RS6 engine Compression testing

[G2]

Anyone have info on PSI readings from their car? Supporting info such as test conditions, mileage, oil used would be icing on the cake.

Just did mine: 175-200PSI. WOT and with diverter valves disconnected. Surprisingly clean pistons (low to very low carbon buildup). Cold test soaked at 45-55F ambient. Battery charger used (auto selecting 40amp smart charger). 90K miles, fresh Amsoil 5/40 Euro EFM full SAPS. All spark plugs removed.

Happy with the results, and seems to coincide with the 9.8/1 compression ratio prett well.

OE PSI spec is 10-13 BAR new, with 7 BAR minimum (or about 100PSI which is the lower limit to >even< support combustion) which is a lame spec for the factory to publish-- but have seen this a lot in the last 10yrs as OEM's get away from providing any hard #'s.

The only thing that was sort of botched was accidental fuel contamination (fyi- the fuel pump relay must be removed, NOT just the fuel pump fuse. I've been learnt). Tried to dry out the cylinders with compressed air, and with all the cranking (testing and retesting to get stabil readings). Seemed to have recoated they cylinders with oil and restabilized the PSI readings. Makes a BIG differenc. Need to do the V/C's soon and will do a retest, but wanted some sort of a baseline....next time will do a warm or hot test as factory prescribed. I view a cold test better to pinpoint possible issues, however. An engine starts when it's cold, not warm/hot......

Hope to see some comparitive data.

[SteveKen]

The RS6 has two fuel pumps on separate fuses.

[G2]

Thanks....apparently the 2nd fuse is hidden elsewhere.......

[Bigglezworth]

The only thing that was sort of botched was accidental fuel contamination (fyi- the fuel pump relay must be removed, NOT just the fuel pump fuse. I've been learnt).Please clarify? How did you contaminate the fuel doing this process? Do you mean that you flooded the cylinders with fuel because the pump was still pushing through a charged line? That makes more sense.

I question why you wouldn't have simply clamped the fuel closed or worse case, removed the line at the fuel rail and block off prior to running this test.

As for numbers, I've done two of the rides here and they were both less than 5% off OEM spec. Yes, that included the one with 235000 miles too.... Have run both OEM spec synthetic and AMZ Oil with comparible spec.

[G2]

The cylinders were washed down with fuel. Thought the context was there...

Dead heading the fuel pump by clamping off the supply line is not good for the fuel pump or the fuel hose. Only dead head a pump for diagnosis for few seconds.

5% of spec sounds great. But it's a range, very wide range at that. Hoping for actual PSI readings.....

[Bigglezworth]

The cylinders were washed down with fuel. Thought the context was there...

Dead heading the fuel pump by clamping off the supply line is not good for the fuel pump or the fuel hose. Only dead head a pump for diagnosis for few seconds.

5% of spec sounds great. But it's a range, very wide range at that. Hoping for actual PSI readings.....Disconnect fuse for fuel pump and disconnect all injectors from the electrical harness. Run test just like you have for years on other engines.

[vodeftones]

fresh Amsoil 5/40 Euro EFM full SAPS...This oil is 50200, 50501 is the Amsoil mid-sap oil. FYI

[G2]

fresh Amsoil 5/40 Euro EFM full SAPS...This oil is 50200, 50501 is the Amsoil mid-sap oil. FYI



That's another topic, but:
Sure is. I use nothing but EFM (since it came out 1-2yrs ago). In the Amsoil line, EFM full SAPS oil is only about 3/4 up the scale of "full SAPS". The goal is to protect the engine, NOT the (damn) emission systems.
AFL 5/40 is the Mid-SAPS. It's Only put out to make the "OE Spec Only" crowd feel better and to get their sales. Besides EFM cost less and is a better oil :jlol:

[Chung]

I had a compression leak down done when I bought the car.

152-161 on all cylinders. Leakdown was 1-2%, Mileage was 111129.

[G2]

I had a compression leak down done when I bought the car.

152-161 on all cylinders. Leakdown was 1-2%, Mileage was 111129.

Thanks for the email Rian- saw your post afterwards. Looks vary consistent, which is sometimes more important than the exact #'s.

These tests and results are and can be very exacting in the evaluation of upper engine sealing. However, the process used can and will show widely varying results.
Process issues:
1. engine hot or cold?
2. battery charger connected? (to maintain even cranking speed)
3. fuel system fully disabled?
4. WOT?
5. Quality of tools? (compression and leak down testers)
6. Number of engine revolution counts?

Personally I did not (Yet) perform a leak down test. However it is the most crucial and accurate to engine condition by elimination many variables that a compression test has. A mechanic race-car friend of mine with vast experience said the only engines that sealed down to 2% were carefully built race engines. I recall seeing Honda specs that called for 15% max leak down, which were at the time some of the best in the industry.

Maybe our Cosworth engines are built that good, and stay that good if well cared for. I recently bought a new Cornwell Tools leak down tester for a trouble engine I was working on. It's very consistent and shows repeatable test and re-test figures. A older B5 V6 30V recently test was just under 10%, except one that was 35%--- might just be debris under the valve seat. But still very good for 15 years old.

It's a lot of work to produce accurate #'s. Be great to see some more....

[ben916]

I had a compression leak down done when I bought the car.

152-161 on all cylinders. Leakdown was 1-2%, Mileage was 111129.

Ryan, how is So Cal treating you?

On Topic: I didn't bother with compression test when I owned mine.