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Old 08-29-2014, 09:53 AM   #21 (permalink)
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Thats the first thing I did when I got my sg2 was search for shift points, then the overall crusing speed'gear'rpm combination.

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Old 12-07-2017, 07:14 PM   #22 (permalink)
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I was looking at increasing low end torque on my Honda as well. My transmission is shot so I'm replacing it with the a000 which drops my hiway rpms quite a bit and I was wondering if my d16y8 would make enough low end power to still be efficient at the lower rpms. I believe the new hiway rpm would be around 2200. Instead of the 2700~2800
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Old 12-07-2017, 07:58 PM   #23 (permalink)
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I expect you'll be fine. You may need to downshift for some hills, but you'll be able to maintain speed.

Remember, the more open your throttle is, the better. Part throttle is less efficient.
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Old 12-07-2017, 11:13 PM   #24 (permalink)
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Really? I didn't know that. How does that work? Because with the throttle open more doesn't that mean more fuel? Usually when I'm trying to get higher mpgs I figured that having the highest vacuum would be the most fuel effiecnt which occurs at a midrange rpm and less throttle. Is this just on maintaining speed or is this for acceleration as well? Teach! ��
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Old 12-08-2017, 12:45 AM   #25 (permalink)
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Here's a base-specific fuel consumption chart for a Prius engine:



Here's one for a more traditional Saturn engine:



Source: http://ecomodder.com/wiki/index.php/...on_(BSFC)_Maps


In brief, higher cylinder pressures are more efficient, and generating vacuum wastes energy. There's also a best RPM for each engine geometry, which has a lot of factors but probably has a lot to do with flame speed vs piston speed and the fact that friction goes up exponentially as RPM increases.

In a perfect world, an engine would be able to operate at its best RPM and generate no wasteful vacuum. Unfortunately, the power needed in a car is highly variable, while engines are only efficient in narrow windows. Engine sizing, then, is very important.

In a vehicle with fixed ratios, increasing vacuum does indeed reduce the fuel burned, but you're also losing efficiency. It would be better, rather than running at higher vacuum, to have a yet taller gear and keep vacuum low. After all, doesn't upshifting always hurt economy? And downshifting help? But it reduces vacuum? If high vacuum we're good, you'd always want to drive around in first gear at redline to make the most vacuum possible.

In something like a Prius, where engine speed can vary effectively infinitely, the throttle plate is left wide open and engine speed is varied to produce the power needed to move down the road. Diesels are more efficient in part because they generate no vacuum, but instead have a variable air:fuel ratio.

Many engines start to enrich AFR near wide open throttle, which is a large part of why peak efficiency is often just below that, rather than at it.

Systems like variable valve timing and cam lobe profiles are examples of technologies which make the high efficiency windows larger.

If you wanted to run your engine at high load all the time with fixed gear ratios, you would, unfortunately, accelerate past the speed limits, because most engines are oversized so you can still climb hills and such. Many on here practice a technique called "pulse and glide", whereby they accelerate, then cut power to the engine and coast for a bit. This isn't always feasible, but it usually provides large returns. My previous car had stupid gearing and would deliver ~30mpg at 45mph, but could average over 50mpg with very dedicated pulse and glide averaging the same speed.

Hybrids oversize the engines less and provide burst acceleration assistance with an electric motor. My Insight's gasoline engine actually varies air:fuel ratios too, to a limited degree, which allows diesel-like efficiency in some cases. Hybrids also get rid of a lot of lossy accessories; my car has no power steering pump or alternator. For these reasons (and more) I can see 100-120mpg under optimal conditions, without the need for many driving techniques. For you, there are a lot of tricks you can use to overcome engineering limitations and improve economy. Driver technique often provides more return than any modification to the car.

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Old 12-08-2017, 01:23 AM   #26 (permalink)
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It's kinda late. Somewhat pick up what you're saying. Is this kinda how lean burn works? Less fuel and less power so you have to give it more throttle which in turn increases your throttle efficiency? Is that along the lines of the same concept? Cause I get the throttle efficiency because more vacuum the more your piston has to work to draw in air.
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Old 12-08-2017, 01:37 AM   #27 (permalink)
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This is probably why egr works because it's an inert gas. So the more inert gas the more your throttle opens. That makes sense. But I still hate it. I don't like egr at all. My brain is going to town with appifanies right now. It's all making sense.
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Old 12-08-2017, 07:05 AM   #28 (permalink)
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That's exactly right.

What's wrong with EGR?
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Old 12-08-2017, 08:21 AM   #29 (permalink)
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The only thing wrong with ERG is people not understanding what it does
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Old 12-08-2017, 12:10 PM   #30 (permalink)
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I don't know. I'm still pretty young and inexperienced. But everytime I've deleted the egr my engine has stayed cleaner and my mileage has increased. On my 87 Nissan I'm not sure how much it increased but doing the delete on my xterra gave me an extra 3 mpg. Now that I have this untampered Honda and a little more knowledge and experience I can do some more testing. But I understand your theory. From what I've read egr is just to decrease compression temperature down to reduce Nox or something. I'm going to test it within the next couple months. Try to set it up so I can do a Aba test.

The only trouble reading about this stuff is a lot of information on the Internet can be misleading from all the opinions and hear say. Only good way to figure it out is to test it and get personal experience or find more factual content. I'll have to get an afr and egt gauge to really prove any of the "known" egr facts.


Last edited by Ni87; 12-08-2017 at 12:35 PM..
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