Question for all you car gurus and techs, Now, the new accord is listed at 240 horses with 3.0 liter vtec engine. But the S2000 is listed at 240 horses with 2.0 liter i4. Taking into consideration of weight differential, torque, shouldn't the S2000 have a better mpg and be more efficient because its using less cylinders for the same horsepower output. Just wondering

 

i think the fact that the accord is a SOHC engine and the S2000 is a DOHC engine plays a role in this.

 

Do you mean thermodynamic efficiency (work out / energy in). I couldn't tell without instrumenting the engine and putting it on a dynamometer. As for MPG, roadsters generally have poorer coefficients of drag than hardtops. (0.29 for Accord Coupe, not listed for S2000.) As for displacement specific power output, the S2000 is clearly the winner with 120 hp/L vs 80 hp/L. This is not thermodynamic efficiency, however.

I can conjecture about the efficiency, however. The S2000 has a higher compression ratio, 11:1 vs 10:1. That helps both power and efficiency. Fewer cylinders often means better volume per surface area ratios. Smaller cylinders means less surface area which reduces heat loss. Heat loss kills power and efficiency. Thus, producing more power from a smaller displacement is desirable. However, hi-po cylinder heads like I imagine are on the S2000 usually have larger combustion chambers (with larger surface areas) to accomodate larger valves, which hurts efficiency, while boosting power. The S2000 probably runs richer with the higher compression ratio. The S2000 indeed has alot going for it, but there are too many factors involved to really be sure.

BTW, the DOHC just means the exhaust valves are controlled by VTEC, not just the intake valves as on the accord v6. This is mostly a performance mod, although the efficiency benefits can't be entirely discounted.

 

It depends on the HP and TQ at cruising speed. The S2000 really blows at the lower RPM. Get her on a strip where you're pushing the engine to redline, and she'll rock your world.

Even though the PEAK horsepower is the same, it's how it's distributed throughout the power band that impacts the MPG. For example, if the S2000 has no low RPM torque and you approach a hill, you'll have to really open the throttle to maintain speed. If the accord is anything like the CL-S, it has a really flat torque curve so it'll pull nicely without lots of throttle.

On a flat surface, or where you can maintain constant speed, then the S2000 would get better MPG. In the real world, it's a different ball game.

 

Actually, the location of the peak power and amount of torque really has no effect on the MPG (unless you cruise around in low gear). In fact, holding the throttle open makes the engine more efficient. If the throttle is closed, it causes a vacuum in the cylinders which creates negative work during the intake stroke. This is known as "pump work". It decreases the overall power output and makes efficiency suffer. This is one of the factors that makes smaller engines get better fuel economy, because smaller engines cruise with their throttle open more than large engines.

Engineers have been trying to eliminate throttles from gasoline engines for years for this reason. Instead of throttling the airflow, they want to inject less fuel and run it lean. Evidently, they've gotten it to work on the high quality gasoline in Japan and Europe but not on American gasoline. We'll probably have it soon, however. I believe they just need to remove sulfur from the fuel.

 

That's sort of an apple and oranges comparison. Honda was striving for maximum output in the S2000 motor while the motor in the accord was striving for the best balance between economy and drivability. However, it's interesting to note that one of the best engines in IMSA's sports car racing history was a 4 cylinder Toyota 2.1 liter turbo. It was very efficient while producing nearly 1000 hp. On the tracks where INDY cars and IMSA raced the Toyota eagle reset track records that stand to this day.

 

ahem...... sir, my '03 accord v6 coupe(630miles) has 260HP with premium fuel. right now she drinks regular fuel like crazy, but doesn't have quite an appetite for premium! Don't know what this extra bit of info brings to the dynamic.....

 

Is that a marketting gimmick or does the '03 Accord really give 260hp with 91 octane? It's 3.0 Liter unlike the CL-S's 3.2 Liter. Does that mean the CL-S puts out 280 hp on 91 octane ?

 

In a recent Car & Driver article on the new Accord I read that the new V6 has a pretty sophisticated knock sensor. The compression ratio is fairly high for a car designed to run on 87 octane fuel. The knock sensor can detect ping well enough to retard the timing just enough to ward off detonation while running on 87 octane. Without such a good sensor, it would probably detonate itself to death unless the timing was permanently set retarded.

However, if you give it 93 octane, it will not detect any ping, and will let the timing be fully advanced. This should make it both more powerful and get better mileage. It may also prolong the life of your engine. I imagine there would be little different between 90 & 93 octane fuel, so mid-grade might be all you need for optimal performance. It would be pretty interesting to see the dyno tests from different grades.

If the CL-S has the same technology, it may have the same advantage. Anyone know if they have the same electronic engine controls?

 

i think the cl-s has older knock sensors, but it doesn't matter 'cuz it specs for premium gas and i think the compression ratio is higher. I don't remember the numbers off hand though.

so what that means is that we can't run on cheaper gas without affecting performance.

the accord can run optimized on cheaper gas, but i really really doubt it can get an extra 10hp from premium. Maybe a couple hp, but 10hp is stretching it.

and if it's the engineers know that the accord v6 can get 250hp from premium, why woudlnt' they sell it with 250hp to beat the altima and put in fine print "with premium"? the answer I think is because they can't actually "prove" it scientifically.

 

awesome, and informative post!! No wonder, I've been getting SIGNIFICANTLY better gas milage on premium 91+!! THe thing drank regular like crazy. and yes I noticed the HP gain for my self while driving. here is a link to the dyno, of the car on 91 octane:

http://www.vtec.net:8080/article_fil...dexv6_dyno.jpg

article:

http://www.vtec.net/articles/view-ar...ticle_id=58735

 

I have a strong suspicion the CL-S has the same knock sensor... maybe slightly different. Comptech has seen the CL-S motor retard timing by nearly 25 degrees just due to bad gas!