lincolnlocker
Well-known member
you will need a new block when it calls for it but there is no reason at all that you cant run pmr's to 450hp.. gearhead is very good with pmr tuning..
live life full throttle
live life full throttle
4100 rpm with a potentiometer on the ICP
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Blown262
New member
What are the benefits of a 238/80 over say a 160/80. I've seen 238 more than a few times. What's the reason for that number?
Its the size they end up being when they build a hybrid. Its just how big the fuel capacity is.
A 160/80 is a good injector i guess. Its a towing type injector with a slightly larger nozzle. Its good at 400-425hp. Im sure someone has done more bla bla bla.
A 238/80 is a hybrid that will do the 400 that a 260 will do but it will also do closer to 500hp.
Then when you get a real motor setup together you can turn those 238s the **** up and go. Or throw 200%nozzles on them and have 550hp of hotrod.
Or you can do the 160s and be 400ish and have a turnkey setup that serves you for years.
A 160/80 is a good injector i guess. Its a towing type injector with a slightly larger nozzle. Its good at 400-425hp. Im sure someone has done more bla bla bla.
A 238/80 is a hybrid that will do the 400 that a 260 will do but it will also do closer to 500hp.
Then when you get a real motor setup together you can turn those 238s the **** up and go. Or throw 200%nozzles on them and have 550hp of hotrod.
Or you can do the 160s and be 400ish and have a turnkey setup that serves you for years.
Blown262
New member
This right here. I have done countless hours of reading and the 160/80s stuck in my head more than anything else for some reason. Being as I don't have a ton of first hand experience, there's only so much reading charts and whatnot will do. But what you said is EXACTLY what I'm looking for for the long haul. I don't have a proper understanding of hybrids to really make a proper educated decision on them.
91turbogsx
Active member
The first number is cc's of fuel delivered per 1000 shots. Therefore it can provide more fuel than a 160cc injector.
ja_cain
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This is what I was thinking if you have forged rods. It will keep you honest and the truck will have a higher probability of lasting longer. With the hybrids, it could be a waste of the extra capacity if you never upgrade the nozzles. Also, if you do up the nozzle size then the motor could go pop at any time even with forged rods. Based on some if the comments from Dave at swamps, 500 horse power (with some reliability built in) is a big jump in cost. It just doesn't make sense to me to throw that much money at these trucks. Now if you have a few extra motors sitting around that you didn't pay an arm and leg for, that's a different story. Lincoln made a good comment that the tuning has come a long way with regards to PMR longevity. Still better to error on the conservative side though. The other thing about your situation is that you have a zf. Once you get above 400 hp, it's hard to shift fast enough to really take advantage of the extra power. Plus, the single disc clutches can't handle a whole lot of power. The dd clutches slow the shifting down even more. 400 hp is a good healthy number that doesn't require a bunch of expensive ancillary mods. Turbo, injectors, up-pipes and clutch. The chit really starts to add up quick on these trucks.
Some food for thought on several subjects floating around in this thread.
High RPM 7.3L
There are many inherent factors that make it difficult for the 7.3L to spin at higher RPM efficiently. First, as mentioned, the nature of the HEUI system. It's slow, period. If you want to make RPM under load AND maintain power, it takes serious modifications including:
- very large nozzle injectors (able to push more fuel with shorter pulse width)
- high-flow modifications to the injectors
- mods to sustain ICP (such as HPOP upgrade)
- mods to the IDM (to shorten the electrical delay)
- overcome flow restrictions at the heads (clean up the heads as much as you can, also a cam really helps here)
- upgrade the weak links at the pushrods and valve springs (too much RPM under load will case valve to piston contact and bent pushrods, you won't see much of that spinning 4,100 RPM in neutral in your driveway because you aren't under load demands)
- and finally very creative tuning to overcome the still present electrical timing delays and extremely short window for fuel delivery.
PMR's
The flaw regarding 7.3L PMR's vs PMR's from other motors is this.... When International switched to the PMR rod they remained the same dimensions as the original forged rods. Compare them to say a 6.0L PMR rod, and you'll see a good increase in size, and thus strength.
What kills rods first and foremost, any rod at all, isn't necessarily RPM. It's cylinder pressure. Excessive cylinder pressure will wipe out a rod quicker than anything else you do. PMR's will tend to "shatter", while forged rods will tend to "bend" first prior to breaking, especially if you're right at the threshold of its limit of cylinder pressure.
Excessive cylinder pressure can occur at just about any RPM. The limitations of HEUI on a 7.3L make it difficult to maintain excessive cylinder pressures at higher RPM, so much of the problem is occurring at low RPM. This is controlled entirely by tuning.
If you don't have tools to measure cylinder pressure, you can get a good idea by strapping the truck to a dyno and looking at torque, not horsepower. It's been floating around for over a decade that the 400hp mark is the supposed limit to PMR's. That's not accurate, because horsepower can be manipulated by RPM. The real limit to PMR's is torque, and a good rule of thumb number to stay under is 900 lb/ft. Going over that torque number can almost certainly result in a short lifespan of PMR's.
Tuning will control the amount of fuel delivered at any given RPM. Excessive fueling at lower RPM will result in a spike in cylinder pressure, which gives you a massive increase in torque. However, that's extremely stressful on the rods. Limit the fueling at lower RPM, and then maintain fueling as RPM increases and you'll see lower overall torque numbers, but similar peak horsepower output as RPM's climb. That's the secret to keeping a PMR motor alive. Nothing special there, no magic wand. Just common sense.
Injectors
Injectors will help determine the availability of fuel delivery, especially as RPM's increase. Let's start with the first number in the injector size identification, which is measured in CC's. In simplistic terms, that number is just a capacity, what the injector can flow in CC's in 1000 shots under ideal conditions. Now most 160/80 injectors can easily do just that. But let's say you have a 400 cc injector on stock nozzles..... you actually can't get it to flow 400cc's of fuel unless you increase the pulse width beyond what is physically available for an injection window at RPM.
The 2nd number is nozzle size. It's very simple here, you have to find a balance between tuneability/drivability and available fuel flow. As you increase nozzle size, the amount of fuel you can flow at a given pulse width also increases. The downside is that as the nozzle size increases, it also becomes more difficult to tune properly and maintain daily drivability and street manners. Nozzles are critical for maintaining higher horsepower at higher RPM. As your RPM's increase, your injection window decreases. Larger nozzles are capable of injecting more fuel within smaller injection windows.
Then of course there's different types of injectors - A codes, B codes, and hybrids. Most often people use A codes or hybrids, as B codes can get a bit oil hungry when pushed. A codes will be limited in size, and thus power potential. Hybrids can be built in just about any size, so the power potential is far greater. In addition, hybrids require less oil volume than A codes at equal pulse width, so it's easier to maintain a steady ICP. The drawback is that with hybrids you loose a bit of injection pressure at the nozzle, so in certain instances you loose efficiency and a "clean" burn, typically at lower ICP and lower RPM. As ICP and RPM's increase, that effect is diminished or minimized, and the positive attributes of hybrids tend to greatly overshadow the downfalls. Plus it's not as if the 7.3L is a very clean burning motor, so some of those effects aren't extremely noticeable to most.
Ok so I've rambled on quite a bit. Hopefully this helps to clarify a bit of what is being discussed in this thread. To sum up, a very high RPM 7.3L that is capable of making serious power is difficult to achieve in current HEUI form. Cylinder pressures are the #1 rod killer, not RPM's. And last, if you want to make power at RPM to offset having to make huge torque numbers, get a larger injector and pull back the fueling at lower RPM.
That's what I did on my old 7.3L, and it's still alive after all these years. I sold it about a month back, so someone else is having fun with it now. As a real-life example, when I hit the dyno and put down the numbers in my sig, there was another guy with a near identical truck as mine. His injectors had smaller nozzles, but everything else was the same. He made 1 hp more than me, but well over 100 lb/ft of torque. With his setup, I'm positive my PMR motor would have blown a long time ago. But the approach I took was to go with larger nozzles to give me better fueling at higher RPM, but rely on tuning to limit the fueling especially at lower RPM. The result was a PMR engine approaching near 500hp, and remained alive for years without windowing the block. FWIW I ran it up to 3700 RPM max on those dyno runs, and subsequent drag races. Still had stock valve springs, pushrods, etc. In fact, heads never came off the truck. Ever.
Anyway, this post has gone on long enough. Carry on.
High RPM 7.3L
There are many inherent factors that make it difficult for the 7.3L to spin at higher RPM efficiently. First, as mentioned, the nature of the HEUI system. It's slow, period. If you want to make RPM under load AND maintain power, it takes serious modifications including:
- very large nozzle injectors (able to push more fuel with shorter pulse width)
- high-flow modifications to the injectors
- mods to sustain ICP (such as HPOP upgrade)
- mods to the IDM (to shorten the electrical delay)
- overcome flow restrictions at the heads (clean up the heads as much as you can, also a cam really helps here)
- upgrade the weak links at the pushrods and valve springs (too much RPM under load will case valve to piston contact and bent pushrods, you won't see much of that spinning 4,100 RPM in neutral in your driveway because you aren't under load demands)
- and finally very creative tuning to overcome the still present electrical timing delays and extremely short window for fuel delivery.
PMR's
The flaw regarding 7.3L PMR's vs PMR's from other motors is this.... When International switched to the PMR rod they remained the same dimensions as the original forged rods. Compare them to say a 6.0L PMR rod, and you'll see a good increase in size, and thus strength.
What kills rods first and foremost, any rod at all, isn't necessarily RPM. It's cylinder pressure. Excessive cylinder pressure will wipe out a rod quicker than anything else you do. PMR's will tend to "shatter", while forged rods will tend to "bend" first prior to breaking, especially if you're right at the threshold of its limit of cylinder pressure.
Excessive cylinder pressure can occur at just about any RPM. The limitations of HEUI on a 7.3L make it difficult to maintain excessive cylinder pressures at higher RPM, so much of the problem is occurring at low RPM. This is controlled entirely by tuning.
If you don't have tools to measure cylinder pressure, you can get a good idea by strapping the truck to a dyno and looking at torque, not horsepower. It's been floating around for over a decade that the 400hp mark is the supposed limit to PMR's. That's not accurate, because horsepower can be manipulated by RPM. The real limit to PMR's is torque, and a good rule of thumb number to stay under is 900 lb/ft. Going over that torque number can almost certainly result in a short lifespan of PMR's.
Tuning will control the amount of fuel delivered at any given RPM. Excessive fueling at lower RPM will result in a spike in cylinder pressure, which gives you a massive increase in torque. However, that's extremely stressful on the rods. Limit the fueling at lower RPM, and then maintain fueling as RPM increases and you'll see lower overall torque numbers, but similar peak horsepower output as RPM's climb. That's the secret to keeping a PMR motor alive. Nothing special there, no magic wand. Just common sense.
Injectors
Injectors will help determine the availability of fuel delivery, especially as RPM's increase. Let's start with the first number in the injector size identification, which is measured in CC's. In simplistic terms, that number is just a capacity, what the injector can flow in CC's in 1000 shots under ideal conditions. Now most 160/80 injectors can easily do just that. But let's say you have a 400 cc injector on stock nozzles..... you actually can't get it to flow 400cc's of fuel unless you increase the pulse width beyond what is physically available for an injection window at RPM.
The 2nd number is nozzle size. It's very simple here, you have to find a balance between tuneability/drivability and available fuel flow. As you increase nozzle size, the amount of fuel you can flow at a given pulse width also increases. The downside is that as the nozzle size increases, it also becomes more difficult to tune properly and maintain daily drivability and street manners. Nozzles are critical for maintaining higher horsepower at higher RPM. As your RPM's increase, your injection window decreases. Larger nozzles are capable of injecting more fuel within smaller injection windows.
Then of course there's different types of injectors - A codes, B codes, and hybrids. Most often people use A codes or hybrids, as B codes can get a bit oil hungry when pushed. A codes will be limited in size, and thus power potential. Hybrids can be built in just about any size, so the power potential is far greater. In addition, hybrids require less oil volume than A codes at equal pulse width, so it's easier to maintain a steady ICP. The drawback is that with hybrids you loose a bit of injection pressure at the nozzle, so in certain instances you loose efficiency and a "clean" burn, typically at lower ICP and lower RPM. As ICP and RPM's increase, that effect is diminished or minimized, and the positive attributes of hybrids tend to greatly overshadow the downfalls. Plus it's not as if the 7.3L is a very clean burning motor, so some of those effects aren't extremely noticeable to most.
Ok so I've rambled on quite a bit. Hopefully this helps to clarify a bit of what is being discussed in this thread. To sum up, a very high RPM 7.3L that is capable of making serious power is difficult to achieve in current HEUI form. Cylinder pressures are the #1 rod killer, not RPM's. And last, if you want to make power at RPM to offset having to make huge torque numbers, get a larger injector and pull back the fueling at lower RPM.
That's what I did on my old 7.3L, and it's still alive after all these years. I sold it about a month back, so someone else is having fun with it now. As a real-life example, when I hit the dyno and put down the numbers in my sig, there was another guy with a near identical truck as mine. His injectors had smaller nozzles, but everything else was the same. He made 1 hp more than me, but well over 100 lb/ft of torque. With his setup, I'm positive my PMR motor would have blown a long time ago. But the approach I took was to go with larger nozzles to give me better fueling at higher RPM, but rely on tuning to limit the fueling especially at lower RPM. The result was a PMR engine approaching near 500hp, and remained alive for years without windowing the block. FWIW I ran it up to 3700 RPM max on those dyno runs, and subsequent drag races. Still had stock valve springs, pushrods, etc. In fact, heads never came off the truck. Ever.
Anyway, this post has gone on long enough. Carry on.
Blown262
New member
Wow thanks a ton Curtis. You are a gentleman and a scholar and I appreciate the time and effort put into that post. I couldn't have asked for a more thorough explanation and you clarified a bunch of things. Once this thing goes under the knife again, I will be sure to keep everyone posted. Thanks again to everyone
ja_cain
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I would think that would be worthy of a Sticky post.
ja_cain
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Curtis
What was your exact setup with that dyno run? Also, could you post up the dynograph? I think it would definitly illustrate what is going on with the torque vs rpm and hp vs rpm.
What was your exact setup with that dyno run? Also, could you post up the dynograph? I think it would definitly illustrate what is going on with the torque vs rpm and hp vs rpm.
Blown262
New member
+1 on sticky-ing that post as well
The setup was:
250/200 FFD injectors
38R with deleted EPBV
AFE Stage II
MBRP 4" exhaust
6.0L intercooler
BTS Trans
5r110 trans cooler
Stock HPOP
Billet aluminum intake plenums
Home built fuel system with Walbro pump and regulated return
6" lift, 36" tires, 4.30 gears
My own tunes. Pulsewidth maxed at 2.3ms, about 3100 psi of ICP, boost I don't know because my gauge pegs out at 35 psi... probably close to 40 psi on those runs.
Here's the dyno sheet. First run didn't record torque correctly, 2nd and 3rd run did. Granted this was with correction, but also done close to 6,000 ft elevation. Notice how the torque curve leading up to the peak doesn't resemble a stripper pole:
Last edited:
Hotrodtractor
Moderator
It would be hard to see piston to valve contact with a scope down the injector hole.
Blown262
New member
Well if I do have valve kisses, My son would love the pistons. He's a huge Mickey Mouse fan lol
Hotrodtractor
Moderator
There is no IF. You do based on the limited time at the RPM you describe.
Isobaric
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Great post Curtis.
One thing to remain cognisant of, when spinning 4000+ rpms (free rev or not), is that you have a rather large chunk of aluminum accelerating rapidly at BDC and TDC.
I have not done an FEA on a 7.3L piston to see what the acceleration threshold is, but per Mahle the limitation of a stock 6.6L duramax piston is 5150. Consequently, there is a bowl full of piston pieces and a windowed 6.6L block that was attained at 5151rpm.
Hopefully this touches on your question regarding why the Mercedes is mechanically capable of 7k, but a PSD is not.
Sent from my XT1060 using Tapatalk
One thing to remain cognisant of, when spinning 4000+ rpms (free rev or not), is that you have a rather large chunk of aluminum accelerating rapidly at BDC and TDC.
I have not done an FEA on a 7.3L piston to see what the acceleration threshold is, but per Mahle the limitation of a stock 6.6L duramax piston is 5150. Consequently, there is a bowl full of piston pieces and a windowed 6.6L block that was attained at 5151rpm.
Hopefully this touches on your question regarding why the Mercedes is mechanically capable of 7k, but a PSD is not.
Sent from my XT1060 using Tapatalk
lincolnlocker
Well-known member
yuppers!!
can you make curtis's post a sticky? that's good info for those like the op.. and most in general..
live life full throttle
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