HE mention Compression ratio, nothing to do with Boost.

If your truck only has 45-50 psi of compression it wouldn't be running too well.

 

can you explain the difference between compression ratio and boost? You lost me there.

they lowered it to 16.8:1 (from 17.5:1) on the 2006 model year. This was only for emmissions control. The cummins is 17.2:1.

 

no, but he was mentioning how aluminum heads are impossible to make work, and im simply stating how mine are working fine with no head studs or nothing. Guess I got one of those rare good ones! I win!

The new cummins V8 (oh god!) diesels have aluminum heads too.

ben

 

They claimed it was for emissions, but no regs changed for 2006. The 2007 regs changed sulphur content. So, you take it as you wish. IMO, the CR was lowered to assist the head gasket problem. It also allowed the engine to accelerate slightly more quickly, making more HP. Further, it lowered stress on the bottom end. All of this could be taken as a coincidence, or it could be taken as a good idea for a number of reasons.

Compression ratio is the ratio between cylinder swept volume plus combustion chamber and combustion chamber volume. In a diesel, this can be a bit different given recessed pistons are a part of the design. For a diesel, it would be swept volume compared as a ratio to combustion chamber.

Boost pressure is the pressure inside the intake manifold. Neither will have any effect on the other.

Boost pressure will affect PSI in the cylinder, and compression ratio affects PSI in the cylinder. However, just because your intake PSI (boost) goes up 20PSI (to pick a number) does not mean cylinder pressure will go up that same 20PSI.

 

Well they increased the power a substantial amount. 310hp to 360. Some people say the 360hp is underrated too. 4x4 Crew cab 2006-2007 dmax's run 15.1-15.2 bone stock. When you increase power (fuel rate) you increase emmissions output. LB7 is rated at 90mm3 max fuel rate. LLY is 95 mm3, LBZ is 100 mm3. Every model year engine is subjected to emmissions testing. With the extra fuel required to make 360hp, at the existing CR, emmissions would not have passed. So they dropped the CR so they could have 360hp while still keeping EPA compliance.


Theres no head gasket problem on the duramax. I dont know why that is so hard for you to accept. Even the dodge guy who works as a tech at at GM dealer says hes only seen like 4 come in for blown head gaskets in his time working there. If 80,000 miles of abuse and 50psi boost on stock bolts and gaskets isnt enough to prove that to you I dont know what is.

oh really? thanks for that explaination, im new at this stuff.

ben

 

Obviosly each cylinder has a pop off so that the extra 20psi of boost doesnt increase your cylinder pressure. But what do I know I only went to school to be a diesel tech.

 

Oh really? I must have missed that, I'm new to this stuff.


Just because one guy says he only saw four, and yours works fine, is not an indicator of the failure rate over the thousands sold. I dont know why that is so hard for you to accept.

It certainly seems so.

 

Clearly reading comprehension wasn't part of the curriculum.

 

Well, all right then................

I guess we've all been put in our place and learned something too. I, for one, am very grateful.

It's good to know there's one person on this board that knows everything. Now, if GM and Isuzu would just read a few posts they could get clued in too, and stop making such obvious mistakes.


John

 

they dont have head gasket issues!!!!!

You are barking up the wrong tree. Pick on the stupid LB7 injector fiasco. Pick on the LLY's overheating. Pick on the fact that the rods are pathetic and wont hold more than 675rwhp without spitting out the side of the block. See Im not blindly brand-loyal like you and I can actually admit my engine's shortcomings. But for the last time leave the aluminum heads and head gaskets out of it because you are wasting your breath needling something thats not even an issue.

I guess sarcasm is also hard for you to accept. I learned what CR and boost were when I was in 5th grade and built a jet engine when I was in 9th grade.

 

Clearly, you didn't read what I started out with, which was an endorsment of what amounts to the worlds largest diesel engine builder. I also stated that I didn't think the Duramax was the best compromise possible for the parameters given. Then, you asked why I figured they chose illogical design features. Now, if you didn't wnat my opinion, why ask for it? And then, once getting what you asked for, why act like a bunch of asshats?

Every board has a bunch of jackholes that resort to personal insult once they run out of facts. I think I've found this boards bunch. Whatever.

 

Yay for you. Since you did these things, you must be an expert.

 

good lord, i can hardly see as how 80,000 miles on a truck engine with no blown head gaskets really says that much about whether there's a problem or not. Check back in a couple hundred thousand miles.

80,000 miles SHOULD be just getting broken in, and intact head gaskets at that point should be a given. If I worked in a dealer, on new and almost new trucks and had already seen 4 or 5 blown head gaskets, I would think that might mean something.

Not to get into the nitty gritty that you guys are hashing over, but I couldn't help but say something about the "80K and no bad head gaskets thing". For that kind of money, I would sure hope so! Have our expectations been lowered so far?

 

It appears Ive pushed max to the point insults, so its not worth me wasting my breath anymore in this thread.

ben

 

At some point, after repeating the obvious, I have to respond with less than just facts. Interestingly, insults were all you had, no facts. So you were wasting your breath all along, because I'm not particularly insulted.

It does however, prove a lot about certain people on this board.