Looking for Input on boring 6.9 to 7.3

[Brad S.]

Looking at the whole thread I noticed your using Total Seal rings.
Been thinking alot about these rings, since I'm rebuilding a IDI too.
Do you think because the rings are "thinner" that a person looses some long term durability/reliability???
Talked with a guy I know that runs 3 big block chevys on a "tractor", about total seal rings.
They don't use em, they really didn't notice a difference in ring sealing/power etc.
BTW the rockers do look nice, hope they add a little more hp.

 

[bronco78idi]

Hey Brad, Thanks for the question about total seal rings. I talked to the guys at the machine shop and we think there should not be an issues in durability or reliability. The reason for the rockers is really just for a smoother valve train geometry and cut down on guide ware. If I do get any performance from the rockers its just a bonus.

 

[bronco78idi]

I have been busy working. I am down to the frame. will be a little while before I start the mock for the engine.

http://i1345.photobucket.com/albums/p679/bronco78idi/45668_10153660172300467_112248085_n_zps32944cf3.jpg

 

[ken74amx]

Any new updates yet?

 

[bronco78idi]

Hey all,

Wow where did the time go and the money..

Ok so the update on the 6.9 I am not sure if you all know the studs from ARP 8740 chromoly after 80ft lbs. are past its yield points and will not work. This caused failures in other engine builds due to stretching. After waiting of others to come up with options and talking with ARP. I am going with ARP +625 alloy custom made. It going to cost a pretty penny, But it’s cheaper than losing the engine or starting over. It really sucks because the motor has been sitting build and wrapped for over a year now at the shop. The +625 Alloy is 260 to 270 ft. lbs. before they pass the stretch point and are reusable as long as you don’t pass the yield. Talking to Mike at the machine to order new gasket set and get ready to tear down the motor and toss the old ARP studs.

 

[TahoeTom]

Glad to see an update. Hopefully you made some progress on the rest of the build over the summer.

 

[jaluhn83]

I am not sure if you all know the studs from ARP 8740 chromoly after 80ft lbs. are past its yield points and will not work.

Where does this number come from? This is going to be dependent on the thread lubricant used. Using the frictional value for 'lubricated threads' I get a torque of 118 ft-lb. I come up with ~80 using certain low friction moly anti-sieze numbers.

But, the more important part is that the actual clamping load at the yield point is ~18,000 lb/bolt. That gives you 306,000 lb of force clamping that head down. Is more really needed? I would submit that the existing ARP studs are more than sufficient for any realistic idi application. If you really need to run super high boost pressures, deck the pistons and lower compression that way. I routinely run 18-20 psi using standard studs and 0.015" decked pistons and have had no problems in over 20k miles.

 

[jaluhn83]

BTW the rockers do look nice, hope they add a little more hp.

They may look nice, but they're no reason to need them. I strongly doubt you'll see more than a fractional HP improvement from them. These engines don't run high enough rpm for it to matter that much. Aside from the early aluminum pivot rockers, the stock rockers show no evidence of wear problems, major losses or the causation of significant wear on valves/guides.

 

[bronco78idi]

Where does this number come from? This is going to be dependent on the thread lubricant used. Using the frictional value for 'lubricated threads' I get a torque of 118 ft-lb. I come up with ~80 using certain low friction moly anti-sieze numbers.

But, the more important part is that the actual clamping load at the yield point is ~18,000 lb/bolt. That gives you 306,000 lb of force clamping that head down. Is more really needed? I would submit that the existing ARP studs are more than sufficient for any realistic idi application. If you really need to run super high boost pressures, deck the pistons and lower compression that way. I routinely run 18-20 psi using standard studs and 0.015" decked pistons and have had no problems in over 20k miles.

I am not sure what your motor build looks like but it not just about boost. it about overall cylinder pressure (Fuel/Boost) on a 7/16 stud. The 6.9 motors of similar builds failed within 3 month with a 180cc pump. We talked to ARP for days over the failure and Justin also talked to ARP we all came to the same answer. The problem is you just can't get the preload out of the studs before they reach yield, so it wants to lift and push the gasket out. The only answer from ARP was three different Studs ARP-2000, which gave you 95ft. lbs of preload, the L19 that gave you 105 ft. lbs the PSI 250-260 and the +625 give you 110 ft. lbs 260 and 270 PSI and is reusable if you don't pass its yield can be reused. I choose +625 just because! ARP recommended for my application L19.

 

[bronco78idi]

They may look nice, but they're no reason to need them. I strongly doubt you'll see more than a fractional HP improvement from them. These engines don't run high enough rpm for it to matter that much. Aside from the early aluminum pivot rockers, the stock rockers show no evidence of wear problems, major losses or the causation of significant wear on valves/guides.

I am not sure what my rockers will due and a lot of people on the IDI forums have different opinions. So time will tell. wait for the video's to see.

 

[stealth13777]

I like the time and effort being taken to do a thorough build, including the studs and rocker arms. While some of it may be overkill, better to go that way and not have problems. Looking great, and the more time and effort people put into these motors the more support the rest of us will find for them!

Can't wait to see the finished product. You've been very patient taking your time to get this done right.


Sent from my iPhone using Tapatalk

 

[FORDF250HDXLT]

They may look nice, but they're no reason to need them. I strongly doubt you'll see more than a fractional HP improvement from them. These engines don't run high enough rpm for it to matter that much. Aside from the early aluminum pivot rockers, the stock rockers show no evidence of wear problems, major losses or the causation of significant wear on valves/guides.

yeah i agree.i would have kept the $800 for fuel.

 

[jaluhn83]

I am not sure what your motor build looks like but it not just about boost. it about overall cylinder pressure (Fuel/Boost) on a 7/16 stud. The 6.9 motors of similar builds failed within 3 month with a 180cc pump. We talked to ARP for days over the failure and Justin also talked to ARP we all came to the same answer. The problem is you just can't get the preload out of the studs before they reach yield, so it wants to lift and push the gasket out. The only answer from ARP was three different Studs ARP-2000, which gave you 95ft. lbs of preload, the L19 that gave you 105 ft. lbs the PSI 250-260 and the +625 give you 110 ft. lbs 260 and 270 PSI and is reusable if you don't pass its yield can be reused. I choose +625 just because! ARP recommended for my application L19.

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.

 

[bronco78idi]

Justin or known as RacinNdrummin stop posting on this site, but he did reply on FTE about the above thoughts. I don't get into ******* matches with others, You do it your way and I do it mine. Here is what Justin had to say

"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...

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 for all your support and help on my project!!

 

[IDIoit]

those rockers are hotter than my ex wife when she took her prom dress off in highschool!!!
well worth the 800 bucks IMO
i am currently building a mental 7.3 for my 87.
i had a few questions if ya dont mind.

was there a reason that you didnt use a complete shaft mount rocker set up when you ordered these custom rockers?
i know these engines dont rev enough to warrent them. but raising the bar eliminates competition!

did you do any resarch on aftermarket rotating assemblys?
this question was prompted by a dream i had a few weeks ago, where i had a scat rotating assembly with some gnarly rods.
again this was just a dream lol.

what material are your valves made of? i have been building gassers for a while and i use nothing short of stainless valves.
i know diesel engines are another animal, but the strength of material does not care what kind of fuel or abuse you throw at it.
greatly appreciate the write up and videos, truly an inspiration to myself, and certainly to others on here.

you have alot of coin in this build. as a fabricator by hobby, i have dumped bucket loads of cash on projects that just seem to sit. nothing like having a bar of gold that you can only look at lol
one day this jewel will be slingin mud and hope you get decades of service out of her.

there always seems to be that one guy that hates what you're doing, and if you are a chevy fan, im one of those

good luck on your project! hopefully i see you at pismo or other and i get smoked!