[andrewb70]

I found a big thread where various people compare SBC and BBC mileage:

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

Andrew

 

[Matty B]

My lack of being impressed was never over whether the LS is a better engine than the BBC -- I was not impressed by the presumed improved mpg of an LS swap in a Chevelle, which is the original theme of this thread. Stick to the point. Some posts following mine gave some concrete, apple-to-apple examples of swapping an LS into an older car. Food for thought.

As far as this engine or that engine, of course smaller packages can make bigger power. You can give engine examples all day -- professional race engines are under 4 L and make 800+ hp. But if we're talking mpg in relation to performance -- again the original theme of this thread -- and make all things relatively equal, you'll see a very comparable fuel efficiency for cars that have 13 second 1/4 miles time, 12 second 1/4 mile times, 11 second.... so on and so on.

Go ahead. Look at other cars. The links are there for you. Compare performance, curb weight, and mpg. Plot a graph if it helps. Fast cars go equally (~) fast from gas station to gas station.

Sorry to burst your bumble but that reply was directly on point.

Point being that a BBC is definitely down on efficiency. Even if a BB tuned for a lean cruise getting 16 mpg is 25% less than the average for almost every owner that has replied.

THATS HORRIBLE

Efficiency is directly related to fuel consumption.Either you make more power for a given displacement with less fuel or you dont.

The fact that an equivalent sized engine is make way less power (about 25% less Wuddyaknow??) goes to show that it isnt burning gas very well for the power it produces. That is directly related to MPG at any speed and any RPM.

Im not about to search for enough engine dyno graphs posted on line that had BSFC measured during pulls to find a mean average but it has to be utterly obvious to the most dull of mentalities that the LS engine platform does make more power per gallon of fuel.

If you have even something close to contradicting that Im definitely open to the conversation. My proof is that GM stopped making them. If they were good they woulda skipped the ultra pricey Dmax for their trucks when big torque for towing was necessary.

 

[658Chevy]

Please stick to the two original points, the first being the theme of the thread "mileage with an ls swap", and second with my not being impressed with what's being reported. This has never been, at least from my side, an LS vs. BBC war.

Most posts here, with a car that has a comparable weight to a Chevelle, report low 20's highway mpg with an LS. Your statement that a fine-tuned BBC will get 16 mpg at the most is correct -- with a three-speed trans (TH400, 350 ,etc). I've had couple big blocks that got 15-16 mpg with no problem. With an overdrive setup, BBC's can get 18, 19, 20 mpg, depending on power level. I assume most, if not all, LS engines mentioned in this thread are backed by some kind of overdrive. Going from 18-20 to 20-22 is, of course, an improvement. It is making more power per gallons of fuel. But it's not that impressive. That was my whole point. I'd been reading post after post while continuing to be disappointed. A 10% gain after 30 years of technological advancement is pretty weak. And that sentiment is not only with the LS, but with all other makes, the Prius included. That's why I provided those links.

In 1977, we had the Atari 2600. Now we have supercomputers that fit into lap tops, not to mention the computing power of a phone. The strides the LS has taken over engines from decades ago -- in terms of MPG -- is as though the most advanced computer on the market today would be a Commodore 64.

And as I began my first post, the LS is a great engine, undeniably. Better than a BBC, is most ways, yes. Better handling, emissions, power bang-for-buck, etc. But as far as mpg, despite the outcry on this thread, I'll continue to be unimpressed.

I'm always amused when a sacred cow is prodded. I feel like I'm surrounded by the women at work and had just unwisely criticized Oprah.

 

[Matty B]

I was gonna write this fact filled retort regarding a BBC being somewhere near close to an LS engine and then I stopped.

Why should I when up till now the best someone could claim to getting was 16ish MPG and the worst Ive seen is 20 (well other than the guy that fot 11 but something was obviously wrong)

If the best you can find is 16 and the worst everyone else get is 20 modified and normally untuned, its pretty clear that the BBC lost this race. I can account for quite a few 5.3's that make over 24 mpg combined and make 330 rwhp or more.

I do want to add this. Chevy would have used the big block if it was worth it in Le Mans back no 427 BBC[/U]


Hope that makes it clear.

 

[658Chevy]

Please re-read the previous post carefully: 16 mpg on BBC is with a 3-speed transmission. The 20 mpg mark on a BBC is with an overdrive transmission, as also used by most, if not all, LS swaps.

When you're comparing things, make all things as equal as possible. Apples to apples. In this case it includes the use of an overdrive transmission.

As ridiculous as it sounds, how about we discuss the mpg of an LS with a Powerglide behind it, and a BBC with a TKO-500 behind it? It's like haggling over the price of something, but the seller is talking in dollars and the buyer in pesos. Somewhat of a difference.

The 2011 V8 Camaro should be the flagship of LS cars. It's also a good candidate as it weighs the same as a BBC Chevelle. Look at the real world MPG reported: Between 18-22 mpg, highway. Some more, some less, but most right around 20.

What is impressive is the V-6 Camaro. Over 300 hp and up to 30 mpg, in a 4,000 lb car.

 

[69-CHVL]

Just for the record, and to add "fuel" to the debate, my ~16mpg 502 @ 600hp cruises at 2100rpms. I havent tried REAL hard to squeeze more mpg out of it. Its possible that the 15:1 cruise may be too lean, and reducing tq requiring more throttle opening - might be better off at 14:1. But even so, how much of a difference could that make in the end?

I went from a 850DP running at 12.8:1 to the EFI at 15:1, mileage went from say 15mpg to 16 - so calibration isnt that crucial at these low rpms. Its just a BIG motor, big motors want more fuel.

Now, what kind of mileage would a 550-600LS produce w/an OD trans - that would be the question.

This is what makes a turbo 6.0 appealing to me...600-700-800HP, with a 20mpg potential!

 

[rfrankb4]

You do not have to agree that is the good thing about this hobby you can do whatever you want with your car from 283 -> 572+, 2JZ, LS or whatever else you can dream up.

However, that said it is a bit silly to argue that the LS swaps are totally unimpressive. You state that it is common to see BBC in the 20mpg range with with an OD trans (usually a manual) and proper tuning. I for one have not seen evidence that this is at all common.

I have seen from my reading and conversations that it is fairly common to reach 20mpg and still have both the power to run high 11s, longevity and reliability from an LS motor that would be at a minimum exceedingly rare from a BBC. That MPG will be achieved with a stalled 4l80e as well which is at a disadvantage to the TKO600 or T56 BBC. Moreover this can be achieved for the same cost as a BBC would have cost me.

I priced both options and if the evidence showed that the reliability, power, cost and MPG was in the same rage I guarantee I would have gone with a BBC because it is simply more cool in my mind. Unfortunately the evidence to back up me being able to get 20mpg range, 400+rwhp, and every day reliability for cost in the same ballpark was simply not there.

 

[rfrankb4]

Just for the record, and to add "fuel" to the debate, my ~16mpg 502 @ 600hp cruises at 2100rpms. I havent tried REAL hard to squeeze more mpg out of it. Its possible that the 15:1 cruise may be too lean, and reducing tq requiring more throttle opening - might be better off at 14:1. But even so, how much of a difference could that make in the end?

16mpg with a 502 and likely reliability too from the EFI is still an accomplishment.

If this combination was even about the same price as my LS Swap I would have preferred it. I would like to have a BBC over my 6.0 but could not justify the extra price

 

[andrewb70]

So instead of arguing I thought that it would be good to let the data speak for themselves. Of course the data collection method is not perfect and there is sampling bias, but it is the best we have to work with. I recorded the MPG from the above posted BBC thread and the current thread. I did not include non-swap vehicles in the LS group. I also coded for transmission type. The attached file shows the means for each group and the ANOVA test showed that the mean differences were significant at alpha .05. All analysis was performed using SPSS V17.

Limitations: The sample for BBC and OD transmissions is very small. More data would be better to accurately assess the results. I suspect that with more data we might discover that there is a strong interaction between engine type and transmission type as predictors of MPG. From this limited sample there is signs of a trend towards using OD transmissions behind LS engines, which makes intuitive sense. One very important variable that would be of interest is the cruising RPM or the MPH when the observes MPG figures that are being reported. Some people reported this information but many didn't, thus I did not code for it. I strongly suspect, from observation, that what is happening is that people with OD transmissions are cruising on the highway at higher speeds than people without overdrives. Most states have a highway speed limit of at least 65 and many are 70 or 75. We all know that even with mild 3.08 gears engine RPM can be rather high even at a modest 70MPH. It also makes intuitive sense that when people get an OD transmission they start cruising at slightly higher speeds on the highway.

Hope this helps.

Andrew

 

[658Chevy]

It comes down to whether you are impressed, or unimpressed, by a marginal increase in fuel efficiency. I notice the increase to be about 10%, but maybe as high as 15%. Let's go with ~ 15% to side on generosity and put it in tangible terms of money.

Let's say you drive 250 miles a week. For an LS, with overdrive, at 21 mpg, that's 11.9 gallons, at $3.60 a gallon for midgrade, and comes to $42.84. That's about $171 a month.

For a tuned BBC with overdrive, at 18 mpg, that's 13.9 gallons, at $3.60 a gallon for midgrade, and comes to $50.04. That's about $200 a month.

The difference per month is $29, and that's if you use your muscle car as a daily driver. I'm not impressed by a $29 savings in my monthly fuel bill. Money is money and I'm not about to flush a twenty, a five, and four ones down the toilet, but if you're impressed by a monthly savings of $29, you should really reevaluate your budget and determine if you can afford driving a muscle car in the first place.

If you have a fresh shell of a car or want a major power upgrade and plan to go LS, economically, it's a great idea. But for a swap, how many months at $29 does it take to recoup the investment?

 

[andrewb70]

It comes down to whether you are impressed, or unimpressed, by a marginal increase in fuel efficiency. I notice the increase to be about 10%, but maybe as high as 15%. Let's go with ~ 15% to side on generosity and put it in tangible terms of money.

Let's say you drive 250 miles a week. For an LS, with overdrive, at 21 mpg, that's 11.9 gallons, at $3.60 a gallon for midgrade, and comes to $42.84. That's about $171 a month.

For a tuned BBC with overdrive, at 18 mpg, that's 13.9 gallons, at $3.60 a gallon for midgrade, and comes to $50.04. That's about $200 a month.

The difference per month is $29, and that's if you use your muscle car as a daily driver. I'm not impressed by a $29 savings in my monthly fuel bill. Money is money and I'm not about to flush a twenty, a five, and four ones down the toilet, but if you're impressed by a monthly savings of $29, you should really reevaluate your budget and determine if you can afford driving a muscle car in the first place.

If you have a fresh shell of a car or want a major power upgrade and plan to go LS, economically, it's a great idea. But for a swap, how many months at $29 does it take to recoup the investment?

The above statements are once again based on some fictitious numbers that you have yet to prove. My sample, albeit small, showed BBC cars with over drive getting 13MPG. You keep pulling numbers out of thin air and claiming them to be "facts."

Regardless of what the numbers show you will always have a way of rationalizing your position. How does cognitive dissonance feel? It's OK. Everyone suffers from it. We all want to see and believe what we want to believe. You can keep talking about the 20mpg Unicorn BBCs and Ill keep putting thousands of miles on my GTO and keep getting 21 mpg while cruising at 80 mph, running mid 12's on street tires, trapping 113 mph in the quarter at a race weight of 4000 pounds.

Cheers....:beers:

Andrew

 

[658Chevy]

Do a search here on Team Chevelle. You will find examples of BBC's with OD getting 18-20 mpg. Some with manual transmissions have reported up to 21 mpg. There are not a ton as most don't build a BBC with mpg in mind, but they are there. Those reports are as valid as any of the reports in this thread, including yours. I researched this a couple of years ago as I was thinking of getting some type of overdrive. After I worked out the cost vs. savings, based on the low-end of 18 mpg, I found it would have taken me 8 years to recoup my investment.

That's what it's based on. I'm sure you can figure out how to use the search function. Taking into consiideration 69-CHVL's huge 502 getting 15-16 mpg without OD, it's very easy to see where he'd be with a reduced final drive.

As for cognitive dissonance, there is nothing for me to rationalize. I have no stake in LS vs. BBC wars. My mild 454 gets 15 mpg with a TH400. Much less than an LS -- so what? I simply saw a thread regarding mpg with LS swaps, was very unimpressed with the numbers, and stated it as such. I probably shouldn't have stated it -- kind of like off-handedly mentioning to the wife that she's gained some weight. Sorry if any feelings were hurt.

Regarding your $29 a month, I suggest you invest it aggressively. It's a veritable goldmine.

 

[658Chevy]

Dug through my notes and did a search and here are some examples:


__________

Mar 4th, 09, 3:18 PM
Robinls5
Team Member
Bob Join Date: Mar 2005
Location: Jeannette Pa. near pittsburgh
Posts: 3,423

Re: chevelle gas mileage?

My 70 SS 454 Sta. Wgn. ( All interstate milage ) The wagon has a 700R4 and a 3:07 -12 bolt. At 75 MPH the engine is turning 1950 RPMs. With a low Horse 396 it was getting 21-22 MPG. With the 454 it gets 20 with the new 468 it gets 18-19 MPG. The engine has a mild cam and a Rebuilt Q-Jet from Auto Zone. I will be driving it to CB-09 again this year.
Bob

_________

Mar 5th, 09, 4:01 PM
509Merlin
Tech Team
Sid Join Date: Feb 2007
Location: Buda,Tx
Posts: 585

Re: chevelle gas mileage?

My ZZ454, 850dp Holley, 3:70 gear TKO600 tranny dynoed 390rwhp gets 20 sometimes and 18 highway reliably.

Sid
67 Chevelle
ZZ454
TKO 600
3:70 Moser 9"

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May 13th, 07, 5:47 PM
Got_CID?
Tech Team
Justin Join Date: Feb 2000
Location: Omaha, NE
Posts: 681

Re: big block fuel mileage.

I can pull about 18 mpg on the interstate with the 454HO, Tremec combo and a wideband tuned Edelbrock 750cfm carb.

-Justin-

70 Chevelle SS 454 clone
GMPP 454HO
Tremec 5 speed
3.42 gears, Eaton posi
100 shot N2O

70 Chevelle Malibu (stock)
Numbers match L48, 300HP
Original M20 trans
Original 12 bolt rear
Complete documentation

69 Chevelle SS 396 (sold)

"If it doesn't go, force it. If it breaks, it needed fixing anyway!"

__________

Feb 2nd, 05, 12:57 PM
Big James 4XL
Team Member Join Date: Jul 2000
Location: Columbia SC
Posts: 4,107

454, 3.31, 700r4

14.9 at 80-85mph interstate driving

When I was running a 2.73 gear, 18+mpg highway driving.

After I get a few runs in at the track to see what it'll run now with the 3.31s, the 2.73 goes back in!!!

ACES member# 5093
Elcaminos are special!
I'd rather walk around with a Chevrolet hubcap in my hand than drive a Ford

454/700R4/3.31 posi
8.30 @ 82.23/ 60ft 1.82
AND
14.5 MPG average on HRPT 2006

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Jun 9th, 04, 6:53 PM
Big James 4XL
Team Member Join Date: Jul 2000
Location: Columbia SC
Posts: 4,107

As I stated in another post, 20mpg on the highway, 454/700R4/2.73 .

BTW, can run 8.50s in the [email protected] Not at 20mpg then obviously!

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Jun 10th, 04, 1:59 PM
Big James 4XL
Team Member Join Date: Jul 2000
Location: Columbia SC
Posts: 4,107

Quote:

Originally posted by 427L88:
James, a rat doing 20 mpg and still making good HP. That's impressive!
I have been amazed!!!

I've done everything I could to ruin the milage, put a lighter spring in the secondaries, upped the primary jets 2 sizes, added a secondary metering block with huge 88 size jets, and I also carved the choke housing of the Holley. Not to mention the 280/288 cam and 2.19/1.88 valves in the heads!!!

Things that are helping the milage though are the 700R4, 29" tall tires and 2.73 gear. I also have an air fuel ratio gage installed and a manifold vacuum gage. The A/F gage is a must to tune the carb and I drive with one eye on the vacuum gage when crusing, high vacuum=good milage!

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Jun 10th, 04, 11:52 PM
jakeshoe
Senior Tech Team
Jake Join Date: May 2002
Location: North Texas
Posts: 3,596

My '72 Camaro with a 454, T56, 3.73 12 bolt, 275/60-15 BFG's, averaged over 20 mpg, and as high as 24 mpg on a road trip from Seattle to Dallas, mostly in 5th gear at ~65-70 mph.

Ran 8.20 in the 1/8th at 90 mph with the BFG street tires, easy launch (2.1), and almost granny shifting.

 

[Matty B]

When the BEST you can quote is UNDER 20 mpg and then discount a motor that can make more hp/litre AND average better than 20 mpg... Well youre smokin and I want some lol.

Just remember that a mean average of 15 mpg vs. 20 mpg (which I have observed as the low side and in need of a tune) is a 25% increase.

Would you be impressed if you went from 300hp - 375hp?

Most people would say :HELL YEAH!!!:

An improvement of 10% would make a magazine article... This motor still impresses after a decade since its first release.

I think you are just trying to save face and justify youre beloved engine choice.

BTW, I made a direct compraison of two trucks that were the same so no issues with weight or aero. They had the same tranny, rear end, tuner (GM), same ignition system, fuel system... Hell they were sold side by side at the dealership. After all that the BBC went BYE BYE. The Dmax proved it can tow and the LS can haul...

If thats not a fair comparison I dont know what is.

 

[658Chevy]

The average of 15 mpg for BBC is very attainable and there are numerous posts to support it -- but that is with a 3-speed transmission. How about you put a TH350 behind your LS and then report the mpg? What I have quoted from the beginning for a BBC is 18-21 mpg with an OD, and the posts I supplied support it. You wanted the "proof" and there it is.

A 10% increase is $29 a month in your pocket. Less than a dollar a day. Not even Sally Struthers wants that small of an amount. How are you spending all that big money?

You keep implying that I have dogged the LS motor, which, as in the very first line of my very first post, I have not. What I have dogged, however, is the notion held by born-again LS owners that a few dollars a week saved in gas money is some kind of huge stride in fuel efficiency.

 

[andrewb70]

The average of 15 mpg for BBC is very attainable and there are numerous posts to support it -- but that is with a 3-speed transmission. How about you put a TH350 behind your LS and then report the mpg? What I have quoted from the beginning for a BBC is 18-21 mpg with an OD, and the posts I supplied support it. You wanted the "proof" and there it is.

A 10% increase is $29 a month in your pocket. Less than a dollar a day. Not even Sally Struthers wants that small of an amount. How are you spending all that big money?

You keep implying that I have dogged the LS motor, which, as in the very first line of my very first post, I have not. What I have dogged, however, is the notion held by born-again LS owners that a few dollars a week saved in gas money is some kind of huge stride in fuel efficiency.

Please stop talking about the fictional $29 a month and how much or little that kind of money is. That is not the point of this discussion and frankly its a cheap shot.

As Matty pointed out you are presenting extreme cases of BBC mileage (mild engines with 2.73 gears AND OD) while we are presenting the MEAN or average cases with aggressive gearing. Talk about apples and oranges.

Again, cognitive dissonance is a bitch. You should really have a more open mind, and stop ignoring an analysis done with a statistical software package over your anecdotal extreme case examples.

Andrew

 

[93Polo]

The average of 15 mpg for BBC is very attainable and there are numerous posts to support it -- but that is with a 3-speed transmission. How about you put a TH350 behind your LS and then report the mpg? What I have quoted from the beginning for a BBC is 18-21 mpg with an OD, and the posts I supplied support it. You wanted the "proof" and there it is.

A 10% increase is $29 a month in your pocket. Less than a dollar a day. Not even Sally Struthers wants that small of an amount. How are you spending all that big money?

You keep implying that I have dogged the LS motor, which, as in the very first line of my very first post, I have not. What I have dogged, however, is the notion held by born-again LS owners that a few dollars a week saved in gas money is some kind of huge stride in fuel efficiency.

The examples provided above appear to be mostly mild 454s with hwy gears. Mild LS motors are likely making better power and mileage. Andrew's car is just one example of what the LS is capable of Stealth71 has also posted up some impressive #s. I do find it interesting that you are now debating in the post above that, the extra economy of the LS is not worth the price of investment.

 

[658Chevy]

Well, not much more to say. "Proof" was demanded and proof was provided. You may want to add those figures into your software package and see what happens -- or better yet, use only those numbers, as they are the only ones that are relevant. 13 mpg BBC hogs built solely for the track with 3-speed non-overdrives are not relevant.

The numbers and supporting posts are there to examine, and you may continue drinking the Kool Aid if you like -- the ninety-six cents you save each day will buy you that Kool Aid. If you want the last word, have at it, it's yours. It's gotten tiresome dickering with people who can't tell the difference between a 3-speed transmission and one with OD. Best of luck to LS owners and enjoy your engines. I'm sure they're fun, and I say that genuinely without any sarcasm.

Now if you'll excuse me, I have to go to the message board on www.KrisKringle.com and let all the kiddies know there ain't no such thing as Santy Claus.

 

[93Polo]

Now if you'll excuse me, I have to go to the message board on www.KrisKringle.com and let all the kiddies know there ain't no such thing as Santy Claus.

Please stick to the two original points, the first being the theme of the thread "mileage with an ls swap", and second with my not being impressed with what's being reported. This has never been, at least from my side, an LS vs. BBC war.

As you posted please stick to the original points. Insults are not needed and a sign that the debate is being lost.

 

[rfrankb4]

- undisputed mileage increase even comparing average LS swap to best possible BBC performance

- Increased reliability (although not yet discussed I would be a little surprised if anyone aside from 658 argued that a BBC would get more miles between rebuilds than a comparably built LS)

- Decreased Weight

- More power available per ci.

- Cheaper to get. (6L w28kmiles +4l80 + cam+ intake+ basic swap stuff ~$5k without cutting corners for what should be ~500fly wheel hp) If I could have had a Fuel injected, reliable BBC that would even have 90% of that power and 75% of the fuel economy + the trans to back it up for that same price I guarantee I would have that instead of my LS

seems better to me basically all around unless you are going for max NA power where a BBC would win due to brute cubes available.

It is useless at this point to continue the discussion since 658 had his mind made up before looking at the facts but to me when I have the option of a better motor by every metric I care about for less money or spending more money both upfront and on a continuing basis for less my choice is easy.