Through my searching, I have not found the answer to a question that occured to me when considering which turbo to use and if I need to stud the head. All the talk is about "how much psi is safe?" That answer varies some, but is in the neighborhood of 50psi before needing studs. My question is this. Isn't it actually a matter of cylinder pressure? If so, the safe psi level would depend on what turbo you have, right? In other words, if I run a sledpuller66 or a silver bullet at 50psi, that is way more cylinder pressure than running a sps62/12 at 50psi. It seems to me that just because my stock turbo at 450cfm and 45psi is safe for the gasket, it doesn't mean that a turbo that moves 1000cfm is also safe at the same 45psi.
Someone smarter than me please help me out here.

 

i don't think that the volume that the turbo can push through it means anything in respect to psi numbers.
i think that 50psi going into the intake, is 50 psi, no matter what turbo you are using.
kinda the same thing when asking if a ton of bricks weighs more the a ton of feathers!!!!
just my thoughts, i am no expert.
i think that a turbo flowing more volume might be more effecient at lowering temps, but if it pushes the cylinders with 50psi, its 50 psi at the head, gaskets ,etc.

 

I have an II SPS66 on mine and had the wastegate set to 55psi. At the track the wastegate is open quite a bit. I ran with the mods in my signature for a year before I had studs put on. The only thing I blew was the rear freeze plug.

 

I don't think you got the point. I understand that 50psi is 50psi. Let's say that I put a nozzle on my gardern hose at home and I regulate it to 50psi. Then lets say I hook a 3" diameter fire hose to the hydrant on the corner and I regulate that to 50psi as well. Then let's say I stand you in the front yard with your family jewels exposed and blast you with the hose of your choice. Which one are you going to choose? Obviously the garden hose. The fire hose would put you on your ***.
The point is that a small turbo at 50psi and a large turbo at 50psi may both have 50psi, but they are not moving the same volume of air. The larger turbo is cramming more air into the cylinder. That is my concern. Not the psi, the amount of air be compressed in the cylinder to abtain compression.

 

I like the bit about the garden hose - it works. I don't think that you'll have a problem at all. Most of the 3rd gen trucks are running well into and over 50 lbs with aftermarket turbos and having no trouble with head gaskets.

 

That theory is way different than the point at hand, the reason a fire hose puts you on your back, compared to a garden hose is the weight of the volume. I agree with pullin hard, a larger CFM turbo will be more efficient, once you get it moving...

If your motor could flow 10,000 CFM at 50psi you wouldn't have head gasket problems, you would have crank problems trying to keep up with the RPM to move all the air. 50psi is just 50psi not matter how fast it gets filled. As far as head gaskets are concerned you only need to worry about how much pressure, not volume.

So you would think I will go get the biggest turbo I can find and it will be efficient right? NO, now you have all this weight to get spinning and you will have turbo lag. That is where compound turbo systems come in to play, the quick spool of a small turbo, and big boost(and volume) of a large one.

Like the turbos on the new new Fords, a turbo that self adjusts the wheel to smaller for spool, larger for boost. A pretty ingenious idea, as long as it lasts. I know Mack had a problem when they first came out with them.

So you are left to decide do you want lag and top end power, or quick spool and take off, or both with a twins setup?

Hope this helps you out bud, later

 

I blew a headgasket running 50psi. It's not all caused by boost.

 

I think the stock turbo at 40 PSI along with a 9cm wastegate is the worse combination for head gaskets. If your exhaust can't get out faster than the boost coming in then you would have high cylinder pressures. But you also have a nice revving engine. The bigger the exhaust housing the slower the thing will spool because there is no pressure in the cylinder to compress the air from the other side of positive boost, basically there is no "pushback". That's why the lag on some of these bigger turbos is present. It's too much flow for the bottom end. Now once you get to the volume and it starts to build pressure then the boost comes on on the positive side.

That's just how I look at it. It might not be right but it seems to make sense to me.

 

Yes sir, there are also other power adders that can raise your cylinder pressure, suck as nitrous or propane, ect.

Luken, what were you running to blow it?

 

OOPs I meant "such as" not "suck as". sorry dudes

 

I was at the track runnin tst 7x3+Crazy Larry+mp-8 on 30%.

Truck has never seen anything but #2 only...

Timing probably has alot to do with it...

This winter Im going to make a few changes to the truck

 

I think Luken was running alot of timing as that will also raise cylinder pressure. I don't think he has anything beside #2 in his truck.

 

Yep. Hopefully I can get it dialed in with the adjustable timing on the tst or the smarty. With 2 blown headgaskets in 700 miles I'll know what to do if it goes again It's really not that bad. Just alot of hours...