Hydro-idi
Full Access Member
Where are you getting this information from? It ain’t true.
Is a turbo mandatory for fuel economy?
- Thread starter DarkDownDeep
- Start date
Where are you getting this information from? It ain’t true.
Macrobb
Full Access Member
True and false. In a way:
...Because if you are already running at a high RPM(due to gearing), you don't need the boost... because it's just extra air getting pumped through the system. Unless you have too much fuel(black smoke), you do not have "too little boost", at at highway cruising(empty), you don't need /any/ boost to burn the fuel required to maintain speed.
Repeat after me: Boost does not make power. Boost(air into engine) is simply half of the equasion; you need matching fuel to make that power.
Give it some throttle(fuel), the turbo will spool up and you'll have more power... which will make the truck accelerate. Let off the throttle; boost will drop to 0... which is fine, because you aren't burning any fuel!
(That being said, with the Banks turbo on my '92, it'll push 3-ish psi of boost just free-revving it to 2500 or so, 5-6 unloaded on flat highway, and 15+ at full throttle)
Now, when you add lower-numbered gearing(say 4.10 to 3.55s), you drop the RPM the engine needs, and increase the torque required by the same factor. More torque = more fuel needed to burn per revolution, and this is where your turbo can come in handy on the highway, due to the higher torque requirement and lower RPM(so more fuel burned per rev, more air required per rev).
genscripter
Full Access Member
DarkDownDeep
Registered User
Is it possible to increase the compression more? Would that allow the ip to be turned up more?
genscripter
Full Access Member
The point of this thread is dealing with MPG. Since my primary focus on my IDI is MPG, I'm just relaying my experience with how best to reduce fuel usage. Since most IDI guys are using their turbos to haul stuff in a truck, they neglect to understand that there are many other uses for an IDI and not all IDI's are trucks. For the typical ecomodder, like me and I'm assuming the OP, hauling stuff typically defies the point of ecomodding.
So, when it comes to a turbo kit on an IDI for mpg reduction, it is rather pointless, because as @Macrobb stated, driving an empty IDI vehicle in the hopes that a turbo will increase MPG is fruitless. The vehicle already performs well at regular highway speeds without a load as NA.
That all changes if the vehicle is used for hauling, steep grades, and very high highway speeds. But if you are doing that, then MPG isn't really a major issue.
DarkDownDeep
Registered User
mpg is always an issue. Im curious if a turbo helps burn fuel more efficiently than NA.
Im curious if raising the compression from stock burns fuel more efficiently also.
Hydro-idi
Full Access Member
Regardless of how complicated some may want to make this thread, a turboed diesel engine will be more efficient than N/A, even going on down the highway with very low boost. That low boost turbo setup running down the interstate is throwing more air down the throat than any N/A would be able to compare to.
Having said this and going back to my first post, a turbo engine will likely be more efficient than a naturally aspirated one. That doesn’t necessarily mean that it will increase fuel economy.
Having said this and going back to my first post, a turbo engine will likely be more efficient than a naturally aspirated one. That doesn’t necessarily mean that it will increase fuel economy.
Hydro-idi
Full Access Member
Yes, a turbo helps burn fuel much more efficiently in general.
Don’t mess with the compression with these engines. It’s high enough at almost 22:1 CR in stock form.
david85
Full Access Member
Just thinking aloud here.
In theory...a turbocharger not only helps pump air into the engine; it also recovers waste heat from the engine exhaust, thus increasing net efficiency. This is why an ideal supercharged engine will never match the efficiency of an ideal turbocharged engine. I might even argue the same could be said for peak power (the ultimate in artificial aspiration being the turbo-compound engine, which increases energy recovery even more).
This would mean that under all conditions, if you are burning any fuel at all, the turbo is *trying* to spool. Even at idle. Exhaust gas volume has to be larger than intake gas volume, otherwise the engine cannot perform work. However, this can get skewed when you factor in the efficiency map of the turbo. Rather, the fact that it's nowhere near efficient at those speeds. Like all mechanical devices, a turbo must consume some energy before it can transmit energy on to the next component in the process. At high engine loading, there is enough exhaust gas flow to render the turbocharger's friction and parasitic losses more or less insignificant.
Whether or not the turbo can actually result in a net loss in efficiency at extremely light engine loading (such as idling) is difficult to say without a controlled experiment. But I guess it might be possible. Once cruising at 55mph, my gut tells me the turbo is efficient enough to at the very least not be a net negative. This is only my conjecture though.
EDIT: Sorry, Hydro. Looks like I went and made it more complicated
In theory...a turbocharger not only helps pump air into the engine; it also recovers waste heat from the engine exhaust, thus increasing net efficiency. This is why an ideal supercharged engine will never match the efficiency of an ideal turbocharged engine. I might even argue the same could be said for peak power (the ultimate in artificial aspiration being the turbo-compound engine, which increases energy recovery even more).
This would mean that under all conditions, if you are burning any fuel at all, the turbo is *trying* to spool. Even at idle. Exhaust gas volume has to be larger than intake gas volume, otherwise the engine cannot perform work. However, this can get skewed when you factor in the efficiency map of the turbo. Rather, the fact that it's nowhere near efficient at those speeds. Like all mechanical devices, a turbo must consume some energy before it can transmit energy on to the next component in the process. At high engine loading, there is enough exhaust gas flow to render the turbocharger's friction and parasitic losses more or less insignificant.
Whether or not the turbo can actually result in a net loss in efficiency at extremely light engine loading (such as idling) is difficult to say without a controlled experiment. But I guess it might be possible. Once cruising at 55mph, my gut tells me the turbo is efficient enough to at the very least not be a net negative. This is only my conjecture though.
EDIT: Sorry, Hydro. Looks like I went and made it more complicated
genscripter
Full Access Member
Just thinking aloud here.
In theory...a turbocharger not only helps pump air into the engine; it also recovers waste heat from the engine exhaust, thus increasing net efficiency. This is why an ideal supercharged engine will never match the efficiency of an ideal turbocharged engine. I might even argue the same could be said for peak power (the ultimate in artificial aspiration being the turbo-compound engine, which increases energy recovery even more).
This would mean that under all conditions, if you are burning any fuel at all, the turbo is *trying* to spool. Even at idle. Exhaust gas volume has to be larger than intake gas volume, otherwise the engine cannot perform work. However, this can get skewed when you factor in the efficiency map of the turbo. Rather, the fact that it's nowhere near efficient at those speeds. Like all mechanical devices, a turbo must consume some energy before it can transmit energy on to the next component in the process. At high engine loading, there is enough exhaust gas flow to render the turbocharger's friction and parasitic losses more or less insignificant.
Whether or not the turbo can actually result in a net loss in efficiency at extremely light engine loading (such as idling) is difficult to say without a controlled experiment. But I guess it might be possible. Once cruising at 55mph, my gut tells me the turbo is efficient enough to at the very least not be a net negative. This is only my conjecture though.
EDIT: Sorry, Hydro. Looks like I went and made it more complicated
I'd agree with the 55mph comment. Even with low pressure pushing into the intake, it's better than the intake sucking air thru a filter like in the NA setup. And in a scientific experiment, it would likely show that in a perfect situation with all variables accounted for, the IDIT would edge out the NA at any RPM's.
When it comes to real world driving, the minor MPG increase from that analysis will be overtaken by the thrill of being to keep up with traffic, accelerating at stoplights, hamming on it up a highway on-ramp, and passing that grandma plodding in her Buick. The turbo is just way too much fun. Keeping the vehicle at 55mph to save efficiency gets thrown out the window once the turbo is installed.
plywood
Recovered N/A
My old 85 Jetta n/a got about 40 like most. The turbo ones all got 32-35. Mostly a gearing thing vs where the turbo is efficient but same with these trucks. Gears...crusing rpm....turbo type....load...etc
plywood
Recovered N/A
Turbos are less efficient outside their ideal rpm range.
DarkDownDeep
Registered User
How can it be more efficient but not increase fuel economy?
Kiwif150
Full Access Member
Real world experience in a 3.0 diesel hilux na vs turbo ..... with the turbo 3.0 your foot isn't right up it to maintain 100km/hr cruise - non turbo you'll have your foot flat on the floor far more often. Same with the Nissan Avenirs - 2.0 diesel n/a and turbo with 75 and 100 hp respectively. I can assure you that those extra 25hp are extremely welcome and the fact you aren't flogging the backside off it to maintain 100km/hr means that in a most cases the economy actually improves with the turbo version.
I have a 3.2 turbo intercooled Nissan Elgrande which i brought to replace my Nissan Homy which had the 2.7 turbo intercooled diesel in it - both are auto and about the same size ..... the 3.2 bowls the 2.7 any which way you care to look at it.
I have a 3.2 turbo intercooled Nissan Elgrande which i brought to replace my Nissan Homy which had the 2.7 turbo intercooled diesel in it - both are auto and about the same size ..... the 3.2 bowls the 2.7 any which way you care to look at it.
Macrobb
Full Access Member
No. There is literally no room to increase compression. The valves come within a few thousanths of an inch(a human hair is about .003" or 3 thousanths) of the pistons as it is; the pistons come out of the block, into the space of the head gasket at TDC; the heads are flat-bottomed. The engine is literally at the maximum compression you could attempt to get without breaking something.
Generally people talk about going the other way, towards less compression... but IDIs like high compression and will smoke when cold without it.
Also, I recall reading a white paper where the effects of compression were tested in a small diesel engine; varying it and seeing what happened. I think ~20:1 was found to be most effecient, with higher compression actually losing effeciency.
The '83 6.9s were at around 20.5:1 compression, all later models are 21.5:1, to make cold start easier and less smokey.
An '83 6.9 that I recently messed with... would not start on Ether. Glow plugs would fire it right up, but Ether wouldn't do much when it was cold... so I can see why they upped the compression.
