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Compression Ratio

I had 205-210 with my b230f back in the dizzay. I haven't checked it on any of my 16v motors, stopped caring about that a while ago. if it doesn't sound 'off' while cranking, and it runs out good, meh.
 
i used adverised numbers from the rsi pistons....compressed elring and advertised 16v combustion chamber and ran it through a calculater. 2 different ones gave a close 8.5 to 1 motor. i was seeing if using a cometic and going to tight squish would work but then you mentioed that the 16v dont have enough squish area to worry about so i went elring.
the cranking does seem high but it is what it is....nothing fancy in my motor but more stroke.
initial cranking was 180psi before start and now with 600 miles its rockin the 210 number.
 
Engine, battery and starter condition all matter of course...sort of hard to compare apples to apples.

How it actually drives and makes power matters more than a # on a piece of paper.

Being able to consistently compare #s, and apples to apples, regardless of what they are can be useful...

Raise the SCR? Maybe. The driving experience and fuel econ of a stock B21FT isn't exactly exciting.

Better exhaust and head flow will really help that motor out, regardless of any of the other stock parts in use on it.

Tighter squish and higher SCR doesn't hurt for more usable power without having to rev it to the moon.

B230 is fairly comparable, though has higher SCR and displacement than the B21FT started with...
Verifying the condition and dimensions of the existing motor (we ASSume it is used?) parts would be a start.

Making basic flow and efficiency improvements is often nice on a basic street application. Reward without a lot of compromise of reliability, service or drivability is nice...all without spending your whole life or whole life savings...cheap, fast, good pick two or something like that...

Where one goes from there is a topic of much debate.
 
Karl Buchka said:
If your rings are shot you won't get any compression. Blindly comparing compression numbers from a junk-yard motor to a freshly assembled shortblock doesn't make a whole hell of a lot of sense.
Click to expand...

Yeah that I of course agree with 100%. My comment was because I've noticed you often can't correlate leakdown and compression tests I've noticed - ie you have have piss poor leakdown on a motor with big ring gaps but great compression because the air becomes sonic when being tested dynamically at which point increases in chamber pressure don't results in more leakdown, at least not proportionally), but sounds like you mainly mean that of course a worn out old pos is going to have poorer ring seal than something fresh and affect compression.


Even if Nate's motor is greater than 8.5:1, it's not necessarily a bad thing I also agree, but that doesn't change the fact that 210 would be considered unexpectedly high for the CR by pretty much anyone's standards. If it were me I'd just be careful tuning since it might not be what you think it is.



All in all on a stock motor, gaining thermal efficiency by increasing static cr, then counteracting it with more cam is a great thing to do, tight squish is great too.

The main timing to keep in mind is varying these parameters significantly alters what the timing curve should be, so if you don't have a way of re-mapping the gains are somewhat limited. but yeah cr is awesome.
 
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