A Query for those technical out there

[adsgreen]

Those numbers for a dry test are pretty much bang on.

[P_G]

'R'e'S'pect_4, whenever the manifold is taken off it is recommended that you replace the core plugs as standard. When the manfold was replaced after porting / polishing and deflapping one of the newly inserted core plugs came out hence the problems. With the modified plugs no chance of this happening as they are now aluminium alloy like the manifold so the expansion of the manifold and plugs is more consistent unlike alloy manifold and steel core plugs.

The core plugs are there to seal the holes that allow access to the flap screws which Doug previously mentioned are required to get a torque setting tool onto. There'e a few theories on why this may happen. One is steel plugs not expanding as quickly as the alloy manifold leavin ghe plugs slack but then it would happen in normal cars, the other more precise theory is the porting / polishing may increase expansion rate of the manifold as there is less alloy to heat up and therefore the plugs slacken. The other is that simply core plugs inserted at less than dead straight may slacken off and could pop in / out.

HTH.

[P_G]

Those numbers for a dry test are pretty much bang on.

Good to know.

[scaghead]

Happy days fella, glad it all worked out fine.

+1 after you have had a drive of course...

[Revolution]

I, we didnt post any replies on this topic as its P_G's car and wanted himself to do the talking sort to speak....

Glad its all sorted now and if anyone else is planning this type of mod i would strongly recommend the core's to be chemically welded or even better get core blanks made like P_G did.

One very lucky RS4 driver and still baffled how/if it went into the bore nothing went caboom...P_G defo has only have 8 lives left now...!?!

Were never sad to see the back of an RS4, not one as nice as P_G's but we were getting desperate for space as we have an Impreza WRX and an R33 in for rebuilds at the moment.

Glad its all sorted and my team looked after you well...all part of the Revolution service

Glenn

[ArthurPE]

+1 (except I'd say 10PSI is too much. I'd want it within a couple of PSI at most on the same bank).

If something entered my cylinder I'd probably get a leak-down test done. You probably won't feel a slightly lower compression on one cylinder.

Hopefully everything is all good though.

Cheers.

10 psi (+/-5%) is fine for this engine with it's 12.5:1 ~180 psi, so 10 is 5% tolerance, or 2.5% from the average

[P_G]

So not being that hot on compression testing, why the difference between the pressures I had and the ones you have quoted Arthur as looking at the difference that is 35psi or 19.4% difference? Are you saying they should have averaged higher on the dry test? I suspect some of that will be down to airflow? The valves either side were seating perfectly fine when examined on all cylinders.

[ArthurPE]

So not being that hot on compression testing, why the difference between the pressures I had and the ones you have quoted Arthur as looking at the difference that is 35psi or 19.4% difference? Are you saying they should have averaged higher on the dry test? I suspect some of that will be down to airflow? The valves either side were seating perfectly fine when examined on all cylinders.

don't know?
without being an alarmist they shouldn't be that low (I'm guessing 175 to 190, 12 to 13 bar, is spec)

there are 2 tests, dry wet
do dry first, then wet

engine should be at operating temp and cycled 4 to 6 strokes
generally an engine should make 1 atm x comp ratio...
spec for the e46 M3 is 160 to 175 psi (11 to 12 bar) or so cr = 11.5:1 (11.5 bar to one)
max deviation is 7 psi

wet is the same but a teaspoon of oil
if test is substantially higher rings may be worn

does anyone know the shop spec for the RS4?

[P_G]

Yet only a few weeks ago it made 407 bhp on a dyno and adsgreen suggests the figures are near spot on? I can't see how in the space of a few weeks the piston rings have become so worn that they are all below minimum tolerance which is what that bulletin you have attached suggests because all the pressures are similar. Has anyone else done compression testing on their cylinders and can share their numbers?

I'll do the 3k-8k rpm test tomorrow and see what the results are. If near the same as they were before then either the readings were down or something else is amiss.

[ArthurPE]

Yet only a few weeks ago it made 407 bhp on a dyno and adsgreen suggests the figures are near spot on? I can't see how in the space of a few weeks the piston rings have become so worn that they are all below minimum tolerance which is what that bulletin you have attached suggests because all the pressures are similar. Has anyone else done compression testing on their cylinders and can share their numbers?

I'll do the 3k-8k rpm test tomorrw and see what the results are. If near the same as they were before then either the readings were down or something else is amiss.

I'm guessing the numbers are wrong, ie, low...perhaps the throttle wasn't held open, it wasn't cranked long enough, etc.
I think the compression is fine for the reasons you stated, but perhaps the test results are incorrect

I'm trying to get the manual spec numbers...

[P_G]

My consolation is that the numbers are pretty consistent across all cylinders given what has happened so no damage there from a missing core plug.

[ArthurPE]

My consolation is that the numbers are pretty consistent across all cylinders given what has happened so no damage there from a missing core plug.

yep, VERY consistent, a few %
and it would indicate none are damaged or deviate from the others...also wear is very even...
I would like to see the spec and some numbers just to see how much loss a car with your mileage sustains...

since torque T ~ (displacement x vol eff x Cr) / 4Pi, compression is the single biggest component in torque (and by default power = T x w, w ~ engine speed) generation (vol eff varies by a few %, displacement and 4Pi (obviously) are fixed constants)

if you lose 10% compression you will lose 10% torque

[P_G]

That's the weird thing, torque has nevere been an issue as it was 319 ft lbs on V-power and 312 on Momentum 99 which has high Ethanol content and therefore doesn't produce as much on the torque front. So if the compression was down by 19% at 312 it should be doing approx. 370 ft lbs.

Just researched on the internet and according to Audi the BMEP is 188.30 psi

[P_G]

Just a thought, if there is no vacuum in the system would this affect the compression test as this was doen when the vacuum was pinched?

[2manytoys]

Because your're even across the board I wouldn't worry about it. The compression tester may not be too accurate. Even the length and type of tube to the gauge can play a part. Maybe it wasn't done with the throttle open either?

If you are worried get a leakdown test done.

Maybe it's tiny bits of carbon holding each valve slightly open haaa