High Compression High Knock
Dec 19, 2007, 01:05 AM
#1
Newbie
Thread Starter
High Compression High Knock
Hello,
We've got EVO 8 EDM with no MODS.
Stock map also.
On high load knock sum goes over 13 and retards ignition for -3 and turns off boost control.
We've checked compression pressure:
#1 - 13 bar
#2 - 13.5 bar
#3- 13 bar
#4- 13.5 bar
All around 188.5 PSI (for our imperial experts
)
Service manual says that this should be around 10 bar (145PSI) normally.
So I think that this excessive knock is caused by too high compression.
"What is even stranger all engine components seem to have factory spec dimensions. "
What do You think??
Have You ever meet this problem??
I'm going to use http://www.hksusa.com/products/?id=732&rsku=0 - Can anyone help me to get the best size of thicker gasket??
Thanks for Your help.
Best regards
We've got EVO 8 EDM with no MODS.
Stock map also.
On high load knock sum goes over 13 and retards ignition for -3 and turns off boost control.
We've checked compression pressure:
#1 - 13 bar
#2 - 13.5 bar
#3- 13 bar
#4- 13.5 bar
All around 188.5 PSI (for our imperial experts
)Service manual says that this should be around 10 bar (145PSI) normally.
So I think that this excessive knock is caused by too high compression.
"What is even stranger all engine components seem to have factory spec dimensions. "
What do You think??
Have You ever meet this problem??
I'm going to use http://www.hksusa.com/products/?id=732&rsku=0 - Can anyone help me to get the best size of thicker gasket??
Thanks for Your help.
Best regards
Last edited by lukasz4turbo; Dec 19, 2007 at 01:29 AM.
Dec 19, 2007, 07:45 AM
#3
It might be excessive carbon buildup on the pistons causing a bit higher compression. I would also try using a different tester to see if you get the same results. Are you removing the cam position sensor and opening the throttle plate 100% before turning the car over?
Dec 20, 2007, 12:05 AM
#5
Newbie
Thread Starter
cpoevo
Yes I can tune it to stop the knock, but I cannot get higher power output than 260bhp.
TeStUdO
There's no excessive carbon build-up, combustion chamber is clean.
We started work on this car by eliminating every possible cause in fuel injection and ignition systems (AFR, injectors, ignition coils, spark plugs, fuel delivery, intake and exhaust leakage, timing belt etc.)
Compression check #1 - 11.5 bar #2 - 13.5 #3 - 13 #4 - 13.5
We stopped when we made combustion chamber leakage test, first cylinder failed.
So we guessed that some exhaust gases leaked into the inlet manifold which caused excessive knock.
We removed cylinder head, repaired leaky inlet valve and installed on 1.2 HKS gasket (because compression
pressure was too high).
And what??
Before that knock sum was around 8 on high load, now it is 14...
So I guest that we need to change compression ratio.
But there is a question - do we need new cylinder head or simply change gasket for 1.6??
Have You got any experience??
Yes I can tune it to stop the knock, but I cannot get higher power output than 260bhp.
TeStUdO
There's no excessive carbon build-up, combustion chamber is clean.
We started work on this car by eliminating every possible cause in fuel injection and ignition systems (AFR, injectors, ignition coils, spark plugs, fuel delivery, intake and exhaust leakage, timing belt etc.)
Compression check #1 - 11.5 bar #2 - 13.5 #3 - 13 #4 - 13.5
We stopped when we made combustion chamber leakage test, first cylinder failed.
So we guessed that some exhaust gases leaked into the inlet manifold which caused excessive knock.
We removed cylinder head, repaired leaky inlet valve and installed on 1.2 HKS gasket (because compression
pressure was too high).
And what??
Before that knock sum was around 8 on high load, now it is 14...
So I guest that we need to change compression ratio.
But there is a question - do we need new cylinder head or simply change gasket for 1.6??
Have You got any experience??
Trending Topics
Dec 20, 2007, 02:38 PM
#8
Newbie
Join Date: Apr 2006
Location: Lutz
Posts: 83
Likes: 0
Received 0 Likes
on
0 Posts
Dec 22, 2007, 12:42 AM
#12
Newbie
Thread Starter
Check your compression pressure...
But You need to know, that there are many possible things which can make excessive knock (fuel quality, spark plugs, fuel pressure etc.).
But You need to know, that there are many possible things which can make excessive knock (fuel quality, spark plugs, fuel pressure etc.).
Dec 22, 2007, 08:25 AM
#13
Did you not read any of this thread??? Thats basically alll anyone has talked about.
Anyways...
Thinking about messing with your compression issue as in depth as you are is going to do nothing but waste your time and money. There is nothing abnormal about your compression numbers that every other evo owner doesn't see. Getting high knock at peak torque is easy to remove with a tune. If you are still getting issues, search on this forum of how to disable 'Lean Spool'. The Lean Spool feature can fight you quite a bit when it comes to removing knock in the 2500-3500rpm range.
310-320BHP can be obtained with practiacally no mods and a really good ECU re-flash. If thats your goal, take out the 255 Walbro, the stock pump doesn't overrun the stock fuel pressure regulator like the walbro does (causes excess fuel consumption at low loads and idle) and flows enough for 400BHP at the least. Don't upgrade the FP until its holding you back. With your mods (depending on the quality of fuel and octane rating you have available) you can get well beyond your BHP goal.
Anyways...
Thinking about messing with your compression issue as in depth as you are is going to do nothing but waste your time and money. There is nothing abnormal about your compression numbers that every other evo owner doesn't see. Getting high knock at peak torque is easy to remove with a tune. If you are still getting issues, search on this forum of how to disable 'Lean Spool'. The Lean Spool feature can fight you quite a bit when it comes to removing knock in the 2500-3500rpm range.
310-320BHP can be obtained with practiacally no mods and a really good ECU re-flash. If thats your goal, take out the 255 Walbro, the stock pump doesn't overrun the stock fuel pressure regulator like the walbro does (causes excess fuel consumption at low loads and idle) and flows enough for 400BHP at the least. Don't upgrade the FP until its holding you back. With your mods (depending on the quality of fuel and octane rating you have available) you can get well beyond your BHP goal.
Last edited by Jack_of_Trades; Dec 22, 2007 at 03:55 PM.
Dec 24, 2007, 02:08 AM
#15
Newbie
Join Date: Oct 2007
Location: Poland
Posts: 12
Likes: 0
Received 0 Likes
on
0 Posts
Hello Guys,
I am lukasz4turbo's co-worker and I'd like to clarify things a bit because I can see he was misunderstood.
The problem is not with tuning the car rather that it won'r run properly in standard form. AS a rule we won't tune cars that don't run normally. It's not a prolem of retarding ignition, adding some more fuel and getting rid of knock but why it won't run on standard mapping, we already found this leaky valve, but it seems it's not all.
Surprising are those hgh compresion numbers compared to service manual, original question of Lukasz was intended to find out if this is more common. We have some Evo 7 and 8 in our workshop that have smaller cylinder preassures even though they have lower head height and we can hardly explain that.
Anyway whenwe have solved this we'll post something up to let you know what was it, but we always look for interesting input of course
I am lukasz4turbo's co-worker and I'd like to clarify things a bit because I can see he was misunderstood.
The problem is not with tuning the car rather that it won'r run properly in standard form. AS a rule we won't tune cars that don't run normally. It's not a prolem of retarding ignition, adding some more fuel and getting rid of knock but why it won't run on standard mapping, we already found this leaky valve, but it seems it's not all.
Surprising are those hgh compresion numbers compared to service manual, original question of Lukasz was intended to find out if this is more common. We have some Evo 7 and 8 in our workshop that have smaller cylinder preassures even though they have lower head height and we can hardly explain that.
Anyway whenwe have solved this we'll post something up to let you know what was it, but we always look for interesting input of course