Turbocharging? Vacuum? Too much thinking. Smart people unite
 

On 2 identical motors.. one n/a , one turbocharged.

Cruising at or closer to 0 inHg
Vs
as much vacuum as possible....

which is better for MPG?
I know cruising closer to 0 inHg is counter to what is efficient.

My thinking is while cruising at

(Example incoming)

60mph at 2000 rpm in N/A car at 16inHg (or whatever a vx cruises at)
Or
60mph at 2000 rpm in Turbo Car at 0 inHg/PSI ( give or take 1 or 2 in either direction psi or inHg)

The turbo car has more loss in Mechanical Efficiency (ME) from driving turbine wheel (albeit small) and Thermal Efficiency (TE) but it is also using free wasted energy (in the form of Hot exhaust gases) to spool turbine to Force more air into a cylinder thus increasing Volumetric Efficiency (VE). Also at closer to 0 inHg/PSI there is less pumping losses associated....

This is alll just early-morning-drive-to-work thinking....anyone want to chime in.


Also to add.. this was originally posted on my Facebook and the loss and thermal efficiency was a problem because I was referring to normal car and heat soak. However in the interest of this form a lot of people use a warm air intake so I'm wondering if the thermal efficiency will actually be a benefit as far as this conversation

this was literal verbal diarrhea this is my morning commute and i was thinking alot apparently. If anything doesn't make sense or is missing details or something let me know I'll fill in any plot holes I can I'm just trying to figure something out

I would think that an engine running at boost is efficient, but the problem is, it's making too much power. If the comparison was a 2 liter NA motor vs a 1 liter boosted motor, the boosted motor would be more efficient. Your comparison makes sense if we are talking about diesels.

Ok let's specifically use the VX engine. My thinking was hotter IAT, quicker warm ups, less pumping losses, more VE while cruising would help.

nissan bluebirds here with turbos were more economical than respective 1.8's. if you drive absolutely same pace as a NA, id think you'll get more out of a turbo, i guess?

Acceleration and getting up to speed maybe but i mean cruising

Once again, the problem is, running 2 other wise identical engines at different intake pressures results in one making X hp and the other making 2X hp in a gas ICE. I understand that a VX can run in lean burn, but not THAT lean. It would melt.

I do believe that the future of ICE powered cars will be very small highly boosted gas engines as part of a hybrid system. Imagine your civic with a 500cc turbo engine and a fairly stout electric motor. It would cruise on the ICE at pretty high load into the boost a bit and use the electric assist when more power was needed. Honda already has a 500cc V-twin on the shelf. It is 300+ years old and could surely use updating but I would think this would be a fair bit more efficient than say the 900 cc 3 from the first insight.

Plus a 90 V twin sounds a damn sight cooler than an inline 3.

Not 2X horsepower. Im talking purely cruising...not makinh power. At most 4psi. Nothing more. We will handle one subject at a time.

OK lets jump back a few years to the early to mid nineties and we're looking at a Volvo 940. They came with either a NA 2.3 liter inline four or an intercooled turbo charged version. The NA was rated at 114hp and the Turbo motor was rated at 160hp.

The big difference was at highway speeds the fuel mileage difference between the two motors was dramatic. The Turbo version topped out at a max of maybe 27.5-28 at 55 mph. The NA 2.3L on the other hand would easily pull 32-33 mpgs at speeds of 60-65 mph.

Driving a Turbo for mileage takes some skill, one is you want to keep the turbo out of boost as much as you can. The issue is the computer tosses in extra fuel under boost, one for more power, and for another reason to cool the incoming compressed air to avoid detonation (Knocking). That is why Turbos appear to not get the best fuel economy even though they have smaller engines. You may have a 2.0 liter motor but under mid boost you're burning fuel like you have 2.5L-2.7L and under heavy boost probably more like you're driving a car with a 3.0L to 3.5L motor.

I modified a 87 2.3L Turbo Volvo wagon for fuel mileage years ago. I dropped the Cd by lowing it and removing the roof rack. Pulled the automatic and replaced it with a five speed manual. Swapped out the 3.90 automatics rear gears for 3.31's. Highway mileage jumped from 325-340 miles per 15.8 gallon tank to 425-440 miles per tank. The biggest factor was replacing the non locking torque converter automatic transmission with a manual.

If you can drop the Cd and weight of the car you can easily increase the fuel mileage of a turbo car. Less air resistance and weight to haul around the less need for you have to force the turbo into boost.

The biggest issue especially with highway mileage in a modern manual transmission turbo car is the manufactures are always lowering the OD gearing for better performance instead of fuel mileage. Most of the manuals are running 300-400 rpms higher than the same car with an automatic. Same applies most of the time to the NA version over the Turbo version.

The difference there though ..again the turbo motor was 8.5:1 compression and the N/A was 9.7:1 ... therefore of course the n/a would get better gas mileage.... and not to mention gearing is different also between the two...

I have a hf trans and vx motor. No positive psi here... purely... cruising..at 65mph.. not racing, not top speed.. 65... mph.. cruising.

An apples to apples comparison is going to be nearly impossible to find. But look at this link, Compare Side-by-Side

At cruise, a car doesn't need much power at all compared to how much power it needs during acceleration, particularly if the vehicle can't feel underpowered. So what has to happen, and what we're finally seing automakers doing, is producing smaller displacement/high(er) boost engines. This combination produces power comparable to a larger displacement engine but much lower fuel consumption while cruising because the vehicle does not require the power.

If you want to turbocharge a vx engine you're going to increase fuel consumption. If you instead get an engine half its size and increase compression, add direct injection, add a turbo, properly tune it, and add a lower gear ratio top gear, you may very well improve efficiency.

Merely aiming at efficiency... closer to 0 inHg on Turbo motor (without going positive) to increase intake temps (warm air intake) and increase VE SHOULD yield more though correct?.

No, example, my cts cruises around 18"hg vacuum. Add a turbo and cruise at 0" hg vacuum? What do you suppose would happen to fuel consumption?

Lol, id be cruising at 150mph!!

Edit: if you want to reduce fuel consumption, you either need to reduce air intake(warm air intake) or increase the equivalence ratio(lean).

Would not 'smart people' assemble, rather than unite?

Maybe I'm missing something here, but as I said before, if 2 engines are the same displacement, the turbo one, if it is making boost is making a lot more power. If you back off the throttle and run it off boost, the NA motor will get better mileage, partly because of the drag of the turbo, but more so because it is a low compression engine.

Yes, but there's a middle ground. Running just barely any boost and staying out of enrichment.

At 50MPH my Fiat gets 70- 80MPG. My 2 ton van (diesel) gets 60+ MPG @45MPH.

So it's not all bad for turbos, but I'd say the amount of optimization that went into those engines is well beyond what a bolt on DIY kit would offer.

You're thinking incorrectly...and maybe I am too...I'm just thinking a small turbo would "push" more air in rather then making engine suck.

Like i said ... drag of turbo is like a muffler if anything.. so delete a catalytic converter (rear one) when you install turbo.. offset Mechanical efficiency.

And I'm never refering to POSITIVE PSI.....

Only vacuum....

Small turbo at 18 inHg vs N/A at same 18 inHg .. thought turbo would do better.

(I've adjusted my thinking now)

Turbos are ONLY used to increase power on gas engines.

By "pushing" more air into the engine the ecu will see a lean condition and increase fueling. Turbos are for reducing brake specific fuel consumption (more power per unit of fuel), not reducing fuel consumption.

A diesel is a whole different story. A turbo increases power and mileage. Remember the difference. Power is controlled by fuel, not air. There is no 14/1 ratio to maintain. This is why basically every single diesel made today that makes more than 50 hp uses a turbo.

I wasn't saying push MORE in.. i was saying less of the engine having to SUCK in and more of the exhaust spinning the turbo and PUSHING SOME air in...(not MORE..just some.. less effort on motot)


Both turbo and na cars are at same inHg for this conversation between me and you.. think we are gettin somewhere

Actually, his thinking is spot on.

You seem to have trouble understanding how a gasoline engine controls power output. If you are close to atmospheric pressure at the intake manifold, you are either running a NA engine at wide open throttle or a turbo engine at a lower throttle opening combined with boost. The result is high power output, which as he said will result in a much higher speed.

I think the problem may be that you are thinking in terms of engine efficiency, rather than fuel mileage. A turbo engine, running with some boost very well may have a higher "efficiency", the problem is, it also has way higher aero drag because it is pushing the vehicle at a high rate of speed.

Maybe I'm thinking efficiency will improve mph too much. And i was thinking lowèr inHg was just making it easier on motor. Makes sense though now.....

What about same inHg though.

So you're talking about reducing the pumping losses of a n/a gas engine, i.e. the vacuum. This will reduce fuel consumption but ONLY IF the amount of oxygen is not increased. This is why warm air intakes are good because they reduce the density of the air and thus the concentration of oxygen and then the ecu doesn't have to increase fueling (as much).

I'll say it again for emphasis, turbos only increase power in gasoline engines.

Ok I'm not even gonna bother reading the rest of the responses, but Turbocharged engines are more efficient than NA engines period. You are taking waste gas and turning it into power, and the engine doesn't have to work as hard to make the same amount of power. You are also adding back pressure in the exhaust which is another +1 for efficiency.

Im not going to argue with... Anyone about this. I have been beating this dead horse with people on these forums forever. I'm currently in the process of turbocharging my insight, and when I'm done, I'll post the efficiency gain results.

well you get more torque. And i've owned NA and now a turbo celica all-trac, and the turbo sure is a bit lazier at the lower rpms (and drivetrain loss) but the twin-scroll turbo for sure makes up for it.

but i kinda want to swap a VVTI 3S-GTE from a caldina into my celica. And add water injection.


or some other toyota's turbo engine, would be cool to get a lighter but same hp engine for improved weight distribution. Maybe a 20V 4A-GE as a turbo XD

Of the 3 not so old VW engines the 1.9d turbodiesel, 2.0L N/A and 1.8t turbo gas. The 1.8t got the worst milage and on top of the lower MPGs it needs more expensive premium gas.
In stock emissions compliant, corner cut, cookie cutter engines the turbo will get lower fuel milage.
To make a turbo gas engine get the best cruise mileage possible you need to make it act like the N/A engine as much as possible.
A turbo gas motor could be made to get better mileage than an N/A engine, but I wouldn't bother.
Another big thing for turbo gas motors is can it use regular gas?

Honda EarthDreams 1.5T can.

Warm air intakes do it enough? Ok gotcha

As long as yoi dont go to deep into boost.. like i wasn't going to do. Yes.

Not true. It can do 15psi on 87.

Psi is irrelevant, It depends on the turbo. CFM is what is important and not to mention the k03 on the 1.8 Volkswagen SETUP for turbo didn't even run on 87 octane.

Ok, well, Honda makes 177hp out of a 1.5L turbo engine that runs on 87 pump gas, and gets 45mpg highway. Just saying.

Has advanced ignition and cam timing change, direct injection, atkinson cycle and extensive friction reduction measures.

All those are why... cam and ignition timing are huge..

Hell 5.0 coyote can run 87 octane... they dont make their advertised power tho

What a few others have said and I will agree on most of the engines that are turbocharged mainly do it for power and just use a smaller motor but yes there are few Motors out there like the Earth dream setup that are specifically for fuel mileage and they do it very well.

(Using talk/text) so if their is any grammar or fragmented sentences. My bad



Edit: because i have the turbo off my civic we can try on your miata at 15psi.... im not sure it will like it.

I was hoping this thread would die a natural death. :(

#26 ——>#29

I count three.

I mean... to be honest you don\'t have to be a dick.

Could contribute something useful. Might be asking a bit much

I was only trying to be helpful.

I don\'t unsubscribe to threads, but I\'ll just start ignoring the notifications.

HAND

The die a natural death comment then?