dooby-do

iTrader: (2)

Hi people i have a 04 sti with a forged 2.5 block and avcs heads.
Have noticed lately that its using a fair bit of oil,so decided
To do a compression test. On 3 bores i got around 26psi and the front passenger
Got roughtly 27-28psi, the car runs fine, boosts fines, oil pressure is
Ok drops a bit on idel but when driving holds strong, does get a bit of white smoke on high boost other that that all is fine, any ideas why the compression is so low, i borrowed my mates tester, is it a case engine is shot or any other reason why its so low any help would be great thanks in advance

sssssteeeee

hi , my understanding of a forged engine after chatting to a well known Scooby garage in west mids PP is piston ring clearance is different for different applications. so for heavy abuse at cold there will be some space , once warm this space is then closed. could it be your 2.5 had this in mind at build? I assume u did your test when engine was fully warmed up? also the obvious is how many miles has the unit done ? under what conditions etc. do u have an oil pressure gauge? was the oil pump an uprated type? this may cause slight loss of oil to. forged engine would I think be equipped with better pump. u may want to try oil cooler this would decrease the loss.

dooby-do

iTrader: (2)

Engine was built around 30k ago all rcm
Parts pistons , rods , crank, i warmed the engine up before doing the test.
Its fitted with a uprated oil pump and oil cooler aswell, the oil pressure gauge reads
Around 6-7 bar when cold and drops to around 3-4 when hot and ideling but when driving does rise with pressure

merlin24

iTrader: (1)

You need to do the compression test again or you have been reading the gauge wrong as the engine wouldn't run with 27 psi compression

dooby-do

iTrader: (2)

think ill try another test as I borrowed a friends one but not sure if it has a issue,
so will get another and run another test

dooby-do

iTrader: (2)

Ok so took the compression tested to my corsa today and was fine well
Over 100psi, came back to the scoob started it up and left it running for a good 10-15 mins.
Took all the plugs out and also removed the ignition fuse, foot flat to the floor and still
Only going to around 26-27psi on 3 cylinders,managed to get the front passenger cylinder to around 45 psi, i have read somewere that under 90psi the engine wont start, but it starts first time first turn, from cold oil pressure is around 6-7bar once warm it drops to 2 1/2 bar - 3 bar on tick over but get driving and will go back up again 6 bar upwards, the engine sounds perfect no knocks or missfires it uses a bit of oil but been told all forged 2.5s do,
So my engine is a 2.5 scd block rcm pistons and rods and crank 14mm headstud conversion, with 2ltr avcs head modified to fit the 2.5 block, oil cooler fitted aswell. Running 435 / 425 lb torque md321 turbo, and ideas why the car wont give me the correct readings. When it works fine on a corsa bit not on the sunbari amy advise would be much appriciated

merlin24

iTrader: (1)

Thats odd then, does the battery have enough power in it to crank it over fast enough when doing the compression test ?
How much oil is it consuming ? Any more than a litre per 1000 miles then it would be deemed as excessive.
When the car is ticking over, does the engine have a wobble/hobble to it ?
Remove the oil filler cap while its ticking over and see how much blowby/crankcase pressure you have coming out of it.
Does it sound like it has compression when you are testing it - should have a definitive kick as its building compression up on the cylinder you are testing.
If it sounds like it is spinning over without any spark plugs in it, then it sounds dead to me ( hopefully not ).
You can have perfectly good oil pressure and worn out bores btw

Mick

dooby-do

iTrader: (2)

Its definitly using more oil than nessasery, but with the engine running it sounds perfrct
The engine does not bounce around or rattle just ticks over nicely, when i put the compression tester on and turn it the first turn jumps straight to 26psi then just doesnt move from there, but with 26psi if that was right surely the engine wouldnt fire up first turn, and tick over and run and drive perfect, ill run it up tomorrow and take the oil cap
Of and see how much pressure comes out. I did read somewere that under 90psi it wouldnt start, maybe its time i took the emgine out and had a look

merlin24

iTrader: (1)

I would beg/steal/borrow a decent compression tester and try again before doing anything else