Why stock head bolts are not good for 30+ psi
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From: Taftville, CT
I'm no expert, but I do know cylinder pressures during detonation can be an order of magnitude higher than good clean combustion.
Peak cylinder pressure using a good tune will occur at peak torque, right? With that said, the more torque you make, the more cylinder pressure you are running, and the higher strain you are putting on the stock head bolts. And you can stretch stock parts well before you can stretch ARP parts. No one is trying to say the ONLY way to stretch a stock head bolt is through detonation. Peak torque can very well do it also.
So what type of peak torque were you running that night vs. others? That might answer the question of when stock head bolts aren't any good anymore. My opinion is it would be better to talk about stock head bolt capacity in torque instead of boost.
Peak cylinder pressure using a good tune will occur at peak torque, right? With that said, the more torque you make, the more cylinder pressure you are running, and the higher strain you are putting on the stock head bolts. And you can stretch stock parts well before you can stretch ARP parts. No one is trying to say the ONLY way to stretch a stock head bolt is through detonation. Peak torque can very well do it also.
So what type of peak torque were you running that night vs. others? That might answer the question of when stock head bolts aren't any good anymore. My opinion is it would be better to talk about stock head bolt capacity in torque instead of boost.
Here's the graph from the last tune shown with stock and pre-speed density numbers:
30psi, 35 psi isn't enough pressure for air to aid in stretching head bolts. Like stated earlier, it has to come from the peak pressure, which is during combustion and compression of the piston (P-V diagram). Do you honestly have enough injector and fuel pump to run 35 psi? To me, that sounds like grounds for detonation, or possibly pre-ignition which resulted in cylinder pressures too high.
Have you ever removed these head bolts before? I'm wondering if they were at proper pre-load. If not, they may not have enough clamping force to keep the gasket from blowing out. What were the measurements on those bolts after teardown?
Sounds like you have a good plan with the stoker, but if you were to rebuild, I would be replacing all the bearings down there, as you more than likely have coolant in the oil pan.
Have you ever removed these head bolts before? I'm wondering if they were at proper pre-load. If not, they may not have enough clamping force to keep the gasket from blowing out. What were the measurements on those bolts after teardown?
Sounds like you have a good plan with the stoker, but if you were to rebuild, I would be replacing all the bearings down there, as you more than likely have coolant in the oil pan.
I do not have logs from when it happened, I only log the car when I am tuning. Outside temp as 37degF. Car had been running for 20-30 minutes, 3rd gear starting around 3k rpm, WOT, freeze plug blew out around 4500 rpm or so, peak hold on ZT-2 displayed 33.1psi. Car was tuned less than 2 weeks ago with 1-2 counts of knock after several consecutive 4th gear pulls on the dyno. Oil was changed before the tune and had no signs of coolant. Plugs were changed as well and looked good. There is no pitting on the piston tops, valves or cylinder walls indicating sustained detonation. The piston closest to the cam gears where the gasket popped was steam cleaned when the gasket blew which is why it looks the way it does. The master auto tech that works at the shop with me even said he saw no signs of detonation.
If the only way to stretch the stock head bolts is from detonation, then why buy ARP hardware? Why not just run high boost with a very very conservative tune?
The "experts" here can believe what they want. I know that I wasn't detonating and that the gasket let go from running 30psi for the last 15k miles on the stock head bolts.
Now, for the car, I'm pulling the engine later this week and putting the rolling chassis in storage for the winter. The engine will be receiving a 2.3l stroker, race prepped head and HTA35r turbo kit. Then everything will be going back in when I get back from Africa at the end of next summer.
If the only way to stretch the stock head bolts is from detonation, then why buy ARP hardware? Why not just run high boost with a very very conservative tune?
The "experts" here can believe what they want. I know that I wasn't detonating and that the gasket let go from running 30psi for the last 15k miles on the stock head bolts.
Now, for the car, I'm pulling the engine later this week and putting the rolling chassis in storage for the winter. The engine will be receiving a 2.3l stroker, race prepped head and HTA35r turbo kit. Then everything will be going back in when I get back from Africa at the end of next summer.
Your expert mechanic has not looked at the sides of your pistons so any opinion he has about detonation not being present is pretty useless.
I tested stock studs on my own personal 2.3/ 35r setup. On the dyno the stock studs held 550hp/511tq. I believe they will hold even higher but testing stopped there for other reasons. There is no way your 450tq was enough pressure to lift the head .
Unless they weren't pre-loaded enough to keep the head gasket compressed. You can get more preload out of stronger bolts/studs, which is where higher HP engines are in need of this. I think it is less important on the UTS of the bolt, but more important on the pre-load (although the 2 usually go hand in hand). The cylinder pressure doesn't add directly to the pre-load of the fastener until it uncompresses the flange. Only a small portion of the pressures of combustion add to the load on the bolt.
This is why I still point to a pre-load problem, or bolts not torque to specs. Still would like to see the measurements of the bolt lengths.
This is why I still point to a pre-load problem, or bolts not torque to specs. Still would like to see the measurements of the bolt lengths.
all this stock head bolt talk is really what evom needs to realize that the stock bolts are more than strong enough for most of our needs. i have been running 472whp 426tq daily with no issues on stock bolts. granted i dont beat the **** out of my car all the time, but still. if there was one weak spot, better it be in the stock head bolts then blow a hole in the side of your block. its when people start with the 1 by 1 method installing the ARP head studs when u have gasket issues.
OEM torque to yield head bolts have held up fine for 20,000 miles of water methanol injection on my car, which has seen 35psi (once with 5 counts of knock).
I think the main point here is what would have happened to this man's car if ARP's were in there at the time?
I think the main point here is what would have happened to this man's car if ARP's were in there at the time?
+2 the tune is very critical. i just recently blew a head gasket thats how i know that. i replaced with a greddy hg, arp head studs, ferrea valves intake side, ferrea inconel valves exhaust side, ferrea dual valve springs/titanium retainers, bronze valve guides, valve seals, ble lifters and threw in a set of hks 272's with aem cam gears and greddy timing and balance belts. i did all the work myself. got a good tune at a local shop and havent had any problems since. so be sure you stay on top of your tuning as you add mods or else itll be sitting again. sorry to hear about what happened and best of luck with getting it all back together and up and running
I can see some signs of det in that pic that I doubt are just from the aftermath of the lifted head. The MLS facing the driver side (?) is black and deformed showing there was high heat right before it popped. While its possible that caranage happened after the "event" I highly doubt it. I am running almost the same setup and have hit 33psi with my Green as reported by the 3 bar (well maxxed voltage anyway) on C16 and still have no problems. The piston has been steamcleaned but without taking it out or taking a closer higher res picture I cant really see much more than that.
What was the timing and AFR when this happened?
What was the timing and AFR when this happened?
I lifted my head with the stock turbo and it never detonated. The two head bolts closest to the trans were loose. I replaced them with ARP studs using the one by one method and never got the mysterious oil leak.
To the OP: put the studs in, it's the correct thing to do.
To the OP: put the studs in, it's the correct thing to do.
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