Why's the 3.1 weak?

[THe_DeTAiL3R]

 

Here's the one case that REALLY baffles me: the new Corvette. The base 6L model gets 18 city 28 highway. The z06 with its 7L(!) engine gets 16(!) city and 26 highway. Both with manual transmissions. These are pushrod engines and all 8 cylinders are always firing--no variable displacement technology employed. How does an engine with double the displacement manage only 1 mpg worse in the city than my 3.1? Based on those numbers, I would expect to consistently return better fuel economy in a new Corvette than I get in my Cutlass. I just don't know how they do it.

 

Well if my car is SUPPOSE to get like 22mpg "city", and I'm getting 16mpg (because of the short trips, all stop/go corners and stopsigns)... I doubt the Corvette will be pulling 16mpg city. It all depends on how they test "city" and "highway". Is there some official guide to test this properly? I just don't think an average reading from my DIC is anywhere close to what GM says I should be getting.

[Nick1234]

does anything what know at what speed their mpgs stop increasing and start dropping. I wass doing about 73-74 and a 140 mile trip and averaged 31.55555 mpg, and i sat in some traffic.

 

Also another idea i was pondering. I wonder if there is a big difference between motors that come from the factory. There has to be. No one motor can be the same. you hear it all the time, this motor is weak, this motor is fast and is stock....

[Vegeta]

I got in the 40s stock with my 3.1. That was straight highway. I couldn't tell you city anymore, too long ago. Anyway, throw a gen 4 top end on that sucker and see what happens:)

[peeeot]

the 40s!!! whoa.

 

C-Bad, have you ever computed your mpg without the DIC and then compared their respective results? I wonder how accurate the DIC is.

[19Cutlass94]

Well you have to remember, that vette doesnt have to work as hard to get up to speed, and alot of members here beat the piss out of it off the line and rev it up to get going. Thats the difference. ( besides aero. and stuff ) Last time I took my car for a highway trip ( about 4 yrs ago ) I was getting almost 40mpg straight highway. But driving around the city if you sit and idle, there goes your gas mileage down the drain...

[peeeot]

I don't think the corvette mpg can be so easily explained away. If it's just a matter of how hard it has to work, explain to me why a Ferrari 360 modena, for example, which has a 3.6 liter engine making 394 hp and weighing just shy of 200lb less than a base corvette (6L, 400hp) only gets 11 and 16 according to the EPA tests.

 

The EPA tests are not necessarily excellent representations of real-world driving, thus the disclaimers on window stickers that give a range of values around the official EPA value, but they ARE standardized so every car is measured with the same ruler.

 

Earlier I said something about efficiency changes based on rpm, throttle, load, etc. I read something a minute ago that gives a little insight: when an engine is operating at minimal throttle, the throttle plate acts as an obstruction (duh) which actually works against the pumping action of the engine, reducing efficiency. That makes sense, I just hadn't thought of it that way.

 

 

[Rdrckt_92]

my 3.1 gets between 17-20 city depending, I never really have to drive thr highway so I don't know what my milage is there. I dont think the 3.1 is "weak", it isnt the most powerful engine I've driven, not by a longshot, but it isnt the weakest either. My grandmothers focus is weak, it can barely make it up the hill to my house unless you get a good run at it. driving the focus makes me love driving my car.

[mfewtrail]

I got in the 40s stock with my 3.1. That was straight highway. I couldn't tell you city anymore, too long ago. Anyway, throw a gen 4 top end on that sucker and see what happens:)

 

That was w/ "lean cruise" enabled though, right?

[Psych0matt]

i think i average around 20 (3.4), but i still have a few quirks from the swap to work out, as well as new plugs too, but ive just been lazy

[peeeot]

I just replaced the original plug wires a couple days ago and the car is definitely smoother. I wonder if my mpg will improve at all.

[Nick1234]

what is lean cruise

[slick]

what is lean cruise

 

Pretty sure exactly how it sounds. Ben's able to mess with the Air/Fuel ratio, so I'm sure he cut back some fuel for highway cruising.

[Robby1870]

what is lean cruise

 

Pretty sure exactly how it sounds. Ben's able to mess with the Air/Fuel ratio, so I'm sure he cut back some fuel for highway cruising.

 

If the refresh rate on my DIC was right, I could take a video and you'd see, but its hard to even get a pic of what it displays. Anyway, with the cruise on, steady load, you can see the instant mpg go up. Mine usually goes from 32 to 39-40, then comes back down to 32, then starts over again. Pretty neat to watch. Just gotta find some nice flat roads.

[ns87]

I think the 3.1 just is the wrong engine for W body. I like 90 degree engines better, but thats just me

[peeeot]

what difference does the angle make, other than external dimensions? I've heard something about 60 degrees and balance but it didn't make sense to me.

 

[ns87]

Oh. The 90 degreee engines have bigger displacement..... 3.3,3.8. They have more torque in my opinion...idk about real numbers or ratings. I just like them better

[Euro]

i just think GM didnt have any kind of performance in mind when they were desgning this motor. It was strictly for economy/family cars to compete with fuel economy and reliability. theres no doubt they're reliable, so +1 for GM on that one, and fuel economy is pretty good...so +.55 for them on that one too

 

June 05 on my way home from the Michigan w-body meet, i got like 36.2(give or take a couple tenths) mpg, so that was a shocker to me. just normal driving.

 

and one more thing, I'm still impressed at their power from below 3500rpms, i mean when i ran at the track. i got a 2.1 60ft and a 17.5 1/4 time. just imagine if that torque pulled thru like 4-4500rpms, it would definityl be alot faster

[peeeot]

I think I know what you mean, this evening I had to accelerate hard and it made plenty more noise past 3500 rpm but didn't pull much more. I read something somewhere that torque gives the seat-of-the-pants feel and that beyond an engine's torque peak you aren't reaping any benefits in that department. The 3.1 peaks at 3500 rpm.

 

Of course, I did have 2 passengers. It wasn't a good gauge of anything.