1.4 Twincharger Cylinder Compression - what should it read

[Jabozuma]

As per title, anybody knows what is the correct PSI reading? I looked last night but could not find anything for 30 mins so I went to bed

[PhilTheGeek]

Compression ratio is 10:1 so you should be seeing a maximum of 147PSI. Exact figures are less important than balance.Look for <5% variation between cylinders. Any one cylinder at less than 80% of the highest one probably has a reasonably major defect.

[Jabozuma]

Yes, one can calculate the theoretical maximum, good info and appreciated. I was more after the "normal" values for this engine, what is to be compression figure expected from this engine having taken into consideration normal leakage loses.

 

I swapped OEM NGK plugs for BKR7EIX ones last night. While I was at it I also checked the compression in cylinders

 

Here are two photos of OEM and new side by side to see the difference between the two plugs. OEM is longer than replacement which is considered advantageous as it seemingly does not sit in the spray cone of the injector.

 

 

 

 

 

OEM plugs I pulled out with left being 1 and right being 4 if you stand in front of the engine bay facing the engine

 

 

 

Measurements were done using mechanical compression tester, picture below. I pulled fuse No30 (if memory serves) which cuts the ignition and fuel delivery and with other plugs still in I measured each cylinder in turn, cranking the engine with as if I wanted to start the engine.

 

 

Results

 

1. 130 PSI

2. 130PSI

3. 136PSI

4. 145PSI

 

Cylinder 4 seems to be the odd one here.

 

All pugs (perhaps apart form No1) exhibit mild ash fouling indicative of oil burning. Please not plugs 1&4 and 2&3 are similar in appearance. This is in my opinion to very poor log type exhaust headers geometry design.

 

I always had lumpy cold starts. This morning it started as usual but was completely flawlessly smooth, lumpiness gone entirely. It also felt much eager to respond.

[mannyo]

Could look at it the other way around, cylinder 4 could be the good one, and 1,2,3 have lost compression.

[Rooted]

Sorry i have no good picture, and not near the Spark Plugs right now.

This is the old original plugs as VW/ Skoda fit, the  NGK next to a new Plug of the type i use,  the DENSO.

Edited 10 October, 2014 by goneoffSKi

[Jabozuma]

There is always a range of pot compression values considered as within parameters. Engine runs great so I am not looking to solve a problem I do not have. 

I just want to know what that range is as I was not able to find it ...

If we take the top vale as base line then the lowest two are 10% lower on compression. If the 136PSI is base line than lower ones ar 3.7% percent down and the higher one is 8.1% up . Cup half full or half empty?

 

George, I cannot see anything on that photo, too out of focus I am afraid my friend!

[PhilTheGeek]

Number 4 does look rather too close to theoretical max.But to get that high I'd expect the engine to be running very rough as that cylinder would have to be hugely coked up. Do you know if your gauge reads accurately?  Was the gauge seated and sealed properly for cylinders 1 to 3?

[sharkrider]

your plugs look ok Jab, but a bit sooted up like mine were before I replaced them .......

 

I have read something about them in the line of fire of fuel, and the BRK7's being better.... I have some BRK8's but think they may be too hot..... gonna change mine again before next years track season! lol...

 

dont know bugger all about compression ratio's, but enjoying the posts

 

do post any conclusions you get about how your car is running!

[GeneralPurpose]

Let me guess Jabozuma. You tested no 4 cylinder last...yes? If so thats a completely normal result and if you had gone back and tested the other cylinders in reverse order, using the same technique as you used before, you'd have found the pressures are up on those other pots too, particularly no 1. The reason is oil will have circulated properly around the compression rings. Although as you say, readings do fluctuate a little from pot to pot anyway. To get a really accurate reading we always turned the engine over on the starter for several seconds with the engine warm before testing each cylinder. Don't do it cold unless the book specifically tells you to. This allows the oil to seal each ring and you get a proper reading. Cold readings are always less, but should be within specified limits from the workshop manual. Sorry but I don't know what those should be on your engine. But it looks to me as if you have nothing to worry about. 

Edited 11 October, 2014 by Estate Man

[Jabozuma]

Yup, bang on the money there! I thought it was either that or the fact that I started testing with engine warm and by the time I got around testing pot 4 it was stone cold as I was being interrupted lol.

 

I think I might just call my Skoda delearship and ask them

 

I was on the track this Saturday and it was all fine, run like a dream  

[GeneralPurpose]

Good! She sounds as if she's lovely! I've not had the privilege of driving the Vrs on the track but I gave one a good run to Wales and back a year or so ago. Total miles driven that day was over 600. Had great fun. The miles just flew by. 

[Jabozuma]

When you take out everything from the back vRS is REALLY loud inside the cabin lol. But with helmet on it is not a problem ha ha ha.

I own 520d as well and unfortunately vRS is in a different league - I simply notice how much more tired I am when I travle long distances in vRS compared to the beemer. 

My problem is too much noise... even with back seats installed .

 

Dashcomand (Palmer's iPhone engine monitoring app) having been fed with all the relevant data showed 194bhp calculated. I know that only rollers can tell but it is a good number for a 100% stock engine, including stock air filter

[sharkrider]

thats the figure most CTHE cars are making on the rollers though! good stuff

[Jabozuma]

Wasn't there a RR day organised for November or sth?

[walterwilson85]

Do you not take all plugs out to do test or just one your testing?

[newbie69]

From what I'm reading (and asking around) they generally remove all 4 plugs, but Jabo has his own method I guess!  Will be testing very soon as well.

[walterwilson85]

Just done it I got 170 across the 4 so take it this is fine..

[Jabozuma]

I did the each one in turn as I wanted the system to be sealed and as close to its normal operating mode as possible. With all plugs out the cranking gets easier so perhaps it has historical background? Also, with all plugs out crank case will not be pressurised (with them in still less than with normal combustion) so results might be wrong.

[Jabozuma]

Just done it I got 170 across the 4 so take it this is fine..

As far as I know 1.4 twinchargerhas compression ratio of 10:1 so max cylinder compression at TDC is 145 psi - how did you get 170??

[walterwilson85]

Just watched the lad at the garage. Did each one in turn. Turned ignition key so the engine tried to turn and he shouted out the reading he said each one was roughly 170?

[newbie69]

Sorry I didn't understand, you meant he was testing every cylinder with the other 3 plugs in place or he removed all of them prior to the testing?

[walterwilson85]

No all plugs were removed m8. Did cylinder 4 down to 1. The reading indicated was 170 on each test. Anyone else had any.other readings my car is the cthe engine

[newbie69]

No all plugs were removed m8. Did cylinder 4 down to 1. The reading indicated was 170 on each test. Anyone else had any.other readings my car is the cthe engine

 

Ok, so he did it in accordance with what the workshop instructions state: "remove all plugs first".  I will have something to share soon, but I think absolute values are not very important due to inaccuracies during the test. But them being all similar is a good sign I would imagine.

[walterwilson85]

Yeah bud. Let me know what you get. I.have read various thingS. I'm sure 170 is within range of what it should be

[Wakey]

Yes most important thing is equal +/- 5psi spread.

 

Also its important to crank the engine for the same number of cycles