Proper Technique at 100 km/h?

[JacobLeSann]

Hey all, I’ve been relying on my scangauge for a while now and assuming I’ve been doing 45-50 MPG. After doing manual estimations, Ive realized I’m closer to 40 MPG. My manual estimate comes from burning almost a whole tank going to Winnipeg, around 600 km from me (forget the exact number). It’s a nice number, but very low to me considering my modifications and techniques.

I pulsed to 90 Km/h and coasted in neutral to 80 km/h the whole way. Only did 39.3 MPG. Scangauge said I did 55 MPG. Bummer.

On my commute, I used to DWL at 90 km/h, with the scangauge telling me I was pushing 40-45 MPG. Unsure how accurate that is.

Now, I’ve tried two techniques. First is pulsing to 100 km/h and coasting to 80 km/h in neutral. That gives highest at 37-40 MPG on my mostly highway commute. The second is the same technique but with EOC, which gives somehow less, at 32-34 MPG. I’ve got the SG set to hybrid mode to keep track while the engine is off, but it still does this weird glitch where it will read ultra low numbers for a second or two before kicking into the 9999 MPG range.

I have streamlined my work schedule so I fill up verrrryyy rarely, which makes manual measurements a monthly occurrence. I’ll have to start tracking a manual measurement next time I fill up.

My main question is: what is best? I’m driving a ‘97 Civic Si with a manual trans. Getting only about 600 km or maybe 390 miles per tank seems sub par considering my techniques. Maybe I’m doing them completely wrong? Feel free to school me on technique

As a side note, anybody know why my SG is so off? It’s commonly 10-30% off. I’ve had it tell me I’m pushing 70 MPG when I’m totally not. Don’t event trust it for averages anymore.

[M_a_t_t]

I've never had a scanguage, but have read that it uses intake air to calculate fuel economy. Works ok, but not the most accurate since the engine doesn't always run at 14.7

Not sure on the techniques. I've still got an auto so I don't have any experience with PnG.

[California98Civic]

What matters most for EOC and pulse & glide is RPM and engine load. The d series engines like approx 75% engine load on the acceleration. The scan gauge should be able to display live engine load (not throttle position). It works like a vacuum gauge would. It reads the MAP sensor output. Don't use hybrid mode.

[Vekke]

Also the ratio of pulse vs glide time taken. If speed goes down fast on glide there is no sense to do P&G in my opinion. You can do some rough calculations yourself based on your consumption. When I used that technigue in diesel my push were few seconds and glide should be over 10 seconds easily to give better consumption.

If glide was not working I used glide with load meaning let the speed go down slowly by giving it proper amount of gas. Gliding with load you could say.

[Ecky]

Pretty sure the US 6th gen Civic Si had the B16A(2?), not a D series. And, in my opinion, that's pretty darn good economy if it is in fact a B16. It's an undersquare engine (very short stroke, large bore), with a lot of internal friction. The transmission is incredibly short (making pulse & glide essential), and though they're incredibly stout engines, they're not particularly thermally efficient, at least compared with a D series or even later K series.

As California98Civic says, a vacuum gauge (or better yet, an OBD II dongle + the Torque app) could be valuable. Generally speaking, higher loads are more efficient, but above a certain point (maybe 75-80% load, 20-25% vacuum) the engine starts to pull ignition timing and run at a richer air/fuel ratio, which really kills fuel economy. With proper instrumentation you can likely increase your numbers a lot.

Something like this should work for you.

EDIT: A Scangauge may need calibration, which could be why it's off, but they also don't take air/fuel ratios into account when calculating economy. If the engine is running rich when you pulse & glide, your fuel economy is going to be lower than it reads.

If you have access to being able to swap the transmission, the B18B (Integra LS) transmission could give a pretty serious improvement. They're pretty cheap, and it's reversible.

[MeteorGray]

I don't Pulse-and-Glide so I can't help with that, but I do use a ScanGauge so maybe I can help with that via some observations.

As I'm sure you have discovered, at each fill-up, the SG prompts you to fill in the actual amount of gallons used, and if it is different than the SG had calculated, you are prompted to decide if an offset factor regarding MPG should be changed. By this methodology of changing the offset factor as needed, the gauge can be finessed to achieve very accurate MPG for each tank used and during intermittent trips while on the road. In my case, my offset factor happens to be 13.9%, and with this value the SG predicts within a MPG or two the actual mileage on each trip.

Now, I will note that most of my driving has been very consistently highway on the same route and driving conditions, and I fill up at the same station, so I've got the SG dialed in very well and thus see very accurate MPGs as verified at the pump. However, I'm under the impression that if I were to change driving habits significantly, such as varying a lot between city and highway and idling and whatever, and if I were to use different stations that might tilt different ways that can change the actual fill-up fill line, then the SG likely would not be as consistent and might need to be adjusted at each fill-up in order to follow the varying conditions. IOW, wide variations in driving conditions might degrade MPG accuracy of the SG.

For this same reason, I would guess that that using a P&G technique, which is inherently very inconsistent as determined by on-and-off throttle and/or ignition and related varying speeds, as influenced by traffic conditions, terrain elevations, etc and etc, all of this would throw so many variations at the SG that MPG accuracy might suffer significantly.

Just my unconfirmed musings on the topic.

[JacobLeSann]

Can vouch for consistency: my SG reliably and accurately read out 40-43 MPG when I used to use DWL techniques. Now it’s all over the place.

A new gauge is a good idea, but I’ve already modified and messed with mine! No way I can sell it and buy a new one now :/

Engines and trans swaps seem interesting to me. I both hate working my butt off all night in the shop and love learning new things, so I may very well do just that. I’ve found a $600 parts civic near me. It’s a 1992-95 hatch, and I’m thinking it may be a CX, with a nice and tall trans. It’s been swapped, sadly, so the B16A in it isn’t very useful to me.

At the point of swapping and changing the car all up, I wonder if I’m making the wrong move. It’s a clapped out Si, but I could very well fix it up and sell it, then find a model better designed for FE. Then again, used car prices are stupid right now.

[Ecky]

I'm sure someone would be thrilled to trade you a clean VX, HX, or even CX + cash. B16's are very desirable engines right now, and the only thing people like about the models I've mentioned are that they're lightweight and accept a B series engine. Most people consider their drivetrains to be garbage.

[JacobLeSann]

Maybe I’ll join Honda-Tech and ask around. Would you know if engines/trans from the 92-95 gen would bolt up? I’m thinking they would. I do love the EG hatches, though. Would be easier to carry all my junk around. I’ll probably stick with mine regardless.

I do worry about the state of the engine. ~250k+ km on it and it feels really gutless. I’ll carpool with my friends and watch as it can barely accelerate. Probably needs a cleanup/tuneup.

Edit: Missed the point. Using the engine in the $600 car could be a good option for a trade, as you say. Wonder if it’s also clapped out.

[Ecky]

To the best of my knowledge, B and D series use the same engine side mount, and most transmissions have a different side mount (the mount that holds the transmission to the car), because the posts on the transmission that the mount bolts to are different. However, B and D series are popular enough that you can probably find a mount for the transmission and chassis combination you want.

The tallest transmission that bolts to your engine is the B18B Integra LS/GS transmission. The most efficient engine that will bolt into your chassis is probably the D15Z1 from the 92-95 VX. The wiring from a 96-00 engine (such as the 96-00 HX's D16Y5) is probably easier because the wiring will be more compatible. All D series transmissions bolt up to all D series engines so you could use whatever one you wanted. If you set your mind to it, you could make any D or B series engine work with any D or B series transmission, in your car. Some will simply be easier / less involved.

Ultimately though, it's probably more cost effective to swap cars than engines. VX's are relatively rare because people like to buy them to put different engines in, but HX's aren't that hard to find. My absolute favorite 90's Civic is the 92-95 VX, and I was lucky enough to get one for free from a forum member.