too low at least. failed the MAF, VVE in 2-3 revisions and reenabled MAF and timing is where it should be.

[TriPinTaZ]

I didn't mean to imply it wasn't valid anymore. I just don't typically do it that way anymore. There are certainly instances where it is necessary but I haven't had to in quite some time.

[GHuggins]

I still fail the MAF, but honestly with Cringer's or even my own old MAF correction formula it's not necessary. I've done it and I still find it necessary to tweak the torque models to get everything balanced out. Especially if you want gear engagement and accessory engagement to not be felt and it's really required on the cams idling at 80kpa...

Have you ever logged delivered torque with a stock calibration vs one with the VE and MAF dialed in and I mean actually log delivered torque in the torque model layout form - in other words for each spark and cam position - not just regular delivered in a single table??? If you do you'll understand what I'm talking about, because it's completely obvious when you start plugging the numbers back into the cal. When you dial in the VE you typically for the most part lower it for cams right? Watch what that does to delivered torque - guarantee it's way lower than it was originally in the map models. The airmass side will stay close because typically the MAF is increased from the Cai's and this actually counters the map side of the equation some..... What can wind up happening if it's not dialed in - especially on the blown ones - is timing will do screwy things on take offs, auto's will shift all over the place with any sort of hills or mountains and so on. I just corrected a 4th gen for a guy not a week ago that had his MAF and VE both dialed in to +/- 3 % and his was engaging and disengaging the TCC with light throttle input. All I did was log and correct his torque model. No more problem and per him - it was driving and idling the smoothest it has...

Plus something I find to be pretty true on these 5th gens is I guarantee it might be running on different timing an hour or two of operation after tuning due to how the models learn - they'll actually shift up to 60 or so Nm's I'm told before they hit their capped limit. 60 Nm's can make a big difference on idle timing and drivability both...

Now if it's simple mods, those are a whole other story and in this case leave the VE tables and torque models both alone

[edcmat-l1]

So the car is a C7 Z06 with a Magnuson 2650, big cam ported heads and about 21psi. I rebuilt the engine after the oil pump froze up on me during a pull. Clearances were good, everything went together fine.

But while it's warming up if you try to put it in gear the car starts to backfire. Timing goes straight negative and it's like the car is going into boost at idle. I suspect it has something to do with not enough vacuum with the big intake and tb. Anyone else have any issues with the big intakes and tbs? Pretty sure the vacuum drops and the bypass opens open and it's a run away effect.

On the mechanical side the oil pressure started dropping.

Edit: I see it's an auto. Still think they're possibly related.

I'd bet these 2 symptoms are not coincidence.

PS would love to see a crank sensor O-scope waveform in P/N/D.

[Alvin]

I didn't mean to imply it wasn't valid anymore. I just don't typically do it that way anymore. There are certainly instances where it is necessary but I haven't had to in quite some time.

I notice the ones I do forcefully with a failed MAF drive quite a lot better at parking lot speeds and the power comes on more predictably. They drive more like a GEN 4. Backing out VVE works for a portion of them. But even the ones that seem satisfactory I wonder how much better they would be if I did them with a failed MAF first.

Torque reads the same although this is so dynamic hard to know 100%, it takes surprisingly little work to get the idle straight, MAP is what you'd expect with whatever cam..etc.