ncsurveyor2007

I have a 2008 Zo6 with 13,000 miles on it, bout last year with only 8000 miles. So I had my heads addressed with AHP PACKAGE 4 heads and decided to go ahead and have a stage 2 BTR cam and kooks headers. I had the work done last spring but I haven't been happy with the way the car has driven since. It was dyno'd at 534/440. I wasn't that concerned about power as much as I was about drivability. The car has had quiet a bit of surge, more than I felt like it should have. So, fast forward to now, I finally made an appointment with a highly recommended shop in the area to get the car tuned last week. Now bare with me, as a lot of what I was told is way over my head but basically during the tune, there was a lot of knock retard and after finally getting the tune pretty good they guy could hear a knocking noise in the engine that had them really concerned. So after some testing, doing the wiggle test, and changing the timing he was able to determine the noise is caused by "detonation". He said the wiggle test checked out ok, there was a little movement but it was "acceptable". Please forgive me if I sound like I have no idea what I'm talking about because I don't. But bottom line, the shop wants to pull at least one head and cc it and send it off to be flowed? I think that's what they said. They seemed concerned that I shouldn't have had the heads milled by .030" and are concerned that the compression may be more than it should be with that small of a cam. They said the car was really underpowered and can't figure out why. I think it dyno'd somewhere around 525/470 I think he said. What do you guys think? Again I apologize if I got something wrong, a lot of this is over my head and I'm just trying to understand the best I can. I guess I'm gonna just have them do whatever they need to do to fix it, if that ends up being replacing the heads again or replace the cam or whatever. I wonder if something was installed improperly when I had the work initially done.
Anyway, what do you guys think? Any ideas on what the issue could be?

lamboworld

Where are you located in NC?

ncsurveyor2007

In western NC, Lenoir. The car is currently at Tick Performance in Mt Airy.

lamboworld

What shop did the original tune and install? I hope that it was not the shop in Mooresville that is no longer in business. Tick is a good shop and they know what they are doing, but something seems off to me.

Did you have AHP do your heads or did you buy the car and the previous owner told you what was done to the heads?

If you had the heads done by AHP yourself then I highly doubt that there is an issue with the heads.

vertC6

With that cam and headers you should be closer to 550 and 510 torque. I do know from experience that Headers can cause a false knock and it can be tuned out but he has to know what is doing. Do you have a stock intake?

farmington

Cam could have been installed way advanced or has a high lsa

ncsurveyor2007

I'd rather not say who did the original work but they weren't located in mooresville. I bought a set or core heads from AHP. and I agree, I doubt it's an issue with the heads unless it's like Farmington said, maybe they hAd already been milled and then milled again? This seems unlikely though doesn't it? Could that happen? That's why Tick wants to pull one and CC it. I'm wondering if maybe the cam was installed incorrectly.

ncsurveyor2007

And yes, stock intake

Cap'n Pete

Prior to, or since the heads/cam/headers, have you had any dyno tuning, or just a dyno pull to check the HP? Wondering if maybe it has too much timing advance??

Also, what fuel are you running?

It "sounds" (via the interweb!) like a case of too much timing, and/or crappy (not enough octane) fuel, BUT, may be hard to give an exact diagnosis over the web.

I don't have any personal experience with dyno tuning, but I believe that the issue could probably be resolved with a good tune ..... ie: maybe the combination of increased static compression (cut heads) plus more dynamic compression (camshaft) means you either need to run higher octane fuel, OR, pull some timing via a tune, so the knock sensor isn't getting such a workout, which is inevitably pulling timing anyway, thus, causing you reduced power output.

Or just pour in some 100 octane and your problems should go away!

ncsurveyor2007

If it were the headers causing a false knock, would it have gone away when he reduced the timing to basically flat is what he called it? This seemed to convince him 100% that it is detonation. Obviously it seems like something is definitely wrong to be getting such low numbers...

ncsurveyor2007

I'm running 93 octane. I do t race or track the car and just drive it weekends and hate to have to run anything other than just premium pump gas. I believe the shop now tuning absolutely knows what they're doing as far as tuning and from my understanding, has continued to take timing out to the point of being excessive before finally getting the knock to go away, which told them it was detonation. When the current shop got the car he said the knock sensors were going berserk.

lamboworld

I am running 12:1 on 93 and I don't think my tuner had to pull any time and he didn't see any knock. If your heads were possibly milled twice at .030 I think that you would still be less than 12:1. This is probably highly unlikely. I guess that it is also possible that the previous shop used a non OEM head gaskets, but this also seems very unlikely as well.

I bet your cam is installed with too much advance as mentioned above.

I am running this cam 236/250 .635"/.635" 115LSA +4 and I can cruise in 5th or 6th gears at less than 1200 RPM's with no surge. I know for sure that you can at least run a 12:1 compression on 93 without the issues that you are currently experiencing.

Josh B.

Something is wrong if the timing was pulled out and it was still detonating (if it was in fact detonating). But you know what, if it were detonating while you have been driving it, I kind of doubt it would have lived to tell the story and would still be running. Especially if reducing the timing didn't have an observable effect. Either the tuner is mistaken...or there is a breakdown in your description of the scenario. Something is off here. Or something really strange like a single fuel injector that is faulty, and that one cylinder is causing a problem.

Have they tried reading the plugs at all?

I have built several LS7s with the heads milled .030" with mild cams on premium pump...no issues.

ncsurveyor2007

Well, they were able to finally pull enough timing out to make it go away, I think he said he pulled the timing down to 10 and it went away. I'm beginning to suspect the cam install more and more.

rabrooks

A few thoughts.
Tick is a good place to be. They will find the problem
Timing shouldn't have to pulled down that low. You are losing alot of power. The exhaust can be rattling against metal and causing the knock sensor to retard timing. Something on the front of the engine can do the same thing. AHP may have accidentally shaved one head twice or had teh machine set too deep for the cut. I can't imagine that but stranger things have happened. CC'ing the heads is a great idea.

I had a bolt back out of the power steering pump and rub on the pulley causing a timing retard. now im making 620 whp you should be at least 550-560

vertC6

I was foolish enough to believe the same thing, until we ran my car with 102 octane at 16° total timing and it still knocked! It was clearly false knock. My tuner who is a well known Turner, I won't say his name, said he couldn't get out that's just the way these motors are. And then took it to Michael at serious horsepower and he turned each cylinder individually and got rid of the false knock. it took him 3 to 4 hours but he was able to do it, and I gain 15 hp and 20 pounds of torque.

vertC6

Exactly, I don't think it's detonating at all, I think it's false knock the same as I had. My heads are milled .030 with a very mild cam, and the tuner told me it's just the way the headers are on these cars that create a false knock.

Twinscrew

I did the cam install. Car had 0 knock when it left our shop. It made almost identical numbers as before when we tuned it. I'm 99.9% sure the cam is installed correctly without too much advance. I'm also 99.9% sure AHP cc's their heads and there isn't a chance that the heads got milled twice. I believe either the car is picking up false Knock from another source or it possibly has some bad fuel. If I can be of help with resolving your issue Phillip let me know.

Unreal

I doubt it is the heads. .030" mill is fine, I've never seen issues unless you pick a really crappy cam, combine that with a really thin head gasket, or have really crap gas.

Was the gas good? That is first place to check. Then mechnical issues. False knock can be something banging around, or even something like pushrods wrong size/etc. I don't know if I would jump to pulling a head until everything else is sorted out. Could just be a loose bolt, or bad sensor.

Headers don't cause false knock unless they are banging on something.

And tuning each cylinder individually, please tell more. What aftermarket ECU do you have that allows that?

Tech

I'd take it back to Twinscrew. Tick is a reputable shop but you shouldn't need to flow a head. Sounds like Tick can't explain it and wants to blame the previous shop/work.