[Z06] Detonation
02-14-2019, 01:36 AM
#1
Heel & Toe
Thread Starter
Detonation
I recently had a cam done with milled heads (about 20), lifters, push rods and roller rocker arms and also added a catch can. I already had, heads reworked, headers, intake and cold air box. I got the car back and it is detonating horribly at 4,000rpms and over. I verified springs (went with a stiffer spring) and replaced the cam sensor, as well as verified by multiple tuners that the tune is not causing the detonation. Any ideas what this could be?
02-14-2019, 01:55 AM
#2
Le Mans Master
Step one, buy a scanner, monitor to see if it is pulling timing and by how much. Step two, make sure your tuner didn't detune or disable the knock sensors.
Step three, triple check the catch can routing - there have been a few folks that have mis-routed the PCV lines, causing excess oil to pull into the intake, so check for that, as well as vacuum leaks.
Also, what roller rockers? Pretty much anything besides stock requires a spacer or taller valve covers. And if they are YT and you are using the rubber spacer they provide, I can tell you that is a marginal solution; you can have the rockers tapping on the cover with any slight mis-alignment of the cover.
What octane are you running?
Step three, triple check the catch can routing - there have been a few folks that have mis-routed the PCV lines, causing excess oil to pull into the intake, so check for that, as well as vacuum leaks.
Also, what roller rockers? Pretty much anything besides stock requires a spacer or taller valve covers. And if they are YT and you are using the rubber spacer they provide, I can tell you that is a marginal solution; you can have the rockers tapping on the cover with any slight mis-alignment of the cover.
What octane are you running?
Last edited by Dan_the_C5_Man; 02-14-2019 at 10:30 AM.
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Landru (02-14-2019)
02-14-2019, 02:04 AM
#3
Race Director
Why not take it back to who did the cam install if this problem was not an issue prior to the cam install?
I am not sure what detonation feels like, but if the vehicle is sputtering like it is hitting redline at 4,000 and over.... for me it wound up being a spark plug with a hairline crack in it and was arcing under high load.
Good luck
I am not sure what detonation feels like, but if the vehicle is sputtering like it is hitting redline at 4,000 and over.... for me it wound up being a spark plug with a hairline crack in it and was arcing under high load.
Good luck
Last edited by WICKEDFRC; 02-14-2019 at 02:05 AM.
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TTHIEL1@gmail.com (02-15-2019)
02-14-2019, 12:20 PM
#4
Race Director
Why not take it back to who did the cam install if this problem was not an issue prior to the cam install?
I am not sure what detonation feels like, but if the vehicle is sputtering like it is hitting redline at 4,000 and over.... for me it wound up being a spark plug with a hairline crack in it and was arcing under high load.
Good luck
I am not sure what detonation feels like, but if the vehicle is sputtering like it is hitting redline at 4,000 and over.... for me it wound up being a spark plug with a hairline crack in it and was arcing under high load.
Good luck
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TTHIEL1@gmail.com (02-14-2019)
02-14-2019, 01:10 PM
#5
Burning Brakes
Check physical cam timing. If the cam was installed a tooth advanced or retarded it may be causing detonation under load, even early in the RPM.
If the cam was installed a tooth off in advanced, it will bring way too much pressure and will cause detonation even worse if the cam was already grounded/cut with 3, 4, 5 deg advanced timing.
Cam timing and ignition timing are two completely different things.
Check cam timing.
If the cam was installed a tooth off in advanced, it will bring way too much pressure and will cause detonation even worse if the cam was already grounded/cut with 3, 4, 5 deg advanced timing.
Cam timing and ignition timing are two completely different things.
Check cam timing.
Last edited by Da Z06; 02-14-2019 at 01:10 PM.
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TTHIEL1@gmail.com (02-14-2019)
02-14-2019, 02:30 PM
#6
Team Owner
Careful, careful, careful...detonation is no joke on these cars. Were the heads milled twice by mistake, or only milled once along with the recent cam. In any event...take it back to the guys that did the work...something isn't right.
The following users liked this post:
TTHIEL1@gmail.com (02-15-2019)
02-14-2019, 05:14 PM
#7
Pro Mechanic
Pro Mechanic
I recently had a cam done with milled heads (about 20), lifters, push rods and roller rocker arms and also added a catch can. I already had, heads reworked, headers, intake and cold air box. I got the car back and it is detonating horribly at 4,000rpms and over. I verified springs (went with a stiffer spring) and replaced the cam sensor, as well as verified by multiple tuners that the tune is not causing the detonation. Any ideas what this could be?
If you took .020 off the heads, you've increased the compression ratio somewhat and, depending on the octane of the fuel, the spark calibration and the WOT fueling, that can cause detonation. It's likely that the camshaft is increasing cylinder pressure at high rpm.
You say "mutiple tuners" say the calibration is ok, but can you tell us something about 1) the spark tables and 2) the AFR at WOT?
02-14-2019, 05:54 PM
#8
Heel & Toe
Thread Starter
Step one, buy a scanner, monitor to see if it is pulling timing and by how much. Step two, make sure your tuner didn't detune or disable the knock sensors.
Step three, triple check the catch can routing - there have been a few folks that have mis-routed the PCV lines, causing excess oil to pull into the intake, so check for that, as well as vacuum leaks.
Also, what roller rockers? Pretty much anything besides stock requires a spacer or taller valve covers. And if they are YT and you are using the rubber spacer they provide, I can tell you that is a marginal solution; you can have the rockers tapping on the cover with any slight mis-alignment of the cover.
What octane are you running?
Step three, triple check the catch can routing - there have been a few folks that have mis-routed the PCV lines, causing excess oil to pull into the intake, so check for that, as well as vacuum leaks.
Also, what roller rockers? Pretty much anything besides stock requires a spacer or taller valve covers. And if they are YT and you are using the rubber spacer they provide, I can tell you that is a marginal solution; you can have the rockers tapping on the cover with any slight mis-alignment of the cover.
What octane are you running?
02-14-2019, 07:46 PM
#11
Team Owner
Great response....It pulls a ton of timing out, up to 12 degrees or more; sometimes negative timing. I don't believe that the knock sensors are disabled because the scanner picks up the knock. I am mildly skeptical of the catch can and have not yet verified that since the car is at the mechanic that did some of the work. I went with Harland Sharpe rockers and Holley 1/2" tall valve covers. I run 93 octane pump fuel, but ruled this out as being a possible issue since we added race fuel.
02-15-2019, 08:42 AM
#13
Burning Brakes
02-15-2019, 01:53 PM
#14
Heel & Toe
Thread Starter
That is interesting that you say this about these roller rockers. These are always debated on the forums because some have had success but others have not. Many feel that a stock trunion-upgraded rocker is the way to go and is proven. I ran with that with modded heads and bolt ons and the car ran great. One of the builders involved in putting the car together when I did the cam cold me on the roller rockers. I am a bit suspect and still have my upgraded stock rockers. I think that after verifying the catch can I will try the other rocker arms and see if this might be the culprit.
02-15-2019, 01:56 PM
#16
Heel & Toe
Thread Starter
You can hear the detonation/pre-detonation. Its bad and the engine fall all over itself. Under normal driving, drives perfectly ironically. As far as the spark tables, you can pull out a bunch of timing and it really does not make any difference.
02-15-2019, 02:27 PM
#19
Supporting Vendor
I recently had a cam done with milled heads (about 20), lifters, push rods and roller rocker arms and also added a catch can. I already had, heads reworked, headers, intake and cold air box. I got the car back and it is detonating horribly at 4,000rpms and over. I verified springs (went with a stiffer spring) and replaced the cam sensor, as well as verified by multiple tuners that the tune is not causing the detonation. Any ideas what this could be?