Exhaust Back Pressure

Ok, So I did some searching on this topic and it has been touched on in numerous threads but not a lot of solid info about it. I would think for newer guys it would be nice to have a thread discussing a few things about EBP.
1. How much can the stock head bolts handle?
2. How much EBP does a completely STOCK motor see? i.e.(dpf still on truck)
3. How much EBP can a studded motor handle?
4. The difference a different set of turbos makes.
5. Cures for the EBP. (wastegates, new turbos, etc..)
I know a lot of this has been touched on and there are threads dedicated to wastegate discussion but I thought it would be nice to compile some data directly related to back pressure in one place.

Oh, one more thing..
6. Barometric pressures role in EBP.

subscribed. im pretty lost on this topic actually..

powerstrokedub said:

Ok, So I did some searching on this topic and it has been touched on in numerous threads but not a lot of solid info about it. I would think for newer guys it would be nice to have a thread discussing a few things about EBP.
1. How much can the stock head bolts handle?
2. How much EBP does a completely STOCK motor see? i.e.(dpf still on truck)
3. How much EBP can a studded motor handle?
4. The difference a different set of turbos makes.
5. Cures for the EBP. (wastegates, new turbos, etc..)
I know a lot of this has been touched on and there are threads dedicated to wastegate discussion but I thought it would be nice to compile some data directly related to back pressure in one place.

Oh, one more thing..
6. Barometric pressures role in EBP.

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well it seems you have cylinder pressure and exhaust pressure confused. Studs are what contain the higher than stock cylinder pressures. Exhaust pressure is the pressurized air(exhaust) between the exhaust side of the turbo and the exhaust valves in the head. The limit on exhaust pressure is when the valves are forced open by the pressure which I believe is around 66-68psi gauge or roughly 80-82psi atmospheric depending on altitude. How atmospheric pressure is connected to all this is hard for me to word correctly so I'll let someone else deal with that. So to answer your above questions here we go.
1. Stock bolts are 60,000psi tensile strength, so that's when they start to stretch.
2. No idea what ebp is on stock as I never even thought to look but I'll see if I can convince the dealer to let me try it.
3. Elite studs are good to 240,000psi tensile strength and there has yet to be a failed set of these stud but there has been some failed gaskets due to nitrous related incidents and various other scenarios.
4. Bigger turbos drop or raise the ebp depending on the exhaust housing side of the turbos. Another thing that controls the ebp is a wastegate.
5. Cures are a wastegate. Nothing else really is able to regulate the pressure and has a set point to open at when pressures start to get to high. Stronger valve springs are an addition that can be made to allow the system to maintain higher pressures but again the higher pressure is controlled by the wastegate. The thing the stiffer valve springs do is keep the valves from floating(staying open) when the boost or exhaust pressure is bumped up.
6. Like I said I have trouble putting into words how atmospheric pressure comes into play. I know how it does but explaining it isn't so easy. Hope this helps and if anyone knows I'm wrong please feel free to correct me. Were all here to learn and pass on information.

Another thing high ebp does is it can potentially overdosed the turbo. Not sure what point that happens at thou. Guess I'll have to find out one day.

White_monster said:

Another thing high ebp does is it can potentially overdosed the turbo. Not sure what point that happens at thou. Guess I'll have to find out one day.

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I may have done it. Just 2hrs at 60 or so bp and that may be enough.

while i agree with what shane said for the most part, back pressure is relative when considering the strength of studs or headbolts. back pressure makes head gaskets that are not held down correctly go by-by. this, in a sense, relates bp to cylinder pressure.

Erikclaw said:

I may have done it. Just 2hrs at 60 or so bp and that may be enough.

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absolutely.

Good call Mike. There's so much info on this subject, from just looking at it from the exhaust side of things to bringing boost pressure in to the equation. Also pumping more fuel into the cylinders. I wonder if lower intake temps effect exhaust pressure in some way, shape or form.

Great info so far guys! Shane I really appreciate the depth of your response!

No prob. I'm trying to find more info for this thread. Give me some time. Good chance I can snake a stock 6.4 from the dealer and see what the stock ebp is, maybe even burn a little rubber too.

He is now the professor. :redspotdance:

White_monster said:

No prob. I'm trying to find more info for this thread. Give me some time. Good chance I can snake a stock 6.4 from the dealer and see what the stock ebp is, maybe even burn a little rubber too.

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That would be fantastic, I would really like to see what the stock max reading is. That would give us a good base to go off for what our max reliable tuned levels would be.

Also, I feel that cylinder pressure and exhaust pressure are all intertwined seeing as one affects the other. Its just so much info to process and put into perspective.

My guess stock ebp is like 45 or so. Turbos don't make over 25or so psi do they? jI don't remember. Stock fuel and all, makes me think it is a really low number.

Erikclaw said:

My guess stock ebp is like 45 or so. Turbos don't make over 25or so psi do they? jI don't remember. Stock fuel and all, makes me think it is a really low number.

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stock, the turbos make peak at 36 i believe.

i know with the newest "overboosting" flash, mine wouldnt do over 30

The most I ever got out of my truck stock was 34psi.

well i dont know if the reflash did anything to boost pressures but i know it was for a overboosting problem. and i believe i see less boost now that i got the update.. i might not be right though.. havent seen stock pressures for around a month.

I can put my DashDAQ on my dad's stock 6.4 and see what boost and back pressure reads.

08stroker250 said:

I can put my DashDAQ on my dad's stock 6.4 and see what boost and back pressure reads.

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That would be awesome if you could Jeff. Having a baseline to go from would be nice!

powerstrokedub said:

That would be awesome if you could Jeff. Having a baseline to go from would be nice!

Click to expand...

I should be able to do it this week sometime.

K well after talking with multiple mechanics, engineers and failure analysts the consensus is exhaust back pressure doesn't directly cause a head gasket to fail. It can indirectly cause a failure but I'll get to that later. Cylinder pressure on our trucks is incredibly high, I'm talking thousands of psi and while cylinder pressure is high the exhaust valves are closed thus sealing the cylinder from any pressure coming in, which won't happen cause ebp is up to 80psi so that's not going to overcome thousands of psi in the cylinder. So this is why back pressure isn't going to directly cause the hg to fail. Now when the ebp gets high enough to push the valve open, similar to floating valves, the cylinder pressure escapes into the exhaust but again the pressure doesn't spike cause of the volume of the exhaust piping. With the valves are forced open by pressure the piston can hit the valves and damage can occur and the hg can possibly fail for any number of reasons.

So to conclude, ebp is from the exhaust valve to the exhaust side of the turbo. Cylinder pressure is it's own thing and that's why we need studs cause adding boost and more fuel will increase the pressure in the cylinder to the point stock bolts can't hold the pressure and they stretch. Hope this clarifies things for everyone and if you want more info just search google and there's pages of info on these subjects. I'd be days typing it or trying to explain it. There are ppl way smarter than me that have figure this stuff out for ms to read and learn from. Good day