Potential causes for detonation
Thread Starter
Joined: Nov 2001
Posts: 768
Likes: 2
From: Spring Hill TN
Potential causes for detonation I'm just thinking out loud about the possible causes for detonation in my setup.
I have MTI S2 heads milled .030 with a C1 cam and a stock shortblock with Hypertech tuning. I have been running this setup for two years now without a problem. I have numerous dyno pulls showing A/F in the 12.4-13.1 range with Autotap showing a max of 27 degrees timing. Every now and then I get a little pinging in 6th under 2K rpm.
A few weeks ago I thought I had a blown headgasket so I pulled the heads and found some damage in cylinders 5 and 7. The damage appears to be detonation related. I will have a better idea once MTI gets the heads in hand as to what caused the damage.
My concern now is that I need to fix what caused this damage. If it is detonation, what would be causing it to be this bad now?
1) 80K miles of carbon build up on the piston crowns and CCs causing a decrease in CC volume making my compression ratio climb
2) burning oil due to the PCV system causing a loss of octane
3) fuel injectors getting dirty causing less fuel in those two chambers
4) a couple of partially collapsed lifters not allowing full lift on those intake valves
Maybe a combination of these issues caused the problem.
I have MTI S2 heads milled .030 with a C1 cam and a stock shortblock with Hypertech tuning. I have been running this setup for two years now without a problem. I have numerous dyno pulls showing A/F in the 12.4-13.1 range with Autotap showing a max of 27 degrees timing. Every now and then I get a little pinging in 6th under 2K rpm.
A few weeks ago I thought I had a blown headgasket so I pulled the heads and found some damage in cylinders 5 and 7. The damage appears to be detonation related. I will have a better idea once MTI gets the heads in hand as to what caused the damage.
My concern now is that I need to fix what caused this damage. If it is detonation, what would be causing it to be this bad now?
1) 80K miles of carbon build up on the piston crowns and CCs causing a decrease in CC volume making my compression ratio climb
2) burning oil due to the PCV system causing a loss of octane
3) fuel injectors getting dirty causing less fuel in those two chambers
4) a couple of partially collapsed lifters not allowing full lift on those intake valves
Maybe a combination of these issues caused the problem.
Last edited by 1madss; Apr 13, 2004 at 09:42 PM.
Thread Starter
Joined: Nov 2001
Posts: 768
Likes: 2
From: Spring Hill TN
Maybe I should have asked if carbon build up in the CC could actually raise compression ratio. It looks like it could easily be .010-.020 thick.
I had also expected to find detonation damage on the piston or rings before head damage.
I had also expected to find detonation damage on the piston or rings before head damage.
Sorry to hear about the troubles Mark..
From what I've seen, tuning is the key for controling detonation. May want to talk to the MTI folks about a tune.
I'd also mention that you car is a 2000. Maybe the smaller injectors are contributing some how.
From what I've seen, tuning is the key for controling detonation. May want to talk to the MTI folks about a tune.
I'd also mention that you car is a 2000. Maybe the smaller injectors are contributing some how.
Thread Starter
Joined: Nov 2001
Posts: 768
Likes: 2
From: Spring Hill TN
Thanks, I'm looking into maybe picking up some 28 lb injectors. Maybe the 80K miles on my 26s is getting to be too much for the H/C setup. I'm trying to hold off on tuning until I can go with a bigger cam. But with putting 1200 miles a week on the car I am hesitant to go with a bigger cam.
TECH Junkie
Joined: Dec 2001
Posts: 3,242
Likes: 0
From: Lakeland, FL
basically detonation will occur if the the a/f mixture ignites before the spark that is supposed to ignite it happens. You just need to make sure you get enough fuel in there and if you are seeing knock retard have it professionally tuned out. Couple other things to consider might be a clogged fuel filter, weak pump, shitty gas. I also seem to remember some others having issues with the hypertech tune even though it barely adds any timing. It probably wouldn't do you any harm to remove the hypertech tune until you can get it dyno tuned.
Just curious though,, how much damage occurred? Is the shortblock salvagable?
Just curious though,, how much damage occurred? Is the shortblock salvagable?
Thread Starter
Joined: Nov 2001
Posts: 768
Likes: 2
From: Spring Hill TN
Here are the pics of the head damage. Its really pretty minor looking. The short block seems to be ok.
http://www.picturetrail.com/gallery/...29&uid=2081909
The damage is next to the valve seat at about 12:00 on the intake valves of each cylinder.
Fuel pressure might be an issue. I changed the changed the fuel filter at about 40K miles. i have not had a chance to get a good look at fuel delivery (pressure, A/F, injector duty cycle) in a while now.
Another factor maybe the issue that I had with throwing belts until I replaced the belt tensioner last month.Anytime I reved over 4.5K the belt came off causing some over heating problems. I never pushed it into the red, but it did run hot a couple of times.
http://www.picturetrail.com/gallery/...29&uid=2081909
The damage is next to the valve seat at about 12:00 on the intake valves of each cylinder.
Fuel pressure might be an issue. I changed the changed the fuel filter at about 40K miles. i have not had a chance to get a good look at fuel delivery (pressure, A/F, injector duty cycle) in a while now.
Another factor maybe the issue that I had with throwing belts until I replaced the belt tensioner last month.Anytime I reved over 4.5K the belt came off causing some over heating problems. I never pushed it into the red, but it did run hot a couple of times.
