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Camaro ZL1 2014 Smaller SC Pulley + Bigger Crankshaft Pulley

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Hi, I'm getting issues with a customer 2014 ZL1 which I've tuned in Mexico (7800 feet over sea level) and now he took the car to Spain (sea level). Car was running perfect and making good power but now at WOT from 4,000 is making a hard hesitation, I don't think is a torque limit since I disabled all of them and also boost controls. At the beginning car was reducing boost and RPM, so I reduced ignition a lot (just for testing purposes) and now boost keeps almost stable but still RPM drops. How is this possible if there is not throttle closure, no boost decrease, no fuel cut, no spark cut. Attached you will find a HPTuners log.

If someone could take a look and help me, I would appreciate it!

Thanks in advance.

Attached Files

Hi Victor,

So the main issue we are looking at is the boost dropping after 4000rpm then not coming back yes?

Is the boost level the same it was when you initial tuned it or is it higher now? Seems to be running quite a big of boost and with no ignition timing at all?

To me it almost looks like the bypass valve is opening or if it is running more boost now are you hitting the factory boost limit. I would check both of these things, if you're still stuck, post a copy of your map and I will have a look.

Hi Chris,

Actually, there is a test where you can see that boost level keeps on 20-21 psi (test 3) and latest test it drops a lot (test 4). What I can see on test 3 is that MAF read decrease very quick, so I suppose there is a valve that is opening inside so engine is not sucking that much air.

But the main question is why? I disabled all kind of limit or boost control I could found, maybe there is something I can't find. Or maybe do you think I should reduce boost with boost controller and test it? (that will be my next step)

In Mexico, supercharger was making less boost of course because of high altitude.


Attached Files

Sorry I can not open the tune file, it is locked into a remote tuning session.

I would suspect you're encountering a boost limit, bypass valve setting now that you're at sea level and running more boost. Try drop the boost to the level it was at when tuned and see what happens. Is this on a stock supercharger? I am assuming running this sort of boost it must be upgraded.

You might even find running less boost and more timing you will make more power, or at least the same power but with less strain on the engine and heat. Running 23psi and ignition ATDC you might be able to drop to 18psi and now firing BTDC and still make the same numbers.

Sorry Chris,

Now is unlocked. I did try to enabled boost control by activating Torque Management Spark and ETC with no luck, car was constantly pulling out like 13 degrees then adding them. So now, I just let ETC activated and see how it works.

I supposed the way I can handle boost is with Torque Desired under boost control so I reduced it a lot in order to test it.


Attached Files

What we can see is we are losing air flow and boost although the throttle is not closing, there is only a few ways this can happen. S/C slipping (I don't believe this is the issue as you wouldn't see a sharp drop and then no boost, it would only be higher rpm I would expect to see this)

Bypass valve is opening, but why, is it from an over boost condition or a fault

Intake or exhaust collapsing, I would also only expect this at a certain rpm

So the things I would check and try from here.

Things I would try, I see it always happens around the same airflow (470g/s) and your max airflow vs rpm at 4000rpm is set to around 470g/s, this could be triggering potentially the bypass to open. This should also bring on code p0068, which I am assuming you have checked for codes? Maybe try disable this for a test or max out. Found under Engine diagnostics, air flow, P0086 enable rpm set to 8192 or raise table more.

Assuming its on a dyno, have some check the bypass valve while on the dyno, is it open, what happens if you force it shut, does it still open with solenoid unplugged, is the ecu controlling it or is it pressure related.

I would then try drop boost back to what it was when tuned and see how it reacts, if that is a stock S/C that is way more than they like to run. Might need to swap out pulley

Disable boost control for a test set map disable and enable to 256.

Is the intake collapsing, having someone check when running or take off intake pipe at the throttle body and try

The idea here is to see if any of these things causes a change or the fault to stop, then once you can narrow it down to a system can investigate why.

Hi Chris, thank you so much for your help. Let's see.

1. SC pulley slipping: checked and it's not.

2. Valve opening because of fault: I don't think so because it would throw me a code which is not giving me, this cars always throw "Reduced Power" message but this one is not doing it. At the beginning thought it could be because of MAF limit or MAP limit which is 37psi, but it would give a code also, which is not.

3 and 5. Valve opening because of overboost: wouldn't give a code also? should I try to disconnect any vacuum line to this valve in order to test it? I have read a lot of forum that this valves is only for idling, after it feels + pressure, it will keep closd. Car is in Spain far away from me that's why it turns so difficult to me. But yeah, I will try disconnect the valve.

4. Engine Diag->Airflow->Airflow Correlation: I have maxed out values in order to test it, but I think it should throw that code. (Let's wait for next test)

6. It has a smaller SC pulley and bigger crank pulley and customer left the smaller pulley with me in Mexico. :( (it will be next test if other things don't work).

7. Disable boost control (another test).

8. If I remove the intake pipe MAF sensor is going to be crazy, isn't it? I have had others SC cars on my dyno with intake collapsing and what they do is power curve keeps straight since they can't suck more air in order to make more boost or power. With exhaust collapsing I have no idea how to detect it, but I think it should also maintain airflow stable, don't you think? I installed big headers on it so I hope they are not collapsing.

Yes, I know the idea is going step by step and see how car responds. This is the first time this happens to me :( but it doesn't surprise me, Chevrolet and Ford cars always give me new experience hahaha.

Thanks again my friend.

Yes you're correct running without the MAF pipe won't work, just have someone check it is not collapsing under higher rpm (I don't think this will be the issue)

Not a problem Victor, let me know how you get on.

Air filter?

I know some designs have caused problems with other engines, IIRC, it was the filter assemblies/elements being too small, deforming and reducing airflow even further.

Hi guys,

Definitely, it's something mechanical inside de SC which is limiting. If I disabled boost control is the best test, but still after 4,000RPM it decreases boost. If I try to play with duty cicle of SC on the map, it gets crazy so boost goes up and down but it is not stable.

What I can't understand is that in Mexico (7800 feet over sea level) it was making 13.6PSI so at sea level where it is right now, it was supposed to make +3psi more because of altitude. Why would it be hitting 21psi like crazy? I'm gonna send smaller SC to my customer and test it again.

Thanks guys.

Oh wow sorry I didn't realize it was 13.6psi previously, I must of missed that.

While 7800ft is quite high, I would be surprised if that was 7psi. Whats your average baro reading there? I would expect around 77kpa? So I would guess around a 3psi increase as you mentioned. Is this on a stock supercharger or aftermarket?

Do you know the diameter of the pulleys currently fitted?

Hi Chris,

Yes, that's something I can't understand how it is making so much boost now.

At this altitude is 77kPa or 11.2psi so turbos or superchargers make ~3 psi less which are the amount they need to create 1 Atmosphere=100kPa=1Bar and "compensate" theoretically.

Yes, currently it has 8.66'' crank pulley and 2.38'' SC pulley which results in 40% overdrive according to Lingenfelter and they said with this overdrive to not go over 6500RPM, but car barely gets into 4,300RPM.

Did you check the filter arrangement, or at least try it with the inlet TO the MAF, so it isn't something upstream of that? Just remembered something that happened on a vehicle with a low mounted cold air feed to the filter housing, it picked up some debris that got caught in the ducting and partially blocked the intake, that took a bit of figuring out.

What happens on intermediate throttle openings - say, a run at half, 3/4, 7/8th throttle - does it still drop off at the same rpm, or does the point it falls over move up the rpm range?

Have a good think about what else might have changed.

Hi Gord,

I already checked the inlet and filter and nothing wrong there. With partial throttle car is fine because it doesn't make that much boost (low boost actually).

That's the issue, car was running fine in Mexico, it just go to Spain and the first day was doing that.

Thanks for your help.

With those pulley sizes you shouldn't be seeing 21psi.

The issue is too much boost and why it has raised is the main question. The only other reason I have seen this in the past is when the cats have collapsed and blocking the exhaust.

Hi Chris,

Sorry I stopped the tests. But now, I asked customer to remove high flow cats (it has 2 smalls). Now, it is making 2 psi less, so that cats were an issue. But car is still doing the same.

I'm going crazy with this car :(

What else could be collapsing?

I have never seen this before on one of these cars and we have done plenty over the years.

I just flicked back through our thread and I can't see if it was ever mentioned what Supercharger is this. Is it the standard ZL1 charger?

Yes, I have tune some also but never see this. Yes, it's a standard ZL1 supercharger with lingenfelter SC smaller pulley and bigger crank pulley.

Assuming it was checked no mufflers etc had collapsed or an exhaust restriction when the cats were removed.

Was the bypass checked? Because you can get 1 run with max boost then after it drops to low boost, I would be checking what is causing the boost to drop (assuming it is the bypass opening). Do a pull then when it faults and boost drops, get out and check the bypass, is it open?

So now it has dropped down to 19psi, I am surprised the stock S/C is even producing that we have never managed to get them over 15psi.

I would also Email Lingenfelter and confirm the overdrive

I notice you're within a few percent of the MAP Estimated Max when this occurs.(255 Kpa) Maybe raise this value above the boost ability by 20% or so and test?

Hi guys,

I called Lingenfelter and they told me that with my configuration they have seen maximum of 17psi, so it's possible that the safe valve opens or get crazy and they is not way to adjust it, maybe disconnect the line (they don't know if that works).

Also, he told me that with that kind of boost they change camshafts and springs, because that amount of pressure could make valves floating or doing crazy things, do you think that at 4,000RPM this is possible? and could do that?


Hi Johnny,

I can't raise that value because HPTuners is limiting it to 255kpa :(

Sounds like you're hitting a hard high limit for MAP in the ecu? I couldnt tell from the discussion if you were getting into a sort of limp home condition that would clear on a key cycle or ecu reset. probably worth testing the MAP sensor with compressed air to see if the value is actually correct up to 25 psig. If its actually overboosting that much you may need to change pulleys to reduce, but that doesnt really line up with what experienced people are telling you about the pulley config and pressures. On the valve float some others can chime in but I'd assume you run into more of a MAP and hp wall rather than the significant MAF drop that the log shows.

Yes if you're running to much boost on stock springs you will start to lose valve spring control.

If you fitted a bigger cam and springs it will actually drop the boost pressure since you're reducing valve train restriction.

I think you're at the point where you need to reduce boost via pulley change.