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afgunn
10-06-2006, 15:03
I was just reading an ASE 8 training manual and it stated that in 1999 the compression ratio was changed to 19.5:1. I am assuming this was done with the pistons or the heads since the bore and stroke are the same as the other 6.5s. Does anyone know which it was and would 19.5 be as good/better CR to shoot for with the GM heads or pistons (which ever it was)? Which would be better the 19.5:1 or 18:1? Seems the GM parts would be less expensive than the aftermarket 18:1 pistons!? Are these GM parts hard to come by?
AndyL
10-06-2006, 15:58
Popular belief says the 19.5:1 engines were never installed into GM trucks.

However, I wouldn't be surprised if the new AM General engines are 19.5:1.
DA BIG ONE
10-06-2006, 22:26
I'm guessing only the the 1999 65 HO did come w/lower compression, however, there are those who say it never made it to production. So, is it a rumor, or?

Thinking parts manual would reveal the truth................but, I have had some bad luck with GM parts manuals too even when using vin#.
Craig M
10-07-2006, 10:04
Some of the parts houses, selling surplus military pistons, mention 19.5 compression ratio pistons. I question them and usually get ???
afgunn
10-07-2006, 13:54
Craig M,

Do you have the link or phone numbers of any of these part houses that are selling the surplus military pistons?

Also, I guess I will check on the post here at Ft Bragg on that 19.5 CR, since I live here and work on the post. Here are the GEP CURRENT Specs: http://www.amgeneral.com/vehicles_gep_specifications.php (20.2 or 18.1). Still do not know if 19.5 was made in the past and how they did it - most likely the pisons though since the heads do not have a combustion chamber except for the IDI chamber.

Thanks for that info!
Craig M
10-07-2006, 16:37
Go to ebay and search under "6.5 diesel" and "6.5L diesel". A couple of vendors should come up.
TurboDiverArt
10-09-2006, 17:38
So does that mean if you buy a replacement engine from GM it's 20.2? How would you order the 18:1 version, tell them you have a boat? :D

Art.
Robyn
10-09-2006, 18:49
I am going to venture a guess that Military stuff wont show up in regular listings.
Mil spec stuff is definately a horse of A different color.
I bought a 6.2 Mil spec IP and the rebuild house had to do some digging to get the info and parts to freshen it up.
I think the pistons may also be special for them too.
Just a thought
Craig M
10-10-2006, 16:25
E-bay item 160039335127 lists some 6.2 pistons as 20:1 compression ratio
TurboDiverArt
10-10-2006, 17:07
I am going to venture a guess that Military stuff wont show up in regular listings.
Mil spec stuff is definately a horse of A different color.
I bought a 6.2 Mil spec IP and the rebuild house had to do some digging to get the info and parts to freshen it up.
I think the pistons may also be special for them too.
Just a thought
Robyn, does you post apply to the availability of military parts in the civilian market or that the link provided to AMGeneral is for military spec engines only?

I'd love to know if I purchase a replacement engine through GM if it will be to the specs posted on the above link? Meaning, will it have 20.2:1 compression and all the goodies of a stronger block? 20.2:1 would seem like a nice compromise between lower compression performance and the ease of cold weather starting with slightly higher compression than 18:1. Naturally for all out performance you would want 18:1's. I need the ability to easily start in single digit temperatures without plugging in. It would be nice to see that they learned something by lowering the compression a little. The site also states that the engine is capable of 300HP.

Art.
TurboDiverArt
10-13-2006, 03:27
I'd love to know if I purchase a replacement engine through GM if it will be to the specs posted on the above link? Meaning, will it have 20.2:1 compression and all the goodies of a stronger block? 20.2:1 would seem like a nice compromise between lower compression performance and the ease of cold weather starting with slightly higher compression than 18:1. Naturally for all out performance you would want 18:1's. I need the ability to easily start in single digit temperatures without plugging in. It would be nice to see that they learned something by lowering the compression a little. The site also states that the engine is capable of 300HP.

Art.
Anyone know if the above is true?

Art.
TurboDiverArt
10-18-2006, 13:22
To put a period on this. I emailed AM General and asked about the 19.2:1. They said all the engines they have produced are 19.2 or 18, 18 being marine. You would need to change the intake manifold to use the marine engine but it would work. I also asked if I were to purchase a replace 6.5 from a dealer if I would get a 19.2:1 replacement. He said yes, all the engines they provide to GM, Hummer, etc. dealers are the 19.2 version.

Nice to know that if you purchase a replacement engine from the dealer you'll get one that is a little lower compression than stock. I didn