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

 

My USDM VIII does the same thing. All cylinders are 180 psig +/- 2psig and she knocks like crazy. I have also done a leakdown test and only have 2% leakdown on all cylinders. Just tune til the knock is gone.

 

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?

 

145 psi is for the Evo IX.

 

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??

 

A thicker head gasket could make your problems worse by loosening the quench between the piston and head.

 

Many Evo 8s see 180-200 psi:

https://www.evolutionm.net/forums/sh...d.php?t=127709

 

How much HP are you trying to get without any mods? What kind of gas are you using?

 

Target is 310-320 BHP.

Mods: 3" complete exhaust (w/o cat), Walbro 255, HKS intake kit.

 

Were the balance shafts timed correctly after you pulled the head off?

 

In 4th gear pull at 2300-3100 rpm my knock highest at 9 and doesn't go below 6 until 2937

 

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.).

 

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.

 

this is funny : )

 

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