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Mild compound turbo setup

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  #16  
Old 02-12-2017, 11:00 PM
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The bit about piston speed is an interesting take for sure, and is relevant im sure. Bottom line is you dont want 10 psi at 1000 rpm the stress involved would destroy the bottom end in short order. IDI's are stout, but dont forget they were designed to run at the governor under load, and without a turbo. The cylinder pressure and stress on the rotating assembly is massive just lugging an NA engine, now double that with a turbo. Have a look at tractor pullers and such, theyre not spinning 5.9s to 5k just because they make more power there, its equal parts engine preservation. If thats not enough, compare the bottom end of a modern "de-speeded" OTR diesel to one from 20 years ago. The 13L in our volvos pull as hard at 1000 rpm as they do 1600, but i seen a rod out of one, and it is MASSIVE.
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Old 02-12-2017, 11:13 PM
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Quote:
Originally Posted by hairyboxnoogle View Post
The bit about piston speed is an interesting take for sure, and is relevant im sure. Bottom line is you dont want 10 psi at 1000 rpm the stress involved would destroy the bottom end in short order. IDI's are stout, but dont forget they were designed to run at the governor under load, and without a turbo. The cylinder pressure and stress on the rotating assembly is massive just lugging an NA engine, now double that with a turbo.
But the question is: why is it more stress to run 10 psi at 1000 rpm than 10 psi at 2000 RPM or 10 psi at 3000 rpm? Assuming similar relative amounts of fuel. The cylinder pressures should be the same, right?
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Old 02-12-2017, 11:24 PM
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Originally Posted by hairyboxnoogle View Post
Have a look at tractor pullers and such, theyre not spinning 5.9s to 5k just because they make more power there, its equal parts engine preservation. If thats not enough, compare the bottom end of a modern "de-speeded" OTR diesel to one from 20 years ago. The 13L in our volvos pull as hard at 1000 rpm as they do 1600, but i seen a rod out of one, and it is MASSIVE.

For the 5K 5.9's - to get 2K or 3K horsepower out of 5.9 liters takes a lot of air - way more air than turbos can provide at 2k or even 3k RPM.

For the big rig engines - I would be willing to bet that the rod out of an old Cat 1693 is bigger than the one out of your 13L. And while 1K to 1600 rpm seems like a "low" RPM operating range, take a look at old D9 cats with a MAX rpm of 1200 - or the John Deere R that governs at 1K. RPM isn't really what matters. Look at piston speed.
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Old 02-16-2017, 02:19 PM
88 Ford IDI 88 Ford IDI is offline
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If you go compounds, I would go with something are a 57-60mm for the high pressure turbo. Justin is running a 57mm BW turbo iirc and a 75mm BW for the atmosphere turbo. For what you want I would stick around a 72mm on the big turbo. That would make a decent spooling setup.


Also a guy on the Cummins forums makes a He351ve VGT controller for a decent price using an Arduino controller. I think it is called A Banshee Controller. Could always go a compound setup with a VGT and a big turbo on top that would be cool. I've seen a few newer trucks with them and they spool like crazy! It would be harder to tune though for sure!
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Old 02-16-2017, 02:39 PM
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How much power are you aiming for? That's the biggest question. You have to size the turbos according to how much fuel you have for power. I have a calculator for all of that, but the power goal has a lot to do with it.
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Old 02-16-2017, 04:50 PM
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Originally Posted by 1972RedNeck View Post
For the 5K 5.9's - to get 2K or 3K horsepower out of 5.9 liters takes a lot of air - way more air than turbos can provide at 2k or even 3k RPM.

For the big rig engines - I would be willing to bet that the rod out of an old Cat 1693 is bigger than the one out of your 13L. And while 1K to 1600 rpm seems like a "low" RPM operating range, take a look at old D9 cats with a MAX rpm of 1200 - or the John Deere R that governs at 1K. RPM isn't really what matters. Look at piston speed.
Its all relative to what the engine is designed for, which, like you say im sure has to do with rod / stroke ratio, and bore vs. stroke.

Macrobb, im not a physics engineer. All i know is the faster something moves, the less stress / pressure there is, be it rods, transmissions, or gearboxes. If i had to hazzard a guess, its because the piston cant "get away" from the combustion pressure. Like redneck says, piston speed. Amount of fuel doesnt control how fast it burns, just how big of boom there is. To get the most out of a given amount of fuel / air, the piston needs to be moving at given speed to accept that energy to convert it into motion efficiently.

Not sure if that makes any sense or not.
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Old 02-18-2017, 09:32 PM
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Pretty sure hairy is spot on in this last post. In cylinder pressures can go sky high with big boost at low rpm. In large part because of the amount of time the forces act on the piston at low rpm. The torque the engine produces is related to the force applied to the piston by combustion x time. At low rpm the time that the combustion has to act on the piston is significant like maybe 9-10ms. At 3000rpm the piston is passing outside of the 90 degree window within 3ms. The effect is multiplied at low rpm with the piston not racing away from the combustion event the combustion occurs more completely and at higher pressure. Sending combustion pressure spiking even higher.

Now I would take anything I said with a grain of salt, it's been ten years since took thermo dynamics and I haven't used it in work for five. And to boot I had my ankle reconstructed yesterday and I'm dopped up on my couch with nothing better to do.

But it all sounds right in the fog right now.
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  #23  
Old 02-19-2017, 05:16 PM
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Originally Posted by JoeF250 View Post
Pretty sure hairy is spot on in this last post. In cylinder pressures can go sky high with big boost at low rpm. In large part because of the amount of time the forces act on the piston at low rpm. The torque the engine produces is related to the force applied to the piston by combustion x time. At low rpm the time that the combustion has to act on the piston is significant like maybe 9-10ms. At 3000rpm the piston is passing outside of the 90 degree window within 3ms. The effect is multiplied at low rpm with the piston not racing away from the combustion event the combustion occurs more completely and at higher pressure. Sending combustion pressure spiking even higher.
Well that's helpful! I wonder how we could determine the "limit" is before putting the engine at risk. Some kind of cylinder pressure vs. RPM calculator with a general idea of a safe limit.

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Now I would take anything I said with a grain of salt, it's been ten years since took thermo dynamics and I haven't used it in work for five. And to boot I had my ankle reconstructed yesterday and I'm dopped up on my couch with nothing better to do.

But it all sounds right in the fog right now.
Haha that's pretty funny. Hope the healing goes well! The good thing about your advice is that thermodynamics hasn't changed in ten years so what you know is still good.
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Old 02-19-2017, 05:52 PM
JoeF250 JoeF250 is offline
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After I wean myself off the opiates and can be up right for more than 30sec I might try and dig out my thermodynamics of internal combustion engines book. The problem isn't wether thermo has changed or not. It's my lack of practice and relative stoned-ness at the moment. I think estimates of cylinder pressures can be calculated but it's probably more work than is worth. And if I recall the difference between calculated and reality in this could be substantial.

Any way the best way to figure out what they can handle is probably to ask one of the Justin's. Pretty sure they've both blown apart a few idi's in the quest to eliminate the weak links.
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  #25  
Old 02-19-2017, 11:31 PM
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Well the upside, as long as you dont have studs, the headgaskets will go before anything else.
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  #26  
Old 02-20-2017, 11:53 PM
southern-old-bold southern-old-bold is offline
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Originally Posted by hairyboxnoogle View Post
Yea VGT would be the way to go with what youre wanting, 6.0psd or 6.7ctd... but theyre a bit small for a 7.3 with any real fuel. That said, you can always drop a wheel in it. An S258sxe will spool "lightning fast" , and still flow enough on paper for a 110cc pump.
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Originally Posted by Macrobb View Post
But the question is: why is it more stress to run 10 psi at 1000 rpm than 10 psi at 2000 RPM or 10 psi at 3000 rpm? Assuming similar relative amounts of fuel. The cylinder pressures should be the same, right?
typically, the vee configuration of our engines shifts potential torque UP the rev range compared to an engine built with the same number of cylinders in a straight line. Also, air flow through camshaft and valving, the porting and volume of manifolds and cylinder heads promotes torque at designed rev ranges.
Note, to modify air and fuel flow and delivery so that higher pressure mixtures are available at low rpms will require other engine mods as mentioned, these mods will probably narrow down the useful range of power at other engine speeds.
It may also effect operating temperature.
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