V8 vs Inline four???

[johnc]

So why don’t we normally compare engines in terms of power to engine weight?

 

First you say compare the engines using power to weight. Then you say:

 

Large-displacement engines are not necessarily very heavy, while small-displacement engines aren’t necessarily light.

 

Which do you want to discuss? Powerplant power to weight or powerplant displacement to weight.

 

If you want to discuss powerplant power to weight then the new Mazda Renesis 13B rotary engine is my guess at the winner. 250 horsepower from a fully dressed engine that weighs just over 200lbs. If you want to discuss displacement to weight then some of the built off-road VW flat fours at 3.3L and right at 200lbs fully dressed would be the winner if I had to venture a guess.

 

Remember, a fully dressed pushrod V8 is pretty heavy. A lot of the weights people quote don't include manifolds and that stuff.

[Guest DaneL24]

To answer Damn Cracker's question...diesels don't make very much high RPM power because they have no way to advance the ignition timing...their fuel mixtures are ignited by compression...and max compression always occurs at TDC. The faster a normal gas powered car engine spins, the earlier the spark plugs fire before the piston reaches the top of the cylinder. This gives time for the burning gases to build some pressure before they push down the piston. In a diesel, the faster the motor spins, the less time the gases have to build pressure before they push down the piston...and the less power the motor makes. That is the difference.

[Guest Damn Cracker]

I wasn't really asking a question, i know how deisels work. It was more of a statement...

[Mudge]

here's another thing: look at the prices. squeezing that much hp out of a 2 iter motor takes alot of enineering, while 300 hp out of a bigger v8 i nothing, in fact chevy made a 265 ci (i think) v8 in 1955 tht made 265 hp, 1 hp per ci. thats even better than a crammo's 300 hp out of 350 ci

 

Unfortunately dyno rating in those days was what we call dishonest by todays standards. The allmighty ZL1 was putting out under 400 HP, in stock form. I agree though, getting a small engine to make big top end requires RPM and generally, expense, and precise machinery. Bike engines would be one great place to look, there are 600cc bikes now putting out 100RWHP stock, not even 1 liter, but again look at thier ~14k peak powerbands. I am curious about the engine aspects though

 

I have run into an F1 guy on a board, who says the engines are "nothing anything closely related" to street car stuff and it would be ridiculous to try and steal opinions. I am sure this is only semi true, I am aware that they had run oval pistons for a time, must be quite interesting stuff.

 

Why pay so much for an engine close to maxed out though? When you can for less money, make streetable and affordable power with a V8. Now if weight is a concern or liters for a race class, then you obviously have no choice. FWIW Honda had a 250cc V8 engine which I believe had a 22 or 24k redline, this would have been many moons ago.

[Drax240z]

The closest engines to F1 that you or I could buy are in sportbikes... Nothing in any car is close.

 

Some very interesting phenomia begins to contribute at above ~8000rpm, and I suppose it isn't financially feasible for automakers to make engines to these extremes.

[Guest DaneL24]

Drax240...what are these phenomena past 8000 RPM? I thought it had more to with max piston speed to maintain lubrication on the cylinder walls...or force on the rods due to acceleration and deceleration as the pistons changes direction every rotation...both of these are directly affected by the stroke of the motor, and with a shorter stroke you get less piston speed and stress due to piston acceleration/deceleration at high RPMs. Theoretically, if an engine did hit its max piston speed and rod stress at 8000 RPM, if you reduced the stroke by 50% you would see the same phenomena at 16000 RPM (I'm aware that literally calculating piston speed involves some trig, not just simply dividing by two...but I'm too wiped out from work to actually use the trig right now...but you see my point). There is centrifugal force on the crank...but that can also be reduced by shortening the stroke.

 

Or do you mean that the phenomena has something more to do with the behavior of gases flowing through the intake/exhaust...or the ever shortening duration of the combustion stroke (assuming timing advance stops at a certain RPM) Is it valve float...why not just reduce valvetrain inertia, increase spring tension, or reduce the slope of the cam lobes (less increase in lift per degree of cam rotation) I just don't see how there are any strange phenomena past 8000 RPM...please enlighten me.

[johnc]

My uneducated guess would be standing wave formation in the intake and exhaust and the track length/shape tuning issues that go with wave control. On a high rpm normally aspirated engine you're constantly fighting to accelerate and maintain momentum on both intake and exhaust charges.

[Drax240z]

John answered for me pretty much. I use the 8000rpm number as a ballpark, the waves are of course present at all rpm, but as you rev higher the gains and losses associated with wave propigation become VERY significant. Actually, the Jaguar D-Type had some interesting tests done on it way back when, and at high RPM on that engine (3.8 inline 6?) they found that volumetric efficiency could vary by as much as 30% at high rpm just by changing the intake runner length. (80% to 110% VE!) Of course, this was 40 or 50 years ago, things have gone much more in depth since then.

 

A quick overview: intake air comes rushing in at ~the speed of the piston, valve closes, air 'bounces' off the back of the valve and this negative (because of direction only) wave propigates back into the intake. It bounces around in there, and then comes back down the runner again at some point. If you time the intake to be open when the positive wave propigates back down to the valve back, you get extra air forced in by the wave, if you are a split second too late, the wave has bounced back (negative), and instead it pulls air away from the valve, lowering VE.

 

What you say about the stroke is true, and I'm sure the biggest reasons we don't see engines like this in production cars are torque, and fuel economy. 850hp and 216ft-lbs of torque don't make for a great soccer-mom SUV.

 

As soon as you get into the upper echelon of RPM's, assuming you have a valve train that can support it, you really need to put a bunch of time into intake and cam design. (and you don't need pneumatic valves like F1 to spin 16,000rpm... I've seen a valve spring'd V8 turn 16,000 (see picture), and inline 4's in the 15,000 area using valve springs as well) Depending on the geometry of your intake, you can see very real gains at any RPM you tune it for, a-la the D-type. If you are particularly fancy about it, you can see these gains across the entire RPM range, or most of it. (infinately variable intake runner length) However, as easy as it is to get right, if you get it wrong you'll see losses of the same magnitude.

 

It's not really rocket science, and I am sure the OEM's know all about it and have the money to design for it.

 

Had to thorw in pics of this, its just too cool not to show. The rear part is a 6 speed transaxle... you can get an idea of how small this engine is. (554cc)

 

[johnc]

I want one! I'll figure out the chassis later. Is this a one-off for FSAE or are they making a few?

[Guest blue73z]

Here you go John http://dot.etec.wwu.edu/fsae/v30/v30pics.html The V8 was built for the 2001 FSAE competition by Western Washington University, but I don't think it ever actually ran at competition.

[Drax240z]

They built 4 engines actually. I believe many components are from a pair of kawasaki 250cc engines. The car didn't run at the competition, due to a bit of a disagreement over rules interpretation. (it uses a remote starter)

 

We raced WWU at a washington state autocross, but they brought out one of their older cars. As far as I know, the car with this engine installed is not run, and is now a show piece.

 

The engine does run though! What a great project that would have been to be involved with.

[Drax240z]

Check this out John:

 

http://home.mira.net/~iwd/

 

http://www.22000rpm.com/

 

 

990cc V8 - 4 stroke

Cylinders 8

Redline 20,600rpm

Power 165kW (220hp)

Engine width 330mm ~300mm

Engine mass 52kg

 

"The engine revs and power stated above are quite conservative - with ongoing development it is not unreasonable to expect 22,000 rpm and 180kW (240 hp) from a short stroke 990cc V8."

[johnc]

$37,000 US. The fun just went right out of it...

[Drax240z]

Egads, that is a lot of change.... Is that for the whole bike, or just the engine?

 

The more I think about it, the more I want to build another small displacement, open wheeled race car... anyone want to fund me?

[johnc]

The whole bike, but I'm betting the engine is 75% of the cost.

[Michael]

Johnc,

 

Regarding my earlier post - the idea was that since engine power to displacement ratio decreases rather strongly with increasing engine size, the larger engines appear to be less “efficient”. In going towards larger displacement, engine power to weight ratio generally also decreases, but much more gradually. So when comparing power to displacement, the smaller engines look tremendously better, but when comparing power to engine weight, the smaller engines look only marginally better, and in some cases (such as for older cast-iron inline engines in compact sedans, vs. cast-iron V8s of the same era) no better at all. Since the car itself doesn’t care about engine displacement – it only cares about engine weight, support accessories’ weight, and hood space – one has to wonder why power-to-displacement has become the standard metric of efficiency. And of course these various comparisons are apples-to-oranges, because given the trends in manufacturers’ philosophies, the smaller engines will have technical innovation on their side.

 

In the typical modern OEM street application where accessories such as air conditioning and power steering have come to be considered essential, the larger displacement engines have an additional advantage: big engines do have bigger and heavier accessories, but not by much. The starter, alternator, water pump etc. in my 454 aren’t much bigger than the corresponding stuff for the 2.2L L4 in my 1974 Toyota Corona, just to give one particular example. So the difference between “bare” and “fully dressed” – for the larger engines – is less that it is for the smaller ones.

 

 

Wringing out high hp numbers from a small-displacement engine is impressive, but not necessarily meaningful, for street applications. I wish that OEMs such as Toyota and Honda would apply their prodigious engineering resources to design large-displacement, low-rpm, thinwall-casting aluminum V-block (not necessarily V8) engines. But that just won't happen, because such an approach would contradict these manufacturers design culture.

[johnc]

Power to displacement became an important comparison criteria due to racing regulations. Engine displacement is a fairly easy parameter to measure for sanctioning bodies (as opposed to removing an engine and putting it on a scale) and its been done since the inception of motor racing. I think every sanctioning body in all types of motorsports regulates and measures engine displacement in at least one class. There are even agreed upon conversion factors for rotary and forced induction engines. Its natural for that comparison criteria (in existence for almost 100 years) to be used as a reference by industry and the trade press.

 

Whether its fairest or the most ideal way of determining the efficiency, performance, desirability, or whatever is irrelevant. It is what it is.

[Guest Hceline17]

As far as putting my two cents in on the debate between American V8's and Japanese inline 4's go, I would have to say its pretty easily broken down like this:

JDM engines have size (by liter) restrictions on them. To produce engines capable of motivating cars quickly they need high RPM's to create high HP figures (based on the equations listed earlier in the article, although I'm not sure any of the listed equations were exactly correct).

A high revving engine, for instance the S2000's engine, producing 240hp and spinning to 9000RPM has just about the equal stress of the 5.7 liter engine in a Camaro churning out 550 at 6500RPM.

The difference between American and Japanese engines, and the reason Chevy engines don't produce 550hp is because A) they don't have to to make their cars fast Producing an engine that can do that, of that size is going to be not only more expensive than the japanese engine, but out of the price range of the average buyer of Camaro's.

As GM can see itself making a buck from producing engines that begin to fit the bill of their potential (based on displacement) you and I will se those types of engines being created. For instance 415hp in the Z06.

 

Anyway, if you disagree, please don't flame me, just my opinion.

[pparaska]

Hceline17, great post.

 

As far as what the OEs decide to build, they build what will sell.

 

Thrust/Torque/Power delivery:

Some of the US public wants easy to drive grunt. They want their 3500+ lb car to accellerate well, without having to listen to alot of rpm while doing it, or rowing gears alot, or listening to the automatic transmission shift down 3 gears to do it. It'd be interesting to see what other country's auto buyers would buy if fuel prices were similar to the US, and they had no displacement regulation. I bet it'd be similar.

 

So, we have this situation: The US automakers CAN build larger engines, and have them turn very much more slowly in cruise due to their increased displacement (with respect to smaller engines). That's a fact. And that doesn't mean that the larger displacement engine will use more fuel at cruise (where fuel economy is usually most important).

 

Anecdote alert! Looking at my mileage for my 240Z, the L6 got about 22-23 mpg. My V8 powered one gets 21-22 on a road trip, with a bad very rich carb. But look at the mileage figures between new large and small displacement engined cars and you won't see large differences - because the larger engine cruises at a lower rpm.

 

PEAK power/displacement vs insurance cost

The other factor in this OE power/displacement issue is this. The buyer wants grunt, and goes for the larger engine (in the US anyway). But if the automaker made the engine have the same PEAK power/displacement as the S2000 engine, many fewer people would be able to afford auto insurance.

 

So the knuckle dragging 5.7L V8 Camaro driver just has to accept that his engine makes such an inferior power/liter number. I bet he doesn't care one bit, since he can out run (on a straight, from a light, etc., out of a curve) an S2000 without even thinking about it.

 

To me, arguing about who has better engines or engineers, based on PEAK power/displacement numbers of OE engines is silly. If I gave you a 1 liter engine that made PEAK 200 hp, it'd be 200 hp/liter. But I doubt you'd want to have it in anything but a dedicated lightweight race car.

 

What I'd really like to see the manufacturers and auto magazines start giving us is average torque (over say 2000-6000rpm) versus vehicle weight. Now THAT is a useful number. Better yet would be to have the actual torque vs rpm data as well. Maybe average rear wheel torque over mph in 1:1 gear over a range of mph (to take gearing out of the equation).

But even better would be to give use the entire torque curve data and engine weight as well.

 

Me, I'm very glad that fuel is not so expensive, and that my government doesn't tax on engine displacement or prohibit what size engines the OEs can build. I'll just take my high-tech-enough-to-get-the-job-done, "low tech" V8, and go have some fun.

[Drax240z]

Pete your comment on torque curve sparked a dim memory. I believe it is the Audi S4, with a torque peak at 2000-6000rpm. Thats not 90% of maximum torque over that range, but 100%. A very impressive feat IMHO.

 

Neat cars, the 2003 S4 is getting a 344hp@7000rpm/410ft-lbs@3500rpm, 4.2L, 195kg V8 this year. I see a future Z donor engine.