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Seems like the threads would pull out of the block. No problem with that you think?
I don't think that would be an issue. The Root of the thread is important to anchoring the fastener, and for the amount of pull you are getting even at 130ft/lbs, you aren't going to pull the root out of a 14tpi thread over 1.25".
I wanted to address some points that somebody brought up over on the other site in Bronco78idi's thread, and since I cant do it directly, Ill do it here. The poster is a member here, so he can reply here if he wants...
What he posted:
Okay, perhaps I should reword. Max boost has a very direct relationship with cylinder pressure when you assume that sufficient fuel is supplied for complete combustion. Yes, high boost without fuel isn't going to raise pressures much, (ie 20 psi with a stock pump) but neither is overfueling. Beyond that, you shouldn't be overfueling to begin with, so specing based on max boost is a reasonable metric.
How much boost are you trying to run? The only motor I know that has had problems was trying to run something like 45 psi, which is so far over design specs to be meaningless. A "mild street build" shouldn't need that kind of work. This is why I cite my engine - I'm running about what i consider a reasonable long term reliable max power setup and am doing it on stock studs with no issues, and it was what i would consider a mild to moderately high power setup. I cannot imagine why pretty much any straight truck would need more power unless you're trying to race or playing the ***** size game. Hence the questions of why you think it's needed.
Based on numbers quoted above, I get a theoretical max cylinder pressure of ~7100 psi before the studs would start to yield. That's a pretty decent number. Doing some quick research, I find general max pressures around 2500 PSI even for modern turbocharged engines. Discussion I cite: http://www.eng-tips.com/viewthread.cfm?qid=215499
What this says to me is that *if* head stud yielding really is the cause of gasket failures (and at that high of load it could be any number of things including block/head deformation), then you're running much higher than designed pressures which can't be good for anything and would not be considered comparable with reliability....
Of course ARP is going to suggest you need their super-unobtainium bolts.... they want to make money! Now, not saying they're wrong, but also not exactly an unbiased scientific source for failure analysis either.... Nor necessarily knowledgeable about high boost idi diesels or culturally inclined to think about longevity. (again, nothing against them, but the business tends toward very high power engines where power outweights longevity, which causes a certain institutional mindset)
Now, I'm not trying to be negative, and clearly there has been a large amount of time, effort and money put into this. That being said, it's also worth looking at the bigger picture and the fact that other folks will be looking for info as well. IMHO, the cost of things like roller rockers and super strength studs is not economically sound for 95% of the engine builds folks on here will be doing, and it's good to convey that. If someone has the money lying around to spend, then sure, but it's not needed, and giving the impression that it is is not helpful.
Overthinking cylinder pressures here.
An IDI at the max, will be lucky to see a 2000psi peak cylinder pressure. It has a relatively low burn rate at the beginning of combustion, where most cylinder pressure would be measured. The main factor on that peak number is going to be compression ratio though, and if you aren't running a severely decompressed engine (~16:1), it can equate into some decent cylinder pressures when you start adding energy release into the equation.
When you torque your cylinder head down, you are putting load on a fastener. Your Yield and Tensile strengths just tell you how much load the fastener will hold before failure. Yield on a 7/16 8740 ARP stud is 130ft/lbs of torque, that was where permanent stretch took place. Permanent stretch means the "spring" isn't preloading the attachment any longer. When you leave a little cushion to prevent Yield, lets say 20ft/lbs, you are applying a force to the joint. A 7/16 8740 stud at 110ft/lbs is generating 26,400lbs of clamp load right at the fastener, the farther you move out from that fastener, the number drops substaintially, and is dependent on the rigidity of the material you are fastening.
At 2000psi peak cylinder pressure, the cylinder head has 27,047lbs of force being applied to anywhere within the bore diameter of the gasket (4.150") pushing the head away from the block. The weakest spot is going to be the furthest away from any fastener, on that sealing surface. Our gaskets are about as far away from performance as it gets, so any release of clamp load at significant pressure is going to push that gasket out of position, and if bad enough, right into the water jacket like mine did on the two most unsupported parts of the gasket clamp. Now in these positions, it would be beneficial to have a good gasket that wouldn't push out and fail, but that doesn't mean you wouldn't see a little cooling system pressurization. Regardless, the issue comes down to the stock 6.9 studs not supporting cylinder pressures at 2000'ish psi, the pre-load just isn't there. The only way to get the preload to be safe is better fasteners that will take the load, and at 130ft/lbs of torque, the 625+ stuff is delivering 31,200lbs of force right at the fastener, that's at least 15% more than peak load pushing the head away.
As far as the rest of it goes... Same old story. I don't understand why it is that people are so adamant about scoffing at people that do modifications they want to do because they want to do them. I don't think the Roller Rockers are worth the squeeze, that's been my opinion since the beginning, I just don't see the gains being there, but I think its cool as hell Rob has stepped up to the plate and is going to do it because he wants to, same with the 625+ studs, hell, I even chickened out on that and spent a bunch of money (well more than the 625+ stuff costs) trying another option that has been talked about, and I failed, by my own standards anyway...
Its like running 20psi of boost... When I got into the IDI thing, there was one guy running over 20psi of boost, everybody else said you blow gaskets at 20psi boost, and that you have to keep it under that. Boy was that wrong, now because a few people that are actually willing to try things, we know that that is laughable. We have people making over 750ft/lbs of torque at the wheels on stock 21.5:1 compression, and not blowing gaskets...
Rob has sunk a bunch of money into any IDI because its something he feels will be cool as **** when its done. Since he has started, some parts like the 7/16" studs have been put to the test and are now marginally too weak for his goal. Im sure if he started all over, he would probably do what a few of us wish we would have done and build a 7.3 based engine, but not having that option now, its time to take a chance on some more trick parts. When they work, it will just be another modification in the now long list that people accept as the norm, whether you think its worth the money or not. Sometimes doing something for the sake of doing something is much more important than playing it safe and not.
Thanks Justin! I use these sites to share "MY" personal build and I talk with a lot of different people about my build. I want to be different. I was never into Diesels this is my first build and I come from the Gassers world were everything makes a difference, So I am dumping money that some say is a waste, well its my money to waste, if you cant afford 800.00 bucks on rockers, don't buy them.
I Know its been a long time. Been collecting parts and as crazy as it seem I picked up a third project. 1977 Ford F250. I guess after all the time I spent on the IDI to find out that it's not really what I thought and having to throw away 300 dollars ARP studs and spend 2k on the 625 ARP studs plus the labor, well it left me a bit pissed so I needed therapy and found the F250. I am almost completed with it so, It's time to move back to the Bronco my true passion! right after Thanksgiving I will start posing pictures and the build.
So if you are interested in how I built his Mounting Plates and what all was modified on the Frame to get this to work be sure to follow this posting. More to come soon.
So if you are interested in how I built his Mounting Plates and what all was modified on the Frame to get this to work be sure to follow this posting. More to come soon.
I can't believe this. I have been searching to see if anyone else had done this swap yet! I am working on my 79 7.3 now
For those that knew him, one of our own, and at the time one of the guys on the cutting edge of the IDI Diesel world, passed on January 5, 2021. He had a long battle with Esophageal Cancer that sasly ended his life, Robert was alot of things, my Mentor, a Brother, my Rock, but many of you may know him more as the guy that had the insanely built 6.9L IDI engine jammed in a 1978 Ford Bronco with the Harland Sharp Roller Rockers. This is a little bit of the story on the Bronco that we built and never finished, one of many to come as I will be trying to continue the Build to give Robert his last ride.
This video is a long one, I performed no editing, but I go over some light specs on the Bronco from front to back. Robert was survived by his Wife Kimber, robert's Son Michael, and their Daughter Amber. They have a Go Fund me started to help cover his end expenses and to help Kimber move up with Family to South Oregon. We are currently trying to find storage for the Bronco so it can be moved and finished. Over the next week I will be assembling the Bronco back in to as much of one piece as I can.
This is the First Video of which is re-launching Locked and Loaded 4x4, a Project myself and Robert started years ago and never completed, I will be featuring both the Bronco alot and my 3 builds (2 of which are IDI swaps).
11-29-2014, 05:58 PM
very nice! 
