jimmy169

I'm a programmer so I actually made my own quick little program to save time and just punch in the numbers (doesn't save that much time actually ). Our vw is auto and I'm assuming your route is much more highway than mine to get a good 10+mpg more. Interestingly, ours is a 2011, probably a decent weight difference too then.

That is pretty mind blowing to me but my mazda is auto and I probably drive a lot less highway than 50/50. Realistically probably 20/80 if that as much as I love to cruise the pike, even that has a decent amount of lights. Just good to see people using math and not just going by what they think they saw between fill ups mileage wise. Makes me that much more tempted to get a 6 speed ls1. Their affordable and would make a fun weekend car that at this point doesn't loose much more in value if anything.


Pretty much exactly what I did, just used the 2 consecutive receipts as note pads and the last one to get the exact gallons I filled up to.

Hardrvin

iTrader: (1)

^ thank you for supporting my argument. How do you improve N? Direct driver is compression ratio. Look it up.

Yes, you can bump up your air density which increases your output for a given displacement, but you have to Puke more fuel in to make use of the air. You're only looking at the aur side of the equation there.

Let's also consider the turbo is an air pump in and of itself, and you don't compressor mass without side affects, and its not 100% efficient either (~70%). So now you're increasing your intake air temp. Take a look at what that does to your N value as well.

LS1vazquez

No, your wrong. The efficiency of an engine is define as the ratio of work done to the heat provided.

N = Word done / heat absorbed = Q1-Q2/Q1

Your placing too much emphasis on compression ratio because anything under full throttle application results in partial compression, thus negating the whole point of having a high compression ratio.

I would love to argue with you endlessly on this subject using long winded hyperbole (but lets consider...), colorful descriptive terminology (puke fuel) and stick figure drawings where appropriate (probably your next move) but I simply don't have that type of time.

You just can't piecemeal parts of equations and suit them towards your argument. It doesn't work that way.

Hardrvin

iTrader: (1)

Am I?

http://mit.edu/16.unified/www/FALL/t...es/node26.html

Section 3.5.1

"The ideal Otto cycle efficiency is shown as a function of the compression ratio"

I will concede that it changes under part throttle, but it's a reduction from your wide open condition.

Here's a "less colorful" article that is easy reading that actually covers part of this exact discussion.

http://www.autospeed.com/cms/A_110204/article.html

Z Fury

iTrader: (1)

The 6-speed LS1s do great on gas for the most part. Some critical points though.
1. The way you drive it matters so much more than the way you drive a Civic. The go-fast pedal will radically alter those mpg figures on the LS1.
2. My Z28 is pretty much stock. I have headers/catback and an LS6 intake, but have never installed them. It is on my bucket list though.
3. The LS1 requires premium fuel. Same as all of the turbo-4s, but an NA 4 will win on gas mileage and gas type. I prefer to enjoy what I drive though.

If you can afford it, try to land a C5. Same drive train but lighter car. I've heard of people knocking down 33mpg highway in one, assuming near perfect conditions. I'd upgrade to a C5, but it would be a fairly lateral move for me, and I don't feel like paying money for a lateral move.

Marc 85Z28

iTrader: (8)

You typed a lot... or rather copied and pasted a lot of information that you clearly don't understand.

deft

iTrader: (7)

My commute is about 45 min, and almost 50/50 highway/city so that is probably part of the difference. Just curious, you're not from central PA are you? We have a good pike for cruising as well.

SparkyJJO

iTrader: (11)

94 White T/A

I think hes referring to the efficiency being lower under part throttle because the effective compression ratio is lower than full throttle. I'm not sure why though, it's going to be a percentage of the full compression ratio, so higher would still be better.

And i bet all his info is from this:
http://en.wikipedia.org/wiki/Engine_efficiency

nate0031

Interesting thread. My own experience is a max of 31 in my 2000 WS6 M6, which was taken after a 400 mile road trip where I drove 60 the entire way. It was at night as well, so there was no traffic to contend with.

My other car, a 1999 A4 Jetta TDI M5 has gotten an absolute worst of 39 when I beat on it and only did city driving, and a best of 56 when driving straight highway between 60 and 65. It's also tuned (Kerma) with a larger turbo (1749VB) and larger injectors (PP520's) putting it at ~160 HP/ 290 TQ. Not nearly as much as the WS6, but not bad for a 2800 lb daily driver.

Hardrvin

iTrader: (1)

Diesel is another animal entirely. Direct injection / lean burn capability make it efficient amongst other reasons. Hence gasoline is attempting the same with positive outlook on improving efficiency and performance. That's part of the reason higher compression turbo'ed gas engines have become possible. The EFI technology is getting there.

nate0031

True. It'll be interesting to see what numbers gassers are capable of as they get direct injection and higher compression ratios. One nice thing about the diesel is the clutch engagement torque and low end torque make it feel like a much larger engine than it is. I should add that my WS6 averages around 26 when I drive normally, about 60/40 highway/city. Not trying to say I average 31, lol. Just that it is capable of it under the correct conditions. Amazes me how it can do so much better than allot of smaller engines of the time. My friends 2003 Taurus with the 3 litre 2 Valve (Vulcan) engine gets a best of 27 on the highway and averages 23-24 daily driving. It even weighs a little less.

Marc 85Z28

iTrader: (8)

That's not a fair comparison. Most vehicles fare well against Fords, even outside of similar models. They're fuel mileage has traditionally been well below average across their entire product lineup.

nate0031

Possibly, but my other friends 2.5 liter 4 cylinder Subaru is lucky to get 24 on the highway, also lighter than my WS6. My girlfriends old Alero, which I had tens of thousands of miles worth of seat time in, and calculated the fuel mileage for, achieved a best of 33 on the highway while averaging 26-27 on daily driving. It had the 2.4 liter I4 'Quad 4'. Better than the WS6, but not by much. My brother's Civic routinely gets upper 30's on the highway, but it literally weighs 1000 lb's less and is a much smaller car. It just seems that allot of people (Not people on this site, lol) think displacement is what gets you good or poor mileage; never taking into account aerodynamics and rolling resistance. I can't count how many times I've told someone my car has a V8 and they respond with, "that must be fun, I bet it really sucks on gas though", or otherwise suggesting it's a gas hog. They never seem to believe me when I tell them it gets better mileage than their V6 or equivalent to their 4. As someone mentioned earlier, putting a small engine into a car doesn't typically give a big boost in mileage because it still requires the same energy to move it along. You just end up with a slower car, lol.

2002_Z28_Six_Speed

iTrader: (19)

Subaru is AWD all the time so not a fair comparison.
Quad4 is a crap antiqued motor. Awful design. Not a fair comparison.

V8s don't get better or similar MPG under similar operating and installation conditions.

Why state your Corvette gets 28 MPG on the highway and then act like 4 bangers that get 30 tank to tank have nothing over them? Congrats because that same 4 banger installed in a similar vehicle is probably getting 34-37 on the highway.

justin455

How is it not a fair comparison? It's a comparison between the fuel mileage that different cars get.

The problem with the statement in bold is that, if you eliminate all other variables, a car with a V8 and one with an I4 will never be under the same operating conditions. Sure, they can be mechanically the same, being driven the speeds, but that will guarantee they won't have similar operating circumstances. The V8 just won't be working nearly as hard as the I4 and that's how you end up with similar MPG's.

If the engines are just perpetually idling, sure the 4 will be more efficient than the V8, but there are too many variables in cars to make a blanket statement about which engine is more efficient. In the case of a T56 LS1 Y/F-body, the variables work well giving the possibility to obtain "good" MPG's on the highway. IIRC you can cruise 80 mph at sub-2k rpm in one, whereas one of the models he mentioned would be sitting at 2500-3000rpm...and an I4 at those rpms sucks down more gas than an LS1 at 1800rpm. I do believe that's all he was getting at. A similar car with an I4 has the potential to get greater gas mileage when hypermiling, but if it comes down to the daily grind and keeping up with traffic, and LS1 won't be working as hard and therefore won't suffer as great of an MPG loss from it's potential.

nate0031

That's actually my entire point. May have just not stated myself well. So much emphasis is put on displacement in and of itself, leaving the more important factors that are inherent to a particular chassy/body unconsidered. Hence my statement that a particular vehicle will require a certain amount of power to drive it along, ergo dictating the required fuel consumption, assuming the engines have similar volumetric efficiency at the required operating range. BTW, this Subaru wasn't AWD. For the reference to the Quad 4 you'll notice I gave both my best observed fuel mileage for both as well as my average for both, and hence was not comparing the absolute best of one to the average "tank to tank" of the other. My point is you cannot simply put a smaller engine in the same car and expect miraculous results, you have to install it under different operating and installation conditions. A more efficient chassy.

Marc 85Z28

iTrader: (8)

I see you failed to read through the entire thread before posting.

Multiple manufacturers market vehicles with different engine options in the same platform. Some are I4 vs V6, others are V6 vs V8. In most cases the difference between the two is a mere 1-2mpg, and some have identical mileage.

The fact that a 350/400/500hp performance oriented Corvette can obtain better fuel mileage than an economy oriented 4 cylinder compact is fantastic. No, a 4 cylinder Corvette would never achieve that mileage due to the gearing necessary to keep some kind of acceptable drivability.

2002_Z28_Six_Speed

iTrader: (19)

Modern four cylinders get 30 mixed driving and 45 on the highway.
A Corvette only gets 30 on the highway.

A Corvette doesn't get better gas mileage than a four cylinder. It might get better than some.


A four cylinder Corvette would get better gas mileage on the highway and in grid lock traffic conditions. During acceleration numbers will be about the same. Say it takes 30 HP to push a Corvette down the road at 70 MPH. The smaller engine is more efficient at this particular non dynamic situation.

SparkyJJO

iTrader: (11)

That's one big generalization, and an invalid one at that. SOME get that, others don't.