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 Post subject: compression test
Posted: Tue Aug 06, 2013 11:40 am 
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Ride: 96 EL XR6

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Hi all, just did a compression test on my el xr6, after doing a mls and got 190-200psi across all cylinders, engine is standard bar the exhaust, and its done roughly 300 000km, just wanna know if thats a decent number for a engine of this age, cheers :)

 

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 Post subject: Re: compression test
Posted: Tue Aug 06, 2013 5:40 pm 
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Falcon96XR6 wrote:
Hi all, just did a compression test on my el xr6, after doing a mls and got 190-200psi across all cylinders, engine is standard bar the exhaust, and its done roughly 300 000km, just wanna know if thats a decent number for a engine of this age, cheers :)


Mine has 235,000km, with shaved head, AU MLS gasket and it only managed between 120-125 PSI.

So thats fantastic.
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 Post subject: Re: compression test
Posted: Tue Aug 06, 2013 6:35 pm 
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Ride: 5 speed XG ute

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Falcon96XR6 wrote:
Hi all, just did a compression test on my el xr6, after doing a mls and got 190-200psi across all cylinders, engine is standard bar the exhaust, and its done roughly 300 000km, just wanna know if thats a decent number for a engine of this age, cheers :)

Certainly is, she's got a lot of life left yet :D

 

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 Post subject: Re: compression test
Posted: Tue Aug 06, 2013 7:08 pm 
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alright, that's good,
thanks for the replys :)

 

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 Post subject: Re: compression test
Posted: Tue Aug 06, 2013 9:21 pm 
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Falcon96XR6 wrote:
Hi all, just did a compression test on my el xr6, after doing a mls and got 190-200psi across all cylinders, engine is standard bar the exhaust, and its done roughly 300 000km, just wanna know if thats a decent number for a engine of this age, cheers :)


Seeing the Factory spec is 145-150psi. I would say that there is more than an MLS Gasket done to it.
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 Post subject: Re: compression test
Posted: Tue Aug 06, 2013 10:43 pm 
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SWC wrote:
Factory spec is 145-150psi


Really? My XG when it was still going alright had 180-185psi across all cylinders with a normal head gasket :? Unless my compression gauge is rooted :roll:

 

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 Post subject: Re: compression test
Posted: Wed Aug 07, 2013 1:50 am 
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Ride: 93 ED sedan

Power: 161 rwkw

Location: Rockhampton
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My ED has 185 psi.....stock bottom end, composite head gasket with an EA cyl head, with an EF XR6 cam fitted......so 190 to 200 psi is all good......worth running premium 95 or 98 in that too.

 

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 Post subject: Re: compression test
Posted: Wed Aug 07, 2013 7:49 am 
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@ cjh
Ohkay, yeah i always run 98, the way i look at it is, i dont like to eat sh*t so why would my car lol,


@swc
And nah shes stock, i originally thought it had a stage 3 cam when i bought it but after stripping it for the mls gasket, proved that wrong ahah.

 

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 Post subject: Re: compression test
Posted: Wed Aug 07, 2013 10:59 pm 
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What is wrong with mine then with an average between 120-125psi across all cylinders?

I haven't done a wet test but ive got CMS Stage 3 head with 2a cam and AU MLS head gasket.
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 Post subject: Re: compression test
Posted: Thu Aug 08, 2013 12:33 pm 
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my repair manual states 1010kpa (146 psi) minimum? ive just rebuilt my engine with new pistons, rings and mls gasket and im getting 200psi from all 6 cyls.
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 Post subject: Re: compression test
Posted: Thu Aug 08, 2013 1:06 pm 
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Damoo wrote:
What is wrong with mine then with an average between 120-125psi across all cylinders?

I haven't done a wet test but ive got CMS Stage 3 head with 2a cam and AU MLS head gasket.


Ask CMS, your cam may have a fair amount of overlap which would bring down the cylinder pressure.

 

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 Post subject: Re: compression test
Posted: Thu Aug 08, 2013 9:38 pm 
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GeZza200 wrote:
Damoo wrote:
What is wrong with mine then with an average between 120-125psi across all cylinders?

I haven't done a wet test but ive got CMS Stage 3 head with 2a cam and AU MLS head gasket.


Ask CMS, your cam may have a fair amount of overlap which would bring down the cylinder pressure.


I've asked them they mentioned they usually see a boost in compression.
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 Post subject: Re: compression test
Posted: Thu Aug 08, 2013 9:42 pm 
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Damoo wrote:
GeZza200 wrote:
Damoo wrote:
What is wrong with mine then with an average between 120-125psi across all cylinders?

I haven't done a wet test but ive got CMS Stage 3 head with 2a cam and AU MLS head gasket.


Ask CMS, your cam may have a fair amount of overlap which would bring down the cylinder pressure.


I've asked them they mentioned they usually see a boost in compression.

do a wet test, if it comes up then your rings are on the way out

 

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 Post subject: Re: compression test
Posted: Fri Aug 09, 2013 1:57 am 
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Ride: 1992 EBII Fairmont

Location: Aga
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Mines currently a very steady 210PSI all round with the reco head and MLS gasket :) It was around 190 beforehand. The car only puts out 80rwkw with XR6 spec head/cam and 4480's I think I've slapped the head on a tired bottom end, and the auto/diff are definitely tired too which could explain the low power.

Somehow I managed after a freshly reco'd head to cross-thread the cyl 6 spark plug so it leaks a little pressure (tho hardly anything), it still puts out 210psi like all the other cylinders but does take a couple more turns of the key for the gauge to reach 210psi. Thought it wouldn't affect power too much but now I'm thinking it kind've would make sense lol, it's only putting out 80 at the rears. Worth fixing maybe?
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 Post subject: Re: compression test
Posted: Fri Aug 09, 2013 2:41 am 
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Damoo wrote:
GeZza200 wrote:
Damoo wrote:
What is wrong with mine then with an average between 120-125psi across all cylinders?

I haven't done a wet test but ive got CMS Stage 3 head with 2a cam and AU MLS head gasket.


Ask CMS, your cam may have a fair amount of overlap which would bring down the cylinder pressure.


I've asked them they mentioned they usually see a boost in compression.


Yeah wet test is the only real way of knowing for sure, I stuffed around for over a year with signs and symptoms with a blown head gasket and wasn't even sure it was the gasket until I got the head off and behold it was blown between the water jackets/cyl of cylinders 1&6.
Water was leaking in but so slightly, the coolant tank dropped only 1cm every 2 weeks and the gasket hadn't blown out enough to notice any white smoke, hadn't split between any oil/water jackets so the engine oil wasn't milky. Just a rough idle, hard start in the morning and the very slight coolant loss I initially put down as evaporation or the slight hose leaks I had but neglected. Only when it started overheating and spitting coolant out the overflow I finally decided on pulling the head. I could've known for sure I now realise if I got the coolant tested for exhaust gases but could never be bothered booking it in haha, ended up pulling the head and turned out to be an easy fix for once.

I'd look at the rings from a similar perspective sure there are telltale signs and symptoms but I'd say the wet test would give a definitive answer. I've never had rings go on me but signs and symptoms wise the car should blow tonnes of blue smoke and burn through a bottle of oil a week or something. Does the car do this? A blown out valve would cause the same thing so doesn't really tell you whether it's the rings or the head still (but you could logically assume its the rings if the head is new). Wet test is the way to go or if you cant be bothered booking it in like me with my head you'll at least need to take the rocker cover off and check the cam timing and if this is ok check the head bolts and spark plugs are torqued correctly. With the head bolts I'd suggest set the torque to 150nm IF they're currently at 160nm (160nm I believe is the final torque rating, you'll want to be sure!). You don't want to move them really and if they are infact loose you want to "nip" them up rather than slow-drag the wrench long arm style.

Compression loss.. it's either rings, valves, or it's escaping through the gasket or spark plug holes I would think that's every possible cause. I'd say maybe the valves are opening wrong if that's possible on the I6 (it's an interference motor I thought). I know if you use AU rockers (like here) the valve timing can be out without them going crunch.
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