Step in experts.

After searching and reading, the general consensus points to 40psi as the lower limit of needing head studs. I understand cylinder pressure plays a big roll in this as well.

Is 40psi on stock head bolts playing with fire?

​​​​​It's typically when loaded and going up grades. Not what I would call "short bursts" more like 10 seconds, maybe 15+ seconds if I am keeping with the flow of traffic. Boost comes up to 30psi at 2000rpm and climbs to 40psi by 2400rpm and levels off from there. On a typical day of towing it rarely drops below 20psi on flat ground, any bit of an incline and it will hold 30psi+ which can be for very long periods (5-10minutes). Stock injectors, S363sxe, 4.30 gears


Good to go?
Rolling the dice?
Stud it?

Thanks

 

I can only confirm that 40 psi is the number I have always read for years is the limit for stock head bolts. No real world experience of pushing that boundary. Im guessing that enough people have said it over the years that did push the boundary and found the limits to make that the baseline and standard.

any idea what your back pressure is at given boost psi levels?

passing 30 psi @ 2000 rpm is pretty awesome in my book. Sounds like a heck of a setup.

 

The actual number that matters here is cylinder pressure. This is the combined effect of compression, the combustion event and forced air (boost).

I’ve always wondered where the 40psi of boost ‘limit’ originated from??

On edit: 40psi from a stock size turbo is certainly different from 40psi out of a HUGE turbo, right?

I bought an engine that a guy built with big hybrids (250/200’s?), twin HPOP’s and a big turbo that dyno’ed 578hp or something like that. He originally built it with stock head bolts and had a gasket failure on the dyno. They replaced the HG’s and put studs in it. This is the only firsthand story I know of a 7.3 blowing HG’s. I ran that engine from 2k miles to 125k miles with 160/0’s and S366.

‘They’ also say that ‘seasoned’ HG’s hold better than fresh ones (like the ones that failed in story above). That’s why they recommend doing studs one-at-a-time and not disturbing HG’s.

All of that said, I don’t think you can hurt anything with stock injectors. But, I’d hate to give that advice and see you break something.....

 

definetly want to do the studs one at a time that original hg deal is important.

 

I'd say any time you are planning to go higher than stock on boost, do as many mods as you can afford to that head/block interface (i.e. studs, gasket, fire rings etc) to give yourself peace-of-mind. If not, you'll be staring at the boost gauge constantly as you drive. The old engineering rule-of-thumb to not exceed 70% of capacity is a good one to abide by here.

 

Thanks for the input Jason. Do you know if studs can be installed with the motor in the truck or without picking up the cab a bit? Just trying to imagine a big torque wrench in there. Casually looking at DieselSite's stud kit for $500.

 

I'm surprised to hear you're getting 40 psi with stock injectors.

 

I’m not sure. I hate suffering, so I’ve always pulled the engine and done a bunch of stuff at the same time.

The other ‘40psi’ limit is valve springs....

 

I'm surprised by it as well, it's pretty spicy. EGTs rarely top 1100 degrees at those numbers.

 

When I'm pulling my trailer at about 29,000 GVW, I'll see 21-22 psi, 1,200 degrees. Bellowed up-pipes. Stock injectors. 6637 style intake with AFE Big Boost air filter. PHP 25hp tow tune. 4.88 rear axle. I hardly ever have to shift down unless I get to a hill that is more than 3% grade.
If I switch to the 45hp tune, the EGTs stay the same but I'll see a couple more psi boost.

 

There are quite a few FTE'rs that have verified boost numbers north of 30 PSI with stock injectors and obviously a tune chip of some sort. Consistently, they have noted running a tune and have minor upgrades like CAC boots, up-pipes, clamps, intake, exhaust, etc... The biggest factor though is the turbo, other than the tune chip. I would see a sustained (while towing the 5th wheel up a grade when towing at 18,000 - 20,000 lbs GCVW) 30 PSI with the MST, but I could tell that was pushing too hard for that turbo. The other FTE'rs and myself have all upgraded to a different turbo or went with a completely new internal setup using the KC turbine wheel and their choice of compressor wheel.

With my 363/68/.91 Borg Warner turbo, I see peak boost PSI at 35+ if I really get into the throttle in 2nd or 3rd gear. It is difficult to see the gauge move that high that fast by that time as I am paying attention to where I am going. That is on stock injectors with 266,000 miles on a PHP 65 HP tune towing the 5th wheel. In my humble opinion, it is not difficult to get up to 35+ peak boost, but it is to reach that boost level and sustain it, safely. SSJ once told me, "I wouldn't change a thing on that truck until you have to, it is one of the best running stock injector truck I have ever driven". That meant a lot to me as it means I was close to or have attained my goal of efficiency, longevity and reliability.

This is a great thread and I am grateful brokstroke started it as there is a bit of internet lore engrained in the "40 PSI" limit. When towing and climbing a grade, I am usually in 6th gear and ~20 PSI or 5th gear and a bit higher in the PSI scale. Although, I could jump up to 30+ PSI, I have seen no real benefit to it unless I was merging with or going around traffic. I am 100% comfortable with this as it puts me right where the OEM had somewhat set the high limit range of the PSI.

Going forward, the PSI reading of my boost gauge does not concern me at all and I don't measure performance by it. I only use the boost gauge as a preventive maintenance tool and just to keep things in check if I do exceed 30 PSI. To me, boost is only a representation of the pressure within the system, not performance. I don't say "if I could get 5 more PSI I could get up that grade faster..." I say "the truck is performing very well for my application and within the specification Ford and International set forth".

I am looking forward to learning something from this thread and seeing how brokestroke proceeds with his "spicy" vehicle. He has done a lot of work to it and it performs quite well for his application to include building his own T4 kit and installing a .83 turbine housing on his 363 Borg Warner turbo. Although, he is always trying to push the envelope while fabricating, designing and conjuring up new methods of pushing that envelope a bit more.

 

That sounds on par with the stock turbo as well the gtp38 based KC hybrids. They seem to be limited to around 30psi +/- before EGTs start warming up. The 4.30 gears really put the motor in the meaty section of the RPM band and when it's on the highway it is basically a 1 speed truck. Grossing 20k from Michigan to Florida it will never downshift unless traffic slows me down. The operating window for the truck is 2000-2400rpm at all times. 2000rpm is 60mph and 2400rpm is 73mph. Bigger grades I come into at around 2400rpm and as soon a I am at the bottom of it I hold it too the floor and don't let off unless the truck gains speed. Some of the longer grades in KY and TN with scrub speed from 73mph to 68mph with a few exceptions that may hit 65mph. My biggest thing is I hate getting stepped on when towing. If you are scrubbing 10-15mph at the top of a hill the back and forth passing traffic is annoying. Semi starts passing you mid way up the grade, you crest the grade and speed back up and now you are going faster than the semi. So you either back off and ride behind him or pass him and try to get ahead of him before the next big grade. Then if I have to pass a slower truck up a hill I can use the passing lane without slowing up traffic trying to get around him. I also travel with another truck and trailer that has around 500hp, if I scrub top much speed I'll hear about it. Old 7.3 has to keep up.

 

Ahh yes, springs. Might as well add push rods while your at it as well. Have been looking at some of the bee hive springs but haven't given it too much thought.

My list kind of goes like this.
Studs
Springs/push rods
T500

It will toss an ICP code once in a while. While it doesn't seem to hurt performance I am slightly concerned that upgrading the hpop will push it further into the 40psi range without studs. So I just ignore it in the mean time.

 

Does anyone know if studs and be installed and torqued in the truck?

 

Seems like yes. HVAC box is in the way. Maybe jack front of cab or removing motor mounts is required??

Ill try to remember someone who did it in the cab and ask them.