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Is My Compression To Low?

ThomasH

By ThomasH,
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ThomasH Rookie

ThomasH

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About a year ago I had my last compression test, with all cylinders between 9.4 and 9.6 bar. I was told these are decent numbers for a 14 year old RB25DET. However, on a differenent forum I stumbled upon a topic where compression was talked about, and several people agreed that the 9bar compression on the engine in question was to low.

So, what gives? Is the compression I have to low, or not?

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https://www.sau.com.au/forums/topic/331102-is-my-compression-to-low/
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Spurdo Experienced

Spurdo

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it does sound just a touch low to me, but generally as long as the compression across cylinders is relatively even i wouldnt worry about it. when it starts burning oil or you get compression variances of more than 10 or 15 psi between cylinders then i would start thinking about a rebuild.

do you know if the heads ever been off before?

ThomasH Rookie

ThomasH

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it does sound just a touch low to me, but generally as long as the compression across cylinders is relatively even i wouldnt worry about it. when it starts burning oil or you get compression variances of more than 10 or 15 psi between cylinders then i would start thinking about a rebuild.

do you know if the heads ever been off before?

AFAIK the head has never come off, but I have no history of the car in Japan.

To the person that PM'ed me, thanks for the help/info! I can't send PMs untill I have a postcount of ten, wanted to say thanks through here. :D

ThomasH Rookie

ThomasH

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After a bit of chatting, and the friendly PM I recieved earlier, as long as the engine drives properly, both on boost and off boost and doesn't use oil or anything, I should be fine.

And other then a lowish compression, the engine is spot on and doesn't miss a beat. I'll try and get a leakdown test done soon, see if that says anything.

t_revz Grand Master

t_revz

Posted
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did a comp test on my rb25det 5 years ago and got 120psi each although never missed a beat apart from burning a litle bit of oil. thought something was up as manual says rebuild at 135ish psi yet i was making plenty of power. just opened it up and found melted piston and all rings rooted. i guess it shows how well these engines perform even when not in tip top condition

ThomasH Rookie

ThomasH

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Well, I decided that it's probably the best thing to start saving up some parts for a little rebuild. Nothing fancy, just OEM or slightly updated parts. I don't want a full forged rebuild, since that's gonna cost a lot, and I'll never reap the benefits of a forged engine, since I'll never go above a stage1 tune. I want a car to get me to work, which I can take to a driftday every now and then.

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