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I have a GSR Sedan with a JDM(P72) B18C swap. I've noticed the car has started to bog down anything past 20% throttle after the car is warmed up fully, like after 10-15 minutes of driving.
There is no overheating problems or anything, it's got a triple core rad etc. Gauge works after I fixed the wiring, it's all good.
It started bogging down so badly that I heard quite the backfire when I left off for a shift. And mind you, I am not driving this car hard, no WOT or going past 3K RPM because I am still in the process of breaking in the new clutch.
Rip the new clutch, because I was starting to have to rev it to nearly 4.5K RPM to get anywhere from how bad it had suddenly and immediately had gotten. Especially up even the slightest hill.
It maybe backfired once more before I got home after that. This has been happening for maybe a week, and I still drive it sometimes just to get some miles on the clutch.

Got a compression test kit and tested it after driving it around for maybe twenty or thirty minutes. I had just recently replaced the old sparks because I had no idea how old they were, maybe 3/4 days ago.
Yet they came out looking like this? Is it normal for them to be seemingly so burnt/dirty that fast? I always thought it took a very long time for them to end up looking like this.






Also these images seem obscenely huge and I'm not sure how to fix that... At least during the time of writing this out :/

Anyway though, onto the more important part. The results of the compression testing. To me, it seems I have two bad cylinders, one half bad, and only one good one.
I wish there was a way to make a simple graph, but typing it out will have to do. The cylinders are numbered from drivers side to the dizzy. First number is Dry, second is Wet.

Cylinder 1: 170/210
Cylinder 2: 145/190
Cylinder 3: 225/300+ (explained further)
Cylinder 4: 150/165

An image of the results



So to me, #2 and #4 seem the worst. I know for most of our engines 180-220 is good? Or is that incorrect.
#3 has phenomenal compression, a little too good almost? The problem with my wet results, is that I think I ended up adding way too much oil into each cylinder for it.
I heard you add anywhere from a couple drops to a teaspoon from different places, so I went with trying to add a tsp.
Using a normal little measuring cup was a terrible idea, as it ended up going against the walls and everywhere else besides the plug holes. So I ended up adding who knows how much oil to each one before testing.
Pretty sure 3 had it the worst when it came to how much I accidentally added over.

Also, during testing, #3 and #4 started to smoke? I had the dizzy off, and the injectors obviously unplugged, so I'm not to sure as to why that started to happen?
It was super hard to get a picture of, but the smoke was much thicker than what it looks like in the picture I took.


Anyway, I was really hoping it was the valves burnt or something instead of the piston rings, as that's a hell of a lot less work and hassle to replace, but it looks like that'll have to be done...

But, this doesn't explain to me why the car drives so smoothly cold start, then has such problems when it fully warms up. Does this bad compression make sense to cause this issue just from cold/warm driving?
Also, the car is actually going to be turboed in the future, with a goal of 400WHP. Should I go ahead and actually buy forged internals, rather than just replacing the piston rings and leaving it at that, just because I'll be having to take apart the whole damn engine once already? The thing is though, is that I like to drive it, if I got new rods and pistons, made for lowering the CR for a turbo setup, the car would need some sort of tune to be able to run those internals N/A, right?
I really don't want to run a low CR and would rather have a really well built decent CR FI engine. I'm talking not less than 10.0:1 CR. Since it's the P72 B18C, it's got 10.6:1. I know that people boost these stock for like 6-8psi range with no problem though.
So maybe I could stick with the 10.6:1 CR and get forged internals for that as exact replacements after all? But, I don't recall how high in power people manage to go with that high CR. But, they also typically don't have internals done.

And maybe I'm just over thinking all of this entirely, and my compression results aren't actually that bad? And I just need to replace the valve setup instead? Or even just adjust the valves? I'd love some input for any answers anyone can provide.
 

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With compression numbers that far apart, I think that the next step would be to do a leak down test to find out specifically where it's leaking. A wet compression test is good for testing the seal from the piston rings, but as you experienced, there's a lot of ability to create variation by how much oil you drop and how well it distributes (or pools). You could go to all of the trouble to pull apart the block, replace the rings, just to find out your valve seals are burnt and leaking oil into chambers & air out too. I did mine a few months ago (all originals except the one ex seal I paid an Acura dealership $100 to do as an add-on service 14 years ago when I didn't know any better). They all looked exactly the same--hard, crusty & cracked. Not saying that's what you have going on, but a leak down test might give you some more insight into what's giving you grief.

I don't know if you can rent them from an autoparts store, but after reading the reviews of the harbor fright leak down testers, I ended up building one out of brass fittings, pressure gauge, flow regulator, and the Lisle hold open hose? Edit: Lisle 19700 because it has a normal [industrial] air pressure connector. The second paragraph probably wasn't that useful to you and I apologize, but someone who has a similar problem in the future might find it helpful.

Good luck.
 

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Discussion Starter #3
With compression numbers that far apart, I think that the next step would be to do a leak down test to find out specifically where it's leaking. A wet compression test is good for testing the seal from the piston rings, but as you experienced, there's a lot of ability to create variation by how much oil you drop and how well it distributes (or pools). You could go to all of the trouble to pull apart the block, replace the rings, just to find out your valve seals are burnt and leaking oil into chambers & air out too. I did mine a few months ago (all originals except the one ex seal I paid an Acura dealership $100 to do as an add-on service 14 years ago when I didn't know any better). They all looked exactly the same--hard, crusty & cracked. Not saying that's what you have going on, but a leak down test might give you some more insight into what's giving you grief.

I don't know if you can rent them from an autoparts store, but after reading the reviews of the harbor fright leak down testers, I ended up building one out of brass fittings, pressure gauge, flow regulator, and the Lisle hold open hose? Edit: Lisle 19700 because it has a normal [industrial] air pressure connector. The second paragraph probably wasn't that useful to you and I apologize, but someone who has a similar problem in the future might find it helpful.

Good luck.
Alright thanks, I've only heard of a leak down test vaguely before but never knew what they were. I've looked more into it and will probably buy a tool for it. Definitely a lot of mediocre or poor models of this tool out there from what I can see for sure. I ended up just playing with the distributor and moving it around until it seemed to run better. After doing that I actually don't have any more bogging down when it gets warmed up, but obviously there's still things that need to be fixed in the engine.
 

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That’s a wide range of compression numbers! Could be everything is tight when cold.

There’s plenty of videos on leak down testing. Ericthecarguy has a great one on YouTube. You will need an air compressor in addition to the leak down tester. It will point you to whether it’s your valves, rings, or head gasket.
 
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