Fuel efficiency between engines?

[gunt]

Thats why all new cars have more gears , less toque from engine less fuel , also rev the engine more make the bhp with less tq and still use more gearing , but ud need to compare the required tq to move the car down the road all being the same then big and small engine would be equal as torque requirements is the same and tq is fuel

[Carnut1]

viewtopic.php?f=1&t=55886&start=210#p802351

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Kenny M designed this stroker 305. The dyno was with a dual plane intake and carb but will run a tpi in car. I like this design and would change it a bit for an economy build. I like the free 305 block the 400 arm will cost a few $ more than a 305 crank but not much. I would use a 305 vortec cylinder head with a vortec tpi base. A slightly smaller hydraulic roller cam with a decent exhaust system. Wouldn't be a road burner but would be a nice DD and get decent mpg. thanks, Charlie

[GARY C]

Being that we have a few different threads going talking about street performance engines and MPG keeps coming up (and in some threads the desire for the OP to stay with a smaller engine is based off of MPG) it makes me wonder if with similar packages would an increase in CI really have that big of an impact on mailage? So here are some of the questions bouncing around in my head. With all things remaining equal (if using a sbc with vortex heads on both and same compression,cam, induction and even rings and valvetrain) would the increase in cylinder volume alone have a big impact? My feeble bind was contemplating that to move a brick of a car down the road takes x arount of power. With the same drivetrain (trans, gearing and such) wouldn’t the larger engine make the same amount of power as the smaller engine, but with the throttle in a more closed position? As such, wouldn’t the manifold vacuum be higher and therefore potentially do a better job of vaporizing the fuel to get a more efficient burn? Now I understand the increased friction of the larger engine would be a handicap to overcome, but really how much of one?

I bring this idea up as in the future I plan on rebuilding my old Chevy wagon and have been mentally kicking around different engine combos. I don’t really want or need more than 400 hp (honestly I don’t even want 250 for when my wife drives it, but that is a whole other thread) and I know I could build that with a 327 to a 400 with no problems. Obviously a 400 would have a very different (and more true street friendly) torque curve, but would I really be suffering on the mileage? I do plan on returning this thing to daily driver status when the time comes so mileage is a consideration. I don’t want to discuss my car or build as much as the efficiency theory.

Paul

If you look at the charts on both the traditional and LS engines and take some time to correlate it with fuel economy you will find that increasing compression is always a plus and increased ci can be to an extent but you still have to feed that volume... an undersized overworked power plant never equates to an efficient power plant. Like everything it all boils down to the combination.
https://en.wikipedia.org/wiki/Chevrolet ... ock_engine
https://en.wikipedia.org/wiki/LS_based_ ... ock_engine
Here is something I found interesting while researching fuel history. I recall my dads biggest bitch about Unleaded gas at that time was the loss of power and MPG, of course at the time no one knew the cars had lost 2+ points of compression to survive on the crappy gas.

tetra ethyl lead is a gasoline additive that was developed in the 1920s so cars could be made with higher compression & use less gasoline because the proven oil reserves at that time indicated the world would run out of oil (&gasoline) by 1940. with the higher compression permited by ethyl it was thought the oil could be made to last until 1950 or so.
as we now know more oil was found but the ethyl was already available so more efficient higher compression engines continued until they reached a high of 10 to1 or more in the late 60s which required 98 octane ethyl gas, standard engines with 9 to 1 compression ran on 92 octane leaded regular.
in order to reduce photochemical smog the government decided all cars should have catalytic converters that changed carbon monoxide (co) into carbon dioxide(co2) & water. tetraethyl lead prevents catalytic converters from working so they mandated any cars made after 1972 would have to run on 87 octane unleaded gas this required reducing the compression ratio to 8 or 8.5 to1 which reduced power & efficiency and also caused cars to use 15% to 20% more gas which made the oil companys happy because it cost less to produce the unleaded,they sold it at the same price,& you had to buy more of it because of the reduced milage.
this did reduce smog, you cant believe how bad the smog was in the 60s. but it also greatly increased the production of greenhouse gas (co2 is a greenhouse gas co is not) through the action of the converters so now we have a different concern.
the lesson from all this is politicians are not scientists & cant be expected to look at all sides of a problem (or even understand it) before they pass feel good laws to get themselves relected & there are no simple answers, everything has both desired & undesired effects. be careful what you ask for,you may get it!

[makin chips]

Manifold vacuum is a poor indicator of fuel economy. Fuel "vaporization" is not an issue with modern fine-atomizing injectors that are correctly positioned.

You want to be operating at the lowest practical RPM and highest practical torque (short of load enrichment or detonation-induced delayed ignition timing) that delivers the power being commanded at any given time. This minimizes frictional, pumping, and other parasitic losses. Obviously this also has to not involve throwing away power through an unlocked torque converter. Nowadays that means using a transmission with lots of ratio choices and the upper ones closely spaced, and if it's an automatic, with capability of keeping the torque converter locked in all the higher gears including through shifts. (Or a CVT.)

Narrow bore, long stroke, fewer cylinders, high tumble (charge motion) in the interest of fast combustion, highest practical compression ratio are things in favour of better efficiency.

If this is a retro build (sounds like it), look at the stuff the auto manufacturers started doing in the early 1980s fuel crunch before they had time to redesign their vehicles. Downsizing (some of the smallest V8 engine displacements were from this era!), silly tall final drive ratios, lock-up torque converters, and the beginnings of fuel injection and electronic engine control were from that era. If you emulate what they did back then, you will also get the side effects that everyone complained about back then: Silly tall final drive + 3 speed non-overdrive transmission = a lazy dog. Lock-up torque converter + simple control logic (that was all they had available at the time) = complaints about hunting and juddering.

Maybe 15 years ago one of the car magazines, Car & Driver I believe, found that with modern manual transmissions, if you short shift and use more throttle to get up to speed, better fuel mileage...I find this to be true on my 09 Ford Ranger 4.0 5 speed...

I think Top Gear did something similar but not the same way. They tested a 4 cyl car vs a V8 somewhere like Willow Springs or maybe on their track where the V8 used partial throttle vs the 4 cyl driving in full race mode trying to keep up. The 4 cyl still used less gas and got better mileage, IIRC.

[PackardV8]

Not thinking of going forced induction,

I think Top Gear did something similar but not the same way. They tested a 4 cyl car vs a V8 somewhere like Willow Springs or maybe on their track where the V8 used partial throttle vs the 4 cyl driving in full race mode trying to keep up. The 4 cyl still used less gas and got better mileage, IIRC.

Saab was right in 1978, but no one believed them then. Today, all the entry level BMW/Mercedes/Audi/Porsche/Mustang/Camaro are 2-liter turbo four cylinders. They're just inherently more efficient for daily drivers.

Many years ago, the late, great John Lingenfelter told me, "All internal combustion engines want to be turbocharged."

[peejay]

Not thinking of going forced induction,

I think Top Gear did something similar but not the same way. They tested a 4 cyl car vs a V8 somewhere like Willow Springs or maybe on their track where the V8 used partial throttle vs the 4 cyl driving in full race mode trying to keep up. The 4 cyl still used less gas and got better mileage, IIRC.

Saab was right in 1978, but no one believed them then. Today, all the entry level BMW/Mercedes/Audi/Porsche/Mustang/Camaro are 2-liter turbo four cylinders. They're just inherently more efficient for daily drivers.

Many years ago, the late, great John Lingenfelter told me, "All internal combustion engines want to be turbocharged."

There's something magic about an undersquare 500cc cylinder, too. Something about an 82-83mm bore being optimal for combustion (on gasoline, at the RPM typically seen in a street vehicle) and the stroke to make 500cc from that is optimal for getting both a good combustion space with good compression. So we see a lot of 1.5l threes, 2.0l fours, 3.0l sixes.

One of the best economy cars I've had was an undersquare 2 liter with 10:1 compression (might have been 9.5) and a small turbo to add a couple pounds of boost when needed. In a 2800-3000lb car i could easily see 42-43mpg, or 34-35 towing a small trailer. And this was with a traditional torque converter style automatic with the losses that go with that! Volvo built it with a generously sized front mounted intercooler, a 2.5" exhaust system with free flowing everything, and a large twin-scroll exhaust housing for minimal backpressure without sacrificing turbo response. Not bad for their "economy car".

IIRC, Volvo's monster SUV also uses a 2 liter four cylinder, with a supercharger and a turbocharger.

[Truckedup]

21 grand will buy a new Honda base model Civic with near 160 HP ,6 speed manual and 36 MPG on the highway..Or a lot less money for a used version ..And for a relatively inexpensive car they are durable and actually fun to drive fast...

[travis]

Not thinking of going forced induction,

I think Top Gear did something similar but not the same way. They tested a 4 cyl car vs a V8 somewhere like Willow Springs or maybe on their track where the V8 used partial throttle vs the 4 cyl driving in full race mode trying to keep up. The 4 cyl still used less gas and got better mileage, IIRC.

Saab was right in 1978, but no one believed them then. Today, all the entry level BMW/Mercedes/Audi/Porsche/Mustang/Camaro are 2-liter turbo four cylinders. They're just inherently more efficient for daily drivers.

Many years ago, the late, great John Lingenfelter told me, "All internal combustion engines want to be turbocharged."

Maybe there is something to this whole “pumping loss” thing. I’ve owned or driven several cars that basically had 2 operating modes...idle or WFO. Gutless as hell but phenomenal gas mileage. A friends mom had a mint ‘82 or so Ford Fairmont with a carbed 200 I-6/3 speed auto that would get 28+ mpg even with Stone Age technology...with only something like 88 Hp you HAD to drive everywhere with your foot buried in it. 0-60mph times was “eventually” if you had a LONG stretch of road

I never got into turbo cars because back when I started driving, there weren’t a lot of options and the affordable options you had were pretty sad...2.2 Chrysler’s, 2L pontiacs, etc. Turbo lag was pretty horrific especially with an auto trans on most of them, although the Buick Grand National and the 280Z turbo was pretty good. It was many years before I ever drove another turbo car...I rented a Ford Escape with the “big block” turbo 2.0L and was absolutely shocked at how much low end torque this thing made. I would daily drive one in a heartbeat, and the 28+ mpg at 80mph was icing on the cake. A friend bought a 2016 Escape with the “small block” 1.6l ecoboost and it is surprisingly spunky for such a tiny engine, and will get well over 32mpg on the highway.

[Rick360]

21 grand will buy a new Honda base model Civic with near 160 HP ,6 speed manual and 36 MPG on the highway..Or a lot less money for a used version ..And for a relatively inexpensive car they are durable and actually fun to drive fast...

Or buy a new Toyota Camry L and get 41mpg Hwy (4-cyl non-hybrid, automatic) MSRP of $24k so could probably be had for $21K.

Rick

[Rick360]

If you look at the charts on both the traditional and LS engines and take some time to correlate it with fuel economy you will find that increasing compression is always a plus and increased ci can be to an extent but you still have to feed that volume... an undersized overworked power plant never equates to an efficient power plant. Like everything it all boils down to the combination.

An undersized, overworked (ie. heavily loaded) is exactly what makes for good fuel economy. The more load an engine is under in the correct rpm range makes for better bsfc. A small engine that has the minimum amount to move the car down the road will get the best mileage.

Rick

[GARY C]

If you look at the charts on both the traditional and LS engines and take some time to correlate it with fuel economy you will find that increasing compression is always a plus and increased ci can be to an extent but you still have to feed that volume... an undersized overworked power plant never equates to an efficient power plant. Like everything it all boils down to the combination.

An undersized, overworked (ie. heavily loaded) is exactly what makes for good fuel economy. The more load an engine is under in the correct rpm range makes for better bsfc. A small engine that has the minimum amount to move the car down the road will get the best mileage.

Rick

Is not the same as incorrect and not enough.

[FC-Pilot]

21 grand will buy a new Honda base model Civic with near 160 HP ,6 speed manual and 36 MPG on the highway..Or a lot less money for a used version ..And for a relatively inexpensive car they are durable and actually fun to drive fast...

Or buy a new Toyota Camry L and get 41mpg Hwy (4-cyl non-hybrid, automatic) MSRP of $24k so could probably be had for $21K.

Rick

I just spent the last three years doing testing for Toyota at their proving grounds out here. I hope you don’t take offense but I would not drive a Toyota if you gave it to me. After having done testing on or for many of the auto makers vehicles there are plenty I would own and some I would not recommend to my enemy. One of the most stupid fun cars I have driven was an 87 Chevy Sprint turbo. That was fun. Then with the addition of the eBay turbo (as you can’t find replacement parts for that old model of tuurbo) that was larger than the original it was down right stupid fun. There is no doubt forced induction stuff is fun, but I would like to keep my classic car a little more simple.

I still love the talk and ideas. Keep it coming.

Paul

[BigBlockMopar]

This weekend I made a 2x 2.5hr drive in my '57 Chrysler with 4bbl 354ci poly-engine, pushbutton auto and 3.31 rear gears. Dual exhaust, manifolds, 'turbo' mufflers, lowered stance. Except for a 2bbl to 4bbl intake swap, the driveline is completely stock.
The car surprised me with a mileage of 19mpg while driving at an average of 55mph. Driving slower with older cars helps.

[Truckedup]

21 grand will buy a new Honda base model Civic with near 160 HP ,6 speed manual and 36 MPG on the highway..Or a lot less money for a used version ..And for a relatively inexpensive car they are durable and actually fun to drive fast...

Or buy a new Toyota Camry L and get 41mpg Hwy (4-cyl non-hybrid, automatic) MSRP of $24k so could probably be had for $21K.

Rick

For having a bit of driving enjoyment, there is no comparison between a 6 speed manual high rpm engine in a light car compared to just sit there and steer hybrid.. ....

[ptuomov]

How about a bigger fuel tank?