Low Compression Raises Blood Pressure

So I get the Stage 3 build done and I am going through the tuning process and I have this nagging P0302 cylinder 2 misfire. It has never once shown its face prior to the build, but now pops up randomly every couple days. I have changed all the normal culprits and I am left with low compression in cylinder 2. It only holds 70-80psi. I had it checked when I bought the car 15k ago, and it has run flawlessly since (minus the blown vf40 I guess). Because I never noticed any change in performance I went ahead with the build (my fault, I should have checked). I didn’t do a leak down test but the engine consumes next to no oil, under 1q every 2500-3000, so I doubt it’s a ringland. With everything I am reading about burned valves at the 100k mark-108k on mine it really makes me think the problem lies there. I know the engine needs to come out at this point, but where to go from here… If I just rebuild the heads/valves then I still have a block with 100k+ and what problems lie in wait there.

 

 

 

A couple questions for the initiated

 

 

 

1) Why not rebuild my own heads? I have a machine shop that clean up the surfaces but I haven’t really seen any build threads for just the heads. They don’t look any more complicated than good ‘ol v-8 heads except for the goofy valve spring compressor needed. Valves, springs, seals, retainers, etc. all seem relatively inexpensive through Subaru or Infamous, etc… then just run ‘er till she blows and then shortblock it

 

2) Shortblock it right away and rebuild the heads- What’s the best option for this route? I want it to stand up to the abuse for another 100k even though I won’t own it long enough to see those miles. I’ve heard replace the stock pistons, but do you leave the stock rods/bearings?

 

3) What would you do in this situation? I’ve seen guys quote $2k numbers for head rebuilds and well that’s a lotta coin if the bottom end is gonna be running on borrowed time.

 

 

 

I suppose I should also state I am running a BNR 18G w/ ID1000cc injectors. I wanted to have some MO POWAH but not necessarily the craziest Subie on the planet (don’t really care about the hp/tq numbers). The thing is though I got the 18G cuz I thought the 20G would be a little overkill given the age of the motor. That being said, if I were to get a new shortblock then 18G be damned and 20G or something large would be in its place. I don’t autocross but I do plan on tracking it at Road America (hence the large turbo for long straights). I am just a little bummed cuz I thought I was done building for a bit and it looks like I am just starting. Any help/ideas are greatly appreciated.

I let my trusted machine shop do my heads, see my click here link in my sig.

I've glanced over your build at least a few times. It will most likely be the route I go more or less. Might as well go with proven results rather than trying to re-invent the wheel.

I've glanced over your build at least a few times. It will most likely be the route I go more or less. Might as well go with proven results rather than trying to re-invent the wheel.

 

They all say it. But will you be the first to actually do it?

They all say it. But will you be the first to actually do it?

 

Well its either do something feasible or end up with some twin turbo 2.7 stroker monstrosity.

Well its either do something feasible or end up with some twin turbo 2.7 stroker monstrosity.

 

I'd go broke for something like that if I wasn't already broke.

Do a leakdown. You might find your heads are the culprit for the low compression.

 

Aside from that, try the normal plug inspection/coil pack/injector swapping for diagnosing the misfire.