: Fuel Economy Theory



N0DIH
04-25-05, 03:48 PM
I would like to start a thread to discuss the theories behind fuel economy. All are welcome to post what you have learned over the years, and what works, what doesn't and what worked and theories on why.

I have looked at EPA estimates on fuel economy as a general "gauge" to a known fixed set of conditions for a known combination.

Aka, a 1976 Olds 98 Regency is EPA rated at 12 city, 18 highway. We know that the car was a 200 hp smogger 455 with a mild cam and a QJet, THM400 w/2.41 or 2.73 gears. This car weighed in around 5000-5200 lbs. It is a "C" body, basically a long B or a short D body in those years. Having the 12 in front brakes and 11in rear drums very kin to our D bodies.

Ok, 18 highway for a brick wall front end BB Olds 455 with out OD. Not bad. I got 16 highway for my 1980 Turbo Trans AM with a 1970 Pontiac 455 with 10:1 compression, small valves with good flow and puny 2in duals. 3.08 gears and a THM350 and a 4000 lb car with moderate drag. That is real world economy at 75 mph, 3000 rpm cruise rpm without cruise control. Not very related to an EPA measurement.

So, my questions are:
1. If I take a 307 Olds V8 with a 2.56 gear and a .67 OD in a 89 Brougham, and baseline my mileage to say 24 mpg (guessing here) and I then remove that engine and drop in a 455 Olds with same everything, only keep a cam that has torque peak at same rpm, or less, what will my mileage be?
2. Now, if I take that same car and go to a 2.14 gear and reduce engine rpm further, with the massive torque of the 455, will it help or hurt mileage?

Look at a diesel semi, they run 1000 rpm with 80000 lbs and get 6-7 mpg. My dad's RV with a 8.1L BBC gets 6-9 mpg @ 2250-2600 rpm with 30K lbs and also a brick wall for aerodynamics. Why doesn't my 455 get MUCH better as it is having a much lighter load?

Night Wolf
04-25-05, 05:01 PM
my grand father has a 39 foot motor home with a Cummins 350hp engine.... it is a big Monaco coach....

it is a 1992 or something, only has like 40,000 miles on it, not even broken in and he gets about 16mpg on the highway with it.... a full size coach motor home....

my fathers Bronco gets 11mpg on the highway, and my '79 DeVille gets about 18......

I dunno how they do it....

90Brougham350
04-25-05, 05:16 PM
First of all, diesel semis, especially the newer ones, are getting 6-7 mpg. Many older models are getting 4-5, maybe 6. Of course that's a 12+ liter engine we're talking about, mated to either a 10 or 13 speed transmition. Semi engines are built for emisions and torque. While Caterpillar's new C-15 engine might be able to make 2250 ft. lbs of torque, it's doing this of course because it's a diesel designed to move extremely heavy loads at, like you said, 1000 rpm.

An automobile engine, on the other hand, produces power either way down low (454), way up high (VTEC), or somewhere in the middle (307). Basically, an engine is most efficient at it's peak torque. At rpms below peak torque, the cylinders have more than enough time to fill with air fuel mixture. At rpms above peak torque, they have less than enough time. Therefore, building an engine that has a Kansas flat torque curve up until or past peak torque is very efficient, and with the proper gearing, provides great gas mileage.

However, once you get into dealing with emissions, the designer is suddenly faced with a dilemma. Compression ratios drop, catalytic converters create back pressure, cams become milder, and most of all, heads become smoggers. Smogger heads are good for a first time port polisher to practice on and not much else. The squish and quench properties of smogger engines from the mid 70s on are greatly diminished, and, combined with a lower compression ratio, you have the recipe for a very inefficient engine. Not to mention, but the combustion chamber shape and size is very inefficient as well on smogger heads. Basically, being able to produce enough power to get the vehicle moving, then keep it moving down the road with as litttle throttle as possible is ideal. A car only requires 30 or 40 horsepower to stay in motion at say, 60 mph. This is why the small V8s can achieve great milage if they're tuned properly, especially if they're running a Quadrajet. They produce enough (but hardly a lot) torque to get the car running, and then keep it there. That 1970 455 Pontiac you had is a whole lot more efficient than the 76, because of virtually no emisions laws in 1970, as well as a much better head design, and higher compression ratio.

Keep those ports tight, keep that squish and quench tight, don't run a massive cam with oodles of duration lift and overlap, and you can build a well running decent mileage engine.

For those who might not be familiar with "squish and quench"
http://www.chevyhiperformance.com/techarticles/94138/index.html
http://www.theoldone.com/archive/quench-area.htm

I got this from the CHP message boards.

Factory design full dish pistons leave a lot to be desired as their squish/quench is weak at best. A lot of power can be had with a flat top or "D" dish design that allows more compression without detonation. The head and the piston shape work closly together, I'll get into that in a bit.

The swirl port heads really need replacement especially if you've got some gears, they work pretty well at low revs but are a choke point once you get over 3000 and die out by 4000 revs. There are many choices that are much better in terms of port flow, chamber swirl, compression tolerance, etc. Vortecs are a large improvement to power with economy and reduced emissions if you don't live in California, which won't permit them without also installing 96 and up emission systems; but there are many aftermarket heads that also provide these benefits and are legal substitutes for the Swirl Ports.

Head chamber design and the piston crown shape need to work together. The heart shape chamber typical of the Vortec design works very well with flat top pistons, actually this is good for any Chevy head. The next most desireable is the "D" dish if reducing compression is a concern. This combination keeps the squish/quench deck close to .05 to .08 inch clearance at TDC. Anything wider significantly reduces the effect of both squish and quench. The loss of squish, which is compression induced turbulance, results in needing more timing lead, gets poorer fuel mileage and increases emissions. Quench is the resistance to detionation where the chamber design absorbs excessive late cycle heat, think of it as mechanical octane. The lack of quench occurs because the greater volume to surface area does not sufficiently control end burn temperatures making the engine more likely to detonate. Actually there is a double whammy here where detonation is concerned in that the lack of turbulance requires more spark lead which increases burn time before TDC, this leads to a pressure and temperature spike at TDC which can cause the remaining mixture to spontaneously ignite. So you get two opportunities for detonation on each and every power stroke when the squish/quench deck does not close to less than about .1 inch as an absolute maximum and .05 to .08 inch is significantly better.


Hope you're not sleeping by now!

Brian

carguy16
04-26-05, 12:21 AM
You're looking at least 1,800 - 2,100 RPM cruising, 1000 RPM you'd be pretty bogged down.




I would like to start a thread to discuss the theories behind fuel economy. All are welcome to post what you have learned over the years, and what works, what doesn't and what worked and theories on why.

I have looked at EPA estimates on fuel economy as a general "gauge" to a known fixed set of conditions for a known combination.

Aka, a 1976 Olds 98 Regency is EPA rated at 12 city, 18 highway. We know that the car was a 200 hp smogger 455 with a mild cam and a QJet, THM400 w/2.41 or 2.73 gears. This car weighed in around 5000-5200 lbs. It is a "C" body, basically a long B or a short D body in those years. Having the 12 in front brakes and 11in rear drums very kin to our D bodies.

Ok, 18 highway for a brick wall front end BB Olds 455 with out OD. Not bad. I got 16 highway for my 1980 Turbo Trans AM with a 1970 Pontiac 455 with 10:1 compression, small valves with good flow and puny 2in duals. 3.08 gears and a THM350 and a 4000 lb car with moderate drag. That is real world economy at 75 mph, 3000 rpm cruise rpm without cruise control. Not very related to an EPA measurement.

So, my questions are:
1. If I take a 307 Olds V8 with a 2.56 gear and a .67 OD in a 89 Brougham, and baseline my mileage to say 24 mpg (guessing here) and I then remove that engine and drop in a 455 Olds with same everything, only keep a cam that has torque peak at same rpm, or less, what will my mileage be?
2. Now, if I take that same car and go to a 2.14 gear and reduce engine rpm further, with the massive torque of the 455, will it help or hurt mileage?

Look at a diesel semi, they run 1000 rpm with 80000 lbs and get 6-7 mpg. My dad's RV with a 8.1L BBC gets 6-9 mpg @ 2250-2600 rpm with 30K lbs and also a brick wall for aerodynamics. Why doesn't my 455 get MUCH better as it is having a much lighter load?

90Brougham350
04-26-05, 12:42 AM
That depends as well. Fortunately for us, our trannies, both 200 and 700 come with a lock-up converter. Since most common automobiles don't have the low-end grunt diesels do, it only makes sense that most gas engines like our small 8's have a cruising speed between perhaps 1600 and 2200 rpm at 60 mph. I remember my 85 Parisienne had 2.42 cogs and 4th gear in the 700-R4 was .70. At 81 mph, I finally hit 2000 rpm on the highway with the converter locked, of course. Fortunately, like I posted above, it takes only 30-40 horsepower to keep a vehicle moving down the road at a cruising speed, and our engines certainly have this at 18 or 1900 rpm. So yes, the cruising speed rpm of 1800 does develope enough to keep the car rolling, but when you try and cruise at 1000 rpm, you're giving the engine so much gas to try and keep it moving you're actually getting worse gas mileage. It would be very much like putting a manual in 5th gear at 30 mpg and flooring it. True, you're only spooling at 800 rpm, but you've got your foot at 3/4th throttle and the engine is starting to bog. Good thread so far!

Brian

N0DIH
04-26-05, 12:55 AM
What sort of rpm does a 6 speed Z28/T-A/Vette run at 60 mph in high gear?

Those cars aren't setup for low rpm torque, granted, they are ligher cars than a Fleetwood Brougham.

I have heard the nickname to the Pontiac and Olds 455's and being "gas fired diesels", hence the make such brutal low end torque.

My desire was to test a couple theories.

Combo 1. Low end torque monster. Build a 455 Olds with a set of 7A heads and 2.56 gears and THM 200 4R OD. My car at the time was a 85 Cutlass, so it was fairly light. The 2.56 gears and OD were commonplace gears on those cars anyway.
Theory: Efficiency per rpm. Max VE per stroke. 9:1 compression Cam, 1985 Olds 442 cam, .440 lift. This combo would be a dream to drive....

Combo 2. Build a higher rpm engine, larger cam like a 224/234 degrees @ 0.050, 115 lobe sep, 11:1 compression, reverse cooling to keep heads cool.
Theory: Higher rpm airflow, with mild gearing as above, so airflow is lazy so effectively displacement is smaller. When you are driving economy should be better because you aren't able to fill the cyl all the way yet still able to maintain more than sufficient power to drive at 60 mph.

Many new cars seem to do this theory, as they are high rpm engines with ultra low cruise rpm with a 6sp.

90Brougham350
04-26-05, 07:00 PM
True, however, "lazy airflow" is exactly what you don't want. Large intake ports and runners may provide great upper-end horsepower but they are torque killers. The Ford Boss 302 is a perfect example of this type of engine. It made power to move the vehicles it was in, but you had to rev the damn thing all the way to the moon to do it. Smaller intake runners keep the velocity of the incoming air-fuel mixture high, thus improving low-end torque and drivablility. It's just like putting a 875 Demon carb on a hot 350 Chevy versus a 650 Holley. The engine will run with both carbs, but the smaller venturis on the 650 keeps the velocity quick and the thottle-response snappy, not to mention a higher velocity in the intake path atomizes fuel better, thus giving better mileage. Unfortunately for the first engine you have theorized about, it's a big block. Big blocks can produce gobs of torque without breaking a sweat, but it's still a big block, with large bores, longer strokes, large intake runners, and a bigger carb or larger fuel injectors. Even though it's not working as hard as small block would be, it's still drinking gas like a fish, because of the above listed reasons. The reason 6-speed monsters like vettes and T/As is because of increasingly efficient engines and gearing. When your 6th gear is .50 and your cogs are anything less than perhaps 4.11, you're going to be getting somewhat decent mileage, as proven by the Corvette especially. Isn't the estimated highway 27 mpg or something like that? Enjoy the transmition ratios.

Brian

N0DIH
04-26-05, 07:39 PM
I guess the question is fuel economy, not drivability. What do the 302 BOSS get for fuel economy on the highway? Lets get one and drop in a 4L60E in it. Gives it a killer first gear to move the lazy aired 302 BOSS and will give it lower rpm OD.

The point I am making isn't a good throttling engine, it is a poor throttle feel, but at that poor throttle feel, will it do better on mileage or will you HAVE to get on it more to still make the same air/fuel flow to get the same HP to keep the car in motion. Am I saying it to make sense?

Another thought:
I have a 96 Suburban K1500, Vortec port fuel injected 350, 3.73's, 4L60E trans. I get 13 city. Pretty much no matter what I do or how I drive. 255 hp, 325 lb ft torque
My friend has a 96 Suburban K2500, Vortec Tuned Port Injected 454, 3.73's, 4L80E trans, he gets mid 12's in the city. 290HP, 410 lb ft torque

Is my 350 working too hard for the weight of the truck? Is his better? I guess what we need to do is make the engine run like a diesel, tons of low end torque and forget HP. HP will take care of itself. Cam it like a 307 Olds with 7A heads in a 455. Don't expect to run over 3000 rpm ever.

My thoughts are are yes, it is working too hard. not so much harder, but higher rpm more of the time on takeoff, and due to the 4L60E. I would like to see the 4L80E on a 350 in same type truck and see if the mileage improves with less first gear.

Might explain the Pontiac, CAdillac and Olds 455/472/500s for economy. They weren't too bad, all things considered. Cadillac should have ruled the roost on economy with the 500 and a small cam like they loved to use.

N0DIH
07-11-05, 11:33 PM
Being with the current gas prices are out of this world ($2.389 here, I have seen $2.499 nearby) this is something to ponder. This might be very doable on a TBI 350 Chevy.

I found the link from the DIY Turbo List. jyturbo@yahoogroups.com

http://www.schou.dk/hvce/

The original message was:
"This weekend I read an article in an old Hot Rod Magazine June 1984
about Smokeys Hot Air Engine. I have just done a Google search and
have found very little information about current applications of
this engine. Here is an article that talks a bit about the engine
concept but its from Denmark, the english is bad.
http://www.schou.dk/hvce/

Do any of you people know what has happened to this engine. I had
never heard of it before and don't know of any current uses. The
article stated this was the future of the internal combustion
engine. For information, the article I read was about a stock
Pontiac 151 CID Iron Duke 4 cylinder in a Fiero 2M4. It gave 50
MPG, 0-60 in 6 seconds flat, had 250 HP and 230 ft. lbs. torque,
passed all emissions, ran perfect, basically a stock engine with a
different cam. The engine uses a turbo charger but more as a check
valve than a boost application. Basically the gasoline is heated in
three stages to 400-440 F before it goes into the combustion
chamber. The expansion of the gas creates about 15 PSI of intake
pressure after the turbo.

The man is dead now but I am interested in the engine. Mean Gringo
Bob there are about 4 pattens on this engine, can you find them? I
just ordered his book, Best Damn Garage in Town and Power Secrets.
That may help me with some of the info.

Thanks for the help.

Jimmie"

90Brougham350
07-12-05, 07:21 PM
The engine uses a turbo charger but more as a check
valve than a boost application. Basically the gasoline is heated in
three stages to 400-440 F before it goes into the combustion
chamber. The expansion of the gas creates about 15 PSI of intake
pressure after the turbo.


The liquid gas is heated? Or the air/fuel mixture is heated? I'm very skeptical. For one, liquids expand and contract very little when heated or cooled. And two, you wouldn't want to expand the mixture, you would want to cool it as much as possible for a denser charge. There's a reason people use intercoolers, not interheaters. No matter how it's done, it will still take the same amount of released energy to provide the same amount of power through and engine. Doesn't matter how much or how little gas is used, it still needs to be close to stoichiometry for any fuel efficiency at all.

Brian

N0DIH
07-12-05, 09:30 PM
The carburator "atomizes" the fuel, much like a fuel injector, except that vacuum pulls (ok, you physics nuts, outside pressure BLOWS it in....) the fuel into the intake manifold. But still it is tiny droplets of fuel and a quantity of air. This here is trying to get the gasoline to become a vapor, so under the extreme heat, 400+F, what will gasoline do? I supsect that this is the point or close to it, where it starts to become gaseous state, becoming a true gas like O2 is at room temp. Solid fuel, even in droplets does not burn easily, hence why we break it up as small as we can get it. Essenitally it is now boiling and becoming a gaseous state. I sure don't want to try to control that with anything less than something forcing it into the engine. Something with a positive displacement that can't allow it to come back out of the carb, throttle body, etc.

Imagine trying to work with pure O2 in a liquid form. And in the temps that it is liquid, keep trying to make it something that isn't a liquid without the temperatures being higher. Gasoline is a liquid at room temp, at some temp it does become a gas, that is the temp we need to be at.

Once in a gaseous state, the fuel becomes very explosive, and should burn under the pressures of the turbo, aka, homogenizer, and the combustion chamber exteremely lean and complete. I would bet you can go down to 22-30:1 A/F ratio with something like this, and less timing, which would explain Smokey's fuel consumption at nearly half the rate of a standard setup.

The use of the intercooler is not even in play for something like this setup. The heat actually CAN make more power, but our engines really aren't in a state to use the heat.

My 301 Turbo would get me 23-24 mpg highway with 3.08's, 28in tall tires (P275 60 15's), no OD, 4030 lb car, a draw through turbo, Q-Jet, super mild timing (like 14 mechanical, and 10 initial), and a cruise rpm of 3000 rpm (@75 mph). Did I need an intercooler? No, I ran around 14.21@97.3 mph down the quarter mile, that is est 290 hp to the rear wheels. Under 10 psi an intercooler isn't really needed, it is nice, but not needed. I am NOT saying it won't make more power, but the costs and design of it don't give you the power gains per $ spent. And the car is perfectly fine without it. Also note that it is a DRAW through, so it is a wet intake system, so there is some adiabatic cooling there. I have seen pictures of dyno engines that are wet flow icing up the intake on a long run, so it in a sense is its own intercooler. N2O is the best intercooler.....

DanTheMan
07-13-05, 12:23 AM
Along similar lines, have you ever heard of Direct Gas Injection (DGI). It is a similar concept as the diesel engine and people have been trying to do it for years. Audi just released a car this year that has actually made appropriate use of this technology. Check out this article I found with just a quick search.

http://wardsauto.com/ar/auto_audi_fsi_dohc/


It is kind of impressive how high they can get the compression ratio for a street legal car.

N0DIH
07-13-05, 01:32 PM
I know a friend of mine was working as an intern at a shop that was working on a direct injection that would do a small squirt to start to the burn, and then once the piston starts to go down, do another shot of fuel to make a very violent and very complete burn. I guess in testing it worked well. Injectors though need to be injecting at greater than combustion chamber pressure, so you can see the issues with this, anything less and the injector may not handle the pressure pressing on it, and if the injector is open at that time, the pressure will push back into the fuel lines or the pump.

As for the Audi DGI, I would challenge them, let me have a twin car, and put my LT1 in it. With all else being the same, my 260hp/335 lb ft will get better mileage for better power.

So, I am not convinced they are doing that well. Although, having 255 hp from 3.2L is repectable, my 5.7L 260 hp will be far more enjoyable (LOTS more torque, which is the drivability factor) and same fuel consumption, if not better fuel consumption. As the mileage there is very similar to a 4700# FWB with 2.56 gears. Couple that power to a 3000# car with 3.42 gears and SCREAM.

I am not knocking them for them not doing a good job, Audi has done well for power from a small powerplant, but with all the $$ stuck into that engine to get that much power from it, the efficiency is no better than an iron headed mild cammed LT1 5.7L. That is 15 years older. And look at Chevy's LS1/LS2/LS6/LS7 V8's now? Take that engine, any of them, drop it in the Audi chassis, same weight, much lower $$ to build, and the LSx V8 will KILL anything Audi has ever made. And fuel economy will be very high to boot.

I like Chevy's approach, old school, high tech. Not OHC's on everything, but keeping with high velocity efficient designs that make as much if not more power than the competition. And keep the economy up. Compare a 5.3L Grand Prix now, bet it is still high 20's in fuel economy on the highway, with nearly 300 hp and that is what the V6 3800's get! I'll lose 1 mpg to get my V8....

90Brougham350
07-13-05, 06:19 PM
Haha, isn't that the truth! It never ceases to amaze me how people think over-engineered German engines are the greatest thing since sliced bread. I mean, the peak torque on the new M5 V10 is at 6100 rpm! You have to get it there first! Not to mention the fact that the high performance German engines don't get crap for fuel economy. Pushrods and displacement, that's all you need for mileage and power. It doesn't matter how you want to get the air and fuel into the combustion chamber, a long stroke and big cubes provide the Kansas-flat torque curve that moves our heavy vehicles through the gears. My friends 4.4 X5? Well, 320 ft. lbs. Does his torque curve look nearly as usable as mine? Not even close!

Brian

N0DIH
07-13-05, 08:56 PM
I think GM was on the right track by tossing the book on the Gen 1 small block. It is an ok engine, but I feel that many GM engines in the time were far superiour. But when you make 10x more, they tend to get popular, even if they suck in comparisson. But that is for another thread.... Ok, keep the Gen 2 Reverse Cooling, it WAS Pontiacs design anyway. (1955-1958 ALL Pontiac V8's were reverse cooled) Still trying to figure out how GM got sued and lost over it.

But with the LS series engines, GM went to concentrated on a high velocity high flow head on a super solid 6 bolt main block that is built to take it and like it. The "other" engines, make power, no denying, but they make it at the wrong rpm, the rpm where you don't drive all the time. I would rather have 90% of my peak torque at cruise rpm. This will make my car ENJOYABLE to drive. I can squirt from 50-80 in nothing flat, not even having to try!

Case in point, a guy at work has a 12 sec Suburu WRX. Runs great, sure, but is a pathetic DOG until boost hits at 3300 rpm. Else, is it suck time. Cruise rpm is around 2500 rpm (guess, with 5 speed or 6 speed, it would have to be) you are below power band, with and 8000 rpm redline with a boxer 4, that is got to be the most annoying car to drive.

Conversely, another guy I work with has a low 12sec 01 Z28. Slight cam over stock (idles like a stock Z28), some porting of the heads, some stiffer valve springs to match cam, and voila, 1.6 60 foot times and low 12 on street tires with 4.10's and a 6 speed. I rode in the car, it was a JOY to be in! Power was abundant everwhere, and top end was endless. We grabbed rubber in the first 4 gears of the 6 speed and backed off at 120 mph. And the pull at 100 was just as strong as 40 mph. He gets 25 mpg highway. He drives it daily year round. Not race slicks, not even street slicks, but BFG KDZ (?) 315's in the back and 275's in the front. The bru with AWD is a pain to drive and gets worse gas mileage!! The Z28 and WRX weigh about the same, 3300-3500 lbs. Those AWD cars are not lightweights.

So with his 300 hp WRX (modified 2002 model) and my slug LT1 and put my LT1 in his car, how well do you think it would run? You'd smoke that little boxer 4 anyday!

So, it just goes to show that marketing is playing the HP numbers again, just like in the 60's.

You guys stop it, you are gonna make me go looking at that 76 Eldo 500 Convertable ....

kdrolt
12-29-05, 03:42 PM
In re swirl port heads:

http://thirdgen.org/techbb2/showthread.php?s=&threadid=336750

The thread linked above compares flow data from contemporary GM production heads, and where possible includes dyno data and track data. The main point of the post was to show that the claims of the swirl port heads being junk were greatly exaggerated; they aren't that bad even stock (no worse than iron TPI heads) and are quite good when ported. And the findings were consistent between the GM swirl port design and the Mopar version (on the 318), which isn't surprising since it's an engineering/physics issue that doesn't depend on the mfg. Swirl ramps have been known for years and been used in diesel engine applications for much longer than in cars because the flame speed (and full burn) is so poor in a diesel -- so they needed all the help they could get.

They were GM's first fast burn head (that's what they were called back then, in the mid 80s) and they were not intended for performance use. But porting them (DIY porting, with very little metal removal) makes them flow much better than stock, and on-par with stock L31 Vortecs on the intake side and much better than L31s on the exhaust side..... plus, they're still high swirl so there is very little ignition advance needed for them. They're probably an outstanding choice for dual-purpose use (mostly street, occasional track) while still giving great part-throttle torque and fuel economy (because they're good efficient fuel burners).

To optimize fuel economy, you want the most efficient burners of fuel you can muster, and you want to minimize as much pumping loss as possible (because this is the main source of reduced fuel economy at part throttle) and ideally you want the smallest engine (or a variable displacement engine) so you get the least pumping loss and the least friction during cruise. In general a bigblock working at a lower rpm and providing the same fwhp to a car to maintain 60 mph won't be as fuel efficient as a small block working at as slightly higher rpm. Likewise, the 4.3 liter v6 will trump both the bbc and sbc in cruise economy.

A hot rodded car can have very good fuel economy provided the engine breathes well (good intake, exhaust, ported heads), burns fuel efficiently (good head and chamber design), and if it has a mild cam. The engine can still make good power with a mild cam if everything else works well (intake, heads, exhaust) which is a Lingenfelter view. The larger the cam (overlap and duration wise), the poorer the fuel economy will be. FWIW.

The Ape Man
12-29-05, 04:05 PM
One thing that gets overlooked when comparing European automotive engines to American ones is many countries in Europe base taxes on engine displacement. This is why you will see lots of tricks used to make power with smaller engines.

I~LUV~Caddys8792
12-29-05, 04:25 PM
Really? Interesting..that would explain a LOT
BTW... Apeman, you have 3 very cool cars!

90Brougham350
12-29-05, 06:53 PM
That definately explains the "over-engineered" German engine. I don't know if it was here at Caddyforums or at FSC but someone made the good point that Germans tend to engineer every last ounce of potential out of their small engines so the only thing you can really do is put a blower on it, whereas here in America, we favor pushrods and leave so much potential left over in our engines that the aftermarket is absolutely huge. Just look at any Summit catalog for proof. I mean, 90% of a BMW upgrade catalog is $450 coffee mugs and floor mats, the other 10% is just pompous *****age. Still, it never ceases to amaze me just how poorly German engines do regarding fuel economy. If the engine truly is efficient, it should make both good power per size and power per consumption. Gearing has a lot to do with this, but then again, aren't the Germans the ones with 7-speed transmissions? Maybe BMW oughta take a look at an LS-7.

Bro-Ham
12-29-05, 07:29 PM
Hi,

Just to be exact and a little anal, the EPA rated the 1976 Olds 98 as 13 city and 17 highway. I'd love to have a 98 from the 75-76 era! Fun cars!

Dave