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Is 460psi compression good enough???
by
shox75
on 17 May, 2005 08:55
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could this be the cause of low economy? Spec. shows 34bar which is approx. 493psi.
What is everyone elses compression? I just rebuilt my engine and after 10,000kms which is way enough for a break-in, I get 460psi across.
The guy who plained the head and block told me to use the thickest of the 3 gaskets available.
Need your input...is this adequate or should I look into replacing the head gasket?
Also if im planning on raising my boost pressures in the future isnt a lower compression better? or does that only apply to gas vehicles?
thanks in advance!
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#1
by
Rat407
on 17 May, 2005 09:13
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That is great compression. From what the Bentley states 490psi is new. I wouldn't complain with what your getting. Did the shop do a piston protrusion measurement? That is the correct way to determine which head gasket you needed 1,2 or 3 hole/notch. Most just use the 3 hole/notch to be safe but if the Bentley wanted everyone to run a 3 hole/notch then they wouldn't bother with giving you specs for 3 different gaskets. Mine calls for a 1 hole and had 460psi accross all 4 cylinders. This was with 5k on the rebuild. It cranked right up every time no matter how cold. But now since I had to go back in since the machine shop messed up and broke a ring on assembly. I was using a qt of oil a tank of diesel. I'm hoping to get that same compression this time around on the new set of rings.
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#2
by
shox75
on 17 May, 2005 09:51
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Well I think the guy just told me to use the 3rd gasket to be safe like you said.
However, my block was also bored .20" over and i installed new piston and rings. Wouldnt this compensate for the heads being plained?
Ayway what advantage is there to having it as high as 490?
Anyone wiht that spec?
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#3
by
Justin
on 17 May, 2005 10:13
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more compression and pressure equals more power, but i wouldnt loose any sleep over 30 psi, i have had a used engine that had like 360 and a blown head gasket and it still ran great it didnt get the greatest milage though around like 33-35 if i remember right. but it still started without a block heater and with 15w 40 oil in 10 farenheight weather
460 is great compression
later
justin
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#4
by
Rat407
on 17 May, 2005 11:05
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Mine is bored .020 over as well. I measured the piston protrusion and it worked out to be the middle of the measurement for the 1 hole.
490psi is a reference in a sense. That means you should have that in a new engine if it was put together correctly. So if you have a ton of miles on the engine and still have great compression then the health of it is still great.
My understanding is the higher the compression the better, now how boost and compression relate, I'm not that sure but the higher the boost the more power your going to get out of a diesel. But you have to make sure the engine can handle the boost, studs instead of head bolts and a good quality head gasket, some say the 1.9 metal is the way to go.
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#5
by
janb
on 17 May, 2005 18:32
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The guy who plained the head and block told me to use the thickest of the 3 gaskets available. !
your compression is fine, but... gasket thickness is determined by piston protrustion from block, as head is flat (no combustion chamber)
There is the issue of valve clearance, when full open. If you plane well below spec, you should be cautious of smacking valves, hopefully this is not the case.
Not sure what the full open clearance is vs. timing, but pistons and valves do get close. :oops:
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#6
by
andy2
on 17 May, 2005 18:42
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My rebuilt 1.9 .020 oversize bore has .022-.026 thou piston potrusion thats at the lowest spec on the scale for even the thin 1 notch gasket.However I will be running high boost (30 psi) so QuickTD and I figured why not try the thickest gasket (3 notch) and see what happens.So the engine is not quite broke in yet and I checked one cylinder it came to 450psi after 5 Revolutions.So needless to say I'll be fine even up here in the winter without a block heater :wink:
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#7
by
shox75
on 18 May, 2005 09:46
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thanks for the responses. Did the 1.9 metal gaskets comeout in 3 different sizes to?
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#8
by
andy2
on 18 May, 2005 19:37
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The 1.9 has the three different thickness gaskets also.
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#9
by
RAMMSTEIN
on 01 Jun, 2005 17:23
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could this be the cause of low economy? Spec. shows 34bar which is approx. 493psi.
What is everyone elses compression? I just rebuilt my engine and after 10,000kms which is way enough for a break-in, I get 460psi across.
The guy who plained the head and block told me to use the thickest of the 3 gaskets available.
Need your input...is this adequate or should I look into replacing the head gasket?
Also if im planning on raising my boost pressures in the future isnt a lower compression better? or does that only apply to gas vehicles?
thanks in advance!
A diesel is not broken in at 10 000 km.
Check back at 100 000 km. :wink:
Compression should also be higher.
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#10
by
srivett
on 01 Jun, 2005 19:31
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Heck, it'll run just find when you're back down to 360PSI.
Cheers, Steve
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#11
by
BlackTieTD
on 02 Jun, 2005 07:28
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compression on my engine after rebuild with under 200km on it was 500-515psi across all cylinders. before rebuild it was in the 340-380psi range, about 260,000km on the clock.
20 thou overbore. proper gasket for piston protrusion, 2 notch if memory serves.
490psi is great. givr
