3k rpm at 80mph cruising on hwy 5 in cali with auto tranny of course

 

well i went from miami to gainesville this weekend and my average mpg was 35mpg on the way back driving 80-85 average 90mph max on the way back i drove 80mpg average and i got 37mpg. while the car is meant to be driven at such high rpms. its bad for the mpg because more rpms= more fuel. in conclusion if you wanna get really good mileage u have to drive the 70mph speed limit. which in the florida's turnpike if you do you'll get a lot of flashing lights and honks from annoyed drivers.

ohh and 2.35 gas in gainesville was FTW $23 fill up was awesome it made me remember my highschool days!

 

yeah this is something I don't get with the manual transmission. i use 5th gear to maintain 60km/h on a downhill......i am still within break-in period, so I don't want to gas it, but I wonder how it will drive like when I get it onto the highway....

 

It's a Honda, revs will not hurt it and I get 39 mpg at 75 mph and 3,700 revs.

 

ya got me. Whats wrong with 80 mph in 4th at 4000 rpm? May not be worth it to cruise there but on the way to top speed in fourth - about 110 mph - what would you do?

 

I have that same question when i first got the Fit. Its prolly how it's designed. I'm down with that but in the long run i dont know if it will affect the engine?

 

Its a Honda. They know what theyre doing when it comes to reliability and engine longetivity.

 

Me too, 38 with the AC

I found a car for sale in Atlanta about a year ago on the internet. The guy drove from there to Seattle and back, every week, from the time he first bought it. It was a '95 Civic EX MT. With that S20 tranny it's much like the fit-- just a touch lower, figure 3400 rpm at 75mph. The z6 engine it had was still a short rod undersquare motor just like the L15 (bore/stroke was 75mm/90mm instead of the 73mm/89mm we have, and rod:stroke ratio a low 1.52:1).

The motor nor transmission were never rebuilt. Just got timing belts, clutches, brakes, tires, coolant changes, air filters, pretty much standard maintenance.

The thing was for sale with 943,000 miles on the clock and he claimed it STILL didn't burn oil.

If I can find it, I'll post it up.

Moral of the story, it is NOT something to worry about.

Heck look at all the people running b20 swaps with b16 trannies. Punched out LS block with skinny skinny sleeves churning 4000+ rpm down the highway... that's gotta go thru some petrol.

 

It's nothing to worry about guys, it's perfectly normal for any "low torque" Japanese car.

In a muscle car, displacement = torque. And the larger the displacement, the harder it is for it to handle high rpm's. You ever wondered why a Ferrari engine is a technical masterpiece?

In a Japanese car like a Honda, rpm = torque. The FIT's engine/tranny is a just a glorified D-Series and, like its predecessor, is designed to handle high rpm (well, high rpm compared to larger displacement cars). Power-adders aside, if you had a long-geared transmission, you will be slower than a snail. Like mentioned above, Honda had to make a compromise between efficiency & acceleration.

For the Auto tranny, this is geared differently from the Manual which is why it sits at a lower rpm when compared with the Manual, but also has a torque converter which increases torque tremendously at lower rpm's. The higher the rpm though, the more balanced the torque distribution becomes (it's just the way torque converters work) which is why an Auto doesn't make more "peak torque" than a manual would.

 

its kinda like the f1 series motors that are a v8 but only a 3.2 liter with no stroke but are constantly running in the 10,000+ rpm range. a small stroke can go up and down quicker and more reliably than a longer stroke.

 

Current f1 is limited to 2.4 liter with a 90 degree v8 configuration and limited to 19,000rpm

 

so that would put .3 liters in every cylinder in the f1 cars versus .375 liters in every cylinder in the fit and only 1/3 the rpm limitation. i think maybe dropping in a hayabusa motor would be very affective for mass power.
YouTube - Smart with Hayabusa engine

 

Highway trip with the whole fam damily yesterday and I had to check to make sure. At 80 mph on my GPS receiver, I was turning roughly 3000 RPM. Never did get it up to 4000 RPM, as we hit a sustained 104 MPH at 3800 RPM. The only way I could see 4000 RPM for 80 MPH is if you have your car in 4th gear.

Of course, mine is a AT car which may make a slight difference.

 

You were doing 104mph "sustained" with your whole family in the car?

But yeah, the AT has longer gears than the MT (except the final drive which is shorter)

 

I think Honda might have changed the MT gear ratio a bit starting in '08 models because they want to get the government tax credit, so that it's competitive with the Toyota Yaris (which does have the credit).........they need a combine highway/city fuel rating below 6.5L/100km in Canada in order to qualify.

But one thing that I am curious about is, does that mean the AT should have a higher top speed because of its higher gear ratio?

 

Actually, the limitation for displacement versus rpm is the feet per minute of piston travel. You can increase both displacement and rpm by adding cylinders. There's a limit of diminishing returns of course but there's a good reason why those technical masterpieces are 10 and 12 cylinders, even 16. Reciprocating mass and weght are their enemy.

Currently, most high tech street engines of 1.5L displacement using high quality metals have to be limited to 3500 ft/minute at max rpm. Thats the feet of piston travel up and down the cylinder in a minute at max rpm. The Fit has a stroke of 89.4 mm which means the piston travels 7 inches with every engine revolution. Thats 0.5866 ft per rev; at 6500 rpm the piston travel is 3812 ft per minute. To keep piston travel to 2500 fpm, which is considered a good target for endurance race engines, the engine should not turned more than 2500 fpm for long periods of time like 24 hours.You may turn 4000 rpm steadily for long periods but you are shortening the life of your engine progressively because the piston speed is 2346 fpm, very close to the reasonable limit. (You don't want to calculate the valve and rocker arm speeds)
The closer to the limit the quicker you wear your piston rings, valves. and other mechanical items. There is no free lunch.

The smaller the engine the more rpm needed to generate the power to push the car thru the air and up hills. HP=torque times rpm divided by 5250. Torque is generated by the push of the combustion on the pistons and is generally equal to one foot-pound per cubic inch at maximum. When you need horsepower, add rpm. Increase torque, have larger displacement, pasrticularly piston diameter.
Still no free lunch.

 

Nice info

 

wow. so that is the explination why shorter stroked motors can run higher rpm's.
do you know how they calculate this for the rotory motor?

 

No pistons = no piston speed.
Revs only in this case.

 

Generally speaking, yes. Such was the case with the S2000. The 2.0L engine has a stroke of 84mm and was capable of 9,000 rpm. This created a piston speed of almost 5,000 feet/ minute.

To tone it down the lengthened the stroke to 90.7mm and dropped red line to 8,000 rpm; thus dropping piston speeds about 200 feet/minute. If you would rev the 2.2L to 9,000 RPM it would create piston speeds over 5,300 feet/minute and the result could be catastrophic.

I don't know about the newer rotary, but, the old school RX-7 rotary engines did not have a red line. Those cars were equipped with a light that came on warning that you should probably shift or else the alternator pulley might not handle it. Those rotary engines could rev and rev.