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Discussion Starter · #1 ·
hi guys, i just recently purchased a forte koup EX and its awesome. Looks amazing, and even the EX has some good acceleration. AND everyone is looking at it. so im very pleased with my buy. one reason why i went for the EX was for fuel economy, which is good so far, i think my first tank was 25mpg. but i do alot of highway driving, usually going about 105km/h (yes im canadian ) and when going that speed my rpm are pretty high for cruising( this is a manual tranny) , 2800-2900 rpm. is this normal? my 2007 cobalt automatic 2.2 L always was bout 2200-2300 rpm and same with my girlfriends 2003 ford focus 2.0L, her rpm going 110km/h are 2100-2200 rpm. is this ok? the difference b/w 5th and 6th isnt much, maybe 400rpms, shouldn't 6th drop it down to like 2200rpm range? i just feel my engines working pretty hard to drive. when i speed up to 110km/h is 3000rpm. What do you guys think?

thanks guys, sry for any grammer mistakes.

Dave
 

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Hey I am Canadian also in Vancouver, now I dont know alot about the EX, I have an SX, but mine at 105km (65mph) my RPM's are at 2000 in 6th gear. Yeah I agree with you, 2800-2900 seems high. I hope someone else has info for the EX for ya, but if not, I would check that with your dealer, or go to your dealer and see if you can test a diff ex on their lot with the manual.
 

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Discussion Starter · #3 ·
hey, thanks for the response robsin, ya 2000 rpms sounds like what it should be. going the same speed, what is the difference b/w 5th and 6th gear? i test drove a ex before i bought but i cant seem to remember what the rpms were like. everything else is fine, everything works but sometimes it doesn't feel like a 6th gear because it only decreases the rpm by 500. i also bought the 2011 because of the 6th gear for added fuel economy. hopefully i can get some answers here and then go the dealer to get some answers. but all in all, Love the car and even with the 3000rpm at 105km/h still get 25mpg (only 1 tank of gas has gone through tho)
 

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2700 - 3k is normal at about 65 - 70 on any 5 spd. The reason we get better fuel economy than the 2.4 is because of less gas entering the cylinders. ( obviously due to displacement) 01 civic got 28 - 32 avg mpg highway and my rpms never went below 2800. Of course this was a 1.7 vtec (d17a2). Also if we had a 6th gear in the 2.0 we would actually lose mpg. Mpg is not always based on rpm of the engine, more so on how hard it has to work. And since our best operating rpm, meaning not bogging down nor running lean, is around that 2700- 3200 rpm range, that is where we get our best fuel eco. on a flat surface. Obviously going up hill or down hill will change the best operating rpm range due to gravity. Physics baby, physics!

where I get my knowledge: UNC analytical physics grad. (bach in science)
 

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oh and the reason auto's have lower rpms is due to their wide gear ratios... autos (not so much on 2011 + model cars) usually only have 4 gears including the final drive. However this does vary due to the same situations.. ie displacement of engine and best operating rpm range. Oh and one thing i left out earlier, weight of the car... that has a lot to do with your most economical rpm range. I'll explain it more if you need me to. But think about it like this. If you are flooding the engine with fuel at a lower rpm say 2200 to maintain 65mph then you are actually wasting fuel because all of it will not detonate and will actually go out the exhaust. Now most cars now a days catch a lot of that fuel in the B.G.R. and recycle it. Still the engine is working harder than operating at a higher rpm range say 2700 with the same amount of fuel or less because all of it is getting burnt and it isn't having to push unburnt fuel out of the exhaust valves. It also all depends on the weight of all those moving parts. MOST IMPORTANT are the crank shaft, camshaft(s), and flywheel. Less weight = higher optimal rpm range. Thats why some cars can go 9k plus on the rpms. They have lighter parts but the same surface area is still being moved. There is a lot lot lot more to all of this.....
 

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Discussion Starter · #6 ·
2700 - 3k is normal at about 65 - 70 on any 5 spd. The reason we get better fuel economy than the 2.4 is because of less gas entering the cylinders. ( obviously due to displacement) 01 civic got 38 - 42 avg mpg highway and my rpms never went below 2800. Of course this was a 1.7 vtec (d17a2). Also if we had a 6th gear in the 2.0 we would actually lose mpg.

that 01 civic sounds like a freaken hybrid man :p, this makes sense, all about how much gas is used, while im on the highway, only little bit of gas is being placed into the cylinders. so hypothetically if the engine were to put more gas in the cylinders, the rpms would drop(more waste tho), correct? also you said that if the 2.0l had a 6th gear it would waste gas? i have a 2011 and they do come with the 6th gear, why would that waste gas? just because it would drop the rpms below the optimal rpms or what?
 

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Strange Fact: if you do the math on the gear ratios, we don't actually have overdrive. our 5th gear (6th for the sx and new ones) still comes out to like 2.8:1 ish after factoring in final drive. And yet we still get 30mpg. Very Efficient Engine.
Also explains why I can still accelerate pretty decently in 5th gear at about 55mph.
 

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Discussion Starter · #8 ·
how does that gear ratio avg thing work anyways, whats the math behind it? and for overdrive, isnt that usually the last gear which has a very low ratio, allowing for lower rpms while crusing?
 

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2021 Forte GT w/GT2, Currant Red, SXTH Element Intercooler Kit, Evilla Exhaust, Takeda S2 Intake
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5th and 6th speeds are overdrive gears...you do not factor in the final drive when discussing OD in trannys:

2011 2.0 and 2.4 6 spd Auto Gear ratios
1st
4.212
2nd
2.637
3rd
1.800
4th
1.386
5th
1.000
6th
0.772
Reverse
3.385
Final gear ratio
2.885

2010 2.0 4 spd auto Gear ratio
1st
2.919
2nd
1.551
3rd
1.000
4th
0.713
Reverse
2.480
Final gear ratio
3.681

2010 2.0 AND 2.4 5 spd auto Gear ratios
1st
3.939
2nd
2.093
3rd
1.349
4th
0.962
5th
0.713
Reverse
3.347
Final gear ratio
3.099
 

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Strange Fact: if you do the math on the gear ratios, we don't actually have overdrive. our 5th gear (6th for the sx and new ones) still comes out to like 2.8:1 ish after factoring in final drive. And yet we still get 30mpg. Very Efficient Engine.
Also explains why I can still accelerate pretty decently in 5th gear at about 55mph.
In 6th speed the final ratio is 2.227:1** (6th spd 0.772 X final drive 2.885)

The 5 spd is SLIGHTLY* better for MPG at 2.209:1 (5th spd 0.713 X final drive 3.099)...and in the 5spd tranny there is no 1:1 spd -- both 4th and 5th are actually overdrive ratios (less than 1.0)

Ironically, even with the extra gear, the 6spd is at a SLIGHT* disadvantage over the 5 spd off-the-line:

5 spd 1st gear final drive ratio: 12.207:1 (1st spd 3.939 X final drive 3.099)

6 spd 1st gear final drive ratio: 12.151:1** (1st spd 4.212 X final drive 2.885)

However, the 6 spd has better numerical 2nd and 3rd speeds for better acceleration.

..and if you don't understand what ratios are...think of a ten speed bike. It is easier to start off in 1st and not 10th. The ratio is much higher in 1st just like the 1st speed of a tranny. ...and to be technical there isnt a 1st gear, 2nd gear, 3rd gear, etc. in our trannys...it uses three planetary gear sets to make the different speed ratios (most auto trannys only have 2 planetary gear sets -- BUT some Honda auto trannys DO have gears...LoL!). It would take too much time to write up how these work...if you want to know more look up auto trannys and planetary gear sets...LoL!

*Almost negligible because the difference is VERY SMALL

**...and for those that STILL don't get it:
with the 6 speed tranny in first gear the engine spins 12.151 times for each revolution of the wheel...in 6th speed the engine spins 2.227 times for each revolution of the wheel. in 6th speed when the wheel is spinning at 1000 RPMs the engine is at 2227 RPMs.
 

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Discussion Starter · #11 ·
ic ic, you mention automatic in ur answer, but all this is also applicable in manuals i assume? except manuals dont have the planetary gear set. what is the formula to determine the value for the final drive? Now at the end of it all, is the 2800 rpm normal for going 105km/h(65m/h)? and another question. when going about 80-85km/h, should i be shifting into 6th to lower my rpms or is that less efficient on gas then leaving it in 5th at a higher rpm.

btw guys, thank you very much for your responses.
 

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so even though the final drive for 5th is 2.something, 5th is still an overdrive gear because it is under 1:1? I always thought you figured final drive in first. makes sense though.
 

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OK... wow. Some good info here... but seems to be quite the tangent from OP's issue.

Because I'm on my lunch break and math is fun, let's figure out what gear you actually ARE in:

Velocity = 105 km/h. Assuming stock tire size on an EX of 205/55-16 then we have a circumference of 1.98m. So 105 / 0.00198 / 60 = 883 your tire is doing 883 rpm at that speed.

Work in the known gearing numbers : Final drive of 4.333 and a 6th gear of 0.633 gives us an engine speed of 2421 RPM at the crankshaft. Tada. So if your gauge is showing you anything from 2200 to about 2700 that's a 'needle width from dead on' which is perfectly fine.

I don't see the gear ratios posted here for the actual transmission in question (M6CF3)

1st : 3.308
2nd : 1.962
3rd : 1.257
4th : 0.976
5th : 0.778
6th : 0.633
Rev : 3.583
Final :4.333

COOL! Three overdrives!! WHOA!

Of course, there is also the flip side of the coin... maybe the RPMs are right and your speedo is out to lunch... 2800 rpm nets you 121 km/h. Then again... it's likely a mix of the two as these gauges are simply 'displays'... the ECU takes the info in, transmits it to the cluster which then displays it to you. Not like the old days where a cable connected the gear drive to the needle.

So there you go SCDave... the math don't lie, your car is probably fine. The rather high final drive ratio is what's tossing all the numbers in the air... but it's the engineer's best chances at averaging performance and economy... it's always a trade off.
 

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Oops! I was actually posting off of rickster434's post #5...just gathering so much information I forgot to mention that:eek:

Manual tranny's gear ratios work the same way as the autotranny BUT the SX's 6 speed tranny is unique in that it has two final drive ratios!!! There is a LOW ratio for 1st, 2nd, and reverse gears and a highway ratio for 3rd-6th gears! I don't have time right now to go over this but will when I get the chance!
 

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I would be interested in learing more about the two final drive ratios when you have a chance. Just became a certified tech and would like to know more if you dont mind. The more you know the better off you are.
 

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Discussion Starter · #17 ·
thanks KiaTech, i still probably take it in to have it check out, i mean 65mph = 2900rpm and 68-69mph=3000 rpm so its a bit higher then the values u calculated, just seems like 5th and 6th are extremely close. its good to know that it should be close to 2200-2700 rpm. Another question iv had was how do you get the final gear ratio? and why does it matter. Im no mechanic or not much knowledge about gearing so if someone could give me some insight i would very much appreciate it. and also, how do you incorporate the engine size (2.0L) into the calculate to determine RPM's? because smaller engines will have higher rpms while larger engines will have lower. is that all already in the gear ratios?

thank you everyone for responding
 

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Discussion Starter · #18 ·
my EX 6speed manual does around 2000 rpm at 65 mph
and 3000 rpm at 80 mph in 6th gear.
Really? 2000 on the dot or around 2000? i would love to know the exact rpm just to be able to compare to mine. and 3000 at 80mph(134km/h) wow i am not getting that at all..... this is so weird :p why would my car be at 300 at 65mph(105km/h).
 

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Sorry about taking so long to post. I was merely saying that adding a 6th gear and going at that speed(65 - 70mph) would actually be making the engine less efficent. Due to the amount of gas having to be given at say 500 - 600rpm less
 

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that 01 civic sounds like a freaken hybrid man :p, this makes sense, all about how much gas is used, while im on the highway, only little bit of gas is being placed into the cylinders. so hypothetically if the engine were to put more gas in the cylinders, the rpms would drop(more waste tho), correct? also you said that if the 2.0l had a 6th gear it would waste gas? i have a 2011 and they do come with the 6th gear, why would that waste gas? just because it would drop the rpms below the optimal rpms or what?

haha just realized what i wrote, yeah it was 28 - 32 mpg. I was really tired and didn't realize that thank you for showing me.
 
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