How much boost with 12mm studs?

[SRadke]

I'm considering purchasing a set of 12 mm head studs. For now I'll put them in a stock head but as time goes on and I loose my footing in reality I can see an o-ringed head and boost pressures possibly into the 80's. Will 12mm studs be sufficient at that point or should I just step up and do the conversion to 14mm? Thanks.



-Scott

 

[AK RAM]

I would say 12mm studs would be fine, especially with all the work involved in going to 14mm. However, head gaskets are like women. You know it's gonna pop sometime :-{}, just never know when as they are all a little different.



I have seen posts where a couple have popped close to 65 lbs with twins. Others are running crazy pressures and no problems. Just as an example, Evan at DPP measured drive pressures on his 03 at 75 lbs of drive to 36 lbs of boost with the stock turbo. That is a lot of pressure, with stock head bolts, and never a problem. Many, many people here see 35+lbs of boost with the stock turbo on a daily basis running stacked boxes and haven't heard of one popping yet with 75 lbs of drive pressure. Imagine the drive pressure with the stock turbo for people seeing 40+lbs of boost. I have seen several people post about running it that hard often.



Myself, I ran 65 lbs of boost for a good while with twins on stock bolts. My twins do not have an external gate and are not designed to run that hard, so I imagine my drive pressure was well into the 70's. I now have 12mm studs. I run really advanced timing, 67 lbs of boost, and water/meth, all adding up to some very serious cylinder pressures..... and at 67 lbs of boost, I don't even want to know what my drive pressure is. No problems at all.

 

[Jim Fulmer]

Your probably going to find that most gaskets go because of drive pressure, boost is just resistance. My head porter told me that with what my head would flow and the boost I was running that the cylinder should only be getting about 40-45% of the air that was there available..... FYI!



Imagine a turbo (gasser) motor running 28 psi with a 106mm, that's allot of air, probably about what I'm pushing, the difference is his head flows 400 cfm.



Jim

 

[TCluff]

i see 64 psi daily with stock gasket and bolts, no problems in 10,000 miles, at least no problems YET!, 63 PSI OF DRIVE AT 55LBS OF BOOST

 

[AK RAM]

63 PSI OF DRIVE AT 55LBS OF BOOST

Is that with the 40 or 35 on top?

 

[SRadke]

Thanks guys, I'll go for the 12's. I could probably push it harder but I really don't have time to be replacing a head gasket at the moment so I've got it wastegated back to a max boost of about 50 psi. I'll know more when I get my drive pressure gauge in but I suspect I'm really low right now forcing the wastegate open early and making most of my boost with the big charger.



-Scott

 

[TCluff]

Is that with the 40 or 35 on top?

it is a 40-16, gated at 22psi

 

[TCluff]

Thanks guys, I'll go for the 12's. I could probably push it harder but I really don't have time to be replacing a head gasket at the moment so I've got it wastegated back to a max boost of about 50 psi. I'll know more when I get my drive pressure gauge in but I suspect I'm really low right now forcing the wastegate open early and making most of my boost with the big charger.



-Scott

i read somewhere that the 12 mm studs will hold 90 psi of boost easily, when my gasket blows i will opt 4 the 12mm studs also...

 

[Jim Fulmer]

i read somewhere that the 12 mm studs will hold 90 psi of boost easily, when my gasket blows i will opt 4 the 12mm studs also...

Add to the above statement by asking what was the timing at, and what is the drive pressure.



Jim