Scary overboost...

[TripperFx3]

Today I was just cruising on the highway and decided to drop into 4th and the car felt ridiculously faster! Right when I let off the throttle I glanced at the boost gauge and it looked like I had pegged 26psi (my gauge reads 22 normally, but loads showed I was probably hitting around 26psi), so that would really be like 30 for me, so I did another pull and I actually hit 30psi and pegged the gauge, so i basically hit 36psi. It scared the ever loving shit out of me! I thought I was going to blow the engine or lift the head, but thankfully I didn't. I can only attribute this not happening thanks to the ARP studs and Cosworth headgasket.

I'm not sure why this happened and wanted to see what you guys had to say. We have had significant drops in temps going from day to night (high 70/low 80 during the day and low 50/high 40's at night), so I know thats a contributing factor, but wanted to see if anyone else here has experienced something like this.

[bomjoon]

srsly i think if you hit 36 psi w/o meth or some sort of cooling method your engine would haave blown up.

i boost ... err did boost to 27 lbs before and was fine no knock no pullin timing .

but over 28 i would hit fuel cut.

[TripperFx3]

I sorta figured that, but thats what my tuner guessed I was hitting (my gauge is off by 4 psi), by the amount of load we were getting at the given gear and RPM range.

[TouringBubble]

With that kind of spike I'd double check the vacuum line on the WG actuator. It seems like it's not seeing pressure.

And also, you'll only life the head if you encounter knock at those boost levels. I've spiked 30 psi on a completely stock head with 0 issues. I wouldn't recommend it though. Just remember that it's knock and not boost the lifts heads in most cases.

[GTLimer]

^^ i agree...

[TripperFx3]

Thanks for the feedback and info. I may have to go slap one of my teachers on the back of the head lol. They said it was the excess pressure that caused the head to lift, which makes since if you think about it, but at the same time the force of a large number of knock counts would do it too. Also I got the issue fixed and had to turn the boost controller down ALOT, 8 turns on the Hallman, which is also worrying me because it wasn't boosting that high before. I think what also may have saved me is the fact that we can now get 92 octane out the pump here in Reno instead of just 91. I know just 1 octane boost isn't a large number, but its a good safety margin at least.

[TouringBubble]

Well, it is force that causes the head to lift, but you have to consider how the force is applied. Boost rises slowly and evenly across the manifold/head. This puts less stress on the studs by spreading it across the evenly. There is of course a point where too much boost will cause the head to lift as there is always a point where the studs will stretch.

But, consider detonation in the cylinder. Pressure increases but unevenly and abruptly. This puts more stress on the studs in that area. That causes a lifted head.

So, boost can cause a head to lift, but it would be much more than 30 psi ...

[TripperFx3]

Gotcha and thanks for the clear up. What would your opinion be on the boost controller? I turned it down 8 full turns and it's now where it was before.

[TouringBubble]

Sounds like the BC wasn't tight and it dialed itself down for some reason ... make sure it's secure and double check all of the vacuum lines just in case.

[scoobysam]

I had problems with my hallman cockpit mbc spiking like that. it would do it every so often in 3rd-4th gear. It started doing it more and more even after i cleaned it out. So i took it off and used the extra forge one i had. The forge one has been good since.

[TripperFx3]

I have a TurboXS MBC at home in GA, but it's a piece of crap, but I may have to have my Mom ship it out to me.

[em1toevo]

Wow Tripp, that must have been scary. I would be paranoid as hail after pegging the gauge like that. I definitely would be checking all of your connections like everyone else mentioned.