Tuning a mechanical diesel for efficiency?

Jimbo Mahoney · 24 Nov 2008 at 12:32

Yes, it's a 306 DTurbo.

No, I'm not a "yeh, screw mod +50bhp!!!" type.

OK, with that out the way, does anyone have advice on how to tune this for best fuel efficiency?

I'm guessing - tune it a bit rich / lean, drive a whole tank, caluclate MPG, repeat.

At the moment, it's tuned very lean and seems to be returning less MPG.

Does anyone have the torque curves of this engine and should I be driving at the peak of the curve for maximum fuel efficiency?

I currently try to maintain around 2k RPM in 3rd/4th/5th depending on the speed limit, but I'm not sure if this is the optimal speed in each of those gears. It certainly seems to be in 5th, returning 54mpg.

Many thanks for any help / advice.

Reality Bites · 24 Nov 2008 at 13:20

Jimbo Mahoney said:
Yes, it's a 306 DTurbo.

No, I'm not a "yeh, screw mod +50bhp!!!" type.

OK, with that out the way, does anyone have advice on how to tune this for best fuel efficiency?

I'm guessing - tune it a bit rich / lean, drive a whole tank, caluclate MPG, repeat.

At the moment, it's tuned very lean and seems to be returning less MPG.

Does anyone have the torque curves of this engine and should I be driving at the peak of the curve for maximum fuel efficiency?

I currently try to maintain around 2k RPM in 3rd/4th/5th depending on the speed limit, but I'm not sure if this is the optimal speed in each of those gears. It certainly seems to be in 5th, returning 54mpg.

Many thanks for any help / advice.

i would be happy with 54mpg! I've just bought one of these as a runabout so i can fund a westfield build. Had some cambelt issues (was replaced brand new but long story) and have just replaced the head. before that, on a fill tank i managed 45mpg (which is what the book suggests).

I'm yet to do a long run, but i would hope for 54-55ish.

I will sit at 75mph on the motorway though and that takes it to 2800rpm ish.

Sadgeek · 24 Nov 2008 at 15:50

Your problem will come when you go rich, and spew clouds of dust from the exhaust everytime you look at the go pedal

L0rdMike · 24 Nov 2008 at 15:52

Lets spend a few k "tuning" to get an extra 2mpg LOLS.

Jimbo Mahoney · 24 Nov 2008 at 16:05

Reality Bites said:
i would be happy with 54mpg! I've just bought one of these as a runabout so i can fund a westfield build. Had some cambelt issues (was replaced brand new but long story) and have just replaced the head. before that, on a fill tank i managed 45mpg (which is what the book suggests).

I'm yet to do a long run, but i would hope for 54-55ish.

I will sit at 75mph on the motorway though and that takes it to 2800rpm ish.

Yeh that 54mpg was a long run - pretty much a whole tank @ 50mph in 5th (2k RPM).

The last tank, around town tuned lean was 33mpg though :eek:

It seems that it's more efficient tuned a little rich than lean, as I usually get ~40mpg around town.

L0rdMike said:
Lets spend a few k "tuning" to get an extra 2mpg LOLS.

You obviously have no idea which engine I'm talking about or the incredibly complex procedure involved - a screwdriver and socket wrench are all that's required.

I was just wondering if there was a more technical way to do it than trial and error.

I guess I'll stick with trial and error then.

aproctor · 24 Nov 2008 at 16:24

http://www.club-306.com/guides/306_turbo_tuning

The Edge · 24 Nov 2008 at 16:27

I had a diesel ZX, albeit a non turbo but still the same engine. Those figures sound about right to me, mine was mega economical on a long run at 60-70 but relatively hopeless around town in traffic (what isn't?).

Sounds ok to me

L0rdMike · 24 Nov 2008 at 16:30

Jimbo Mahoney said:
You obviously have no idea which engine I'm talking about or the incredibly complex procedure involved - a screwdriver and socket wrench are all that's required.

Everyone knows the screwmod, its hardly "tuning" is it.

If you really do care though see what the AFR is.

Jonnycoupe · 24 Nov 2008 at 16:43

Block half your radiator off.

The aero benefit could be worth 1-2mpg as more air is guided over the profile of the body rather than forced through a rad, into an engine block, and dragged underneath the car.

L0rdMike · 24 Nov 2008 at 16:45

Jonnycoupe said:
Block half your radiator off.

The aero benefit could be worth 1-2mpg as more air is guided over the profile of the body rather than forced through a rad, into an engine block, and dragged underneath the car.

Dont hotter engines also run more efficient to a certain extent?

Jonnycoupe · 24 Nov 2008 at 16:48

L0rdMike said:
Dont hotter engines also run more efficient to a certain extent?

Yeah you'll certainly help that out even from the forced convection on hot components in the engine bay.

Probably something to be said for the resistance on a water pump being less pumping through an open stat through a radiator rather than a closed stat and following the tighter 'bypass' route.

Clarkey · 24 Nov 2008 at 18:15

L0rdMike said:
Everyone knows the screwmod, its hardly "tuning" is it.

tune (ENGINE) Show phonetics
verb [T]
to change the setting of particular parts of an engine, especially slightly, so that it works as well as possible:
The engine certainly needs tuning but there's nothing wrong with the car.
Could you tune (up) the engine for me, please?

sounds like tuning to me...

Begbie · 24 Nov 2008 at 19:41

Block up the cold air feed.

Dogbreath · 24 Nov 2008 at 19:42

L0rdMike said:
Everyone knows the screwmod, its hardly "tuning" is it.

If you really do care though see what the AFR is.

The AFR is dependant on 'throttle' position though. Measuring it at W.O.T. isn't going to tell you much if you are trying to drive it economically.

TBH by far the largest economy factor is the driver, no amount of tweaking is going to help if the driver is not observant and is on and off the brakes all the time.

BigglesPiP · 24 Nov 2008 at 20:24

Put 2 stroke oil in it, yer.

excaliborg · 24 Nov 2008 at 20:37

Start with the basics, make sure your tyres are at the correct pressure (maybe a couple of PSI over??) shed any unnecessary weight (spare wheel, luggage, rear seats?)

MrFunex · 24 Nov 2008 at 22:19

excaliborg said:
Start with the basics, make sure your tyres are at the correct pressure (maybe a couple of PSI over??) shed any unnecessary weight (spare wheel, luggage, rear seats?)

agree with that, also read the road, look further ahead, accelerate slowly and don't drive too quickly. I know this'll annoy some people on here, but there's a LOT of difference in economy between 80 and 60-65mph on a long motorway run.

Reality Bites · 24 Nov 2008 at 22:58

after i gaave mine a good service, i ran some diesel engine treatment/cleaner. It helped a little.

My daily commute consists of about 18 miles steady and then 5 miles town. 45 was about the best i could hope for. THe pug306 forum would be a good start....loads of people on their crazy about their old pugs.

numnutz · 24 Nov 2008 at 23:33

I've got a 306 DTurbo, 45mpg is bang on the money for efficiency. I do a daily 120miles in it, mainly 50 - 60mph stuff (I'm not after sympathy btw!)

Not sure about tuning it to run at better efficiency :S

Atom · 24 Nov 2008 at 23:34

Disconnect the egr valve.