Best Turbocharging Options for IDI's
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kas83
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I personally like the non-gated pulse turbo for 2 reasons, less cylinder pressure at low engine speeds, and the fact that max power is directly controlled by your right foot. A wastegated turbo brings on boost quicker, creating spikes in cylinder pressures. A wastegated turbo also bleeds off energy, which somewhat limits peak power potential. Most say 10-12 psi is max for an IDI. I disagree. If you're making that boost at or around 2,000 rpm, it's harder on components than at 2,500 or 3,000 rpm. I've run 15-18 psi into a 6.9 with a Banks non gated turbo between 2,500-2,800 rpm for extended periods and never had a problem, hardly any smoke, and relatively decent economy to boot. I've driven a few factory turbo trucks as well, and they didn't feel as peppy at those speeds or rpm, and got slightly worse economy. All trucks were 4.10 equipped, running ~65 mph in direct, and grossing 18-20k lbs combined.
I've noticed a tendency for people to 'lug' an engine more with wastegated turbos, creating higher pressures and temps than necessary as well. There is a reason these engines are making max power at 3,000 plus rpm. They were designed to rev up more than inlines were. Low torque peak gets you moving better, while the broad powerband ensures you stay moving. You're best towing performance is honestly around 2,200-2,500, almost dead in the center of the powerband. Power under that from a wastegated turbo really isn't useful for much other than being ******* parts.
I've noticed a tendency for people to 'lug' an engine more with wastegated turbos, creating higher pressures and temps than necessary as well. There is a reason these engines are making max power at 3,000 plus rpm. They were designed to rev up more than inlines were. Low torque peak gets you moving better, while the broad powerband ensures you stay moving. You're best towing performance is honestly around 2,200-2,500, almost dead in the center of the powerband. Power under that from a wastegated turbo really isn't useful for much other than being ******* parts.
jaluhn83
Full Access Member
What is your source for this info?
I do not have the references to say with certainly, but my take would be that the critical factor in engine stress is the cylinder pressure, which is a function of fuel, not so much boost - in fact more boost means more air to cool the combustion, so the cylinder temps and thus thermal stresses are less. Now yes, if you dump more fuel in with the air then you will see higher stresses.
I believe the higher rpm power band isn't so much intentional design as it is a function of the v8 packaging, which is in turn selected for physical reasons, ie fitting into the available space in a pickup vs a MDT app with a longer narrower hood.
Higher rpm also means higher pistons and bearing speeds, ie more friction and wear. Also more mechanical stresses from acceleration/deceleration. There's a reason that the old 900 rpm Cat engines lived forever.
Also worth noting that there seems to be no trend of WG vs non WG engine failures, aside from overly high boost/egt problems from misuse of either.
I do not have the references to say with certainly, but my take would be that the critical factor in engine stress is the cylinder pressure, which is a function of fuel, not so much boost - in fact more boost means more air to cool the combustion, so the cylinder temps and thus thermal stresses are less. Now yes, if you dump more fuel in with the air then you will see higher stresses.
I believe the higher rpm power band isn't so much intentional design as it is a function of the v8 packaging, which is in turn selected for physical reasons, ie fitting into the available space in a pickup vs a MDT app with a longer narrower hood.
Higher rpm also means higher pistons and bearing speeds, ie more friction and wear. Also more mechanical stresses from acceleration/deceleration. There's a reason that the old 900 rpm Cat engines lived forever.
Also worth noting that there seems to be no trend of WG vs non WG engine failures, aside from overly high boost/egt problems from misuse of either.
kas83
Full Access Member
My source is owning 2 semis, several Cummins and IDI engines of varying degrees of modification, as well personally building a compound turbo, 600 hp 12 valve. Also, basic turbocharger theory.
You're confusing pressure with temperature variants. What takes out headgaskets? Excessive cylinder pressures. What bends rods? Excessive pressures again. Higher engine speeds mean components are subjected to excessive pressures for shorter periods of time, albeit more frequently.
The argument of more pressure at lower engine speeds keeps it cooler is false. It takes longer to fill and evacuate a cylinder, which holds heat, at lower speeds. Overspeeding the engine doesn't do any good either, no matter which setup you have.
You're confusing pressure with temperature variants. What takes out headgaskets? Excessive cylinder pressures. What bends rods? Excessive pressures again. Higher engine speeds mean components are subjected to excessive pressures for shorter periods of time, albeit more frequently.
The argument of more pressure at lower engine speeds keeps it cooler is false. It takes longer to fill and evacuate a cylinder, which holds heat, at lower speeds. Overspeeding the engine doesn't do any good either, no matter which setup you have.
While I haven't driven an IDI with manual trans, I doubt they make so little power at 2000 RPM as to be lugging. My 460 truck is perfectly happy towing at 2000 RPM in 5th on the highway without lugging. Just smooth strong torquey power. My IDI starts making power around 5psi so the sooner it builds 5 psi the sooner it's out of lugging territory, to oversimplify. Higher cylinder pressures are harder on head gaskets and bolts but I wouldn't call anything at 2000 RPM lugging.
when talking about turbos, wouldnt it be beneficial to speak in terms of flow and pressure?
there are so many different turbos out there, its hard to wrap my head around what turbo would be better for a certain truck.
theres also what that certain trucks intent is.
ive always been a "try this and see what happens" kinda guy.
as i deal with numbers on a daily basis, the last thing i wanna do is run numbers in my off hours.
sounds retarded, i know but my bodys EGT's are usually through the roof after work.
my next IDI build will be getting a GTP-38 with the option to run 2 TP-38's if i desire to.
no point to this thread but to set the stage for a debate.
there are so many different turbos out there, its hard to wrap my head around what turbo would be better for a certain truck.
theres also what that certain trucks intent is.
ive always been a "try this and see what happens" kinda guy.
as i deal with numbers on a daily basis, the last thing i wanna do is run numbers in my off hours.
sounds retarded, i know but my bodys EGT's are usually through the roof after work.
my next IDI build will be getting a GTP-38 with the option to run 2 TP-38's if i desire to.
no point to this thread but to set the stage for a debate.
motox tech
Full Access Member
kzf250! Is that the flux capacitor out of doc browns delorian?
Could be! Not exactly sure what it is cuz there is no make/model or numbers on it. It came from a factory where i got some air motors as well, so I wonder if it might compress air to run the motors. It is seized up at the moment.
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