RPM vs Load - Fuelly Forums

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Old 02-23-2008, 08:32 AM   #1
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RPM vs Load

I'm talking about reving up the motor at staying at higher vacuum, say no less then 14-12 at all times, as opposed to speed in the lowest gear possible where the vaccuum can change greatly.

I was under the impression that driving for load netted the best results, but I here the exact opposite here. I've come to the conclusion that it's a combination of both that nets the best results.

Example: There a few driving techniques that get good mileage; slow acceleration, not accelerating up hills, and maintaining a slow speed on the highway 60 or lower.

so driving on a flat road acceleration smoothly staying at as high of vacuum as possible, if you rev it lower then 3k on my car it pretty much lugs in the next gear to stay at higher vacuum

Well, anyway, these are a compelation of my thoughts and is going to be way to long. I've been thinking about this and been aware of this and mileage for awhile, but I've come to the conclusion that you load is better on hills and rpm on straight and highways. even downshifting to get up some hills. at 55mph the vacuum can skyrocket to like 20+ inhg. if you look at a stock fuel map. there's not a whole lot of fuel being injected at all. if you look at that same map, more then 10% fuel is being injected lugging a motor up a hill at say 2500 rpms or less at 10inhg of vacuum. Ireally need a supermid to test all my theorys.
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Old 02-23-2008, 08:41 AM   #2
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really, looking at an aftermarket fuel map, there's really not an instance where running it in a higher gear injects less fuel, unless your maintaining a 55-60 on the highway where the vacuum can shoot way up

in most cases you have to push on the gas way more to stay in lower rpms. which puts you in 10inhg of vacuum or easily less where WAY more fuel is being injected.
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Old 02-23-2008, 09:24 AM   #3
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so you're saying when you have a high load on the engine, downshift to up the rpms into a more usable range where the engine's making enough power to handle the load? basically, when you need torque, put the revs in the middle of the peak of the torque curve? if so... yup. maybe even duh. if not, you lost me.
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Old 02-23-2008, 10:52 AM   #4
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Isn't there something that relates to the piston speed? 1200 fps or something? I think that might be related to the speed that fuel in combustion might burn at. As you start to go over that, you efficiency goes down.
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Old 02-23-2008, 11:09 AM   #5
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Quote:
Originally Posted by kamesama980 View Post
so you're saying when you have a high load on the engine, downshift to up the rpms into a more usable range where the engine's making enough power to handle the load? basically, when you need torque, put the revs in the middle of the peak of the torque curve? if so... yup. maybe even duh. if not, you lost me.
thats what i was thinking, liek my peak torque in my truck and car are around the 2k range. i can spee dup at the bottom and be in a higher rpm but it will slow down till it hits that peak torque then it wont slow down anymore. same with the car, if i can accelerate before i have to go up a steep hill i can climb it in 3rd, granted im only goign about 20mph but the rpm is right where it needs to be so i can climb it.
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Old 02-23-2008, 01:57 PM   #6
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kinda, how many people actually now what rpm they produce maximum torque though??

common gauges in a car are rpm, etc. but a lot of people don't have vacuum gauge. from being on this forum, I get the impression that everyone is driving to get the rpm's as low as possible. I drive according to a vac. gauge and knowing where in the map less fuel is being used. for instance I'll drive, never going above 12inhg, if I can, no traffic etc., and accomidate my driving to that. rev up the motor higher.

and this is all the time. not at all really paying attention to speed. for me, I dunno if it's my tranny dx not si, civic. but I can't take hills in 3rd unless I give it a **** load of gas, so I'll take the revs way up, paying attention to vac. and not go above 15inhg no matter the speed.

if you don't use a vac. gauge or have seen a fuel map its kinda hard to explain. this is more of an idea, for input if, anyone has a clue what I'm talking about and not really a question. a mpg would really help to prove or disprove everything I'm talking about. I want a supermid so bad..... now
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Old 02-23-2008, 10:46 PM   #7
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no u do have a point, like i can climb a certian hill in 3rd in my truck but i also can do it while barely touching the gas, others i can go up the hill but the pedal has to be 3/4- floored to get up it.

but it also helps to know where your torque is at its peak, meanign the engine is most efficent at making the most torque it can at X rpm, meaning you can use less gas at that rpm to do a job(hill climb, towing, etc) while making the same ammount of torque as if you had the rpm's higher/lower but the pedal floored.
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Old 02-24-2008, 08:47 AM   #8
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torque, hmmm that's interesting. I've never really thought about that.
I just use just enough throttle to move...

are there dyno sheets for stock cars somewhere? that wouldn't even help me cause my cars modified..
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Old 02-24-2008, 10:59 AM   #9
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I think what you're trying to do is find measurable, quantifiable data for the generalization we're talking about.

I know the most efficient piston speed for my car is around 1800-2500rpm and the peak torque is around 4400 rpm (according to factory specs) so my ideal hill climbing area is somewhere between. two ways to measure it with the good ol' butt-dyno are 1. easiest acceleration/hill climbing per gas pedal input and 2. best acceleration racing around with friends (which most people here don't get into :-p) too high rpm and you lose torque, too low rpm, you lose torque.

good luck finding dyno sheets from the mfr unless it's an advertising point. your best bet would be to get your car dynod

I completely agree that low throttle high rpm is far more efficient when you actually load down the engine (hills, trailers, etc)
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Old 02-24-2008, 03:57 PM   #10
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You could try to find a stock vs. mod dyno chart by searching the honda boards like I did, but with a turbo, there's no telling how that changed your curve, so the only way you'll really know is with a dyno.

Peak torque can be misleading if, like my D16, you have a plateau between 2500-4500 where tq is nearly the same, but the peak is around 4500.

I've always felt that moderate RPM with light throttle gave better response and is more efficient than low RPM / moderate throttle, but I can't quantify this
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