Hi,

new to the forum, even though I have read quite a lot already.

I own a 2003 6.0 LQ4 GMC Yukon XL 2500 4wd 4ws/Quadrasteer. Currently the engine needs work as it has zero to little compression on two cylinders (other cylinders show perfectly fine numbers). The issue still needs complete diagnosis, but a valve problem seems likely. Note that the engine has close to 200k miles, about 60k of which after a conversion to LPG (european gas prices..). As the latter came with the expectation of needing valvework at some point (burned valves due to no hardened seats), a valve problem is even more likely.

Now, as the heads are coming off anyway and might need serious work I am looking at using the opportunity to freshen up / make some simple modifications to the engine. I am not looking at making some 600+ hp beast, but a little more punch never hurts Also, it is a _heavy_ car, probably weighing in over 6000 pounds, so I am not looking for high rpm hp while losing low- and mid-rpm torque.

Other info about the car:

- The 4l80e transmission is recently rebuilt, and has several upgrades (HD2, stronger clutch plates etc) to increase its strenght and longevity. However, the torque converter that is in it now is not original to the car and exact specs are unknown ("stock 13" from a truck", perfect fit for my car according to seller who actually is technically very knowledgeable). Sounds iffy but seems to function fine without difference to original.

- Exhaust is stock. No intention to change to headers at this time. (Note that German regulations needs paperwork for every modification. So keeping it looking stock and using OE parts results in less headache.)

The car is mostly used for highway driving, but will see towing of a horse trailer (so relatively light) with some regularity.

As it is not supposed to be a full rebuild, it's probably most cost-effective to limit upgrades to things possible to do without removing the engine from the car.

What I was thinking to do now:

• airaid 200-912 intake tube
• TBSS #12580420 intake and 92mm TB (possibly ported) (keeping original MAF sensor should be ok?)
• replace the current #317 heads with #243/LS6 heads, using hardened seats etc, milling them down ~0.035" to get a CR of about 11:1 (texas speed & performance stage 1 or stage 2.5, once I figure out the difference)
• new camshaft (no idea about numbers, not my expertise..)
• probably need new pushrods?
• replace timing chain while its accessible? (what kind would be best? I see single roller, double roller, ..?)
• adjust current blackbear tune for new engine characteristic

Possibly later:

• exhaust if I can find a willing TuV guy
• replace current 3.73 gears with 4.11 gears (with 245/75R16 or 265/70R16 tires)
• add a gear vendors overdrive

The CR should be perfect for LPG (RON of 108-110). Regular gas is about 90-91 here (RON 95), with premium 93 (RON 98) and 94/95 (RON 100-102) easily available. Car starts on gas and switches to LPG when warmed up a little, usually within one kilometer.

Camshaft should:

• increase power (duh..)
• not lose low/mid torque (if not increasing it)
• little 'lopey' idle is always nice for the ears
• should not alter emissions too much. emissions is part of periodic government testing here. however, having two different tunes is a possibility. one to drive with, one for the test.
• have long life reliability (not a strip vehicle)
• not cause valves to hit pistons with machined heads and stock pistons.
• retain mpg or not worsen it too much if not increasing it

Of course I understand it might be difficult, if not outright impossible, to achieve all goals simultaneously.

Thoughts/recommendations?

What would be a good camshaft choice?

Any additional parts needed aside from gaskets and such?

Things to definitely do as well?

 

Okay, so with my very limited knowledge I have found some camshaft candidates:

texas speed & performace stage 1 truck
texas speed & performance truck stage 2 truck (low lift or high lift)
BTR stage 1
BTR stage 2

Going any higher, stage 3 and up, will probably require non stock stall speed convertor, move the power band too high losing too much low-end torque and worsen fuel mileage (?).

Any thoughts on which one would be best?

 

BTR or TSP Stage 2's would both fit your build well, in my opinion.