Exhaust Back Pressure

[Jeff@Spartan]

Good info Shane! I've done a little reading up on it myself and that is basically what I gathered from it.

 

[powerstrokedub]

Awesome info Shane, its appreciated. That actually makes a lot of sense. Does anyone have any info regarding head gasket failures on trucks with properly sized turbos for the fueling upgrades? I would imagine most of those trucks have studs though.

 

[Erikclaw]

Pretty much everyone that has the cab off to do turbos or injectors takes care of hg etc. Do it all and not have to come back and pay to get the cab off again.

 

[White_monster]

I'll try to post more info tonight. There's a situation where ebp indirectly causes hg's to fail and it's def a possible situation for our trucks. Need to get to something other than my phone to type it thou.

Glad to see someones researching this as well. The more ppl read educated ppls articles, no not magazine articles cause there's just not enough info or detail due to space, the more you will learn. This subject can get pretty complex to understand when you bring all the parts together. Breaking each section down is easier for everyone to understand and then once you understand the small pieces it's easier to understand the big picture. Keep reading and I'll try to post more info as time permits.

 

[bigrpowr]

good info, but i can tell you, i have had an experience where bp caused immediate hg failure. im sure that goes back to the correlation of bp and cp.

 

[White_monster]

Okay Mike. But explain how the back pressure directly caused the failure. Mike please explain your situation cause I'm curious if you had an indirect ebp to hg failure or a direct ebp to hg failure. Not saying your wrong, just curious.

The most common way BP can attribute to a hg failure is by having higher drive pressure which increases the boost pressure thus increasing the cylinder pressure and what do you know the hg let's go. What was the reason for the hg to fail? It was the increase in cylinder pressure due to the incresased boost. What causes higher boost? Higher drive pressure or higher BP as most ppl call it. This situation is how BP indirectly causes hg failures.

 

[bigrpowr]

Okay Mike. But explain how the back pressure directly caused the failure. Mike please explain your situation cause I'm curious if you had an indirect ebp to hg failure or a direct ebp to hg failure. Not saying your wrong, just curious.

The most common way BP can attribute to a hg failure is by having higher drive pressure which increases the boost pressure thus increasing the cylinder pressure and what do you know the hg let's go. What was the reason for the hg to fail? It was the increase in cylinder pressure due to the incresased boost. What causes higher boost? Higher drive pressure or higher BP as most ppl call it. This situation is how BP indirectly causes hg failures.

actually im pretty much in agreeance, but the fact is, add a bunch of bp to high cp and bang! you take a combo that has a bunch of timing and high cp, but hasnt blown a hg, its proven to last for 150-200 passes. then add more bp and bang, the hg goes, it seems quite obvious. thats what happened to me with my 7.3. i had a single that made 48-50psi boost and 60-61 bp..... then on nitrous it made 56 or so psi of boost and 68-70 bp ..... motor made 750 horse for 2 years straight, kicked ass without a blink. went to twins and the bp was high, we added a gate but it wasnt enough i guess. it was about 75psi boost and 90+ bp... on a gauge, hg's let go the first day out. in the diesel world , i was learned a long time ago from diesel folks smarter than me that bp could contribute to cp's. i dont think bp is DIRECTLY to blame, but when your $hit is turned way up, its just adding to a problem already presnt. btw this was with h-11 studs.

as far as i know backpressure and drive pressure are one in the same.

 

[White_monster]

I think we are on the same page Mike. Like you stated back pressure can start a problem and the scenario goes from there. But what causes the high BP. One a miss adjusted gate, 2. A undersized gate for the application, 3. A stuck gate. I'm sure there are other possible causes.

I think it's safe to say that BP doesn't directly cause the failure but it can definitely contribute to the problem if said engine is not setup to handle or control the increase in pressure.

Now Mike back to your situation on your 7.3. Your blaming high BP on the failure if I'm reading right. Fact is the failure was caused by a undersized gate which lead to high BP which increased your boost and thus your cp went up and bam the hg popped. So BP didn't cause the failure in your engine. The undersized gate was part of the problem and the other part ofthe problem could've been small exhaust housings on the turbos as well. Again the gate wasn't big enough for the turbo design.

 

[bigrpowr]

I think we are on the same page Mike. Like you stated back pressure can start a problem and the scenario goes from there. But what causes the high BP. One a miss adjusted gate, 2. A undersized gate for the application, 3. A stuck gate. I'm sure there are other possible causes.

I think it's safe to say that BP doesn't directly cause the failure but it can definitely contribute to the problem if said engine is not setup to handle or control the increase in pressure.

Now Mike back to your situation on your 7.3. Your blaming high BP on the failure if I'm reading right. Fact is the failure was caused by a undersized gate which lead to high BP which increased your boost and thus your cp went up and bam the hg popped. So BP didn't cause the failure in your engine. The undersized gate was part of the problem and the other part ofthe problem could've been small exhaust housings on the turbos as well. Again the gate wasn't big enough for the turbo design.

actually, when gating properly based on turbo sizes, i needed 2 gates. one between, and one overall. i only had one for overall. the exhaust housings were absolutely the cause of the bp. the failure is due to bp, the bp is due to incorrect ex. housings. i think we need to distinguish cause vs. effect here.

 

[jdgleason]

opcorn:

 

[White_monster]

No the failure is not due to back pressure. The failure is cause the cp got high enough to pop the hg. Your BP got high cause of a lack of an extra gate. This is how your situation went down. You put twins on. Had one gate that was gating overall. The small housings and only one gate caused your back pressure to go up. With the incresased BP your turbos added more boost. With more boost in the system your cp went up and bang the hg was ***ed. the whole reason your hg failed was cause the cp went up. Your setup was not designed to handle 75psi of boost. I guess it depends what part of said situation you want to put the blame on for the failure.

 

[Danbonzo]

If EBP drops so does MAP and vice versa so there is a correlation between the two. With an extremely high EP is it fair to say the boost pressure is higher also? And over time with a progressively stretched stock head bolt the higher boost would help to lift the head, in turn compromising the HG? Dunno just thinking out loud how the EBP could cause the gaskets to blow.
I can say that with the 6.4 motors the gaskets don't necessarily "blow" when the tell tale puking starts. At least this was the case with my gaskets. When the heads came off the coating on the HG was worn off and a clear path had been worn directly to a coolant passage. The heads were found to be less than 4/1000's off which made them fall within the Ford spec. We decked them anyway and threw 2010 gaskets on, the newer gaskets have been revised and the coating is supposed to be much better than the earlier builds.Mine is an 08 job 3.
I did as much research as I could find on the studs and Elites (A1 Technologies) statistically appear to to be the least likely to fail. As of right now anyway, so I went with them, and of course gated it. The bottom line is with the pressures that the big tunes produce I believe its not just one thing that causes the demise of parts but rather a culmination wrongs. Sort of a domino effect if you will, with the EBP being the "Achilles heel" of the bunch.
Hopefully she holds this time...

 

[White_monster]

The failure is related to BP but that's not the cause. The cause is what made the BP go up. Lack of a gate or gates, small ex housings, tuning, stuck gates are the cause. The effect of these causes is high BP.

 

[bigrpowr]

No the failure is not due to back pressure. The failure is cause the cp got high enough to pop the hg. Your BP got high cause of a lack of an extra gate. This is how your situation went down. You put twins on. Had one gate that was gating overall. The small housings and only one gate caused your back pressure to go up. With the incresased BP your turbos added more boost. With more boost in the system your cp went up and bang the hg was ***ed. the whole reason your hg failed was cause the cp went up. Your setup was not designed to handle 75psi of boost. I guess it depends what part of said situation you want to put the blame on for the failure.

actually it was built for 80psi ..it was fire ringed top and bottom.

btw , boost is not directly proportional to bp. you have to know the maps of the turbos in question before you say that is the case.

 

[White_monster]

There's info missing Mike. Cause obviously the cp got high enough to compromise the hg and make it fail.

 

[bigrpowr]

There's info missing Mike. Cause obviously the cp got high enough to compromise the hg and make it fail.

yeah i dont have any cp numbers, there are so many variables here. i am certainly no expert, i am only giving my own opinion. i just think the drive pressure added to a major tune and major fuel, it happened. what hasnt even been discussed yet is fuel. fuel can also be a large proponent of cp.

 

[White_monster]

Yes it can. I was leaving that out till we got the gate, ex housing part figured out and then start down that road. BP goes up for many reasons. Again BP is all controlled by gates and them being sized right for the engines intended setup, huge nitrous engines require bigger gates than something with no nitrous.

 

[Danbonzo]

What came first the chicken or the egg. If EBP has nothing to do with HG failure then why not just deck and stud? Wastegate's are a must because there is a definite relationship in the cause and effect. I agree with both the arguments actually. Intellectually I understand a blown HG to be caused by what happening within the combustion chamber as what white monster argues. But after dealing with the nature of this problem, instinctively I would have to argue that you can't control the problem any other way but to let off DP as Mike has concluded to.

 

[Erikclaw]

Both sides of the argument is correct. One does not necessarily cause the other. It takes a combination of variables working against each other to become a failure. I don't think high bp alone can cause a hg failure. The math doesn't work. But when both variables are borderline then add one that is too high sh!t is gonna happen, A+B+C=DAMN!

 

[White_monster]

Okay. There's confusion here. Let's start at the failure and work backwards.

Hg fails.
Hg fails dues to high cp.
Cp goes up for a number of reasons but for this case we'll go with increased boost.
Increased boost is caused by spinning the turbo faster by increasing the BP.
BP is increased by lack of a gate, undersized gate, mis-adjusted gate, small ex housings, stuck gate and so on.

So you see the cause of the failed hg is not BP but rather the setup of the gate(s) and such. BP is the effect of that and thus starts the chain of events.

Hope this helps.