LB7,LLY, LBZ piston failure question.

[Killerbee]

Does everybody think that EGT represents cylinder or piston surface temperatures?

EGT is not a predictor of piston conditions, it is a thermodynamic derivative of evolved combustion. Actual temps in the cylinder are 3x higher, over 3000 F, though constantly changing throughout the stroke.

What happens between TDC and the turbine is a long trip. If you really want to understand what is happening to pistons, you have to measure CP. From that you can extrapolate with compression formulas to calculate cylinder gas temperature. CP spikes and temp spikes in the cylinder do go hand in hand...but that is a thermodynamic correlation, pressure=heat. 5 degrees of timing difference is everything in this situation, and will dyno the same, yet the more advanced condition will have a great deal more mechanical and thermal stress. The best way to damage cylinders, is to try to absolutely max out timing. And if you did that on a cool day, low IAT's, no heat soak...then take the same tune out in the summer, do a few 1/4 mile passes, now timing is way over-advanced, and CP is getting way out of control. This condition won't really show up on an EGT gauge either. EGT is not going to tell you necessarily that what is happening to the piston is toxic.

As I have stated before, ECT and IAT timing retard are very important.

But I could be wrong.

 

[duratothemax]

Why is nobody afraid of excess timing? Its always been my number one concern with tuning, and I am adiment about not going over 28* or so. Everyone says its fine, if you want to make power, grow some and take it up to 34* or so... not to mention the engine just sounds like its tearing itself to pieces up there in the 30+ * relm.

But then again, I blew my engine up.

How much timing does an Edge add? I did some stupid stacks early in the engines life, im talking 25* of base timing + Edge on 5.

Even with a built engine I will still not go over 30*. Doesnt feel or sound right.

 

[kodiak]

Has anyone created a tune, using the cylinder pressure gauge yet? I would like to buy a tune that was made using this new technology. Or are we still in the testing phase to find out what is safe and what is not??

 

[redneckbuckeye]

What does PPE advance timing in the Hot+2 on the LBZ Lvl 1
Lvl 2
Lvl 3 and so on

 

[Brayden]

The thing is.... There's no need to run that much timing... Use Michael's pw vs CA degrees spreadsheet and see how much duration is needed for a 3000 us pulse at 4600 rpms It will blow your mind. 82.8 degrees of duration!

So if you subscribe to the 50/50 theory then you need 41 degrees of advance to make that happen. Not an ideal situation...

Shorten up the durations by using a larger injector orifice and you'll be able to run less timing and get the injection duration down to 30 degrees or so. This will decrease heat, increase power output per fuel used and be easier on the motor.

At 1500us duration you only have 41 degrees of total duration, which is roughly 20 degrees of advance for a 50/50 shot.

In JNeals motor we've targeted 12 ATDC for EOI which equates to 26 degrees at 2000us. This has proven to make some very good power on an otherwise stock motor, single pump, w/ cheetah. The truck runs dead clean after spool up and only runs 1450 going down the track with 40,000lbs behind it.

Using Michael's spreadsheet, at 4500 rpm we should use 42 degrees of timing advance for an EOI at 12 degrees ATDC. We're not loading the motor up there though, we just use that for inertia getting off the line. The truck carries around 3400-3000 rpm going down the track, and this is where the spreadsheet tells us we should be running, you guessed it 2000us and 26 degrees advance If the motor was built I wouldn't have a problem running it out to 42 degrees advance at 4500 rpm but if the situation arose where we encountered a heavy load at that RPM I'm sure it would spell disaster on stock rods/pistons.

Just something we've learned and proven on the track. I really need to get some CP data from the truck. I think it would be interesting.

Brayden

 

[malibu795]

i understadn the reasoning behind what you are saying brayden.

here is the problem the the spread sheet doesnt calculate.

drop in rail pressure is one
23,000 to 22,000 is a lot of fuel easy 80% of the truck out there are running stock cpe and maybe a lift pump. good enough on average to hold 20-22k @ 3,000uS at 30* of timeing is roughly 500rwhp on a stock turboed lb7 all this happens under 3300rpm

if you want to spin faster you need to add more fuel. how do you do that?
how do you get 25-50% more fuel in the chamber wiht your 12-15* ATDC for EOI?

i think that they(masses) what to know a bassic safe way too tune with out the worry of cracking piston. which BTW has happend on almost stock hp trucks.

any tuner/builder that has messed engines know that no two engines are alike in tunning. be gas or diesel. i have found some engine that like idleing with 4-5* of timing they queit down and smooth out, while other start sounding liek a cummins @ 2* and idle best @ -X* timing these trucks run the same OS, and completely same tune. go figure

the problem is saying X timing with Y uS at Z rail pressure isnt the best way IMO to go about it.

personally i dont go any steeper the 30* at 3000rpm and 100mm3 and run 4-10* of timing in the curising area 1600-2200 rpm 20-50mm3 and i blend everything to gether form there. that is what i dont go over..


FWIW i am no expert on the matter. what i have said has worked for me.

 

[Brayden]

i understadn the reasoning behind what you are saying brayden.

here is the problem the the spread sheet doesnt calculate.

drop in rail pressure is one
23,000 to 22,000 is a lot of fuel easy 80% of the truck out there are running stock cpe and maybe a lift pump. good enough on average to hold 20-22k @ 3,000uS at 30* of timeing is roughly 500rwhp on a stock turboed lb7 all this happens under 3300rpm

It doesn't have anything to do with fuel at all though really.. You can throw pressure, fuel temp, IAT, anything else out the window. It's just about how microseconds translate into degrees of rotation. If you're going to run x amount of pulse width at y rpm's then you're injection event will take zz CA degrees.

I have further modified the spreadsheet to show the required advance to the SOI per a given EOI..

IMO fuel pressure should be considered a constant while making power. Modify the pulse width to sustain a desired rail pressure instead of living with the pressure drop.

if you want to spin faster you need to add more fuel. how do you do that?
how do you get 25-50% more fuel in the chamber wiht your 12-15* ATDC for EOI?



The only way to be able to deliver high rpm fuel is to cut the pulsewidth back and use larger injectors.

If you look at what we did with Jerrod's tune, we roughly cut the pulsewidth table by 45-50% which corresponds to what we had the injector flow increased by. This enabled the motor to fuel efficiently, with a short duration.

If the formula holds true....

Timing is held constant @ 26 degrees advance which affords an EOI at 12 degrees ATDC.

To run 5000 rpms

The pulse width shrinks to 1300 microseconds. This equates to an injector flow increase of ~ 250 % (over stock)


Will the injector body flow this much... I don't know.. Would be a question for Volker. Are you going to be able to extrude hone a nozzle to that size? No.. Will a 10 hole or 14 hole injector be able to fit the bill? Maybe.

Keep in mind this is farmboy math but it seems to be holding true to what's going on.




i think that they(masses) what to know a bassic safe way too tune with out the worry of cracking piston. which BTW has happend on almost stock hp trucks.

any tuner/builder that has messed engines know that no two engines are alike in tunning. be gas or diesel. i have found some engine that like idleing with 4-5* of timing they queit down and smooth out, while other start sounding liek a cummins @ 2* and idle best @ -X* timing these trucks run the same OS, and completely same tune. go figure

the problem is saying X timing with Y uS at Z rail pressure isnt the best way IMO to go about it.

personally i dont go any steeper the 30* at 3000rpm and 100mm3 and run 4-10* of timing in the curising area 1600-2200 rpm 20-50mm3 and i blend everything to gether form there. that is what i dont go over..


FWIW i am no expert on the matter. what i have said has worked for me.

Just some observations....

Brayden

 

[malibu795]

ok.. we are thinking along the same lines

tunning a engine with bigger then stock inj requires different setup on the tables.

i was talking in a mechanically stock engine.

 

[Brayden]

To add to my post above..

The injection timing being relatively low is what is driving the nozzle size in the last example. If we build the motor and it can take the abuse I certainly would run way more advance than 26 degrees at 5000 rpms. I'd say it would be closer to 40 degrees. Having said that you could run a 2100uS pulse at 40degrees advance and still have an EOI at 12 ATDC.

Which if we're back at 2100uS the 50% over nozzle will work for that "desired SOI, duration, and EOI

The problem is the motor probably won't handle that much high RPM CP.. but maybe it will.. I would have to measure the CP to find out. We have had the motor to 5000 - 5200 rpms before and it doesn't sputter at all even with only 26 degrees advance up there.

Brayden

 

[SmokeShow]

Brayden, I'm really liking where you're at in your tuning and tuning mentality. Seems spot on to me.

I must have missed where Jon posted a spreadsheet though. Perhaps someone can point me to it or maybe you could post your modified one Brayden? I really like spreadhseets and this one sounds like a goodern'.


C-ya

 

[WolfLMM]

Does everybody think that EGT represents cylinder or piston surface temperatures?

EGT is not a predictor of piston conditions, it is a thermodynamic derivative of evolved combustion. Actual temps in the cylinder are 3x higher, over 3000 F, though constantly changing throughout the stroke.

What happens between TDC and the turbine is a long trip. If you really want to understand what is happening to pistons, you have to measure CP. From that you can extrapolate with compression formulas to calculate cylinder gas temperature. CP spikes and temp spikes in the cylinder do go hand in hand...but that is a thermodynamic correlation, pressure=heat. 5 degrees of timing difference is everything in this situation, and will dyno the same, yet the more advanced condition will have a great deal more mechanical and thermal stress. The best way to damage cylinders, is to try to absolutely max out timing. And if you did that on a cool day, low IAT's, no heat soak...then take the same tune out in the summer, do a few 1/4 mile passes, now timing is way over-advanced, and CP is getting way out of control. This condition won't really show up on an EGT gauge either. EGT is not going to tell you necessarily that what is happening to the piston is toxic.

As I have stated before, ECT and IAT timing retard are very important.

But I could be wrong.

But EGT readings are what we have to go by. It is the most readily available gauge that will even give us a glimpse of what is going on. While CP is a better way to monitor that, most do not have time/ know how to run a CP monitoring setup. I think most realize that heat is more extreme in the CC, but 3X?? IdK. Our piston will start to have problems at 350-400 degrees. I just think if cylinder temps were getting that high we would be seeing a whole lot more melted/pitted/cracked pistons IMO.

 

[Killerbee]

Piston temps don't get that high, that is the temp of the gas. Lots of boundary layer protecting the piston.

 

[Killerbee]

Our piston will start to have problems at 350-400 degrees. I just think if cylinder temps were getting that high we would be seeing a whole lot more melted/pitted/cracked pistons IMO.

??

Not sure what you mean here.

 

[WolfLMM]

Piston temps don't get that high, that is the temp of the gas. Lots of boundary layer protecting the piston.

I know piston temps don get that high. Our pistons will start having problems "holding together" at 400-500( I am not familiar with the cast process mahle uses or the material grade) degrees. Actual temperature of the piston. Our pistons have oil cooling, injection event, and intake charge just to name a few cooling boundaries.

I just find it hard to believe that even the gas is getting that high. But you have done the research on it, not me. My probe is mounted in the manifold... that is pretty dang close to ground zero, however, a lot changes by the time the gases get to that probe.

 

[redneckbuckeye]

What do you think of it having to do with fuel, how many of you that have lost a piston ran addative? It seems like this all hit the fan after the LBZ came out and people started modding them. It's not just the LBZ that is loosing pistons, it is just when the majority of failures showed up. This is also the same time frame we were forced to start using ULSD fuel. What I am getting at is, in most cases its just one piston that failed, not numerous, as possibly to indicate a injector malfunction(sticking open,ect). It has also happened to stock trucks as well. Could it be the ULSD's lack of lube in the injector? Don't know if this is a viable therory, but I was just thinking at work today, and this hit me. Am i way off on this as a contributing possiblity?



Anu one know what PPE tunes add, I have the hot+2?

 

[LarryJewell]

What do you think of it having to do with fuel, how many of you that have lost a piston ran addative? It seems like this all hit the fan after the LBZ came out and people started modding them. It's not just the LBZ that is loosing pistons, it is just when the majority of failures showed up. This is also the same time frame we were forced to start using ULSD fuel. What I am getting at is, in most cases its just one piston that failed, not numerous, as possibly to indicate a injector malfunction(sticking open,ect). It has also happened to stock trucks as well. Could it be the ULSD's lack of lube in the injector? Don't know if this is a viable therory, but I was just thinking at work today, and this hit me. Am i way off on this as a contributing possiblity?



Anu one know what PPE tunes add, I have the hot+2?

Something to get you thinking, I've always used additive, but then i'm not running that big of power though .

 

[redneckbuckeye]

Larry, have you had a failure? I always run addative also.

 

[Gasuout]

What do you think of it having to do with fuel, how many of you that have lost a piston ran addative? It seems like this all hit the fan after the LBZ came out and people started modding them. It's not just the LBZ that is loosing pistons, it is just when the majority of failures showed up. This is also the same time frame we were forced to start using ULSD fuel. What I am getting at is, in most cases its just one piston that failed, not numerous, as possibly to indicate a injector malfunction(sticking open,ect). It has also happened to stock trucks as well. Could it be the ULSD's lack of lube in the injector? Don't know if this is a viable therory, but I was just thinking at work today, and this hit me. Am i way off on this as a contributing possiblity?



Anu one know what PPE tunes add, I have the hot+2?

Funny , I think I stuck an injector on my cracked piston still , and did notice at pump prior to fill up that it was low sulfer . Never run additives either .

Ive wondered about the same thing . Could our trucks need something to lubricate injectors better .


Johnny

 

[LarryJewell]

Larry, have you had a failure? I always run addative also.

I have always poured some sort of additive in my tank, just a habit I guess. The only failures I've had are transmission failures, several of them

The motor is about to turn 100K miles, so far its ok, that doesn't say what tomorrow might bring though.

 

[Gmclbz]

Funny , I think I stuck an injector on my cracked piston still , and did notice at pump prior to fill up that it was low sulfer . Never run additives either .

Ive wondered about the same thing . Could our trucks need something to lubricate injectors better .


Johnny

I agree with needing some type of additive. I have been using about 8 oz. of 2 stroke per tank for the last 25k with great luck so far.

What is everyone's thoughts on using a synthetic oil over dino oil for cooler oil temps? Or is that even worth it?