really struggling to get to 40mpg combined
 

I have a 88-91 civic hatch, that I turbocharged. As hard as it is to believe I don't drive fast all the time. Honestly it's main because I've to really get it to run 100% properly as far as the tune, boost leaks, the pcv system, and other things. So the tune I'm using is a stock bin/maps for my car supposedly. though it ran my car great before and after turbocharging, with only changing timing in boost ( a few degrees retard per lbs of boost) and scaling down the fuel map for the larger injectors installed. The program doesn't have the ability to tune for temp changes but the o2 works and I get a 14.7 afr during cruising and idle.

I've never had the car dyno tune. The ignition maps could be way off as far as I know. I messed up on an alingment and did the front first. o and its lowered and I don't have a camber kit. other then that I rebuilt the motor, transmission, extensive tune-up. I incorporate a lot of driving techniques. FCOD, not using brakes as much as possible, not driving fast, not stoping at some stop signs, not really letting my car warm up for more then a few minutes to get settled.

I dunno, I've tried different plug gaps, the most recent thing I've started doing was FCOD and it seemed like I was going to get better mileage but I didn't get much more then 35. started using 5w30. nothing has really got me into the 40 range.

Anybody else kinda struggle or fill like they've maybe hit a wall, like what I fell. writing this I'm thinking a supermid or fuel mileage is what I need??

I could get 40 or better in your car but i would ruin the turbo. I have 2 3000gt vr4s with twin turbos so i know how hard it is to get every thing to run just right. I don't think mpg when i drive them, 35 in a turbo car like yours is just fine i would think.

How??

35 is good. I get better highway, 40 +. I'd love to see 40 combined though.... maybe I will have my ignition timing tuned on a dyno. If I had the car running 100% like I'd really like I'd probably get way worse and drive way faster. having a turbo and complaining about mileage is pointless I suppose. turbochargers are so fascinating to me.

You really do need to get that thing dyno'd and tuned properly - conservatively by a bit though.

if the maximum torque is created when the peak pressure occurs at, what 15-20 degrees after TDC. ( I really don't totally understand this, peak pressure thing totally). then it would impossible to tune for best power with a dyno. but isn't the relationship between detonation and max torque.

no, there was a good link some posted on here. and he was explaining how an engine could be knock limited. so even if you where to tune to where your knocking, then back off the timing. you'd still be off. . or would it be. wait would ether way, being knock limited or not, backing off at the point of detonation would be a good start, or if you didn't have a dyno.

there's this thing people are making called a det can. that allows you to hear detonation really well.

Well, if i drove your car i would not let it warm up. Just start going and eoc before it was ever warm. In traffic would eoc at every opportunity, skip gears when starting from a stop, draft a lot and coast when ever possible. Stay under 2000 rpm and almost lug the engine. This would mean no cooling for the turbo because i would turn off the ignition as much as possible, would not use turbo timer to let it cool off. I do other stuff as well.

I really only let it warm up for a few minutes. but I get the point.

I try eoc for a little, bit it didn't work so well. I could see it using a lot more gas then normal on my fuel gauge ( I look at my fuel gauge to see whats really wasting a lot of gas, I know its not super accurate). I take advantage of the fuel cut-off feature (FCOD). and that seem to help a lot. I also kinda do a variation of pulse and gliding. where, when I drive. I completely let off the gas (fuel injectors cut off), instead of stoping. and brake only if I absolute have to. and if I do brake I kinda pulse width module and only brake as hard as I need to.

I don't and wouldn't lug the motor. its really not good for the motor at all. I'm not going to go that far. I just rebuild the motor and transmission and I'm not about to tare it apart again prematurely.

I really don't turbo time at all, unless right before I stop the car I've been driving really hard. I get what your saying and taking it to these extreme would probably get me to my goal. but if that's the case, I guess I'll just be happy with 35.

I've never seen it abbreviated as FCOD -- it's usually written as DFCO (Deceleration Fuel Cut Off).

I describe your strategy as P&DFCO (Pulse & DFCO). I tried it and it really held me back; when I quit P&DFCO and merely used cruise control, I gained nearly 10%. I quit when I really thought about it and realized that there's not a reason for it to work on most cars with manual transmissions. You're doing the same amount of work whether you're in DFCO or not; the engine is running at the same RPM and accomplishes the same quantity of revolutions. Normal P&G works because you generate power at maximum efficiency and then disconnect the engine from the road so that the engine can idle at far lower RPM, so in the same distance the engine goes through fewer revolutions.

Of course, if you need to decelerate or stop, DFCO is the right choice...but if you didn't need to decelerate and you are going to need to re-accelerate as a result then it's probably not the best option.

We do have at least one other user who seems to be getting good results from P&DFCO, but I suspect that it doesn't work for most cars and most drivers.

As for lugging, I don't know if your car is new enough to have computer-controlled ignition timing and a knock sensor, but if so then it's probably almost impossible to lug. There's a link about it in my signature, but in short, with modern vehicles either it goes or it stalls, the computer prevents lugging. If so, you still don't want to cause the engine to rumble a lot, but you don't have to fear low RPM...if it rumbles you either downshift or ease off the throttle until it quiets. Shifting as low as possible definitely helps my 2008 VW; I can't say for sure that it would help your car, but there's a pretty good chance.

Yes, I meant DFCO, I couldn't remember. but um, I don't do P&DFCO exclusively the whole time on the freeway as a technique for a whole trip. I just do it when I have to stop. in traffic. plus it increases brake life. really don't get p&g? even if your rev up the motor to an rpm where your at a higher efficiency aren't you using more fuel? I dunno, I haven't really read anything on it.

I have electronic ignition. but I don't have a knock sensor. I'll have to check out the article. I shift at about 3-3.4k, cause it seems if I don't I don't go anywhere and I have to accelerate faster.. I really need to somehow put all my techniques together and kinda develop a style so new technques results can really be seen.

do you have a mpg gauge??

OIC. I wouldn't compare that to P&G, and I wouldn't call that P&DFCO; it's just using DFCO when you're planning to slow anyway. That is, IMO, the best way to use it.

You're using more fuel during the pulse, but then using less fuel during the glide -- and it adds up to less fuel spent by the time you get to your destination. You have to look at the big picture and spend the least amount of energy to get to your destination, rather than being too concerned about how much energy you're spending at any given moment. During the pulse you invest some gas, and it pays back with interest during the glide.

Here's why it works:
- You're making gas into kinetic energy more efficiently, by operating closer to your maximum BSFC RPM. The engine produces work most efficiently when it is at 100% load.
- Your engine has to turn fewer revolutions to get to your destination. While in gear, it's going to turn the same quantity of revolutions as before, but when out of gear it will turn less. Each revolution turns some of your energy into engine friction; engine friction is waste.

Above, I wrote that the engine produces work most efficiently when it is at 100% load. This is in part because the throttle is more open (so it doesn't have to work so hard sucking air through a closed throttle -- part of a phenomenom described as "pumping losses"), but probably mainly because it's subject to almost the same friction/reciprocating losses while making a lot more power. Whether you make a little power or a lot of power, the piston rings scrape the cylinder walls, the pistons and connecting rods have to change direction repeatedly, and so on.

Your car can probably lug, then; the knock sensor is what prevents it. Your high RPM needs match Honda's reputation, so if you can't lower your shift points and still accelerate well then I'd say don't worry about it.

:thumbup:

I just got a ScanGauge II for Christmas. It requires a 1996 or newer car.

Previously I've been using a DIY fuel rate meter, which doesn't tell me MPG but it does tell me fuel rate -- great for telling me which gear to use at a given speed, and great for indicating DFCO. That DIY fuel rate meter would work with your car and there is a link about it in my signature. I think inside that post there's a link to another post about using an Acura MPG gauge on a Civic (ok, I just looked, here it is).

A dozen years ago, when I didn't care about fuel economy, I had a 1987 Cadillac with a built-in MPG gauge.

thanks a lot for the info. I'll keep trying. maybe try p&g.

installing that mpg gauge looks a little complicated for me, i dunno I'm sure I could figure it out eventually if I could find one.

Quick explination on that... At 15-20 degrees after TDC is when the connecting rod is at a 90* angle to the "lever arm" created by the offset of rod journal to crank journal. At that point the rod has the longest "lever" to push on to turn the crank, and thus makes the most torque for a given pressure.

For what it's worth, you will likely never be able to get the same fuel economy after installing larger injectors for one simple reason: Reduced metering resolution. Quite simply, at idle the larger injectors will have to deliver more fuel. Unless you can dial back the fuel pressure at idle, you likely can't reduce the pulse width enough to fire the injectors reliably without running on the rich side.

o is that where it's at 90 degrees. give or take for different motors though right? I though is farther down. that makes more sense.

I have a set of 450cc injectors in my car, but I'll easily able to lower the pulse width enough to idle at 14.7 at 40psi of fuel pressure. I can even run way leaner at idle like 20.1 at 35-40psi.

Have you or others verified that via wideband?

The problem I ran into with 550cc injectors on a 1.6L was that the injectors would fail to reliably open for the pulsewidth desired. In other words, I could program it into the map, but there was not enough current dwell time to make it actually happen.

yep, I have a PLX M300.

hmm, 450's support more then effort HP that I want right now so, I'm good, but that's interesting. if I ever up grade. how low did you go on fuel pressure?

I think mine only went down to 45 psi. Now that I think about it, the brand of injector may make a huge difference on this issue however. Not all injectors are built the same, so perhaps the picture I have painted is more bleak than warranted. Certainly I was dealing with 22% more flow at the same pressure over 450s.

another thing that I don't understand is, the pressure inside the cylinder before the plug is ignited is relatively low. when it does ignite and starts to burn, the pressure starts to climb right immediately. so wouldn't that pressure start to push to piston down, even before TDC?? or is force, forcing the piston up is so great, even the peak pressure wouldn't stop it right then?

so, the peak happening at that 90 degree angle, if it happens any where else the total force applied to the crank during the combustion stroke would be less?

I saw a chart either on here or another site on how a gas engine works. It takes time to build power and the best use of the engine is either 2000 rpm or lower and 3000 rpm or higher. Most cars are tuned to run in the 2000 to 3000 rpm range as this works best for city or highway driving. Its not good for mpg however. So the longer i stay under 2k or above 3k the better it is.
I tried early on to shift at 3k or higher with ok results. Better was of course under 2k. The reason is that at 3/4 wot under 2k is the best way to convert gas into forward motion. If you look at my garage chart you can see how i have improved. Launching a front wheel drive car is best at about 1200 rpm, i use this to start when the engine is warm and just "puff shift" through the gears staying under 2k until 5th. I have found when starting the first time when the engine is cold that i can get into 5th gear and cruise at 23mph with my foot off the gas, then into eoc. By the time the engine is warm i have traveled about 2 miles. My mazda at 65 is tacking 3100 to 3200rpm. I usually go 55 to 57mph at 2700 rpm or less depending when i draft and draft with eoc. Hope this helps.

The pressure does start to climb immediately after spark, however the upward force exerted by the other cylinders is far more than enough to keep it from trying to stop. And while the 10-15 degrees of burn between spark and TDC are technically wasted, that is also at the low end of the pressure cycle of burn, so you waste the early, light pressure so that you can better capture the mid burn, high pressure stuff.
If the spark happens at TDC, while you're capturing the early burn pressure that would have been wasted, the real strong stuff about halfway through the burn would be right near the end of the power stroke, and pretty much wasted.

The second question... The total force applied to the crank would be the same, however, with the rod being at 90* to the crank/rod journal lever, that's where most of the force is converted to rotational torque and spinning the crank, rather than the pressure passing through the crank to the main journals and being turned into vibration.
Like if you take a wrench, and turn it with some set force, you spin the nut. However, if you were to put the wrench on the nut and instead of applying the force perpendicular to the wrench, you apply the force in line with the wrench, you'd just transmit the force directly to the nut in a futile pushing manner. Same basic thing.

Technically with the adjusted ignition timing, the total force wouldn't be identical, what with some burn pressure being wasted near the top of the compression stroke, or if it's too late of an ignition, some burn pressure still occurring in the exhaust stroke... But that doesn't matter with the question we're dealing with.

It all boils down that the forces will be the same, however with properly tuned ignition timing, more of that force will be converted into work (rotational force), rather than waste vibration.


Edit: As I forgot to answer one of your earlier questions...
No, if the peak pressure ends up occurring during the compression stroke, that won't stop the pistons... It'll break them. That's called Detonation, and it usually occurs because the mix is too lean, so that little amount of gas just burns right up, very fast. It usually ends up doing nasty things like blowing head gaskets, breaking holes in pistons, and otherwise doing very bad things to the engine.

ok, great info. you brought up some really good points that's helping me understand this. esp. a lean mixture and the waste from ignition until TDC. This forum rocks, even though its about fuel economy other then making power, people seem to formulate better info, thats proven and scientific.

what I meant though on the total pressure. was, when the ignition ignites and starts to burn, after TDC the force at 1 degree, 2 degree, etc. till 180 degree added up together would be less if the peak pressure wasn't happening at that sweet spot.

y not fire the plug at the sweet spot, like direct injection? generate to much and wouldn't that be technically detonation. buy this logic. simply used parts that are way more resistant to heat and stronger, the motor would make more power not allowing the coolant to reduce thermal efficiency. but then are air cooled motors more thermal efficient??

The problem with firing ignition at the "sweet spot" is that the burn is not instantaneous. So, actually, a well tuned motor IS firing the ignition at the "sweet spot" when the peak burn pressure occurs at around 12-15 degrees after TDC "sweet spot". So there's a difference between the ignition sweet spot, and the burn pressure sweet spot.

And you're probably right that there's going to be more power (force x time) upon the piston through optimum ignition timing.

But if you get the timing down right, to where you make the most horsepower for a given setup, you are finding that sweet spot.

All this is a very, very compelling reason to get any modified car dyno tuned, even if conservatively.

Air cooled motors are far less efficient than water cooled. With an air cooled motor, it's ALWAYS losing heat to the outside, and there is no way to accurately control the temperature. A water cooled motor can actively control the temperature through use of a thermostat. There's always going to be waste heat, but a water cooled motor can keep the engine block hot enough for optimum burn efficiency.

I meant, like if there was a way to burn the mixture all at once, like with more then 1 plug, or a stronger ignition. there's this really interesting thread I was reading on how compression actually makes power. and the person mentioned this idea.

https://forum.miata.net/vb/printthread.php?t=307292

o, yeah the thermostat. derr, in a book I'm reading they say how in nascar there using higher temp thermostats. it's about turbochargers but they talk a lot about what actually makes power, heat, and efficiency of an internal combustion engine, recovering wasted exhaust to do work.

There is, and those can be taken advantage of. There are engines out there with multiple spark plugs, and there's always a quest for a better mixing combustion chamber design for faster, more efficient burns. But for most common use... You just need to time the ignition properly.