Stock Compression on a 6.5L Turbo diesel

[xtrempickup]

I have heard different numbers, what is the stock compression on a 6.5L Turbo diesel GMC in 95 and what year did they change the ratio on the 6.5L. also stock on a 6.2L diesel. No military ratios please. I know there are a couple numbers, light duty truck numbers i'm looking for

[chickenhunterbob]

Mine is 21.3 : 1, I suspect yours probably is the same, not sure when they changed though, or to what, but as far as I know there were not too much for changes between 94 and 95.

[gmctd]

The two numbers you are looking for are 21.2:1, give or take a point - well, that's more than two, but those are the numbers for the 6.2\6.5, 1500\2500\3500, naturally aspirated, turbo, marine, military...........boat anchor.

Are some cool 18:1 aftermarket ratios out there, and in here

[DA BIG ONE]

There has been much debate about compression ratio change in 99 to 19.0:1, some say it was a marketing statement only that never made it to production. However, some GM tech training manuals on engine performance for the 6.5td are very clear the ratio was changed to 19.0:1 in 1999 and carried forward...........

[gmctd]

IIRC, that revised piston was never located in any search of the parts directory, tho.

Cylinder deck\piston crown measurements never turned up anything, either

[DA BIG ONE]

IIRC, that revised piston was never located in any search of the parts directory, tho.

Cylinder deck\piston crown measurements never turned up anything, either

Anyway, how much could the 19.0:1 really help the 6.5, if any?

[gmctd]

Reduces loading on starter motor

Allows stuffing more air into the cylinder = more mass + more fuel = more power

What more could you want? :)

[DennisG01]

I'm currently considering RJ's built motor with JK's 18:1 pistons. If this lower compression is so good (and I'm not arguing that) then why did Detroit design it originally at 21:1? Are there benefits to the 21:1? Are there any drawbacks to the 18:1? Inquiring minds... :)

[gmctd]

Ease of starting under most all weather conditions, and smooth drive-away with various fuels and levels of fuel quality - all required when introducing a lite-truck Diesel to an unsuspecting public, most of whom could not even spell Deezle, and who also immensely disliked the noisy, black-smoke belching, evil-smelling things.

It was Stanadyne's smokeless RoosaMaster DB2 and the daily 26mpg that won them over.

18:1 drawbacks?

Ask Jim Bigley about yer drawbacks...................;)