Mileage; and 5th gear may not be your friend

[ericheath]

I'll add that newer cars are running a bit higher rpm at 60 than 10-15 year old cars. My wife's 98 Corolla runs 2050@ 60mph while her 2010 runs 2700@ 60. The 2010 has a slightly bigger engine and the car is bigger. The newer one has variable valve timing which you would think could be computer controlled to run lower rpm without pinging or lugging, but it runs higher rpm and gets better gas mileage.

[millerdog]

Something I found out a while back that I was not aware of is that new car makers base the mpg figures on the sticker based on 50mph. So when you buy a new car, and it doesn't live up to the claimed mpg, now you know why!

[Bugdaddy66]

I have always wondered in a CV style carb how throttle position is related to fuel usage. Since the throttle only controls the butterflies that expose the slide to vacuum and that signal raises or lowers the slide to introduce more or less fuel, throttle position by itself would seem to be a poor indicator of fuel usage. It would be interesting to hook up a vacuum gauge and see where that "sweet spot" is on that gauge. My thought is that lugging in 5th gear, no matter how wide I open the throttle, the vacuum signal is so poor it takes a long time to gain revs and use more fuel, as opposed to being in that sweet spot in 4th gear with a better vacuum signal and instant throttle response. Just my morning ramblings, you guys come up with some interesting topics!

[pistolpete]

Pete IRT the original observation I can not believe that Throttle setting is directly reflective of fuel economy. I think that is only part of the equation. Physics would require that steady state RPM has to be directly related to air flow and in these setups that has to correspond to fuel flow as well right? So more rpm at a steady load/ acceleration state would require more air flow and as a by product more fuel???

The use of fuel is very much dependent on throttle plate position. Let's say the throttle is closed; the vacuum in the intake runners are high, say 10", but the air traveling across the bottom of the CV piston is slow near atmospheric. Open the throttle and the velocity of the air in the venturi speeds up causing negative pressure inside of the vacuum cap. This in turn opens the venturi until the pressure in the cap equalizes (Air velocity, piston weight and spring). At 4k rpm and climbing a hill in 5th gear the throttle wide open and your speed will not increase, says to me that the air through the venturi is travelling fast enough to completely offset the vacuum piston. In turn all of the fuel openings are at maximum flow or very close to it.
When I down shifted to 4th gear I made a significant reduction change to the throttle plate position. I feel that this change reduced the velocity of the air traveling across the piston and it lowered a certain amount. If that amount was enough to close the jet needle to a leaner position, there would be less fuel being used. This would also apply to the transfer ports and the idle spray bar.

Pistol

[jpbadger9]

My daily commute is 65 mile each way. It's almost all freeway at 70-75mph. I use a cheap throttle lock so I can give my right hand a rest once in a while.
With gentle elevation changes, if I lock on 70mph in 5th, I get plus or minus 5 mph. In 4th, I get almost no variation. Seems like no matter how I ride, I'm switching to reserve between 135 and 138 miles......

[Rat]

Just to confuse the issue a bit more .... I've always noticed better MPH on an 1100 than on a 1000.

Too soon to say on the 1200, but so far it seems to be low 40s.

Gord

[robin1731]

snip.......Just to confuse the issue a bit more .... I've always noticed better MPH on an 1100 than on a 1000.

What about MPG?

Yeah, the 1100's do get better gas mileage than the 1000.

[Oldewing]

snip.......Just to confuse the issue a bit more .... I've always noticed better MPH on an 1100 than on a 1000.

What about MPG?

Yeah, the 1100's do get better gas mileage than the 1000.

But, my (now sold and gone) 1000 would run rings around my 1100 MPH is more fun than MPG anyways

[Bugdaddy66]

So if MPG is better on a 1100 and MPH is faster on 1000, can I ride the 1000 fast enough to make the GPH come out even?

[Oldewing]

only if you hit 88 mph and ingage the flux - capacitor......

[joedrum]

yrs ago once i got my 79 1000 up to par ... i check mpg and got 46.8 being rather new to oldwings then i thought that its rpm was rather high at interstate speed and at the time i was doing 1000 miles a week or more ..when i got some off time i change the swingarm final drive to 1100 ...sheesh that was rough deal with not much tooling access ... anyway in the same conditions it lower id say 500 rpm in fifth not sure there as i was going by the tach ...i was surprised the mpg came out exactly the same 46.8 ...the condition were on both test were 1000 mile and the same road trip ...it fair to say it takes a certain amount of energy to do the same thing ...i think overall 4th and 5th are close enough that this pretty much applies ...as it did in final drive change

[Psycrow]

Not to hijack the thread but while we are discussing RPM at speed is it normal for my 1100 to be reving at almost 5000 rpm at 70mph?

Psy

[CYBORG]

If my memory serves I would say no. I might be wrong, but sounds like the speedo is off, or you are down gear or two

[joedrum]

Not to hijack the thread but while we are discussing RPM at speed is it normal for my 1100 to be reving at almost 5000 rpm at 70mph?

Psy

if it is a 80 -81 1100 ..these were the lowest geared oldwings honda made and i think it specs out at 4800 rpm at 70mph

[Psycrow]

It is indeed an '80 and 4800 sounds spot on. Thanks, I feel better

Psy