[EIREV8]

Hi Guys,

I've just acquired this 2018 ZL1 1LE alongside my 2010 Camaro 2SS.

Under load the car is pinging/detonating.

Logging the ECU I can see that the timing looks way off.



The Barret Jackson advert mentioned it had a Metco pulley kit and a PCM tune.

Before I get my tuner here in Ireland I'm trying to confirm what has actually been replaced.

It looks like the Metco pulley kit is just the crank pulley, but can anyone on here confirm if the smaller pulley looks stock also?

I'm here in Ireland, and given the only ZL1 here, not easy for me to do a comparison

[nighttowl]

any idea what fuel is in it?
Hopefully they didnt put the cheapest available.

upper pully appears stock.

[RobZL1]

Cruising timing is usually in the 40's, especially with the stock variable cam.

I'd bet on the fuel, too. Run a tank of fresh fuel through it and see what happens after that.

[EIREV8]

Originally Posted by nighttowl

any idea what fuel is in it?
Hopefully they didnt put the cheapest available.

upper pully appears stock.

The fuel here in Ireland is 95 octane with 10% ethanol.

[RobZL1]

If you have 95 RON in it, that's roughly 91 US octane as I understand it. I guess you could be seeing some knock activity on 91 US octane fuel under light loads, but I wouldn't think it would be audible pinging on 95 RON/ 91 US AKI.

You could always add some boostane and see if it goes away under normal cruising. If it doesn't go away, then it's likely you have headers rubbing on the body or other exhaust contact being interpreted as knock.

I'm guessing it's most likely you either have some exhausts contact or a bad tank of gas.

[EIREV8]

Ah ok, so does that timing above look right?

All my other cars are older carb'd V8's, so it was my thinking I shoudnt have more than 28 degs timing on the LT at WOT.

RobZL1, you're spot on - our EU95 is equivalent to your US 91 and our EU 98 (super) octane = US 93 octane. Am I right in my thinking a stock ZL1 would run fine on US91/EU95?

I should have given more colour on the issue. Cruising at 50/60/70 the car is perfect (it's got 4k miles on it anyway!). Its only when I give it throttle (not quite WOT) it breaks up, power cuts, I get a shudder through the car and a backfire through the exhaust. Its like as if its only happening on boost. I'm wondering is the Metco pulley upgrade causing the issue?

On one of the runs the car did throw a Knock code in one of the cylinders and the engine light on the dash.

I was thinking originally it was an octane issue so I added the octane booster to a full tank of fuel, but it didnt make any difference.

Now, the joys of living in the Republic of Ireland means I cant get the higher octane US93/EU98 gas. I do have the option of driving 4 hours and across the border into Northern Ireland to get it, but just not down here.

Anyway, I've just dropped it off to the tuner for him to do a comparison of a stock ZL1 vs the tune that's on it.

[RobZL1]

Originally Posted by EIREV8

Ah ok, so does that timing above look right?

All my other cars are older carb'd V8's, so it was my thinking I shoudnt have more than 28 degs timing on the LT at WOT.

RobZL1, you're spot on - our EU95 is equivalent to your US 91 and our EU 98 (super) octane = US 93 octane. Am I right in my thinking a stock ZL1 would run fine on US91/EU95?

I should have given more colour on the issue. Cruising at 50/60/70 the car is perfect (it's got 4k miles on it anyway!). Its only when I give it throttle (not quite WOT) it breaks up, power cuts, I get a shudder through the car and a backfire through the exhaust. Its like as if its only happening on boost. I'm wondering is the Metco pulley upgrade causing the issue?

On one of the runs the car did throw a Knock code in one of the cylinders and the engine light on the dash.

I was thinking originally it was an octane issue so I added the octane booster to a full tank of fuel, but it didnt make any difference.

Now, the joys of living in the Republic of Ireland means I cant get the higher octane US93/EU98 gas. I do have the option of driving 4 hours and across the border into Northern Ireland to get it, but just not down here.

Anyway, I've just dropped it off to the tuner for him to do a comparison of a stock ZL1 vs the tune that's on it.

Got it. From the log, the throttle never opens more than 60%, and when it looks like you give it a little throttle, the timing drops down into what looks like the 8 degree range, which on a stock car with a big pulley seems about right. Maximum delivered timing at redline is likely only 16-20 degrees with a big lower pulley on stock blower/stock heads/stock cam car (depending on the size of the pulley). It ramps into that timing as RPM's climb.

If it's breaking up, I'd take a look at your plugs. Pull a plug or two from each bank and check the gap. It could be that you need a set of plugs. Higher boost eats plugs faster and the gap will grow over time. If it's more than 0.040-0.045" or so, then plugs are likely the problem.

Could be other things, as well. I imagine the tuner will have some ideas now that he can see and hear himself, as well as look at the tune.

Likely something simple. Best wishes!!

[EIREV8]

Yeah, the first thing I did when I noticed the problem was check the plugs. Two were cracked and the silicon boots were split, so I thought it might have been a combination of the plugs and arcing against the block.

I replaced them with new NGK LTR7IX-11 Iridium plugs. I was told leave the gap at .043, but I'm wondering is that too big? I've seen LOTS of posts of people suggesting anything from .029 - .044.

Might be worthwhile reducing the gap while I isolate the issue.

[RobZL1]

Yeah, drop that gap to about 0.032-0.035"

I would imagine you are making 15 psi just guessing at the pulley size from the pictures. At that boost level, most people run a gap in the low 0.03x" range, if not starting to dip into the 0.02x".

I make about 14-15 psi and run 0.032" for what it's worth. Obviously run the largest gap you can, but for troubleshooting purposes, I'd close it up to see if that is all or part of the problem.

[EIREV8]

Right guys, finally after a frustrating process I've found the problem - the Kooks CATS are completely blown and have blocked the exhausts and this was causing the excessive boost. I cleaned it all out as much as possible and took it for a spin and the power is back and revving up to 6,500pm.





The rear OEM exhaust still has bits of the CAT stuck in it so the plan now is to replace with new high-flow CATS and a full rear exhaust system.

After some research I've seen lots of stories about the Kooks ceramic CATS breaking up, but it looks like the newer GESi core ones dont exhibit the same problem.

So to match with the existing Kooks headers I'm thinking of getting a set of the new Kooks high-flow CATS and a new Corsa exhaust system.

Problem is I cant tell the difference between the Kooks GREEN cats PN#22603300 and #22603400 CATS - any recommendations? or is there a better alternative to the Kooks CATS?

I was going to match them with the Corsa Valved / Axle-Back 4.5 in Carbon Fiber Quad Tips PN#21789CF and CAT X-Connect Pipes PN#21085

[RobZL1]

I don't know what Kooks is using in those part numbers, but you want the GESI Ultra V2 #85230 cat, which is a 3.0" inlet/outlet, 4.5" outer diameter cat, rated for 850hp per cat. That's what many of us are running. They are used with the CSP headers that Kooks builds for CSP.

[EIREV8]

Is that these ones Rob?

https://www.spdperformance.com/index...4SleuOZCqrpP5V

[RobZL1]

I believe that is the one. I found a pic of mine, too, and it is Kooks GE-90146.

Here is the website, but the description is incorrect on the HP rating:

https://kooksheaders.com/catalytic-converter3132

Unless mine came with the wrong ones...