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Hi, l have recently purchased a LQ4 6.0 truck motor. I was going to change the crank rods and pistons for twin turbo use. I have contacted some suppliers and been told that these motors have slightly different crank length and wider rear seal flange. Can anybody shed some light on this as l will have to reconsider my power output wishes. Thanks
Kev
Some do have a different crank flange from other engines in this series. Specifically, the early ones; something like, 2001 - back. I don't think this has anything to do with "power output wishes"; more, a question of transmission compatibility.
Sort of a bump for kev.. Early LQ4 had an extended crank flange, requiring a different flexplate.
Question for the more experienced builders on here: I have an all original 2005 LQ4 running take-out, have a new oil pump, TruckNorris cam, and Johnson lifters to go in. IF I assemble with Cometic 4.060 bore by .040" thick head gasket, what will I get for static compression ratio? My best guesstimate is around 9.9:1 Sound like a good ballpark?
Just have to find a good calculator for that, several on the internet.
The early 4.8l & 6.0l Crank Flange info has been beaten through the ground here over the years. 1999 & 2000 Engines were this type, 6.0l was easy to spot they all had Iron Heads. Not all the 4.8l Engines had the long Flange, it was the Engines in 3/4 Ton Vans that had a 4L80E on the back of them. In 2001 GM started using the .400" Spacer on the back of the Crank with longer bolts, that means all normal Crank Flanges in everything.
Whatever "Supplier" wants to tell you the above doesn't understand that the long Crank Flange was done to bolt up the 4L80E and you don't need that anymore because of the Spacer which you can find everywhere. One would think people would know their **** better if they are selling parts and what can fit in what, but apparently not.
Nice detail and presentation, Merv. Should help a lot of people out. As for them knowing their **** better, a lot of them don't, and some of them who do, dont give a ****...
Last edited by grinder11; Dec 13, 2025 at 09:53 AM.
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Lq4 engine 
