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S-L-O-W 1993 240 Classic wagon

*BING* The lightbulb is lit!

OK, got it: aim to get the piston tops closer to the head for optimal cooling of the piston tops by either resurfacing the block or using a modestly thinner headgasket. I just found and read a wonderfully entertaining pissing match on this forum over the terms "squish" and "quench". Thank you, John V, outside agitator for enlightenment.

Sometimes dawn comes late in my part of the world.
 
Glad you got the idea of the tight squish/quench. You won't need to deck the block. Just measure the piston height and calculate the head gasket thickness needed. The MLS head gaskets are available in several thicknesses. This helps a lot with detonation resistance and efficiency of combustion.
 
They're nowhere near 9.8:1 as delivered. Mine measured out to 9.1:1. After a 0.040" mill and stock head gasket, it's 9.8:1. I use a V cam and feed it a steady diet of Shell 87 (R+M)/2 and have no detonation issues. Using 93 netted no measurable improvements of any kind.
 
shoestring said:
They're nowhere near 9.8:1 as delivered. Mine measured out to 9.1:1. After a 0.040" mill and stock head gasket, it's 9.8:1. I use a V cam and feed it a steady diet of Shell 87 (R+M)/2 and have no detonation issues. Using 93 netted no measurable improvements of any kind.
Click to expand...

That seems quite a difference from an advertised spec. Was this taken on a new car following delivery and break-in, and are you confident that it's representative of the breed? And was this a turbo or NA car?

Anyone else lurking here have a similar or different experience???? I guess I could measure compression on my motor now for a reference point, but that would only indicate absolute compression on a motor and head with 150K miles, and before a valve job and shaving.
 
I've also measured two uncut late NA 530 heads (93 and 94 castings) at 54cc and change which math's out to the low 9's to 1 depending on the piston height.
 
dmg4 said:
That seems quite a difference from an advertised spec. Was this taken on a new car following delivery and break-in, and are you confident that it's representative of the breed? And was this a turbo or NA car?

Anyone else lurking here have a similar or different experience???? I guess I could measure compression on my motor now for a reference point, but that would only indicate absolute compression on a motor and head with 150K miles, and before a valve job and shaving.
Click to expand...

I've measured enough piston dishes and combustion chambers to know this is absolutely representative. NA car. I concur that a 530 year is about 54cc. Normally a hair more. NA piston dish is 8cc, turbo is 16.
 
shoestring said:
They're nowhere near 9.8:1 as delivered. Mine measured out to 9.1:1. After a 0.040" mill and stock head gasket, it's 9.8:1. I use a V cam and feed it a steady diet of Shell 87 (R+M)/2 and have no detonation issues. Using 93 netted no measurable improvements of any kind.
Click to expand...

Yup :nod:
I?m pretty sure Volvo left out the HG volume when they did the calculation for publication.

My experience with 87 vs 91 may be different (it overall doesn?t really matter), but the CR thing is real 100%
 
culberro said:
Yup :nod:
I?m pretty sure Volvo left out the HG volume when they did the calculation for publication.

My experience with 87 vs 91 may be different (it overall doesn?t really matter), but the CR thing is real 100%
Click to expand...

Anyone know about the higher comp B23F engines? I have one in my 83, it's apparently 10.3:1, but maybe they also left out the HG?
 
dmg4 said:
*BING* The lightbulb is lit!

OK, got it: aim to get the piston tops closer to the head for optimal cooling of the piston tops by either resurfacing the block or using a modestly thinner headgasket. I just found and read a wonderfully entertaining pissing match on this forum over the terms "squish" and "quench". Thank you, John V, outside agitator for enlightenment.

Sometimes dawn comes late in my part of the world.
Click to expand...

How I miss John V.

He's a weird one, but that particular Mr Grinch certainly knew his sh1t.
 
culberro said:
Yup :nod:
I?m pretty sure Volvo left out the HG volume when they did the calculation for publication.

My experience with 87 vs 91 may be different (it overall doesn?t really matter), but the CR thing is real 100%
Click to expand...

Interesting. I always wondered if it was a "highest possible result" given maximum allowable tolerances like deck height and the 0.5mm cleanup they allow on the head. Like you said though, it doesn't really matter.

The truth is out there. Just like on X-Files.
 
2manyturbos said:
Those run a flat top piston. That is what increases the compression ratio.
Click to expand...

I remembered that, I'm just curious if somone has done a CC fluid test on the B23F heads to check for spot on accuracy. I do recall my compression readings being pretty high when I did a comp test.
 
Just for fun, I warmed up the engine and ran a compression test.

1= 132 psi
2= 138 psi
3= 138 psi
4= 140 psi

Assuming an atmospheric pressure of 14.696 psi, a 9.1:1 compression ratio works out to 133.7 psi

It fits.

Not bad for an engine with 145,000 miles. I'll post the new numbers after the head is shaved.
 
culberro said:
Those are really low numbers for cranking pressure on a warm NA motor.
Click to expand...

What am I missing in my assumptions? A temperature effect of compression in PV=nRT? It was a "dry" test (no oil added to cylinders).
 
Last edited:
dmg4 said:
Why would that matter? Aren't both valves closed the time that the maximum pressure is reached, or is there overlap that results in one being open on the compression stroke?
Click to expand...

It matters. My engine makes like 120psi cranking compression with the IPD turbo cam. A stock stock one would make 160+
 
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