Engine working harder

[AgeOfAbnegation]

Hi everyone, I've noticed something odd - I've been finding that in the last 4 months, the engine has been working harder to reach a certain speed. For instance, the tachomoeter reads 4400 rpm when I'm running at 140 km/hr, as opposed to last year when it ran at 4000 rpm at the same speed. The car's aesthetics haven't changed. Have any of you noticed the same trend?

 

[changedman]

it could be the conditions of you going 140km/hr- such as wind speed, drafting or not, etc. Your engine is mechanical, its going to work nearly the same day in and day out.

 

[Gbourdon]

Must be an auto right?

 

[njaremka]

Unless your car has an auto tranny, this is impossible. Very possible with an auto tranny, as wear on the internal clutches will cause more slip.

 

[AgeOfAbnegation]

Nope, it's a 5 speed manual, and it's been consistent for the past several months. I had some snow tires on it before, and it ran at 4000 at 140 clicks, but it was the same with the summer tires on last season. So, there must be something else affecting it.

 

[Glauconite]

tire pressure?? A/C on?? extra weight?? any mods on it recently?? how bout an an filter change/cleaning??

 

[acidbug]

Have you cleaned your air filter? This will cause a loss of power uptop!

Chas

 

[njaremka]

Impossible. A solid link to the gearbox through the clutch, constant gearing in the box, and the fact that engine speed is directly proportional to driveshaft speed say that what you are proposing is in fact impossible.

The ONLY way this would be possible is if you had different diameter wheels on the car, and you were getting your speed from an external (to the car) source.

Failing the latter above, I would suspect gauge faults or clutch slippage. (which would be more apparent at lower speeds, rather than high)

 

[AgeOfAbnegation]

tire pressure?? A/C on?? extra weight?? any mods on it recently?? how bout an an filter change/cleaning??

hmm, some good suggestions here. i have 17,000 clicks on the odometer now, but I drive it hard and fast. Im not sure the air would be an issue, but you could be correct. No AC, I checked the tires, and only my ventshades on the windows lately, but u doubt that would elicit a 400 rpm change at 140 clicks. So far, the air seems most reasonable.


*Edit* I got 4000 rpm for 140 when I had my nokian hakkapelitta 1 winter tires on, with 15 inch rims. Now I use the stock 16's, with dunlop sport 5000's. It may be treadwear as well.. but its unlikely.

 

[CanMP5]

Yah, something's way off there. I usuallly cruise at 120kph and my rpms are only slightly above 3100 rpms. By 140 I am only 400rpms more depending on the inclination of the road. Are you getting any clutch slip when shifting or anything?

 

[tttP5]

this can't be..... at a certain speed the rpm is always going to be the same.

for example if your speed is 65mph rpm will always be 3k at 5th gear no matter if you are going uphill or downhill
if you are at 4th gear then at 65mph your rpm will be higher than 3k etc. etc.

unless your front wheels are slipping then thats when rpm and speed will not line up.

i don't think anything internal such as air filter and stuff will cause the rpm to increase from before

 

[rjmhotrod]

*Edit* I got 4000 rpm for 140 when I had my nokian hakkapelitta 1 winter tires on, with 15 inch rims. Now I use the stock 16's, with dunlop sport 5000's. It may be treadwear as well.. but its unlikely.

I think you just answered your own question. If you put the 15" w/ NH winter tires back on, you should go back to 4000 rpm at 140. What would worry me is if you put them back on and you were getting higher than 4000. If the wheel/tire diameters are different then I could see you getting different rpms. If one wheel/tire combo diameter is less than another, then the smaller combo has to make more rpms to match speed. Please correct me if I'm wrong.

 

[jersey_emt]

What are the size of winter tires and size of stock tires?