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Engine Compression Ratio - GM Supercharged 3.8 V-6

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Engine Compression Ratio - GM Supercharged 3.8 V-6

Old 03-03-2005, 04:16 PM
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Default Engine Compression Ratio - GM Supercharged 3.8 V-6

Its not on the Chevrolet Web-site

Where can I find the compression ratio of the 2004 Chevy Impala SS 3800 V-6 supercharged engine? And does anyone know why it requires premium gas if its the same ratio as the non-supercharged 3800 if it doesn't knock. I would be hesitant to put the high test in if it doesn't knock due to all the alcohol (which is how they boost octane in the Northeast). I understand that you can cram in a larger fuel charge with the supercharger and therefore the high test may be warranted since it is effectively "higher compression"- but don't they all have knock sensors so your timing is just below the knock point?

Thanks

Bob
Old 03-03-2005, 04:32 PM
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Default RE: Engine Compression Ratio - GM Supercharged 3.8 V-6

3800 Non-Supercharged is 9.4:1 (87 Octane Required)

3800 Supercharged is 8.5:1 (92 Octane Required)

http://www.new-cars.com/2004/chevrol...ala-specs.html
Old 03-03-2005, 04:35 PM
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Default RE: Engine Compression Ratio - GM Supercharged 3.8 V-6

http://www.gmcanada.com/english/vehi...impa_opti.html

its about halfway down the page. 9.4 to 1

whoops, formula is right, the supercharged is 8.5
Old 03-03-2005, 04:38 PM
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Default RE: Engine Compression Ratio - GM Supercharged 3.8 V-6

ken2 - 3/3/2005 4:35 PM

http://www.gmcanada.com/english/vehi...impa_opti.html

its about halfway down the page. 9.4 to 1
That's the Non-Supercharged. Supercharged is 8.5:1 for some reason.

I got the same results all over the net.

LI, put the following search words into Yahoo's Search...you'll get a TON o f sites to browse...

"Supercharged 3800 V-6 compression ratio"
Old 03-03-2005, 06:01 PM
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Default RE: Engine Compression Ratio - GM Supercharged 3.8 V-6

Thanks

Strange - the supercharged is lower compression and required higher octane ;? - must be the additional fuel charge - mine seems to run fine on regular and has never knocked.

Yea I didn't do a search - assumed it would be on the cheby site....
Old 03-03-2005, 11:10 PM
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Default RE: Engine Compression Ratio - GM Supercharged 3.8 V-6

Lower compression results in longer life and better reliability. Simple as that.. It's also a little better economically..

I would also say that the engineers didn't want to put a motor on the market that had snapped rods, cracked heads and spun cranks because some minor tweaking for performance/HP gains exceeded the limits with a 10:1 engine..
Old 03-03-2005, 11:37 PM
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Default RE: Engine Compression Ratio - GM Supercharged 3.8 V-6

compression ratios are calculated without the supercharger in use. the units of measure in this figure compare the pressure in the cylinder at top dead center to the pressure at bottom dead center, which is in theory 1 atmosphere of pressure at sea level.
Old 03-04-2005, 08:51 AM
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Default RE: Engine Compression Ratio - GM Supercharged 3.8 V-6

All blower motors are built with lower compression. Why? A blower effectively boosts compression by it's very nature. (stuffing LOTS more air into the same area). The "effective" compression ratio is probably higher than the non-blown engine.

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