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-   -   Typical dry compression test values M54B30? (http://forum.e46fanatics.com/showthread.php?t=977096)

lab rat 03-19-2013 05:09 PM

Typical dry compression test values M54B30?
I just tested my compression/leakdown. Now I'm trying to find some comparison numbers that will help me estimate my compression ratio.
What numbers did you get, dry/wet, cold/warmed up?

lcoleman 03-19-2013 05:39 PM

Estimate your compression ratio? :confused:

What you are wanting to do isn't going to work.

lab rat 03-19-2013 05:58 PM

Ok, maybe I don't know what I'm talking about.
I thought I could estimate my CR based on the compression test.
Don't high compression engines produce numbers around 200 and low CR around 150?

EDIT: ok, it's official. I don't know what I'm talking about.
How can I find out if my head was previously machined/shaved?

lcoleman 03-19-2013 08:32 PM

There's no way that I know of. Even a pretty aggressive skin isn't going to raise the compression ratio by much. Why are you wanting to know?

lab rat 03-19-2013 10:06 PM

I agree that small CR change is not a big deal in normally aspirated engine.
I'm pushing 8.5 PSI and fighting detonation problems.

lcoleman 03-19-2013 10:10 PM

Supercharged? Are you using a canned tune? Running an IC?

Maybe plugs a step or two colder would help. Higher quality fuel, back off the timing if you're able, cool the intake charge more/better.

A <5% change in comp ratio isn't going to cause knock, IMO.

WALKD U 03-19-2013 11:54 PM

PM'd you lab rat...

lab rat 03-20-2013 01:23 AM

It's ESS. Their tunes are often praised. There are thousands of 330s using the same kit, same tune.
I tried couple of different tunes (from ESS), currently on a special one for really crappy gas.
Lowered boost, pulled timing, ran 94octane, added octane booster.
Still pinging.
The only time the car ran right was when I used unleaded 104 race gas.

The plugs are probably the cheapest way I could try to solve it. Then there is meth/water and thicker headgaskets. None of that should be needed for this reliable off the shelf kit.

lcoleman 03-20-2013 06:38 AM

Welcome to the joys of FI. ESS will be able to help you more than I/we will. You probably have some kind of issue, incorrect base timing, worn parts, etc. I am very skeptical that a skimmed head is magically the difference between pinging all the time and not. It just doesn't make that much difference. Your setup is not that aggressive. It's also possible that what you are hearing isn't ping, but I don't know.

I wouldn't try "band-aid" fixes.

lab rat 03-20-2013 10:56 AM

Well, they haven't been able to help me so far. They sent me couple different tunes but the problem won't go away.
I thought of incorrect base timing. But wouldn't that throw a code?
It's not pinging all the time. Doesn't seem to ping more when it gets hot. Pings less when it rains.
The sound was confirmed as a ping by people with tuning experience. Also it went away when I used race gas.

Here is a dyno chart (from mustang dyno with load) that shows timing but I guess I would need better diagnostics to see knock sensor info.


TerraPhantm 03-20-2013 11:35 AM


Originally Posted by lab rat (Post 15265725)
I just tested my compression/leakdown. Now I'm trying to find some comparison numbers that will help me estimate my compression ratio.
What numbers did you get, dry/wet, cold/warmed up?

Compression tests don't really match the theoretical compression values. At sea level, an engine with a 10.2:1 compression ratio should theoretically achieve 370psi. I've never seen a compression test register much above 200 psi

lcoleman 03-20-2013 11:45 AM

Are you sure your fuel pressure is good? Fuel filter is new? Perhaps you have a soft-failing pump that can't keep up with the demand under load.

lab rat 03-20-2013 12:56 PM

Fuel filter is new (OEM). I checked the pressure. It looked good (kept pressure overnight and climbed proportionaly with RPMs).
Soft failing pump, that's another good idea but would't I see the car running lean in that case?

lcoleman 03-20-2013 01:25 PM

Most likely. You have an AFR gauge, right?

lab rat 03-20-2013 01:47 PM

Crappy gauge just reading narrow band voltage from the o2 sensor.

lcoleman 03-20-2013 02:03 PM

A good wideband is well worth the money. That said, I don't know the algorithms for the computer to throw a CEL for lean running, nor how the ESS tune would affect that (if at all).

Perhaps see if you can plug up a generic OBD-II scanner and look at the PIDs for long-term fuel trim?

The only root causes I can think of are running too lean or charge temps too high. Did I miss you mention if you do or don't have an intercooler?

lab rat 03-20-2013 03:59 PM

My OBD scanner broke but last time I was able to check the long term trim looked ok.
The kit comes with air to liquid intercooler. I verified functionality.
Again this is off the shelf kit that's been on the market for years and there are thousands happy users.
Something is different on my car that's throwing it off.
When I talked to one tuner he said local environment is not very high CR friendly. The air is very dense here so at the same airflow (MAF reading) we get more oxygen.

Hmm, I just realized I never checked the IAT sensor. Actually I have a spare one.
With this kit the sensor lives between the TB and the compressor. Stock DME with custom tune is used

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