Tear into it, or bolt in and go???
Well, that’s what the sensible side of me is saying, but I feel like once I start to dig in, it’ll balloon into something much bigger. A lot of, “Well, since I’ve already got it apart…”, types of statements.
The less nit-picky side of me says to just bolt it in and drive!
I know that actual right answer, just looking for some dissenting opinions to help me justify the easy route!
To me the real question is, how much work are you willing to do on this engine? And do you really think it ran ok before?
If you tear into it, how far do you go? Just check torque specs? Check all the bearing clearances? Are you going to change the pistons? Change the cam?
Because to me if the answer is you don't want to totally rebuild it again, why tear it apart? You already have the intake off so it wouldn't hurt to pull the timing cover and look at the timing chain and peep the cam to see if you can get a part number. But beyond that, what's the point? Unless you find something obviously wrong or can't see the piston numbers with an inspection cam, I don't know I'd go much further. In that latter case I might consider pulling the heads just to see what the chamber size looks like, but you don't need anything fancy to get that cranking pressure.
When I bought my Challenger it had a supposedly rebuilt 318 in it, done by the previous owner to the one I bought it from so I knew NOTHING about it. It sounded fine (and stock), the oil pressure was good, and the compression numbers were ok. Nothing spectacular, low compression 318 stuff, but even across the banks. I changed the oil, put a 4 barrel intake and headers on it and drove it 70k miles. And I didn't stop driving it because of the engine either, it still ran fine. Don't sweat the little stuff.
That is ultra high compression for a 318, I am not even sure which pistons to use to get it that high.
No, it's not "ultra high compression" for a rebuilt engine. It's the same cranking compression my 340 has with ~9.8:1 compression and a decent sized cam. Which means with low to mid 9-ish:1 compression and a smallish cam that cranking compression is not hard to get. Could just be KB 167's and a cut on the heads. It's definitely NOT "ultra high" compression.
To run pumpgas at 185psi in that combo, is a recipe for detonation disaster.
Like said ;
If that number is true, then chances are very good that the Q is real tight, so you might get away with it in a lightweight-A,
But you won't know that until you load it up, or it blows up, or you take it apart and look. But
chances are even better that the compression gauge is really optimistic ........
IMO, knowing what piston is in it is not helpful and I wouldn't spend the time to know the answer.
If it was mine, I got three ideas;
1) run it and hope it don't detonate.
2) reduce the pressure to a a known-to-be-safe level, or
3) put it on a dyno. If it takes WOT at full timing, at a normal AFR, and doesn't rattle, then I'm good to go. If it does rattle, then I also know what I have to do.
For me, this would be an ideal opportunity to learn the truth about what many "experts" would call excessive cylinder pressure. So I would just go to plan #3
Man you guys are dramatic, a recipe for disaster? Again, 180-185 cranking PSI is what the 340 in my Duster has had the whole time I've been daily driving it. Yes, with 91 octane at sea level with summer gas
and hot weather it's borderline and I pulled a couple degrees of timing. But any other time it's not an issue. And of course it will depend on a lot of other things, I don't have the best quench on my 340 because its pistons are over the deck so you can do better than I've got for set up to prevent detonation.
And I shouldn't need to tell you that cranking compression isn't a super accurate way to judge static or dynamic compression, the gauges are basic and cranking speed plays a big part too.
If the lifters are bled down. The wallace calculator says a .030 318 would be between 9 and 8.5:1 to match your cranking compression. If your gauge is accurate.
If the lifters are bled down it would be clacking and clattering all over the place. 180-185 psi cranking isn't crazy, low to mid 9 compression ratio and a smallish cam all day long.
