How to increase my mpg?? (98 civic LX 5-speed, AC always on)

[Gealii]

I would go with the Ultragauge at least at first. The only reason i see getting a scangauge is if you have a hybrid. The Ultragauge has all the same functions as a scangauge minus the hybrid help. It can be used as a code reader, is more accurate the factory needle gauges, and can be calibrated to closer to your mpg readouts. The ultragauge is also much cheaper than a scangauge. And plugging into the obd2 port makes it easily exchangeable to another vehicle

[serialk11r]

The guys who are saying keep it under 2000 or whatever, are you sure about this? These small engines tend to hit peak efficiency at slightly higher rpms. My 1ZZ is not a Honda D16 but the 2 are quite similar (91.5mm stroke vs. 90mm stroke, I have 1.794L though), and while there are no published complete BSFC charts that I know of the peak thermal efficiency at maximum load is at 3200rpm or so.

Additionally, I can't go up a very (emphasis on the very) slight incline in 5th below 1600rpm, because the engine bogs. If I hold at 1600rpm (about 30mph) on flat ground my mpg is only so so, high 30s ish. When I go up to 2000rpm or about 36mph then I'm getting 45mpg or so. If I try to hold 1000 rpm, I need so much load that I only get 30mpg according to Torque. Hence, I try to not dip below 1700 unless I'm coasting in gear to a stop. For those pesky 25mph roads I tend to accelerate and then put it in 5th and give barely any throttle so it doesn't DFCO on me. That way I don't need to put in neutral and idle (depending on the ECU's mood the idle can be as high as 1200rpm sometimes :/, or as low as 600), which consumes only marginally less fuel than having the engine do a tiny bit of work in 5th, and makes rev matching a downshift easier, as well as giving me the option of DFCOing.

[California98Civic]

Originally Posted by serialk11r

The guys who are saying keep it under 2000 or whatever, are you sure about this? These small engines tend to hit peak efficiency at slightly higher rpms. My 1ZZ is not a Honda D16 but the 2 are quite similar (91.5mm stroke vs. 90mm stroke, I have 1.794L though), and while there are no published complete BSFC charts that I know of the peak thermal efficiency at maximum load is at 3200rpm or so.

Additionally, I can't go up a very (emphasis on the very) slight incline in 5th below 1600rpm, because the engine bogs. If I hold at 1600rpm (about 30mph) on flat ground my mpg is only so so, high 30s ish. When I go up to 2000rpm or about 36mph then I'm getting 45mpg or so. If I try to hold 1000 rpm, I need so much load that I only get 30mpg according to Torque. Hence, I try to not dip below 1700 unless I'm coasting in gear to a stop. For those pesky 25mph roads I tend to accelerate and then put it in 5th and give barely any throttle so it doesn't DFCO on me. That way I don't need to put in neutral and idle (depending on the ECU's mood the idle can be as high as 1200rpm sometimes :/, or as low as 600), which consumes only marginally less fuel than having the engine do a tiny bit of work in 5th, and makes rev matching a downshift easier, as well as giving me the option of DFCOing.

I know it might seem counter-intuitive but it seems to work well. Look at Palemelanesian's PaleCivic fuel log. He accelerates between 1500 and 2000 rpm at about 80% load. I do about the same, often 2200 RPMs. A distinction worth something might be that we're not at "maximum load" as you say, if by that you mean WOT and 100% load. We are at maybe 30% throttle and seeking about 80% load, which is generally regarded as the best region on the BSFC map for fuel economy purposes. I'm not claiming expertise, just experience. It works, and lots of guys here argue this is why.

[serialk11r]

Originally Posted by California98Civic

I know it might seem counter-intuitive but it seems to work well. Look at Palemelanesian's PaleCivic fuel log. He accelerates between 1500 and 2000 rpm at about 80% load. I do about the same, often 2200 RPMs. A distinction worth something might be that we're not at "maximum load" as you say, if by that you mean WOT and 100% load. We are at maybe 30% throttle and seeking about 80% load, which is generally regarded as the best region on the BSFC map for fuel economy purposes. I'm not claiming expertise, just experience. It works, and lots of guys here argue this is why.

Oh, I understand that. I also accelerate at 70-80% load. I also understand that at lower load, the peak BSFC comes at a lower rpm. For example the S2000 has best 100% load BSFC at ~4700rpm eyeballing it off the chart, but the peak efficiency arrives at 3000rpm.

What I have trouble believing is that the efficiency at 1500-2000rpm is better than it is at say 2000-2500. Most engines have their efficiency falling off at all load levels below 2000rpm. I try to get out of first early if I don't need to immediately accelerate since 2nd gear has much more controllable power on my short geared car, but otherwise I shift at 3000 to avoid landing much below 2000rpm in 2nd.

My car can be driven if I use the 1500-2500rpm range only and I'd prefer to use that range because it makes the shifts easier, but I have a strong suspicion that at 1500rpm the engine's efficiency is already pretty crappy. Maybe my engine is just in bad shape. The only hard and fast numbers I have are 1500rpm in 5th seems to get less mpg than 2000rpm in 5th, which is my best steady state cruise speed. On a road that I know is pretty much completely flat, to hold 1500rpm in 5th requires a somewhat high load, and Torque (which can read fuel flow rate and OBDII speed) seems to suggest that 4th (1900rpm) gives slightly more mpg than 5th. My 5th gear is about the same number of revs per mile as the 6th gear on an AP2 Honda S2000, so we're talking VERY short.

I'd like to do more testing on this as I do a few more tune up things to my engine. I don't burn through gas very fast so it's hard to do tank to tank testing. Yesterday Torque said I got 33mpg on a 50 mile drive even though I was pulse and gliding most of the time on the highway below 60mph, and drafting a semi...perhaps it's just my engine needing some work.

[PaleMelanesian]

I've been doing this for a few years now and I've tried all the combinations of load and rpm. 1500-2000 (sometimes 2200) and 80-90% load (13 psi MAP) is the best for mileage in these Hondas. On flat ground I can gain speed from as low as 1000 rpm, so 1500 is a conservative limit you can stretch and go lower if you like.

[mattrich67]

I just purchased my ultra gauge so I will let you guys know what I find out

[PaleMelanesian]

Excellent! You won't regret it.

[mattrich67]

I didn't know about the ultra gauge. I was looking to buy the scan gauge everyone talks about. But I just did want to spend 180$ for one yet. But for the 1/3 of the price and everyone says its easier to use and does all the same stuff unless u have a hybrid.

I spent 80$ for the gauge and all 3 mounting brackets windshield the Velcro and clip so then I can mount a bracket in my 08 xb and have fun

[mattrich67]

So i can be prepared when i get this ultra gauge what are the main displays should i be using and what should i want to read off of them when driving?

also one thing i have been forgetting to ask is what should my air intake temp be reading at?

[Gealii]

Originally Posted by mattrich67

So i can be prepared when i get this ultra gauge what are the main displays should i be using and what should i want to read off of them when driving?

also one thing i have been forgetting to ask is what should my air intake temp be reading at?

Everyones gauges are different but i run
instant mpg, avg mpg, air intake temp, engine temp, engine load %, rpm

Your air intake temp is probably reading close to the outside air temp considering most cars come with a cai or close to it. But the warmer the intake air is the better