Mpg.... Query on improving mine with the setup i have

Okay really looking for some ideas here as I struggling to think what to do next. If you have any ideas I would appreciate it.

I have a 1776 with twin webers (40s) running a vw speedshop exhaust. Sounds great, pulls brilliantly. Kicks out loads of torque and 100bhp. Engine is in great nick, having been built by Laurie Petit less than year ago. It's regularly serviced and everything appears to be spot on.

Fuel economy is not what I want it to be. No matter how I drive, however loaded the van is i can only get 20mpg to gallon. I am not one of the few who thinks their van should return 30mpg. But I do want to get 25......

The van has been tuned by Tom airey and despite sticking some larger main jets in, which didn't adversely affect fuel consumption, she is jetted okay.

It's a standard 4 speed gearbox
I have a 123 distributor on curve 0.
I use 15/40 oil.
I have external oil filter and cooler. The oil temp rarely exceeds 180.
The van is stock height with stock wheels.
It's a Devon poptop and the wheel is on the front.
The van has standardish interior, in that it is not heavier than the original.

There is a sound of a wheel bearing which needs looking at/ replacing but what other things can i look at!?

Timing. Done
Valve clearance. Done
Tyre pressure. Done
Brake check. Done
Jetting and fuel. Done
Replace wheel bearing. To do
Driving style. Tried everything
High octane fuel. No difference
Air filters are clean

It leads me to think with these carbs I won't get more than 20 or perhaps some resistance ocurs on wheels, bearings, brakes?

Sorry for depth of detail but I hoping someone might state the obvious based on something I missed...

 

Oh yeah 1 more thing....

Yesterday I filled up just before the m25. Drove at 50mph for 2 hrs, with very minimal braking and certainly no overtaking. Filled up again and it was 19.8 mpg.


Andy

 

Why is everyone so insistent on getting 30+ year old vans to do more than 20mpg? VW testing results came back with 23 (I think) in ideal circumstance's.

They are old motors running old tech pulling lots of weight with no aerodynamic's.

At the end of the day it is what it is.

Sorry for the slight rant.

 

A big engine and big carbs will be worse than a small engine and a small carb bigger volume to get more fuel in
So if you where getting 23 and now 20 i would say you have done well

 

You have to remember VW's figures of 24mpg (1600) and 23mpg (2000) were obtained over 6 miles at 3/4 full speed on a dry surface for the given bus. That's 51mph for a 1600 and 59 for a 2000.

 

belly pans will smooth the air flow under the van

and try some larger wheels/tyres on the rear to drop the RPM a little, with the 1776 you now have the extra go for higher gearing

 

I'd take a look at your carbs as well.

A slightly bigger engine with twin carbs I'd expect to give better fuel consumption, as it's more efficient and you're not thrashing it all the time to get anywhere. 20mpg sounds dire.

You may have 40s, but check what size venturis are fitted. 40 only refers to the size of the body. I assume Webers have swappable venturis like Dells. I'd stick with 28mm on a van. Assume you haven't got enormous valves.

Then see if you're a bit over jetted on idle & mains. What colour are your plugs?

 

Feeling better now...

why not go the whole hog?. Ditch the engine, interior windows etc.

Replace the windows with plastic, replace the interior with o.range crates. Get rid of the front beam as that weighs loads, maybe think about welding in some macpherson struts in its place??

Get rid of the heavy engine and gearbox - they're pretty crap anyway, you could probably shoehorn a 1 litre lupo into the engine bay.

Take a sledge hammer to the front to make it a bit more aerodynamic. You could also fit some side skirts to match the aerodynamic belly pans... :laugh2:

For every litre of petrol you could try 100ml of urine to water it down with?

 

Thanks for all the replies thus far. Some useful, interesting and odd replies (Joker!).
Grateful to one and all!

I would have thought that being a slightly bigger engine and driven considerately that 20mpg isnt right. Hence I have to agree with Snotty.

This led me to going back to my MPG figures and i stand corrected regarding what I actually get and what I did get. I think I need to go back and do some trial and error changes on the basis that I have had better mpg. I am a bit sad in that I store every Petrol receipt for the van since I bought it and made little notes against each one in a spreadsheet to say a summary of the journies I took and when I did my valve clearances/service jobs. Hence the information I have below is available easily.

Scenario 1
When I first had the engine running with 55 idles the average mpg was 24.26 over a 2 month period covering 1231 miles
but there was a huge flat spot during gear changes low down on revs. So I had it put on rolling road.
Total Miles covered: 1231
Average Fuel Consumption: 24.26
Date Range: 4 Months

Scenario 2
following the tune up at the rolling road place, the idle jets were changed to 60, which reduced the flat spot significantly.

Total Miles covered: 3436
Average Fuel Consumption: 22.11
Date Range: 2 Months
(This included 2500 miles around France in fully loaded camper with bikes on the back and driving around all roads

This obviously affected the MPG.


I had some problems with my engine (dropped a valve) and Laurie Petit rebuilt it for me (top bloke!)

Scenario 3
After the rebuild which included 2 new heads as reccomended by Laurie (bought new)

Total Miles covered: 1193
Average Fuel Consumption: 19.88
Date Range: 2 Months

I suspect that the new heads have affected the mpg? Could it be there are different size valves??

Scenario 4
Tuned by Tom Airey at Airey Tuning where the Main Jets were changed from 115 to 130. This gave me bags more acceleration and driveability.

Total Miles covered: 739
Average Fuel Consumption: 18.71
Date Range: 1 month

It seems to have marginally affected the fuel consumption which I would put up with given the extra oomph I can get when cruising.

The carbs are currently jetted as follows:
Emulsion Tubes F11
Air Correction Jets 180
Main Jets 130
Idle Jets 60
Choke Size 28

Previous jettings:
included that which was recommended by Eurocarb
55 idle jets

reccomended by Eurocarb:
Emulsion Tubes F11
Air Correction Jets 180
Main Jets 115
Idle Jets 55
Choke Size 28


This leads me to think that perhaps I should go back to some 55 idles, or try the 57's. Clearly I am overjetted but that was to compensate a flat spot and give better driveability.

It does look like some improvements can be made (even by keeping these carbs), starting with the wheel bearing and a set of different idles.

Thanks

 

The problem with your data is its inconsistent. You need to drive the same amount of miles in each scenario using the same roads and the same driving style, then you will have true data to work from.

Basic science 101 - the method must be the same in each experiment to return valid results.

EDIT: forgot weather and fuel also effect the results.

 

i don't think 20 MPG is bad if this is a average with different roads being driven

yes i can get 30+ MPG on a motorway down hill with a tail wind but i can't get close to that driving in town

 

Horses for courses, I don't let it bother me. Lol

 

I got good MPG by having my timing slightly advanced, i thought the timing mark was TDC when i first got the van so idle was at 15 BTDC, went like stink did 30MPG (tin top) avaerageing a steady 70MPH on a stock engine.

THEN i built an 1835 with then dells C35 cam and 32mm chokes it did about 22 mpg (8.2 compression)

then i fitted a long ratio gearbox and got it back to 27MPG.

its now ported and flowed and upped the compresion a bit more and currently getting the fill to fill MPG measurements done on stock timing.

these vans were designed to run on really crap fuel so putting the timing forwards and compression up using modern fuel will not do too much harm and will up your MPG, I usually aim to run ron 95 at an idle timing of 10-12 BTDC. also to get any economy benifit of using super unleaded you have to put yout timing forwards - thats what modern cars do automatically.

secondly if there was a small flat spot acellerating why go up to 60s when the pump jet is supposed to sort it?? or even use a stock SVDA dizzy?? (does your 123 have the vac port as vac advance was an economy mod??)

JB

 

Also don't mind that weirdo obsessed with lupos, he knows liitle - just like to try to spoil it.

Eh? Weirdo? Do you mind, no need to be rude