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My Twin Turbo 6.5 (GM4 & GM8)

Oh wow thats quite a difference in the different generations. I have brand new heads off a 1997 with the diamond pre cups i might enlarge a bit more.
 
could you post up a few more pics of the drivers turbo manifold? i would like to see how you boxed the flange to the manifold... also some have said it is not easy to weld to cast, how did it turn out..... i have had good results welding to cast with the mig.. never had a crack yet....
 
I never did weld to the
Manifold it's self I built the t-3 flange to bolt right up to the manifold using existing bolt holes used for the cross over pipe, I can post photos in a day or 2
 
buddy said:
Here are the several stock type, compliments of MGW, you can see the diamonds are bigger than the squares, but some have ported out larger than diamonds. I cannot recommend much bigger than the diamonds, as I dont yet have mine installed, and I still have the smaller square or dot cups in mine.

attachment.php
Click to expand...


I wonder what CCH's new casting heads come with? Thats what im running. I cant remember the way they look, hope they are the big ones..
 
MGW has commented though, that not all aftermarket heads come with GM spec precups, some larger diameter and inner volume, so that would change the compression ratio if they had a larger inner volume.
 
buddy said:
MGW has commented though, that not all aftermarket heads come with GM spec precups, some larger diameter and inner volume, so that would change the compression ratio if they had a larger inner volume.
Click to expand...

I wonder if there would be any advantages/disadvantages to the larger volume precup. Might be a simple way to lower compression a tad
 
I saw some pictures of 6.2 vs 6.5 precups and the 6.2 has thicker walled precups which makes the internal volume lower, higher compression ratio if put into a 6.5. I might condiser using 6.2 precups to gain back a little compression after modifying the pistons that will drop it. Ideally I would like to maintain 20:1 CR. Although I would port out the mouths of the 6.2 precups to be more like or slightly larger than diamonds. Its slight, but could account for a 0.5 CR change, not enough for most people wanting to drop CR.

GM dropped CR somehow throughout the years, but increased stroke when the 6.5 came out, CR didnt go up, and CR went down in later models with no change in stroke, gaskets or heads. But the diamond precups came out which reduces precup material and may have thinner wall for more internal volume.
 
It will be up soon im making another one now that its all pretty much finnished. Sorry for the down time.
 
buddy said:
I saw some pictures of 6.2 vs 6.5 precups and the 6.2 has thicker walled precups which makes the internal volume lower, higher compression ratio if put into a 6.5. I might condiser using 6.2 precups to gain back a little compression after modifying the pistons that will drop it. Ideally I would like to maintain 20:1 CR. Although I would port out the mouths of the 6.2 precups to be more like or slightly larger than diamonds. Its slight, but could account for a 0.5 CR change, not enough for most people wanting to drop
GM dropped CR somehow throughout the years, but increased stroke when the 6.5 came out, CR didnt go up, and CR went down in later models with no change in stroke, gaskets or heads. But the diamond precups came out which reduces precup material and may have thinner wall for more internal volume.
Click to expand...

gm had the pistons cast shorter after 1997....
 
I have seen standard pistons and - .01" compression height pistons, but never referenced by years that way. All the places I look have the same part number from 92 to 2000 trucks. I figured the -.01" pistons were for if decking the block.
 
We read an article in Diesel World (June 2008). The article is "New life for the 6.5L turbodiesel". In it were many improvements available for the 6.5L. There was talk of lowering compression ratio, with Peninsular's 18:1 pistons, then immediately a reference to GM lowering compression in 1997. Took it as corresponding to GM using their .010" piston to do this, as all came about at approximately same time.

Once again, we got gray areas. That is, until one of us actually does all the measurements necessary to answer questions.

We have a "99" block here, we'll do some measuring and see what we come up with.
 
Hey looks nice man, I always have a hard time judging acceleration with a km/hr speedo :) It sounds nice though, and looks fast
 
That was the first boosted launch I have tryed. the highways finnaly dryed up now that it hit +7 today. It wasent bad I guess
 
sounds good, seems like its going to hold together, sure boosts good in the upper rpms, thats good news about the +7, that means it is coming this way... gotta love them chinooks... where abouts are ya? close to calgary?
 
Though i would post a cold start up for anyone thats interested. It was -28 today and this was with one block heater pluged in. You will notice how it smokes alot more from the cold side. Takes a couple min for the smoke to clear up with the lower compression. I got it to start at -25 a couple weeks ago with out being plugged in.

http://www.youtube.com/watch?v=JmMg3p3VOIA
 
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