93 Civic, mpg not so good.

[roosterk0031]

Accelerating briskly is better than crawling up to speed, take it to 1/2-2/3 throttle without increasing your RPM range. Coasting is the easiest spot to get good gains.

Have you always driven that engine like that since it was rebuilt? Maybe the rings aren't broken in yet?

[liquidzorch]

Originally Posted by roosterk0031

Accelerating briskly is better than crawling up to speed, take it to 1/2-2/3 throttle without increasing your RPM range. Coasting is the easiest spot to get good gains.

Have you always driven that engine like that since it was rebuilt? Maybe the rings are broken in yet?

I will try accelerating more to get up to speed with my next tank refill, to see if it increases. When the engine was just rebuilt I did drive differently, since everyone told me that it did need to struggle less, and get in more rps. Plus as much vacuum as possible, as in getting up to 60mph and letting go of throttle, having the engine brake the car with vacuum. And getting some high rpms in once and a while. That is how most people told me to break in the engine.

[liquidzorch]

Well I am thinking that the bad compression might be because of my high altitude (5000 feet above sea level). That make the compression ratio go from 9.2:1 to 8.2:1 according to the calculator here: Honda D-Series Compression Calculator by ZealAutowerks

Now I am thinking of increasing my compression ratio to help out with better mileage. It might cost more to do, but I really want to find the problem, and have it running like new.

How much can be milled off the head so it is still safe? A guy in a forum says .040 is fine. I just dont want my valves to ever touch the piston, I have had a timing belt brake while operating but thanks to hondas great engines no valves were bent since they cant reach the piston. In a chevy I had 4 of them bent.

Anyways, I am thinking milling maybe .040 off the head since it is cheap to do so, and change the head gasket for a d16y8 gasket. Doing this should get about 10.5:1 and at this altitude it should act as 95.:1.

I do this for experience and as a fun project, and cost is not so bad about 30usd to send the head to be milled and flattened.

Lets say I do this, and do a compression check to be sure of compression, Is there a way to calculate gas octane that should be used with compression psi?

Any thoughts or opinions on this project?

[night9]

Well I was thinking that part of your bad gas mileage could be due to the other problem you described in your other thread about the leaking injectors. If you just fixed that problem then I would think that you should see an improvement on your next tank. ???

[liquidzorch]

Originally Posted by night9

Well I was thinking that part of your bad gas mileage could be due to the other problem you described in your other thread about the leaking injectors. If you just fixed that problem then I would think that you should see an improvement on your next tank. ???

Thats what I thought. But there was no improvement. Only now it starts quickly. If there was an improvement in mpg it was so small I could not notice.

[night9]

I was just curious. They are both fuel related issues. Well then it is probably related to the low compression assuming everything else is running within spec.

[liquidzorch]

I have been thinking, and it occurred to me that I AM at a high altitude (5000 feet). So when doing a compression test I have to have this in mind since air is less dense. I found the altitude compensation factors and checked again and my compression isn't bad at all

Altitude Factor
500 0.987
1500 0.960
2500 0.933
3500 0.907
4500 0.880
5500 0.853
6500 0.826
7500 0.800
8500 0.773

From what I have seen, my engine (d15b7) should have a compression of about 180 psi at sea level. Now I have taken the 4500 feet compensation (0.880) and multiplied it by that. And I get 158.4 psi. So at my altitude I want to get around that number. My last compression test gave 150-160 at 5000 feet, while engine was hot and at WOT. SO this means compression is good. Even taking my lowest number (150 psi high altitude) and converting it with the altitude correction factor 0.880 I still get a pretty good number (170.4 psi at sea level).

Am I right?

Now this make me think of a new question. In higher altitude since it gives me less compression (actually not compression, less air density), would it give me less power and mpg?

I am still thinking of increasing compression ratio should it help? What should I look for in increasing compression ratio in high altitude?

[2000neon]

EDIT: Whoops, I didn't see that there was a second page and that rooster had already covered this.

Originally Posted by liquidzorch

I never press down on the gas pedal more than 1/8th way down, I mostly only tap it down very little to move.

In my opinion, this is part of your problem. Try accelerating "briskly". Don't just floor it, but don't be afraid of the throttle when accelerating, use the engines torque and optimal BSFC range. Do not give it enough throttle (or rpm) to cause the ECU to richen the fuel mixture, but don't be afraid to accelerate. You have to burn fuel to accelerate no matter what, it is better to use a little more fuel for a much shorter time, than slightly less fuel but for a very prolonged acceleration up to speed.

When I had my old Neon and started really pushing for better fuel economy I tried driving like you do (barely touching the throttle), and it hurt my economy.

[liquidzorch]

Originally Posted by 2000neon

EDIT: Whoops, I didn't see that there was a second page and that rooster had already covered this.





In my opinion, this is part of your problem. Try accelerating "briskly". Don't just floor it, but don't be afraid of the throttle when accelerating, use the engines torque and optimal BSFC range. Do not give it enough throttle (or rpm) to cause the ECU to richen the fuel mixture, but don't be afraid to accelerate. You have to burn fuel to accelerate no matter what, it is better to use a little more fuel for a much shorter time, than slightly less fuel but for a very prolonged acceleration up to speed.

When I had my old Neon and started really pushing for better fuel economy I tried driving like you do (barely touching the throttle), and it hurt my economy.

Ok I have already refilled and I am accelerating briskly this week. Lets see if it helps. I also had another question about accelerating. In my city we have a lot of over passes, and under passes, I spend most of my time on them since there are no traffic lights. But when going down hill, sometimes I can go for miles without loosing speed in neutral. Is it better to leave it in neutral until speed starts to drop, leaving it in 5th gear with no gas pedal, or pressing the gas pedal just enough to maintain speed. Like I said, in neutral I dont loose speed for a couple miles, but in gear I do loose a little speed. I just dont know if it uses less gas in neutral (idling) or leaving it in gear. I would guess neutral uses less.

[California98Civic]

Originally Posted by 2000neon

Try accelerating "briskly". Don't just floor it, but don't be afraid of the throttle when accelerating, use the engines torque and optimal BSFC range. Do not give it enough throttle (or rpm) to cause the ECU to richen the fuel mixture, but don't be afraid to accelerate.

That's the good advice again. But the difficulty in finding the right range using a butt-o-meter is the reason for getting a vacuum gauge (to judge where optimal BSFC is), a tachometer, and--as an option--an MPGuino (to see the effects on economy more quickly than with tank-to-tank method).

But I have to think you'll see improvements doing what 2000neon says.