[andrewb70]

I have included the data posted by 658Chevy in the data set. All cases of BBC and LSx are with OD transmissions. I even excluded one of the LSx samples that reported 28 MPG because I was an outlier (more than two standard deviations from the mean). The attached PDF file speaks for itself.

In summary, the reported increase in mileage is just over 26%. That may be impressive or non-impressive, but that is purely subjective, and thus irrelevant. I have also included a small spreadsheet that calculates miles drive, fuel consumed, and dollars spent. Again, the judgment of whether $1, $20, or $1000 is entirely subjective and irrelevant. This is information presented without judgmental value assignment. Take it for what it is.

The box plot (graph) that is shown is a nice presentation of the data at a glace. It shows the range of the samples, the mean, and the quartiles. As a side note, it is interesting to look at the standard deviation of the BBC and the LSx data. The SD represents the "spread" of the individual datums away from the mean as an average. This can be seen on the boxplot which shows that the LSx sample is much more tightly bundled around the mean compared to the BBC sample. That indicates that it is much easier to achieve the MPG results with an LSx engine than with a BBC. This is of course mainly due to the consistency of tuning with EFI vs. a carburetor.

On another note, that was not really part of this discussion, I will put money on the fact that most of the LSx combinations in this sample will run 12 second quarter mile passes, while the BBC combos will not.

Andrew

 

[658Chevy]

Well done, Andrew. Finally, apples-to-apples, set out clearly, without personal bias. Hard to argue with that.

I have a question, and it is serious and without sarcasm: I see by the graph that the lower BBC mpg's started as low as 10 mpg (or is it at 13, at the box?) The examples I provided all got at least 18 mpg. Where did those lower BBC mpg examples come from? The ones I provided were, of course, cherry-picked as they are examples of optimum tuning. I'm sure you can find BBC's with OD that get mpg that low -- I know I have seen posts asking for help with LS engines that aren't getting the mpg they should be. That's where tuning comes in.

The numbers I provided were:

18.5 (18-19)
18
18
18
20
20

Mean of 18.75, bundled tightly.

Please clarify.

 

[andrewb70]

Well done, Andrew. Finally, apples-to-apples, set out clearly, without personal bias. Hard to argue with that.

I have a question, and it is serious and without sarcasm: I see by the graph that the lower BBC mpg's started as low as 10 mpg (or is it at 13, at the box?) The examples I provided all got at least 18 mpg. Where did those lower BBC mpg examples come from? The ones I provided were, of course, cherry-picked as they are examples of optimum tuning. I'm sure you can find BBC's with OD that get mpg that low -- I know I have seen posts asking for help with LS engines that aren't getting the mpg they should be. That's where tuning comes in.

The numbers I provided were:

18.5 (18-19)
18
18
18
20
20

Mean of 18.75, bundled tightly.

Please clarify.

The datum points for the cases that were not your came from this thread:

http://www.chevelles.com/forums/showthread.php?t=357380&highlight=mpg&page=3

Post#35

Clearly there are all kinds of issues with this methodology, but it is what we have to work with. If we wanted to do a more rigorous study we would first identify all the cars on this message board that have BBCs and OD transmissions. Then we would randomly take a reasonably sized sample (50 should do) and control for all the extraneous variables, such as gas pump, driver, course, weather, etc...We would then do the same for LSx equipped Chevelles, etc....

Just to clarify that even though the 10mpg BBC case seems low, statistically it is not considered an outlier (more than 2 standard deviations from the mean) or an extreme outlier (3 or more standard deviations from the mean). The 28mpg LSx case was 2 or more SD from the mean, so I chose to eliminate it, which is in line with statistical practice, although it is a judgement call. I honestly didn't want you to come back and pick on it.

Andrew

 

[Derek69SS]

Feel free to be unimpressed while I enjoy my better mileage in my faster lighter weight car with more horsepower and better handling.

Doesn't bother me any.

 

[magisnyc]

I think you guys were unfairly harsh on 658Chevy (not counting his comments from frustration at the end). He clearly stated that the LS is a better engine and never doubted its potential.

His point, if I understood correctly, was that he was not impressed with the MPG gains from removing a running BBC to swap in a LS motor. The cost and effort involved in the swap to net an estimated 10-15% was not worth it to him. He never debated the power potential or technological improvements the LS has over the BBC.

The cost factor is major and similar discussions were done when OD transmissions first came out. The big question of doing the swap back then was to calculate how long it would take to recoup the cost based on the estimated fuel savings. Some people were ok for it to take 2 years, others were ok for 4 years. Others didn’t care, they just wanted OD! Sounds like the same situation here.

 

[andrewb70]

I think you guys were unfairly harsh on 658Chevy (not counting his comments from frustration at the end). He clearly stated that the LS is a better engine and never doubted its potential.

His point, if I understood correctly, was that he was not impressed with the MPG gains from removing a running BBC to swap in a LS motor. The cost and effort involved in the swap to net an estimated 10-15% was not worth it to him. He never debated the power potential or technological improvements the LS has over the BBC.

The cost factor is major and similar discussions were done when OD transmissions first came out. The big question of doing the swap back then was to calculate how long it would take to recoup the cost based on the estimated fuel savings. Some people were ok for it to take 2 years, others were ok for 4 years. Others didn’t care, they just wanted OD! Sounds like the same situation here.

What you describe are issues of perceived aka subjective value. Here is a great video that defines and demonstrates the concept:

http://www.youtube.com/user/LearnLiberty#p/u/29/AYuHUdE_pys

What I took from 658Chevy's points is that there is no significant empirical difference between a "typical" BBC with OD and a "typical" LSx with OD. In statistical analysis that would be called the null hypothesis. From the data that I collected I clearly showed that the null hypothesis must be rejected, because there is a significant difference between the means of a (typical) BBC with OD and a LSx with OD in terms of mileage. That difference happens to be over 26% and not 10-15% as he was claiming earlier.

Again, whether it is "worth" it or not is completely irrelevant and can be argued to death because we all have our subjective ideas as to what is valuable. See above video...

Andrew

 

[Matty B]

Wow Andrew!

Right on point and is what I expected to see. Unfortunately, the last of the BBC were only put into trucks over 8600 GVW which dont require fuel mileage tests. All you can get is semi empirical data (what drivers claim to get which is heavily subject to inaccuracy).

I dont think anyone that has an LS is going to argue with what is already so blatantly obvious. I hope this info gains some converts as this engine design is simply outstanding. Theres a reason is was given a Motor of the Year award for multiple consecutive years.

Light, powerful, inexpensive, efficient and reliable are the ingredients for an amazing ANYTHING. Hell if this was a comparison of computers or smart phones there would be no argument at all. The only issue is a strictly sentimental one, one that I never was involved with. Its that thought that unless you have a big block it isnt a muscle car. I still dont understand that one but I also wasnt driving in the sixties, seventies or eighties. Back then if you wanted power and torque it came from a BIG BLOCK. You popped the hood and that was the engine you wanted to show off.

In a certain way I can understand that a big block is visually impressive when compared to an LS or any small block. It looks massive and has a psychological effect that its hard to attain with a smaller motor.

Beyond that, the Gen3-4 is a dead ringer.

Thread CLOSED...

 

[64SS427]

This has been an interesting read for me. I'm an old school V8 guy, run a 427 in my Camino, and have been debating between a 283 and a 4.8 swap for economy purposes. I've tuned my BB with a wideband, it runs 15.0-15.5 afr down the highway with a TKO600 with .82 O/D and still pulls 13 mpg with a very mild cam. The 4.8 would cost me more short term, to get the injection up and running, but would alow for me to drive it more often, possibly even daily if I can get it close to 30 mpg. does mileage matter to me? Yes, it does. I enjoy driving my car and that takes gas.

Devin

 

[tommycomfort]

How did this thread go from a simple question about "LS" mileage to an argument about big blocks and LS's? Unsubscribing...

 

[andrewb70]

My apologies to the original poster for hijacking the thread.

Andrew

 

[buddyholly]

A major part of my decision to swap in a LS motor was gas mileage. I drive my Chevelle 15,000 miles per year and have for the past 15 years or so. Pretty much the exact same roads every week. My 454 with OD and fuel injection got on average 11mpg. I calculated it regulary for years. When gas went up a few summers ago and my big block was worn out (how many big blocks go 220,000 miles?) I decided to go with the LS motor. So far it is averaging 17mpg over the exact same roads I drove before. Was I hoping for 20mpg? Sure, that would have been great, but the LS motor allows me to fill up less and has already payed me back a good chunk for my trouble. Good discussion, keep up the input.

 

[rfrankb4]

That sure seems low for a LS3 and T56 from what I have read but then 11mpg with FI BBC is on the low side as well so maybe it is just heavy weight or do you like to drive fairly aggressively? Nothing wrong with aggressive driving of a muscle car I am just curious.

I am curious cause I would be a little disappointed with the 15mpg from my almost complete swap I have 4l80e so that would cut a few MPG.

Does your L76 have DOD and did you keep it? Who tuned it? Do you have an AF gauge? What rear end ratio and cruse speed in general? What is the terrain like where you drive?

Either way that is still a 36% increase in fuel economy so nothing to scoff at.

 

[buddyholly]

17mpg is everyday real world mileage for me. I drive a lot of highway and secondary roads and I drive it fairly hard. But over the summer in city driving it got 16.5mpg and still gets about 17 no matter how hard I beat on it. On the few long drives I have taken it pushed 20mpg.
No, I removed the DoD and installed a nice cam. I tuned it myself with a wide band O2 sensor. Rear is 3.42 or so.
I think your 4L80e will be close. I had a 4l80e behind the big block for a while.
As someone has already mentioned, these cars are not very aerodynamic. High mpg would require some aero mods.

 

[rfrankb4]

Well at least my poorly tuned, leaky, underpowered 350 I pulled out got such horrid MPG I will still pay for my swap in 30k miles or so.

 

[Winkokid]

Can't we all just get along???? i didn't start this topic to have a war big block vs small block vs ls? ...... I was curious what the effect of gear swaps, non od trans, and perf mods would have on mileage. and what real world mileage people are getting. thanks to all who replied with their ls? combo mileage. and please if you want to argue endlessly about big vs ls... start another post.. I DONT CARE!!!!!

 

[nekkidhillbilly]

The 5.3's are the MPG masters!! I think they are the best of every world when it comes to Gen 3/4s. Granted you arent gonna get the output of a 6.0 with a cam and bolt ons but for ALL AROUND performance and drivabilty they are really hard to beat.

Ive been thinking that I should do an attempt once my car is done (hopefully sooner than later) to build a combo that can make big HP/liter and also be able to get the MPG that a modern DD requires.

I dont know if its even possible but with a flex fuel spectrometer, e85 and variable boost controller, It may be possible to get in the low twenties (on ethanol) and also be able to max out in the 700-800 bhp range not wheel hp in combined driving.

Id have to try to get that kind of mileage considering that my car is being built to actually have fun which in turn means burning something flammable at high rates. It would be nice to do it on the cheap but Im not into KERS or hybrids which I guess isnt really that cheap either lol.

I guess lets just all agree that the Gen3/4 motors are easily killing SBC and BBc as far as MPG and hp/lt. Its a great motor and anyone considering doing the swap.. SHOULD!!

actually the 4.8 is the mpg master the old truck i have would stretch out to 22-23 mpg on the hwy this is a 4wd rcsb. it got 15 mpg pulling my car back from indy. my dmax is not any better granted it has a 100 more hp and tripple the tourque.

 

[nekkidhillbilly]

also as for the bb arguement while i cant attest to bbc i have seen bbb buick and nailheads both get excellent mpg. i have seen a 455 with od that got 18mpg and most nailheads get 19 mpg with the stock trans. with a od trans im not sure how high a nail will go. only one i know of with od trans was in a wildcat and got over 21 mpg. pretty good for a car that weighs close to 5k.

 

[69chev350]

yeah the milage with an LS is gonna be way better than with the the 350, 396, etc. Personally I don't have one, but I just helped my buddy swap one in his car. Runs great, especially if you are a "drive the drag car to the drag strip guy"

 

[73z-6sp]

I just did my first road trip and got 18.3 mpg. Stock LS2 and 4L70 with 3.55 gears. 66 Chevelle. A/C on. A little disappointing considering I was driving like an old man. But its better than it was.

Just wanted to update my own post. After several hundred miles of driving my swap, my road trips now are averaging 23mpg without A/C going and about 60 mph average. Not sure why its better. (Maybe my driving has settled down or what?)

Just for fun, here is a pic of a few days ago at Boothill Cemetary and Tombstone Arizona.

 

[Beaux]

actually the 4.8 is the mpg master the old truck i have would stretch out to 22-23 mpg on the hwy this is a 4wd rcsb. it got 15 mpg pulling my car back from indy. my dmax is not any better granted it has a 100 more hp and tripple the tourque.

Got that kind of mileage in my tuned 05 GMC ECSB sierra with the 5.3 / 3.73's doing 70 / 75 on the highway from Tracy CA to Fresno CA (flat). Combined city / highway was a rock solid 18 and I dont drive lightly. Just for comparison, I have no dog in the LS battle because I prefer violent big blocks in muscle cars and have other cars for DD use.