besides blowing head gasket, what determines when you should upgrade headstuds. Is it by how much boost psi your making? what is the max you can run with stock studs? or is it for some other reason. Any help on this would be great.

 

blowing a head gasket is the concern.

 

I guess what I'm trying to get at is..what causes Head Gasket faliure? Why should you upgrade studs?

 

on your truck the vgt turbo has high drive pressure.

 

OK now your talking...please explain more to me Tony..there's a lot I don't now, but sure would like to learn. Drive pressure?? Whats that I'm thinking thats a bad thing?

 

a vgt turbo moves air quickly. boost= drive pressure is about 24 lb. 1 to 1 ratio. after this drive pressure increases faster than boost pressure. when i done a test on my truck i found out that the exhaust brake put about 60lb pressure on the manifold. 32 boost = 60 lb drive pressure on the manifold. the higher boost numbers you put on the truck the more crazy drive pressure you put on the head gasket. this is why i limit my boost numbers to 32 when i tow. this was my own little test with a line kit under the hood and taped to my mirror.

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a bigger non vgt turbo helps this drive pressure problem but i like the exhaust brake built in.

 

There is a "little" mistake in the upper explanations.

It is not the boost or drive pressure which causes the head failure.
The boost pressure e.g. as above mentioned 60lb.is ridicoulous low compared with the forces and the pressure which happpens during the combustion process.
Compare up to 1800psi combustion pressure with the low turbocharger boost pressure.

So what is the purpose of a headgasket?
To seal the mating surfaces between block and head against:
- heat
- movement during warm up
- extreme pressure

What is the purpose of studs?
- to spread and to hold the extreme pressure.
- to provide enough clamping power to hold the movement forces of the head.

To do this the studs must have some special abilities, like a constant material consistence. This makes them so expensive.
If the load is not spread evenly the pressure seeks for the weakest spot, and- voila - here you have your head gasket fail.

Older heads were torqued only, nowadays you torque them and use torque angle measurement.
Why?
Torquing tolerances are going down from +/- 15% down to 5%. Lower tolerances are equal to more even clamping force.
Even clamping force = less head fail

So if you modify your truck for more power than stock, you inject more Diesel and more air via boost, right?
More Diesel combined with more air is more combustion pressure- therefore the pressure rises and you have to strenghten the head gasket and/or the headstuds to keep up with the more developed power/combustion pressure.

 

I have some idea of what makes the HG go. what I'm wondering about,... Is there a rule of thumb or baseline horsepower lvl of when it becomes nessiairy to upgrade the studs. I don't think I'm making enough power to justifie spending the big dollars for better studs yet. But I don't want the trouble of blowing a HG either.. (sorry for the poor spelling)

 

There is a general baseline. Usually behind 30% you have to upgrade.

BUT:

This depends on your:
- hp increase,
- your driving habits and use of the truck

it may necessary to do more upgrades like:
- bearings
- con rod
- bolts
- coolant system
- oil cooling
- clutch
- tranny
- axle shafts
- drive shafts

as you can see it depends on what you want. The modification level is floating, that means there is no fixed border.
Like: with that hp level, you have to do this and so on.

 

I'm guilty of saying Drive Pressure also. You know this as well as I do but we take it for granted that using the short cut saying "Drive Pressure" kills Head Gaskets.

For the Op. Maybe I can either explain it better or confuse you even more. Alot of us say Drive Pressure kill the Head Gasket. Well in reality it does not. Ultimately it is Cylinder Pressure that kills the Head Gasket. But there is more to it then that. You want cylinder pressure, that is the key to making power. The tricky part is where the peak cylinder pressure accurrs during the combustion stroke (where does it detonate). When the detonation happens this will help determine when you blow the gasket or if you are going to make good safe power. To soon is usually where the problem happens. What causes it to happen sooner. Advancing the Timing from a tune, Adding Injection Duration from a tune, and/or larger injectors. Usually a tale tale sign if you have to much timing is engine rattle. It is usually the most noticeable when putting a load on a cold engine. Now back to timing, How do we know how much timing we are adding to a Common Rail engine with a tuner. NO FREAKING IDEA, everybody that builds tuners wont tell us how much they are advancing the timing and how each setting effects the timing. So your guess is as good as mine.

Now Drive Pressure, excess DP is a direct result from more Cylinder Pressure. More cylinder pressure means, more exhaust gases and faster flowing exhaust. DP is just a measure of restriction usually created at the turbo. Your turbo just can not flow the cfm needed to allow the Cylinder Gases to flow properly. Three simple ways to fix this on your truck. (1) the obvious is to get a properly match turbo for your application. (2) Use a external waste gate to control the DP at the manifold. (3) tune your truck to not exceed 10 to 15 psi over the max boost pressure, turn your tune down.

what i was saying is the turbo is not big enough. it reaches 1 to 1 boost = drive pressure at about 24 lb. anything after that the drive pressure goes up more than boost from a direct result from the cyls.

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i copied this from a different forum which has been talked about many times.