Author Topic: what makes an engine more fuel efficient? (Read 6402 times)

hoevesruperd · « **on:** May 22, 2008, 07:03:11 AM »

we often talk about mods for more performance
but with the prices of gas going up, i was wondering what it takes to make a better M42.. more fuel efficient and still powerful.

what makes today's engines so fuel efficient compared to older engines? is it just better tuning? more power = more air + more gas + bigger combustion chamber. is there another way to power/fuel efficiency?

the best mod i have found yet for a better fuel efficiency was to remove weight and drive slowly.

i would like it if everyone could throw in some ideas on how to build a well balanced M42 (fuel efficency / power)

Boyracer · « **Reply #1 on:** May 22, 2008, 07:48:50 AM »

Do as BMW does... Change all pumps to electric ones that only run when needed and cover bottom of the car and especially engine bay and fill all unneccessary hoels in front of the car.

Also, narrow tires and especially lightweight wheels help.

futron.sim · « **Reply #2 on:** May 22, 2008, 10:05:14 AM »

One important thing that could improve the engine efficiency is thru better spark plugs, coils and cables. The more powerful the spark produced, the better the combustion and hence more power. Since you get more powerful, you can be lighter on your right foot.

tjts1 · « **Reply #3 on:** May 22, 2008, 10:16:16 AM »

I think it has more to do with aerodynamics than the engine. Our cars have a CD of .36 vs .25-.32 for most modern car. Even the E36 had a CD .29.

But there are a lot you can do to improve your fuel economy.
Manual steering
3.64 or 3.44 small case differential
electric cooling fan
EV6 ford 4 hole ford injectors
cold air intake to run 87 octane without ping
75w90 synthetic gear oil
synth ATF in the transmission
0w30 (winter) or 5w40 (summer) engine oil
Learn efficient driving techniques like pulse and glide
Change your brake pads if they are worn down. The brakes will drag more when the brake piston is near fully extended.

One technology that makes modern engine more efficient is variable valve timing for low end torque in combination with very tall gearing.

EN318isPDX · « **Reply #4 on:** May 22, 2008, 12:02:35 PM »

I say full tune up and new fuel system really made my car a gas saver

ClodKing · « **Reply #5 on:** May 22, 2008, 02:09:47 PM »

If you really want to notice some fuel savings, switch from an 89' suburban to 318. The difference is amazing! hahaha.

Anyways, I read somewhere on here that installing a wide band O2 sesnor improves your gas mileage.

vonkamp · « **Reply #6 on:** May 22, 2008, 04:13:37 PM »

Some great tips here but enjoy your great mileage you are already getting. Just think, people are running out to buy Prius's, spending 26k with $400 monthly payments for the next 5 years to get 15 more mpg than we are getting. I have less than 4k into my car and I'm not lugging a thousand pounds worth of batteries giving me a 26 second 0-60.

One other tip, keep a good slick coat of wax on the car. It helps...

mkodama · « **Reply #7 on:** May 22, 2008, 06:08:34 PM »

The big difference is just the design and technology of the engine.

A big difference is the improvements in engine control technology. Computers these days in cars can run the most advanced spark timing the gas allows can thanks to knock sensors which makes for the most power and complete burning of fuel. Fuel metering is also better controlled with modern ECU's, so that when you are simply scooting along in traffic, or cruising on the highway, the engine uses the bare minimum amount of fuel.

Other technologies like sequential fuel injection along with coil on plug ignition makes for very controlled engine conditions.

Then there are other things not so directly related to the engine, like electric power steering, electric engine fans, lighting systems that draw less current (HID's and LED's) and variable output air conditioners.

hoevesruperd · « **Reply #8 on:** May 22, 2008, 09:03:35 PM »

its good to hear all these answers. the reason why i'm asking all this is cause i'm about to rebuild my e30. my M42 will need a rebuild. needs new timing gears. i'm also low on compression. for sure i'm tempted to build stronger more powerful M42, maybe a stroker but i didnt want it to drink gas like i drink beer... :p
after all accessories are electric and i removed all the extra weight possible, will the solution for a happy reving economical engine be in its fuel/ignition management? since i'm rebuilding the engine anyways, is there some internal mods i should do? i would imagine lighter internals would mean more efficiency... anything else?

thanks for all the input! this is such a great forum!

the rebuild will start as soon as i get my hands on the volvo v70 as a DD. i'll keep a thread alive

twinpop171 · « **Reply #9 on:** May 23, 2008, 06:03:13 AM »

Quote from: vonkamp;49903

Some great tips here but enjoy your great mileage you are already getting. Just think, people are running out to buy Prius's, spending 26k with $400 monthly payments for the next 5 years to get 15 more mpg than we are getting. I have less than 4k into my car and I'm not lugging a thousand pounds worth of batteries giving me a 26 second 0-60.

One other tip, keep a good slick coat of wax on the car. It helps...

+1

Keep engine well tuned. I replaced all vacuum hoses, filters, plug wires, plugs, installed BavAuto HP coils, JC chip, Red Line oil in trans and diff.

If you think about it, you are better off spending this money for a well tuned car and one that is enjoyable to drive or put the money in the tank more often for decreased performance.

With a light right foot I get 33-38 mpg on highway and 25-28 mpg local running 93 octane.

People bash the dual mass flywheel on these cars but I really believe that it helps mpg cruising at low speeds in traffic. The combination of the BavAuto coils and the heavy ass flywheel keep the torque up and mpg guage down while cruising.

Just my 2 cents worth.

Dan.

twinpop171 · « **Reply #10 on:** May 23, 2008, 06:10:28 AM »

Quote from: hoevesruperd;49917

the rebuild will start as soon as i get my hands on the volvo v70 as a DD. i'll keep a thread alive

BTW Good luck with rebuild and keep us posted.
Dan.

futron.sim · « **Reply #11 on:** May 23, 2008, 09:04:14 PM »

Quote from: mkodama;49909

The big difference is just the design and technology of the engine.

A big difference is the improvements in engine control technology. Computers these days in cars can run the most advanced spark timing the gas allows can thanks to knock sensors which makes for the most power and complete burning of fuel. Fuel metering is also better controlled with modern ECU's, so that when you are simply scooting along in traffic, or cruising on the highway, the engine uses the bare minimum amount of fuel.

Other technologies like sequential fuel injection along with coil on plug ignition makes for very controlled engine conditions.

Then there are other things not so directly related to the engine, like electric power steering, electric engine fans, lighting systems that draw less current (HID's and LED's) and variable output air conditioners.

There is also one more important engine control and its VANOS. Variable valve timings technology have come a long way. There is also higher compression ratios and tighter manufacturing tolerances which all help to improve economy.

christophbmw · « **Reply #12 on:** May 28, 2008, 05:56:20 PM »

Quote from: tjts1;49886

I think it has more to do with aerodynamics than the engine. Our cars have a CD of .36 vs .25-.32 for most modern car. Even the E36 had a CD .29.

But there are a lot you can do to improve your fuel economy.
Manual steering
3.64 or 3.44 small case differential
electric cooling fan
EV6 ford 4 hole ford injectors
cold air intake to run 87 octane without ping
75w90 synthetic gear oil
synth ATF in the transmission
0w30 (winter) or 5w40 (summer) engine oil
Learn efficient driving techniques like pulse and glide
Change your brake pads if they are worn down. The brakes will drag more when the brake piston is near fully extended.

One technology that makes modern engine more efficient is variable valve timing for low end torque in combination with very tall gearing.

+1....except, your running 0W-30 in the winter :eek:, what effects does this have on the engine ?....ive never seen anybody run that stuff in the M42.

ps, i think you meant to say cone filter instead of "cold air" because the M42 already has a "cold air" intake from the factory :rolleyes:.

hoevesruperd · « **Reply #13 on:** May 28, 2008, 08:24:03 PM »

i've been adapting my driving style. it helped so much. and i tried the pulse and glide thing just for fun. i didn't do it long enough to see a difference in fuel consumption.
for the efficient rebuild i think i will work on external parts rather than engine parts. i.e. make the car lighter, lower and well tuned.

colin86325 · « **Reply #14 on:** May 28, 2008, 08:55:08 PM »

Synthetic lubricants, as appropriate, in the gearbox and the diff.
Protects better, lower friction (better fuel economy), lasts longer. But costs more.

You can run higher pressure in your tires