Article: adding a turbo to improve efficiency
 

Yet another good AutoSpeed article: Turbo'd for Fuel Economy - The way of the near future

A good overview of the issues around turbocharging.

The writer compares two 2.0 VW motors, one normally aspirated, the other turbo, and concludes:
Of course, to gain the most from the lower end torque, you really need better gearing.

A turbo is definitely high on my wish list.

Not exactly. You'll still be taking advantage of the increased low end grunt while accelerating, which is when most of your high fuel consumption rates are. You can shift at 2k and get good acceleration.

Of course, having higher gears would add even more benefit.

good article, i noticed that they never did actually tell you that when your going 0 to 60 in 7 seconds, that you are getting terrible mileage.

I think most of the gains they got in mileage is from the gearing. The turbo just let the higher geared car drive more like a normal car. If they can find identical cars one with a turbo and one without there probably wont be any difference.

Adding a turbo to a car and not changing gearing or going to a smaller motor is not going to help anything but acceleration really. Kind of a similar problem of doing aero mods and not changing gearing. The engine load decreases but the rpms are high enough you are still using a lot more gas than you really need to.

"or going to a smaller motor"
that i would like to see, two engines same power, one NA, and one turbo'd.
that would be interesting, OK who wants to do it?

PS. power and economy are usually inverse.

Oh, and let's not forget Autospeed's series on "The Story of Turbo'ing a Hybrid Prius" (1st gen. model.)

Where the author concludes:

He points out that, not surprisingly, the car's CVT contributes to the gains because it permits the revs to stay lower for a given road speed.

Parts 1 through 5:

http://www.autospeed.com/cms/A_2658/article.html
http://www.autospeed.com/cms/A_2659/article.html
http://www.autospeed.com/cms/A_2660/article.html
http://www.autospeed.com/cms/A_2661/article.html
http://www.autospeed.com/cms/A_2664/article.html

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I'm vaguely aware of a couple of Honda Insights that have also been turbocharged.

The turbocharger itself modifies the thermodynamic cycle of the engine and increases efficiency.

You can change mileage without changing gearing. The whole point of the article is to point out that a turbo will increase low end torque therefore the driver can upshift much earlier while maintaining the same acceleration. The 97 Volvo 850 is a good example of this. The non turbo 850 produces 168lb/ft at 4700rpm while the low pressure turbo produces 190lb/ft between 1800-5000rpm. While the fuel economy between the automatics is identical (LPT was only offered with auto in US) a manual trans car would give you the ability to upshift at much lower rpm.

I'll go out on a limb and say that while the ability to upshift sooner while accelerating is good, it's going to have a very small impact on overall fuel consumption, simply because we spend so little time accelerating, vs. time spent cruising (assuming you're not pulsing & gliding).

So unless you're driving a garbage truck or mail delivery route, better gearing matched to the turbo's good low end torque is what will return the largest fuel economy improvement.

I'm going to second Metro's comments and agree with Coyote X. Turboing increases power density. That will allow small gains if you can take advantage of increased low rpm power. However, the main gains are from regearing and using a smaller engine.

I guess i'm looking at this from the point of my mostly street level commute, where I don't have a problem with high revs, but I would like more torque at low revs. My D16 tq curve has a very steep climb between 1800 and 2500 where it reaches a tq plateau, so in order to stay producing high tq values, I have to shift at 3000. I'm at 2000 at 45mph in 5th, which makes for slow response on pulses.
if a LPT can shift that plateau to where I'm reaching near max tq at 2000, acceleration would benefit greatly, and I can shift at 2500 to stay in the torque band.
On the short highway portion of my commute, I'd love a 6th gear, I'm at 3000+ doing 60-70. Aero would give a huge benefit here.

I agree with the aero + gearing idea, but all most of us can do is the aero ;)

I've spent some time with the 80s Chrysler turbo cars and they CAN return some decent mileage. I had a 86 Daytona Turbo with automatic. I could keep an average of 24 with mostly city driving, no freeway. But I also had to resolve all the vacuum line issues and ignored maintenance of the previous owner. The first tank of gas after I could keep it running was only 10 MPG...

I've considered adding a turbo to my Jeep, usually just to make it easier to drive in the mountains. But even at only 6 psi it will provide enough extra torque to make it worth while. The hard part is matching the turbo to the application. I don't want or need to make killer power, but being able to keep a higher gear as mentioned will have an effect. Especially since I do drive a mountain pass to work...

And of course the main caveat... Absolute power corrupts absolutely.

It is easy to say one wouldn't go beyond a certain boost level, but I have seen it get out of hand... And dragracing is completely different...

Yeah, I took about two weeks away from ecomodder to read through as many of the autospeed tech articles as I could.

"Overview" is good description of the article. It'd be nice to have a more information on how to correlate common turbo specifications to an engine size in order to accomplish these kind of goals.

Turbo?
 

If I turbo my electric lawn mower will it allow me to mow my lawn twice on one battery charge as opposed to 1.3 X right now?
Just playin
I had thought of turboing the Metro once a long time ago.
Plumbing issues beat me up.
I looked & i looked but couldn't find one of the turbometro's anywhere. i even looked for a turbo Subaru Justy.
Oh Well.
now i just need to fix what i have and make it as efficient as possible.
S.
HI HO HI HO
Off To Werk
I GO

More reasons for changing gearing
 

During cruising, the turboed car will have worse efficiency than the NA due to the lowering of the compression ratio by about a point. You will certainly need the improved gearing. Of course, you could get away with the same gearing without the turbo, and just be willing to shift the car a lot.

Me, I'd take an even taller gearbox, a bigger turbo (with good horsepower gains for when I want them), and a methanol injector to keep the compression ratio up. Actually, a DTI would make a lot more sense...

wumpus, welcome

if the turbo'd engine were of much smaller displacement, wouldn't it be up on the boost even at cruise? turboing doesn't help economy much unless the displacement is reduced proportionately.

gearing is good, but I can only lug the engine so low before i need a bigger flywheel.

The article specifically mentioned a pair of 2.0l engines. In practice, I'm not sure the small turbos are more efficient than bigger NA engines, but the engine in the article was different from the turbo=sports car that marketeers seem to think is required.

Yes, in practice they can be. And when designed for it, they are. This is the case for power generation (when turbines aren't used) etc. Unfortunately, for us, auto mfrs like to use fuel for it's heat capacitance rather than it's combustible characteristics - but that doesn't mean things have to be that way...

"Unfortunately, for us, auto mfrs like to use fuel for it's heat capacitance rather than it's combustible characteristics "

could you explain, i don't understand what heat capacitance is.

Thanks, trebuchet03, i can google it from there.

In order to prevent detonation under boost in a turbocharged engine during high load, the computer will sometimes increase the air fuel ratio from the stoichiometric 14.7 to 1 ratio to something closer to 13 or 12 to one. Because liquid fuel has higher latent heat than air, the extra fuel injected into the engine is used to absorb heat from the combustion chamber and prevent detonation. This fuel does not get burned in the combustion chamber (not enough oxygen) so its wasted out the exhaust in the form of extra pollution. One solution to this problem is to maintain the 14.7 AFR even at high load and inject water to prevent detonation instead of fuel.
This is was also common practice in most non turbo fuel injected engine but to a lesser extent until very recently. Manufacturers got away with this practice because EPA emissions test did not include a full load (throttle to the floor) cycle.

tj got it.....

To add to why they do it.... It's a way to increase horsepower by having dynamic compression higher than it should be ("should" meaning low enough such that extra fuel isn't needed to remove heat)

So, I was reading a little bit about BSFC (brake specific fuel consumption, or the amount of fuel used per horsepower) and saw that the lowest BSFC occurs at peak torque (assuming the air fuel ratio remains constant). With this in mind, we could build an engine with a turbocharger that runs at peak torque while remaining at 14.7:1 by altering boost pressure.

In the performance world, they set the boost pressure as a constant for performance reasons. This requires the air fuel ratio to be modified to prevent detonation as mentioned above. However, if we were simply to lower the boost pressure to avoid detonation, we could maintain the highest possible torque the engine is capable of @ 14.7:1 air fuel ratio. This would therefore give us the lowest possible BSFC. Now, keep in mind that this would only be at WOT (no different from any other engine), so pulse and glide would need to be used. This is also where gearing becomes so important, especially for highway driving so you don't have to P&G everywhere.

This also brings up a few other things. For example, what if your engine can handle a lot more torque? Now, you have a beast of an engine in your car and the added torque now creates wheel spin because your accelerating at (near) WOT. Well, now we're back to using a smaller engine. Also, what if your engine can't handle more torque? Well, then you won't see much in the way of gains. You could therefore look into alternatives like head modifications to supress detonation, coating pistons and chambers with ceramic coatings, etc.

Legendary mechanic Smokey Yunick developed a low pressure turbo engine 30+ years ago. Scoffed at by the mainstream because he was using a turbo, but not as much for what most folks used one for. His purpose was to heat the air more than the higher pressure to make horsepower.

Anyway, years ago I wanted to turbo my old minivan. THe V6 was OK, and I had modded it as much as I could short of tearing it down. But I wanted more lowend power. I decided a smaller turbo was going to be acceptable, as I was only going to go with 6-7 psi. What I would require was slightly larger fuel injectors, which actually worked quite well without the turbo (once I pulled my head out and settled a fuel pressure problem...).

Most performance guys factor in extra fuel for the purpose of cooling the fuel charge. Wasteful, yes. Not as effective as nitrous (not in large quantities at least). But useful as a form of "chemical intercooling".

Hmmm, I still have the intercooler I was going to use, out in the garage.

Thank you. I've been telling people this for years but never found any way to explain it other than through the theories of physics, thermodynamics, and common sense. ;) Also, I'd love to see numbers (per usual :p)

This bolsters my theory that a LPT that shifts the peak torque down in terms of engine speed will greatly help FE on acceleration.

one of the first turbo'd US production engines i remember was about a '62 buick starfire. it had water injection. are telling me that the first one was done right, and we have gone down hill ever since.


On a different note: why not take two pistons, rods and 4 cam followers out of one these tubo'd 4cylinder's. Wouldn't that keep it out of the waste gate, and on low boost and be eco as heck?

He didn't call it a turbo - he was adamant about calling it a homogenizer. Fuel was injected BEFORE the turbo :eek: I got to speak with someone that worked with him many many years ago. He said the car worked great, got extreme FE and good power but it had one critical problem - it wasn't reliable. He had said the engine was being rebuilt quite frequently.

I personally wouldn't say requiring water injection means it was done right... WI is a band aid because there's too much heat. Perhaps the same setup on modern fuels with modern engine management on a modern engine would fare differently though :)

I think the best technological implementation of a turbo to improve fuel economy would create one hell of a complicated engine.

First, take a small atkinson cycle engine - 13:1 CR with an effective 8:1 CR. Use a small, efficient turbo ducted through an intercooler to raise the effective CR to ~10:1 (i.e. miller cycle). Use variable valve timing to increase the CR to 13:1 w/ turbo (which should already be operating in its most efficient range) and switch the injectors over to feed from a smaller tank holding 91 - 100 (avgas?) octane fuel during acceleration. Route the spent gasses through the primary turbo and feed the residual gas into a turbocompound that sends power back into the flywheel.

Ofcourse, the impact on backpressure will have to be balanced with gains, but it's an orgy for the mind :D. The coolest implementation I have seen so far is the Napier Nomad engine, even though it's a two stroke. Essentially, a diesel engine is mated to a turbine that drives both a compressor and a CVT attached to the crankshaft. During light cruise, the turbine powers the efficient axial compressor and feeds residual energy back into the flywheel. During takeoff when extra power is needed, fuel is dumped into the turbine making a temporary (and inefficient) turboshaft engine.

Link: http://en.wikipedia.org/wiki/Napier_Nomad

- LostCause

I really like this idea... But I'd say remove the separate fuel tank and such....

Just go for a miller cycle engine with variable valve timing. It's probably not very difficult to have a valve profile that switches the engine from Atkinson to Otto while off boost... And considering Atkinson cycle isn't new and VVT isn't new and both concepts are implemented into mass produced vehicles - I wouldn't call it complicated at all :thumbup:

Alas, this isn't something that's easily DIYable :( It sorta has to start from the mfr...

Thanks. I figured high octane gas would be needed for the super high CR, but water injection may work. I like to think big, not practical :). I suppose I might as well aim for a fusion reactor :p.

I was just thinking, its 1:00am on the west coast here so it must be 4:00am over there. Holy crap man, get some sleep! :D Forum, so, addicting...

- Lost Cause

An 04 Cobra buddy has a Nitros setup o his car, he uses a 1 gallon fuel cell filed with 107 low lead. works great for Boosting fuel octane during accel (extreme). I've tried to get him to run ethanol in it (107 octane I believe) but he never will. I don't see why the same couldn't be done with an efficient design.

I knew I was forgetting something. Homogenizer. After seeing some really bad sneezes, I'm pretty sure I do NOT want fuel hitting the compressor blades...

I'm rather surprised I even remembered that much considering I haven't really given much thought to it in almost 30 years...

Early turbocharged engines used water to cool the intake charge because they didn't have intercoolers.

I've seen a dozen or so "draw through" carburator Setups, all drag strip "only" cars.
They all claimed no issues . . . . .
One advantage is that you do not need a BOV, main disadvantage I've heard concerns over is intake side turbo seals (suck the oil out) I have no Idea if they are founded or not.
I would "ass"ume that the turbo would vaporize fuel pretty darn well.

I have run water injection (10% fuel flow) pre turbo before with no ill effects (5k or so on the street) Vanes looked just the same.

For a street/competition vehicle drawthrough is fine. Big issue with a draw through, if you develop a leak between the carb/throttle body and turbo, it COULD run away... This was a major reason Chrysler went to a blow through design after the first couple years of their turbo cars. And, it is easier to intercool before the carb/throttle body.

I don't know about this. But has anyone thought of using a supercharger? From my "tuner car" knowledge, most turbo's make power at the higher end, while superchargers make power more at the lower end.

I could be wrong though, and I'm not much up on how superchargers have an effect on FE, so please correct me if I'm wrong.

Superchargers are powered off the crankshaft, and make power pretty low, and lose efficiency as you go faster. They require a good amount of engine power just to turn (naturally, the more boost you want from one, the more power it takes to turn one...). As I recall, the production GM 3.8 liter V6 cars used some sort of bypass to avoid intake restrictions at higher speeds. But I could be wrong. Centrifugal superchargers are more efficient than the roots style, but again are limited by how fast they can be turned by the crankshaft... A turbo is powered off the exhaust, free power. Has very little parasitic drag on the engine.

There are turbo technologies to allow one turbo to make power throughout the powerband. These "Variable Nozzle Turbos" can easily be referred to as variable displacement too. Basically, the vanes in the compressor side can be adjusted to allow very little or a great deal of boost. If sized correctly, a VNT can act like a smaller turbo at lower engine RPMs and adjust the vanes to act like a larger turbo for more power or efficiency at higher RPMs.

Chrysler toyed with these in the late 80s early 90s, but they are found in very few cars. Chrysler turbo cars are lumped into 4 basic categories, Turbo I which is non-intercooled (early models were draw through, later were blow through, and even later still had increased displacement), Turbo II were always 2.2 liter and intercooled blow through. Not exactly rare, but hard to find (forged crankshaft and crossdrilled heads for better head cooling). Turbo III which was only offered in Dodge Spirit RT and Dodge Daytona RT was a 224 HP DOHC package that consisted of a 2.2 block with special heads. Last was the Turbo IV which was the rarest of all, 2.2 SOHC was essentially the same as any other 2.2 turubo motor, the magic was the VNT turbo and electronics.

Well, Probably rarest of all Chrysler turbos were the 6 3.0 liter V6 engineering mules that escaped from Chrysler. Originally intended for a special model of Daytona for 92 or so, the performance was such that Chrysler felt the Daytona would have drawn too many sales from the Dodge Stealth (same as a Mitsubishi 3000GT) and was nixed. How the motors escaped is anyone's guess. I do know where three of them are, two are in running cars (one is running around in Columbus, Ohio!)... I really only mention them in passing because they were the motors that got me thinking about turbocharging my own 3.0 liter V6 in my old minivan...

And I guess if I mention the Mitsubishi cars sold by Chrysler, I also need to mention the Starion with a tubocharged 2.6 and the Mitsu Eclipse/Plymouth Laser/Eagle talon triplets too. The triplets could be had with turbos and AWD... But I digress from the VNT discussion.

It is my understanding some diesel turbos are VNT. But not having paid a great deal of attention to diesels, I don't know which use them, or if any foreign manufacturer uses them. I can't imagine why not though.

Reiterating zjrog's post...

SC do not recycle power - the use power putting a load on the engine.
Exhaust driven TC recycles waste heat into usable work.

Variable geometry turbines solve some of the issues with operating range. But if all you want is low end boost - use a small turbo :p

Then... There's the Comprex supercharger... Which uses exhaust pressure to directly compress intake air... And synchronized by a pulley. The pulley isn't used to compress air, so you don't have the power consumption of a supercharger. Calling it a supercharger is a bit of a misnomer, but eh...

http://www.supercars.net/pitlane/pics/1315879d.jpg

The only production car to ever have one was a Mazda Capella (think 626) Diesel.

Pressure-wave superchargers are dope, and rare as hen's teeth.

One example of a pressure wave supercharger