Greedy engine - Want to improve economy

M

malreid

New Member
I'm driving a 10.5:1 'S' with 5 speed 'box and the standard twin SU's. Most of my driving is around town at 50-80km/h and I'm getting only 17-18mpg on average. It doesn't seem to matter how the car is driven.

Carb's are in good condition, as is ignition, plugs leads etc. Air filters are about due for replacement. But it's very hard to find an ecocomical tune. Any tips or ideas on improving the economy without loosing too much in the way of performance?

If I could get even just 20mpg I'd be thrilled.
 
Seems about right to me! I can get up to the low 20s on a long run, but I would expect it to drop into single figures round town after all it is a 30 year old 3.5 litre V8.
Cheers
AL
P.S. Thought about an LPG conversion? I had contemplated fitting one of those Donut shaped tanks on the boot in place of my spare (boot mounted LPG!) but never got further than contemplating.
 
LPG is a good option, a diy kit would be about £500, I guess it depends how many miles you do in it each year. If its just weekend show trips, then its probably not worth it.

The kenlow hot-start mentioned on another thread would help remove the need for choke which would save quite a bit on short journeys.

Richard
 
I think no.1 plug is faulty to start with. Start the engine on choke and leave running for about two minutes while clearing the screens and no.1 will soot up and drop out altogether. Big juicy blue spark at the plug, so I'll swap it for no.2 and see what happens. Doesn't soot up if driven straight away or once engine is warm though.

Carbs seems to be set up right. Properly balanced, dampers both have same level of oil and move at the same rate, new springs, jets about even. Using the push pins to raise the dampers indicates mixture is about right, with engine speed dropping off then stabilising. Floats ok.

Am I overlooking something?
 
Mal'
I have owned several V8 models, all autos, and none of them have liked the choke left out for long so suggest return it almost right in as the first quarter inch of movement should increase revs but not richen mixture.
Also, these engines are dependent on accurate ignition timing. A small adjustment can make a big differnce in performance and/or economy. I used to get 20 around town (just!) and 26 (at best!) on a long run in my series 2 autos - slightly less in my series 1 - about 18 - 19 and 24 - 25.
Hope this helps.
Regards, John.
 
Hmmm. Yes I've noticed choke can go in to fast idle almost straight away.

Any tips on how to get the timing just right other than advancing to peak engine speed and then backing it off and doing the old 30mph in 4th pinking test?
 
Hello Mal',
assuming your using super unleaded plus an additive with octane booster I would stick with tdc but if you're using Optimax with an additive with octane booster (such as Castrol Valvemaster Plus) you might advance to 2° btdc without experienceing any "pinking". As you can see, I'm being a little cautious here.
Hope this helps.
Regards, John.
 
I'm in NZ and currently bleeding my wallet dry for 98 octane. I have notcied a smoother idle when I've thrown in some booster as well. Will put the stobe on and have a play tomorrow if I get the chance.

But I have heard that the timing marks on the front pully can be out. The balancer moves or something?
 
malreid said:
But I have heard that the timing marks on the front pully can be out. The balancer moves or something?
Click to expand...
not heard of that but not likley I'd have thought.

The camshft is the timing computer and is libnked to crank by 2 gears wheels and a crappy chain. Wear in these components over time as well as manufacturing tolerances would mean your timing is out by a couple of degrees or more.

you should check this by truning engine - over by had - an putting in a pencil or thin rod though cylinder 1 spark plug hole and noting when the rod is at its highest - a dial gauge with the heads off is beter but .....
 
It is worth checking the timing marks on the pully if you aren't sure. (They can moce and some crank pully/crank combinations may be inaccurate)

An accurate way to find TDC with the engine assembled is to take and old spark plug, break out the nose and weld a small rod into the end (about 20/30 mm long). With this screwed in place it can act as stop against the piston.

With all the plugs removed (to ease turning):

Find TDC on No1 and then turn the engine back from TDC so that the piston is well down the bore. Insert the modified plug and then gently turn the engine towards TDC until it hits the stop. Mark this point on the pully (I wrap masking tape around it for marks)

Remove the dummy plug and then turn the engine well past No1 TDC and reinsert dummy plug. Turn the engine back until it hits the stop and mark the point on the pully.

TDC is the point halfway between the two marks.

This method is very accurate and even if you were using a dial guage you would take measurements either side of TDC and use the midpoint anyway. There are more crank degrees of movement per mm of bore near TDC so it's not accurate to just watch for the dial guage to stop moving.
 
I have a 10.5:1 '69 V8 (on an auto) and I can only re-emphasise John's comments.

Timing is everything once carbs, plugs and HT's are sorted. I had my timing re-done recently.

Mine runs on Optimax and Valvemaster and is set for 3 deg. BTDC.

If anything now, it runs maybe too rich (rather than pink like crazy) under very heavy throttle as you would expect it but under normal driving the economy has improved by at least 2mpg.

I'm getting about 17mpg as an average and clocked a respectable 23mpg on a lengthy run with a brimmed tank and 100 mile trip.

I found the biggest difference was on a cold damp start, choke out to begin but it could be reduced very quickly after the first mile or two, before I wouldn't dare put the choke in until operating temps had been reached.

The choke light never lies anymore. :)
 
Have you tried using the normal timing and blanking off the vacuum advance ? In my case my vacuum advance doesn't work and I think that's how I can get away with setting the timing at 4 degrees BTDC and only get pinking if I floor it. Using supermarket unleaded. I get about 22 mpg on a clear road which is not too bad for a 73 3500S with 10.5 CR
 
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