Engines.. Apples To Apples....

Well let me tell you that the front page article at
www.autospeed.com called The Real Way Of Comparing Engine Designs was very interesting to say the least. Albeit a little hard to understand if you have limited knowledge of engines in general.

In general, the article mentions that you can compare engines, apples to apples, by calculating the BMEP. The BMEP is the effective (actual) pressure on the pistons. The higher the pressure, the better the engine (in general).

But what the Author fails to mention, is that if you compare the Effective Pressure (BMEP) and the static pressure, you can tell how good the engineers are at their jobs. If you get a BMEP higher than the static compression ratio, it is more than 100% efficient at filling the cylinder with air.

Here are the major sub-compact results:

1st gen Aveo: 9.6 (77kw @ 6000rpm, 1.6L, 9.5:1)
2nd gen Aveo: 9.5 (81kw @ 6400rpm 1.6L, 10.8:1)
2010 Yaris: 10.5 (79kw @ 6000rpm 1.5L, 10.5:1)
2010 Fit: 10.9 (89kw @ 6400rpm 1.5L, 10.4:1)
2010 Versa: 10 (80kw @ 6000rpm 1.6L, 9.8:1)
2010 Accent and Rio: 10.3 (82kw @ 6000rpm, 1.6L, 10:1)

Yep, you read right! The new Aveo engine is the only one that doesn't get 100% cylinder fill. But what does it mean? Unfortunately, the only thing I can think of is that the intake system isn't tuned for maximum cylinder fill at maximum power. So lets do the math:

At maximum torque, 142Nm @ 3800rpm, the engine makes 56.5kw. That gives us an 11.2 bar result. Meaning that the engine does get over 100% cylinder fill, just not at maximum power.

Lets look at the 1st gen Aveo: It gets 145Nm @ 3600rpm (54.7kw). You'd think it would do better than the 2nd gen. And it does. The result is 11.4. Now what?

Well it's easy to see that the new ECOTEC...is just plain... good marketing. In people's eyes, on paper, it looks better. Sure, makes more power. It's named after the famous Ecotec that saved the Cavalier. It uses more advanced technologies like variable valve timing. But in the end, the e-tec is simply better.

Well, I'm not sure what to think. The newer Aveo's get better gas mileage, but they also have better aerodynamics. Is the new engine really better on gas? I don't think so. I think if someone was to put one in a 1st gen body, we'd see bad results. Maybe they put more time on the fuel and ignition maps and the combination of better aerodynamics and software works together.

What do you guys think?

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What do you guys think?

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I think all these engines are relatively comparable and that the fuel economy has less to do with the engine design than with the transmission design, if it is an automatic. My 2009 Aveo gets lousy FE in city driving (at any speed under 45 MPH), 22 MPG at most. But once the torque converter locks up at 45 MPH it gets 37 MPG. It's a four speed automatic and the brilliant engineers at Chevy programmed it to have the same delayed shift points as all the other gas hogs they produce. That gives the Aveo decent acceleration in the lower gears, but at the price of poorer fuel economy.

Chevy pitched this car to rural America with a high highway MPG, and it really does achieve it at highway speeds - but if you are a city dweller who does no highway driving the local fuel economy sucks, especially for such a small car. Honda and Toyota apparently are using a more sophisticated transmission (probably a 5 speed?), or at least one that is programmed to lock up much sooner than 45 MPH. The Versa and the Rio are about the same as the Aveo when it comes to relatively poor MPG.

Is the first gen compression ratio versus the second really that far apart? is compression ratio important is his calculation? this is an interesting way to look at it, using his method though i have some questions... i'm not sure what part of the engine he is comparing? technology? looking at only peak hp at its specific rpm, is it sustainable? i know honda can run at 7400 rpm, but are you going to be at 7400 rpm all the time? not that comparing different engines at the same rpm is the solution, but if you could add peak torque at its rpm, and number of cylinders to that equation, i think it would make truer sense of engines. not sure how to do it, mathematically speaking..

i also cannot make sense of what the 1200 multiplier stands for, how did he come up with that number?


but using his equation:

hayabusa :

1.3l with 145 kw at 9500 rpm = 16.03 bmep

an audi tt 225 engine:

1.8l with 165kw at 5900 rpm = 18.64 bmep

vxr corsa:

1.6l with 141kw at 5850 rpm = 18.07 bmep

i put the vxr here because according to my research the ecotec aveo uses the same block, and head. its just a detuned engine.. non turbo, naturally aspirated us emissions design...

the new aveo versus the old is ecotec: 105 ft/lbs @ 3800 rpm and the etecII: 107 ft/lbs @ 3600 rpm so the etec is a slightly torquey motor compared to the ecotec, but with less peak hp.. i believe (not sure honestly) with the variable vale timing change, that the ecotec has more hp and torque through the power curve overall?

i dont think either engine is better than the other.. and that most of the fuel economy is from a slight change in gearing..

i think the 2nd gens peak at 103hp as well

weight and tires/sizes also effect mpg ratings as well

BMEP is the actual average pressure that pushes on the pistons. The higher the number, the more optimized the engine is. It is mesured in bars... Of course, turbo engines will have a higher BMEP. 1 bar = 14.5psi. In 2006, according to this website, an F1 car had a BMEP of about 14.63. A Nextel cup car, 15.1.

Rabbit, I don't know how you did your math, the equation is (kW x 1200) divided by (L x rpm). Therefore the Hayabusa engine gets a BMEP of 14.1. Very good for a N/A motor.

Of course the BMEP is not the whole story, but it allows us to compare engines, even though the power, number of cylinders and displacement are different.

i thought about this last night as soon as i shut my computer off, since his measure is in bar he is comparing how the engine acts like a pump.. in which case the comparison is against "optimal" efficiency. (air compressors only operate at one rpm)..


so if you have a firefly, 3 cylinder .9l making 51 kw at 5500 rpm = 12.3 bar all those vtec boys will have metro envy..


plus these are all stock configurations..


just for fun, dahlback racings gti:

2.1l making 527.6 kW @ 5.780 r/min = 52.16 bar...

thats what ive been doing.. (kwx1200)/(lxrpm)

i dont know how i screwed up that first one..

You know why I like the Ecotec motor more? Usable torque curves. Actually, I could almost say "torque LINE"
http://i14.photobucket.com/albums/a3...h_6a454210.jpg

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Originally Posted by Shibbs

You know why I like the Ecotec motor more? Usable torque curves. Actually, I could almost say "torque LINE"
http://i14.photobucket.com/albums/a3...h_6a454210.jpg

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I dunno, that dyno chart starts @ 3500rpm...pretty high for "normal" driving. I find the torque below 3000rpm pitiful in my 2010. I'd give up a few HP at 5000+rpm for better low-end torque, but I'm sure I'm in the minority; peak numbers sell more cars than a wider torque curve.

i'm usually over 3k rpm when i drive.. its all about choosing your gearing than racing. unless your one of the hyper-milers, it keeps the car responsive.

I have an 06 model hatch i drive everyday at least 100 miles a day 5 days a week ,,i got a great deal on a 2010 so i bought it ,,the 2010 is more predictable ,,u almost know wen u fill it up wen u will need to again ,,,but it has way less power and isnt as econmical as the 2006 at all ...however it seems 09 and 10 models also hav a lot of difference in gears ,,in the 06 sometimes ill b wanting to grab anothr gear and cant(cause im alredy in 5th,,,lol the daewoo people must love pulling holeshots)but the 09-10 models or at least my 2010 has higher gear ratio and more highway suited gears ,,,im almost sure thats why earlier models have more pep ,,,i am building a tbucket or have been for years its hanging up in my garage ,,aveo engines are kinda cheap ,,,i can see a gen one engine in it ,,mmmmmmmmmm

Yes the 2010 models do have a higher fifth gear or final drive. That is known. Yeah... 04 and 05 Aveo's engines would be perfect for small projects. The advantage is that it doesn't have drive by wire.

drive by wire wires in just as easily as the rest of the harness. and it allows you to have one less thing coming through the firewall for a cleaner look.

i guess 09 is where its at, higher rated hp than the etecII and closer gearing. I am always in the power curve in 5th, and ready to shift into 6th.. that i don't have. Amazing how much gearing changes the engines feel, isnt it?

i would almost like a taller 5th, but i agree, i dont think the extra power is there to have it.

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Originally Posted by petrified.rabbit

I am always in the power curve in 5th, and ready to shift into 6th.. that i don't have. Amazing how much gearing changes the engines feel, isnt it?.

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I agree. I am cruzing along and I just naturally take it out of 5th for a gear I don't have. I think a 6 speed on the aveo would rock!

Having a 6th gear would make no difference since gear 1 thru 5 would be significantly shorter ratio then they are now, making the 6th gear pretty much the same as the current 5th gear.

You will gain acceleration thru the gears but the drive ratio in 6th will still make the engive rev over 3k at highway speeds.

The only way to change that is by modifying the ratio of 5th gear so that its way longer then the others, then you could achieve a 2k or whatever you want rpm at highway speeds.

well i mean, it would be nice to have a 6th gear in addition to the current 5th. taller.

I know even the 6 speed in the cruze is about the same as the 5th in the 5 speed.

Wait, hold the phone. The 1.6 Ecotech is used in the Corsa VRX turbo? If so could that be why the rating isn't as good since it was designed as a higher output engine as was mentioned? Assuming I've wrapped my head around this correctly. On that same note though that means that this engine must have some pretty strong internals, and have some good potential in terms of upgrades.

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Originally Posted by Nemasys

Having a 6th gear would make no difference since gear 1 thru 5 would be significantly shorter ratio then they are now, making the 6th gear pretty much the same as the current 5th gear..

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I like driving at 80 MPH at highway speeds. The car settles very nicely there (actual speed maybe 76-78). It's turning 3000 RPM at that speed. I would leave all the existing gears and put in taller 6th gear. So dropping down 5th will "peak" the power for passing.

When I drive around 70 I can achieve better than 34 MPG, over that speed the wind puts my millage at 31-32 MPG. I am hoping that once I do my suspension change and drop the car and inch or two I can achieve at MPG gain. The frontal surface area has not changed but it should reduce the ground interference.

So given the power would having a 6th gear really improve the millage. Yes the engine is turning slower but does it generate enough power to overcome wind resistance?

both mine are hatches i like my 2010 the best its a looker for an aveo ,,one day i was at napa and a gal droppd over her harley looking at it driving by ,,,im geting ready for some funny gas nothing extreme just a 70 shot wet kit ,,im gonna plumb my purge out that chintzy lookmn fender vent

guys if we did hav 6 gear oh my gas mileage would be super especially in first gen cars ,,imagine 50 mpg

u can buy an rpm activated switch for the drive by wire or use a switch under pedal for nos at wot ,,,
i used this rpm deal in mny gt it worked sweet ,,i think ill try it again on the aveo,,that way its added insurance if ud mis a gear or something