We disagree on many points.
But thats ok, we can disagree and still be amicable. That just makes it a healthy debate, not a distasteful disagreement.
Blowing smoke?
Hardly.
Lots of experience with these engines. Certainly a lot more than one H1 installation.
6.2 in the square-bodies right on up to the optimizer. I’ve had or worked on all of them at on point.
It’s just a bad engine design that they just pushed even harder with the turbo application. 6.2’s would crack and break main webs just as a NA engine. But because they were only pushing in the 120-150 hp range, they could live a long time with those faults. You have to remember the orginal intent of this design was MPG, and only MPG. The 6.2 was penned in the early 70’s as a way for GM to post big MPG numbers during the gas crunch, which it did nicely. But Detroit Diesel cut everything to the bone to do it, part of that was weight out of the block, which made it crack prone everywhere. It didn’t help that GM spec’d it as being able to fit in The same space the SBC fit in. That also limited DD in designing the engine. If you know diesel engines and how compact a package the SBC is, you start to see where the problems came from. Then they grew the 6.2 into the 6.5 TD in the 80’s, but they didn’t do anything to change the basic design. The added power just made things worse.
I’ve never taken a (running) 6.2/5 apart (nor has anyone that I know) without finding cracks in the webs. Sometimes you could pin them. Stop drill or even “lock and stitch” the cracks, but 99% of the time they are just scrap. Even repaired ones would eventually come back, having suffered a catastrophic failure of some sort. Most scrapyards won’t even sell the 6.2/5 becuase they know its going to fail. They go as scrap weight. I’ve seen (and built) 6.2/5’s with everything from main girdles to splayed 4 bolt caps. Doesn’t matter, they all fail. Its just a matter of when. It’s an under spec casting for what its asked to do. Thats why they upped the main web thickness, changed the block metallurgy and had the IH foundry cast the optimizers. Well, that and the fact GM had no interest in servicing/replacing a design they had determined as “discontinued”. Thats where AMG and GEP take over.
The turbo only sped 6.2 failures up (and made the failures bigger). The Turbo was a “stop gap” measure where GM was trying to keep up with its diesel competitors at the time and the duramax/isuzu was too many years away (design phase). Gm saw the writing on the wall for the coming diesel HP wars with the DI Cummins/Dodge and Ford/IH , but just couldn’t get a DI deisel design off the boards fast enough. So they punched out 6.2 to 6.5, cobbled on a turbo and electronic emissions controls and set it loose on the unsuspecting public. It was all a bad idea. 120hp design pumping out 212hp by putting it under boost and no other changes? Bad idea. Full stop.
But again: GM had to get something out into the market to carry their banner, even if it was waaaaay outgunned. .
They also changed from the db2 pump (mechaical) to the ds4 (electric over mechanical). That didn’t help the 6.5 TD either. As I mentioned, I’ve seen multiple failures of the ds4 and they’re not all pmd related. But almost all of them were electrical component failures, not mechanical.
I also remote mounted my pmd/fsd. Still ran hot as hell (Bill Heath relocation kit), but it was working when I sold the truck. Pmd was another bad design, no two ways around it.
I’ve got a “turbo master” up on the shelves somewhere.That’s Bill Heath’s design. Ran it for a while and went back to vacuum control. That was key to making more than 300hp. You can calibrate the turbo behavior in the ECM if you leave it as vacuum controlled. When its on, when its off and how much boost it makes and where. Belive it or not, there are points in the rpm range where you actually want the turbo to
back off in order to make
more hp. It counter intuitive, but dyno graphs don’t lie. Turbo masters are pretty primitive. Thats why none of the oems are using mechanical wastegates and haven’t since the early/mid 70’s. Even Cummins (which was a mechanical hold out on the 6bt turbo) vacuum referenced the Holset wastegate “spring control”. A good “tuner” doesn’t just turn up fuel and timing, they “tune” everything in the pcm, from the tailshaft to the cooling fans. Mechanical turbo control just limits you that much further. I suppose theres the argument of “less to go wrong” since its just a threaded rod and a spring, but the vacuum system works perfectly fine, if you take care of it. Same as any other system in a vehicle.
Bill sent me a couple “tune in a can” calibrations. Some worked well, others not as much. I always got better results brainstorming with Lindon and tuning my own truck. Bill’s were good, if you didn’t know better could be had if you put in the time and money to learn. I use John’s “Tunercat II” along with VDF’s from Lyndon Wester. At least I do for odbII gm’s. Tunercat is an awesomely power piece of software, it’s too bad he sold the rights to JET for their diesel-tuner. They charge by vehicle for tuning and lock you in. Point blank: JET sucks. The original TC is wide open: buy a vdf and tune as many of that vehicle as you like. Lyndon is also great and he sells his own version of a diesel tuner (essentially: tunercat II with a few graphics changes). You CAN still get TunercatII, but tou have to by it from Moates.net and it has to be packaged with their “road runner guts kit”. You’ll spend near a grand to get it. But if tou tune 6.5’s, its pretty much the only game in town. Unless you want to get up into the 2 grand range for Lyndon’s software/hardware package.
Also for consideration: I was military until this past Apr. I’ve been on lots of joint exercises with the US army. Every one of thier EME guys (military mechanic) I’ve ever talked with absolutely
DESPISED the 6.5 in the hmmwv’s. Yes, they had to endure abuse from combat and somewhat.....ummm....”careless” operators. But they saw the same things I saw on civvy side: cracked precups, cracked main webs, fractured cranks, etc. thats both 6.5’s and optimizers, although the optimizers were less troublesome. Not a lot less, but less.
you do know that upping the calibration resistor really does nothing for you, right? The resistor is matched to a pump at the oem to compensate for production differences in the pump. Tossing in a higher number DOES get you more fuel, but only at WOT. The resistor calibrates the
maximum fuel delivery point. It has no effect on anything besides WOT.
Thats not just my opinion, I’ve tested it on a chassis dyno. Running a #5, we switched to a #9 and changed nothing else. Absolutely zero effect on the hp or torque curves. Despite what the resistor is supposed to do (according to internet lore), it didn't even change WOT. We tried it on my truck and then two others that were in the shop. Results were always the same: zilch. Better off to just stick with the oem resistor card it came with.
yep, I’ve got lots of experince with them. In fact, I’m one of 5 people (that I know of) who have ever been able to make more than 300 hp out of them. Getting past 250 requires pretty serious work. Not the least of which is a grand to buy the tuning software, more hours than I can count learning the ecm’s code and many, many, many dyno sessions.
oh, and pickup applications were NOT intended to run 100 mph on the highway. That, my friend,
IS blowing smoke. They were designed to run at torque peak at the national (us) speed limit. Which was 55.....
Because you have one truck with a 6.5 and its given you good service, that doesn’t mean they all do. Just like someone, somewhere eventually gets a “lemon” in an otherwise reliable design, someone, somewhere will also get a “jewel” from a line of lemons.
So as you can see, I’ve had several (and I’ve fixed/modified even more) so when I say they’re “junk” I’m basing that on a pretty large sample size.
iI’s just a bad design. Start to finish. Whether you’re talking 6.2, 6.5 or optimizer (yes, I’ve seen one with cracked mains and cylinder bores). Even the “fabled” 599 casting has failed on me. there are no exceptions to the GM 6.x curse.
It’s really quite surprising from a design firm like detroit diesel, who did the work for GM in the beginning. Surprising in the way that DD would even let it off their drawing boards with the compromises GM demanded. Oh well, “money talks” I guess...
What a gorgeous ride that H1 is 
