Jeff, after I sent Brendan to you for a new head he told me that was a concern of yours - short answer is that water jacket and/or exhaust manifold conditions cannot blow a headgasket (pressures are a couple magnitudes lower than what HGs are designed to reliably withstand).
You noticed that as well huh?
There is definitely a pattern involved. I still have my cooler but deleted everything else.
You're right about the pattern - EGR deletes are almost always found with mods which increase power production.
Would a coolent bypass kit help more?
Yes - while BOE kits help retain freeze plugs in the block & head and reduce pump drive HP, don't expect them to "save" your MLS.
1. the VGT exhaust side is to small to keep up with exhaust gasses much over stock volumes.
2. With the Egr cooler in place and FUNCTIONING it performs like a wastegate only instead of blowing the excess gasses out the exhasut pipe it recirculates them into the intake manifold (by product it keeps Drive Pressures lower)
3. Removing the cooler and egr is still one of the VERY best things you can do for your engine (i have dozzens of pics of engines with functioning systems on them when I put a new intkae horn on them. Absolutely horrible and scray crap being recirculated through the engine.
4. All of this is easily controlled by putting a "EXHAUST WASTE GATE" kit on the truck the cooler ports n the factory exhaust manifold make it easier to make a kit, which we did to bolt on a EWG and control the drive pressures which also increases some usable torque by freeing it up from previously Parastatic loss of pushing all those higher pressures around in there
1. HE351VE has a larger hot side than the 5.9L 351 Holsets - TIP issues have as much to do with less than ideal nozzle geometry (housing range is ~3-21cm) for operating conditions as anything else.
I'll be the first to say 409 cubes need more cowbell than 359 do, but drive pressure ratios don't get anymore out of control on the 6.7L than the 5.9L
2. Classic Hobson's choice - I'd rather have excessive TIP than pump soot back through the engine, but the OEM reversion cam will do a pretty good job of backing that up to the intake at high drive pressure ratos anyhow.
3. Agree completely!
4. Adding an external gate makes it easier to keep the Holset as the secondary in a twinset... ironically, reducing excessive drive pressure decreases pumping losses & helps eliminate charge contamination - increasing power production & the possibility of blowing a HG.
And personally I think MLS headgaskets SUCK
The MLS functions pretty well for what it's designed to do - reliable sealing using OEM mass-production techniques - but they have a finite performance envelope.
With the 6.7L's higher peak-torque cylinder pressure, increased combustion deck area, narrower inter-hole web widths and shorter paths to the water jacket - it's 4-layer MLS runs a lot closer to the edge of it's capability than the 5-layer 5.9L version.
Also, on a side note - many machine shops aren't capable of surfacing a head (or block) with a fine enough RA finish... the MLS's Viton layers are only ~3-5 microns thick - don't expect that to fill the valleys in a typical 50-60 RA grind.
:Cheer:
