High-MPG Corvette
 

I think I have posted on this before. MPG is more a matter of how you drive than what you drive. Even a 400 HP Corvette can get pretty good MPG if driven well.

2009 Chevrolet Corvette MPG Test Drive: Will the Vette Meet New CAFE Standards? - Popular Mechanics

Now I personally have no use for anybody that drives 10-under the posted limit. In my view they are as big a hazard as the aggressive driver. FWIW, my sim agrees with the link. Driving the limit would get about 30 MPG.

Now if the ‘Vette were available with the 4.5 liter diesel V-8 GM had to drop, 50 MPG would be easy.

Too bad Corvettes are so headroom challenged. I could get a distressed C5 or C6 and convert it to a Cummins 4BT3.9 and put some even lower rolling resistance tires on it and probably get 40-50 MPG easy.

i'd drive a 50 mippig vette no doubt.

for the money, i'll stick with Cara.

A stock C6 coupe has a wind-tunnel measured CdA of about 8 square feet..

Not a bad start.

Skinnier LRR tires, wheel skirts. Some sort of "plug" for the tail. Other than the engine swap, the whole project is an adventure in fiberglass bodywork.

Gotta find a beater or salvage C6 to start such a project. The little guy has to do it. Ain't gonna happen out of the husk of GM. The Corvette will be lucky to survive at all.

good luck with it ;)

i dont remember what gen, but some of those corvettes, the tail piece comes right off in one section, leaving you with a good starting surface, and a $2000 piece to sell... more if you don't keep the tail lights.

Given how much it costs new, a Tesla sedan would be a better deal.

Forget a diesel if someone is interested in the sportscar aspect, it'd throw off the weight distribution. Just swap one of those cylinder deactivation head setups on and manually actuate it for good ~40-50mpg@55-65mph. Anyhoo, the only danger a driver going 10mph under the limit presents is to the other drivers who shouldn't be driving in the first place. It's not as if noticing another vehicle is driving slower is rocket surgery, and if someone can't deal with another car going ten mph below the limit, what happens when there's a wreck up ahead and they have to deal with a few vehicles going 55-70mph under the limit?

Edit- I suppose this is what can happen.

Well, it kinda does matter what you drive. 32mpg hiway corvette? enh... 45mpg corvette? I'm listening.
http://ecomodder.com/forum/showthrea...-avg-1128.html

P.S. Speed kills.

It's also a matter of where you drive and which route you choose.
Freeway driving up a grade into the wind is worse than driving lower (speed limit) speeds up gentler grades into the wind.
I've done some testing with my Scangauge (and some fillups) and determined that freeway driving doesn't always give the best MPG
My Mustang may not look quite as cool as a Corvette, but it cost less than half as much.;)

No doubt, 10 under is the faster guy's problem.

Speed limits are speed limits. The law doesn't say you have to drive at max speed.

You can go all the way down to min limit for your road. If some ****head doesn't like it, they are free to pass.

We have farm implements, grain trucks, you name it plodding along. What are ya gonna do Dave, ram 'em? :rolleyes:

Be an extremely inattentive driver, pull up on one with a speed differential of at least +60 MPH on a back road, and show him that your car fits in one lane sideways, and your windshield is clear enough to wave through...

That got me to pay attention a bit more on back roads... the waving part didn't happen, but drifting in a Sunbird kicks ass.

Many cylinders + 6 gear ratios = low revolutions per minute on the interstate = good fuel economy

32 mpg = not that great ;)

I would humbly argue that for an 8 cylinder sports performance car, it is pretty darn good :/

It's certainly good enough to avoid the guzzler tax, but getting a vehicle, especially something with a manual trans that's as small/low drag as a vette, to do better than 30mpg@55mph ain't too hard either. I'm hesitant to say it could be done w/ gearing alone, but it ain't like cylinder deactivation is anything new. It's just that people who are paying fifty grand and up for a sports car couldn't car less even if it could pull ~40-50mpg@60mph. All that's needed is a tall enough sixth, and a gear lockout in order to avoid the ~$8k ($10k?) guzzler tax.

hyper, my issue is that the OP wrote:
But now we have to qualify it with "good for a corvette", and even that isn't that good (because the engine has to fight itself and huge tires and downforce, basically it wasn't designed for MPG).

How you drive does make a huge difference, but only in terms of some percentage of what the vehicle is capable of getting in MPG, thus it is not "more important" per-se. If how you drive was really more important than what, then with the right driver, these two should be able to get about the same mpg, or within %50 anyway:
http://www.inhabitat.com/wp-content/uploads/vw1l2.jpghttp://nixonisinhell.files.wordpress...ummer-limo.jpg


Of course if OPs point is to say "use what you got" then that is a very worthy consideration. Please do take the time to wring the most mpg out of your vehicles. Takes energy to build vehicles too. But, this looks like a commercial for new corvettes, with false logic, so I don't think that is the point. Worried stockholder? I dunno, what makes people jump to conclusions like that?

Cylinder deactivation is not really a good solution.

Even if those cylinders don't have any vacuum. . .have you tried to push a piston in a cylinder? Its not bad if you are just moving one piston through the cylinder, but even then. . .it requires a hammer and a block of wood. To turn the crank with no vacuum on a 4 cylinder I have to have a 2 footer and still pull hard enough that working out later would be a mistake. The engine is fighting that same force about once a second in a v8 if you disengage half the cylinders(by disengage lock the valves open during compression, intake, exhaust and expansion, shut off sparks and injectors).

If you really wanted to make a vehicle sporty but FE friendly as well you have pretty much 2 options. Forced induction from a supercharger that you can switch on and off with a secondary air intake that doesn't have to flow through the pre-cooler, compressor and extra piping or two small engines with the ability to completely disconnect either from the drivetrain completely and deactivate it.

Option one is obviously more simple. Its also obviously cheaper(especially if you do it yourself).

Option two is much more complicated. Its most likely 3-4x more expensive and you have to do it yourself.

Most people chose the charger and an on off switch, but those who chose the secondary engine have something thats really honestly worth bragging about. If you for example took 2 H22A redtops and dropped one in front one in the rear you'd have more hp than the 08 corvette(430 for the corvette and 437 for the twin engine). IT also still leaves you the option of integrating forced induction on whichever motor you won't be using for the FE runs(or both if you go with a supercharger-switchoff). Another large advantage to this over the standard corvette block. . .they have 2 valves per cylinder whereas the h22 has 4.

It also buys you awd that doesn't get bogged down at launch like every other awd system ever made. The problem with AWD arises with the differentials to split the power. Even the GTR's enormously expensive drivetrain bogs down as it switches power over from RWD at launch to AWD pull, given its much better than anything else but it still happens. The only expensive linkage to make sure each engine is sharing the load equally. . .is the billions of dollars of. . .asphalt.

Theoretically I am a fan of the twin engine idea, but practically. . .its not feasible. The advantages two engines buys couldn't be outweighed by the difficulties in manufacturing it. Yes if something goes wrong you could limp home on one engine without further damaging the other at all, but you would need to build a rear engine mount, move the fuel tank, and build a shift linkage that mated up to the transmission in the front as well.

You'd buy a Lotus. Pretty close to the top of the US CAFE numbers every year, sometimes #1. Or you could update my old Austin-Healey Sprite.

But first you have to get away from the idea that stuffing a 400+ HP engine in a car is what makes it sporty. That's like trying to turn a bodybuilder into a gymnastics champion :-)

I agree the weight plays a huge problem. But if its going to be the size of a corvette and you rip what you can. . .the next and only thing to increase go is hp/torque.

But I agree with James, smaller lighter and more nimble feels sporty. If you have be heavy. . .

As long as we are discussing speed and weight:
Nascar (3400 lbs, lopsided distribution o)
Formula 1 (min 1334)
Rally racing, determined by natural selection :)

2 wheeled drifting in the snow anyone :D , though I think this drive has succumbed to inertial forces.
http://upload.wikimedia.org/wikipedi...ot_206_WRC.jpg

Nascar is muscle cars, not sports cars... ever watch those clowns try to run a road course... ha... what a crap shoot comedy show that is. I'm glad to see that they are at least trying for FE in a sports car. The big point here is that people paying that kind of money for that kind of car don't give a isht about FE - they ONLY want to tell their buddy's how many ponies are under the hood, and look cool with their mirror shades flooring it to the next stop sign. Kudos, IMO, for trying to boost the MPG.

Compressing the trapped air and the extra friction from the shut off cylinders certainly isn't as good in terms of overall FE as going w/ a properly geared 4cyl, but it's still way better than an improperly geared V8.
Iono, both those sound really complex compared to shutting off a couple cylinders and increasing mileage by a good ~50% at low loads. Granted, they might be good for a ~60% increase instead of a ~50% increase since there isn't as much cylinder friction and no heat loss from compressing/expanding air in the close cylinders, but I don't think the extra couple mpg is worth all the effort/complexity.

Forced induction also usually means a lower CR, which is bad for FE. I lost 3-4 mpg going from 9.5:1 to 8.0.

Like any good project, the key is in the upfront costs. This project requires that I find a distressed Corvette I can pick up cheap. Just gotta keep looking.

The 'Vette offers one other thing: I can easily score 2.73 gears for one as all automatic C5 and C6 'Vettes come with 2.73 gears. That gets me down to just under 1100 RPM@70 RPM. Drivetrain nirvana.

The Cummins 4BT3.9 is about 150 lb heavier than a LS2.

Driving slow is a logical paradox. You drive because you want to get somewhere faster than a walking speed. The most energy efficient speed is zero - you simply don't go at all.

I like to maintain at least a foot in the mainstream camp, but I drive so much that anything over the limit for as much as I drive guarantees you a ticket. Bad enough that so many jurisdictions are writing "revenue tickets." I don't wanna give 'em any more, but I do make the trip for a reason.

Looking from the other side, there are just not a lot of places in this country where you can drive your 400+ HP Corvette at anything approaching its top speed without risking - at the very least - serious speeding tickets. But there are any number of roads where the white speed limit signs say 55 or so, and the yellow signs with the curvy arrows say 20 :-)

With 2.73:1 gears you could move to smaller diameter, narrower tires and generate some clearance for fender skirts.

Supposedly a 4BT is 700lbs dry w/o an intercooler, while an LS2 is supposedly at ~450lbs w/ accessories, so we're looking at a ~250lb more weight at least. There's also going from ~400hp/3000lbs to ~150hp/3250lbs, so we've gone from a two seat sportscar to something w/ about the same power to weight ratio as a new Prius that gets the same or worse BTU adjusted mileage and can only carry a couple people. To each their own I suppose, but if I'm going to the trouble of finding a vette as a donor chasis, I would at least want it to still behave like a sportscar. I think a C6 w/ a blown engine, preferably head issues, along w/ an AFM head, would be the lowest cost/best performance/easiest solution, unless of course the owner wanted to run WVO or something, then they have to go w a diesel.
Um, at 0 mph, there's no context for energy efficiency, since the vehicle isn't even doing anything, unless of course it's just idling, in which case the driver is seeing 0 mpg, which is as inefficient as we can get. In terms of driving slower than traffic, there's no logical paradox, just a desire for lower transportation costs and/or greater safety in terms of accident avoidance.

Something tells me that you're probably not going to cram a 4BT into a Vette without a dry sump oil system, a huge cowl bubble on the hood, or both.

V8 engines are wide, but quite a bit shorter than straight-up inline engines. The 4BT is straight up, has a pretty long stroke and long rods, and was not designed with anything less than a medium duty truck package in mind.

If you could install it at a 30-45 degree angle a la /6 and make it work it might fit, but good luck getting the oil to drain properly and the cooling system to burp air out.

There have been a handful of guys who have stuffed 6 cyl Cummins B engines in older 'Vettes. Whether they used dry sumps, I don't know. Bubble hoods are common among modified 'Vettes and are available off-the-shelf. The four may have some minor clearance issues by the problem is not insurmountable. The Cummins 6 cylinder weighs over a half ton and would make the car too nose heavy. The four weighs about asmuch as a 454 and there is no shortage of 454 'Vettes (C4 and older) running around.

Too bad the GM 4.5 liter diesel is as dead as OJ's acting career.

The bigger problem for me is headroom. "Vettes are designed for 6'1" max guys. I probably should start with a convertible and make a aero but taller coupe top.

Performance is something I don't sweat. The 4BT3.9 can be easily and safely turned up to over 250 HP. A more streetable approach is only turn it up to maybe 150 HP but double bottle (propane/nitrous) the engine for short bursts of fearsome acceleration. The 6b5.9 has been hot-roddedto over 900 HP, and 600 HP versions seem to be lasting, so a short burst (15 sec) double bottle 4BT3.9 should be A-OK at the 400 HP level.

Another option might be a M-B 617.952 engine, but those make very inadequate low end torque. The Cummins is a torque monster and not a bit put out about running at 1100 RPM.

Don't know about the latest gen, but earlier Vettes were pretty junky. I'd start with something else.

I also would avoid juice.

The 08s weren't bad especially the high end.

But Juice is. . .a mistake. Too many variables that can easily go wrong. You nitro dump and your sensors are behind just a tenth of a second and you've lean burned your cylinders about 3 and a half times. Not just a little lean either, very. Also the nitrous oxide is much more flammable than gasoline and much more prone to pre-ignition.

A toasty valve head because your coolant is lagging a little is enough to toast the engine.

Those big hp setups are probably steady state. . .so ALL the components are designed for enormous loads to start with. Yours won't be. Their coolant lines are driven by turbo pumps, they are running specialty coolant and they probably brush their cylinders, pistons and valves every few hundred miles to keep residue out(think glow dust).

I've seen a few juiced engines that are junked just because a little bit of carbon residue was warm when they started purging. The first couple of lean strokes got it glowing and then nitrous ignites and bores a hole through the piston.

The pistons afterward make for good conversation pieces. If its going to drop big power all its systems will need to run as if its going to do it all the time otherwise they go bye bye at the wrong time.

What?
 

Nitrous oxide is NOT flammable or explosive... it's mostly nitrogen, an inert gas. The Oxygen part of Nitrous Oxide is what actually does the work... the Nitrogen is a stabilizer. Either way, that BS part of the Fast and Furious movie where the car exploded b/c the Nitrous bottles ignited was obvious Hollywood Syndrome.

Yes, you can burn up an engine running Nitrous Oxide... but Diesel engines don't run on a "lean or rich" principle... they're almost constantly lean, unless you really turn up the injectors. If you turn up the injectors too high (advance the pump and get into the throttle enough), you need more air than the engine can suck in, even at 100% VE... so you add nitrous. If you don't want to tune your injectors and pump, so you can maintain OEM efficiency, you can get more fuel by adding propane, and get more "air" by adding nitrous... it's a killer combo.

Ah, My bad I didn't catch it was a diesel. disregard all of that then.

Reliability aside, the $/hp ratio favors chebby gas engines, and w/ a taller rear end, the stock six speed, and manual AFM, the $/mile would be pretty close too. Heck, a vette aside, someone could grab a brand spanking new vortec 5300 engine for about a grand less than used 4BTs go for on eh4y, shove it into a mid 80s/early 90s manual Camaro (maybe mess around w/ the rear end/trans ratios), and have a peppy muscle car w/ a brand new engine that can pull ~40+mpg on the freeway for a few grand.

40 with a V8? I'll believe it when I see it.

Just out of curiousity, if all it does is add oxygen, then why not inject pure oxygen instead?

Stability... if you add pure oxygen, the mixture could lean out excessively with very little pressure in the lines, which could cause a serious problem... that on top of the fact that Oxygen alone isn't specifically stable, and reacts with just about everything it touches.

Adding Nitrogen to Oxygen stabilizes the elemental oxygen so that it doesn't react with other gasses before entering the combustion chamber, and since nitrogen is mostly inert, it actually helps to cool the cylinder during N2O use, to prevent hot spots and detonation.

With a hot enough combustion chamber, you could actually use steam as an oxidizer... but you'd have to get the chamber hot enough to distend the bond between hydrogen and oxygen, and then you'd end up with quite the machine... water for fuel, actually.

Didn't ya see it already? Granted, gas engines are a bit more finicky and need to be run at a higher load to see the same (energy adjusted) BSFC, but it ain't impossible, just unlikely because most people w/ enough money to spend on a muscle car don't give a crap about the $/mile side when they're driving it.

I just know how tough it is to hit 40.

There is an enormous amount of experience out there with hopped-up Cummins B-series engines. A 4BT3.9 is nothing but a "12 valve" Cummin 6B5.9 with two cylinders missing, so all that experience is applicable.

A LS2 makes 405 HP. How many minutes of full power do you suppose that a LS2 actually see in its service life You can get some serious tickets by driving 175 MPH.

The diesel is what pushes a 'Vette over 40 MPG. You could put an itty-bitty gas engine in it but I don't think 40 MPG is possible without competition-grade hypermiling. The diesel, with its higher efficiency does it easily.

The propane/nitrous is there for bursts of acceleration. I specify nitrous to avoid having to put a bigger turbo on the engine (and accept more turbo lag) for maybe fifteen minutes of raw power a year. Its simply "turbo logic." With a turbo, a small engine can have a "Jeckyll and Hyde" personality. Economical most of the time, but powerful when needed. How many turbo cars are at full boost much of the time? They'd grenade themselves.

The little Cummins is straight mechanical and I don't have to mess with electronic controls.

This is the sort of thing I wouldn't mind being wrong about.