Better fuel consumption

Aethelric · Post by **Aethelric** » Mon Dec 19, 2011 2:26 am

A few days ago, my back box parted company from the rest of the exhaust system. I detached it from the hangers, bunged it in the back and continued my way. I ordered a new one which I have not fitted yet. I have been using the bongo without a back box for a few days - its not much noisier.
The thing is, that my "around town" fuel consumption seems to have changed from about 22mpg to about 27mpg with the back box off! I'm wondering if its going to drop back to 22 when I fit the new box. If it does I'll try a bit of straight through pipe like quite a few folk on here have recommended.

Anyone else had a similar experience with the consumption?

briwy · Post by **briwy** » Mon Dec 19, 2011 1:04 pm

Let us know because if it does my hacksaw is straight out.

I don't mind a bit of extra noise to save 5mpg

skater · Post by **skater** » Mon Dec 19, 2011 1:18 pm

It's probably the weight saving, assuming it's not still in the boot

wormey · Post by **wormey** » Mon Dec 19, 2011 1:47 pm

Like it,

daz

scanner · Post by **scanner** » Mon Dec 19, 2011 2:12 pm

The standard back box is a waste of space and weight IMHO it does nothing a much smaller straight through box can do better and as you seem to have found out can strangle the engine with back pressure.

Some have fitted a simple length of flexi pipe to the broken end of the exhaust to vent the gasses past the rear bumper and passed several MOTs without problem. I have a small straight through box kindly donated by Mister Munkey that is equally legal (it was fitted by the garage when they did the MOT) and doesn't strangle the engine with back pressure.

Cancel the order for a replacement "dustbin" and go find a small straight through box at a local motor factors.

fatcatlawyer · Post by **fatcatlawyer** » Mon Dec 19, 2011 2:33 pm

When my back box went I had my welder son in law replace the same with a straight through pipe and when the middle box went he replaced that with a straight through pipe. In this configeration in the words of my MOT chap "that is just the wrong side of right. I think I would fail it."
Armed with that info I bought a middle box and had that fitted. Dailed through the MOT!
Ian G

Aethelric · Post by **Aethelric** » Wed Dec 21, 2011 2:17 pm

Skater - it IS in the boot - just in case I get stopped.
Now done most of a tankful around town - getting 26-27mpg. I usually get 21-22.
I wonder why? Maybe the turbo is spinning faster?
I don't know if the saving will be as good on a long run where I usually get 28-30.

Looking at some older posts some folk say you have to tell the insurance company if you "modify the exhaust" i.e fit a straight through pipe. Does anyone know the typical response of the insurance companies?

scanner · Post by **scanner** » Wed Dec 21, 2011 3:08 pm

Aethelric wrote:Skater - it IS in the boot - just in case I get stopped.
Now done most of a tankful around town - getting 26-27mpg. I usually get 21-22.
I wonder why? Maybe the turbo is spinning faster?
I don't know if the saving will be as good on a long run where I usually get 28-30.

Looking at some older posts some folk say you have to tell the insurance company if you "modify the exhaust" i.e fit a straight through pipe. Does anyone know the typical response of the insurance companies?

I've never told an insurance company when I've had an exhaust replaced or repaired - how would I know (or care) whether it was the same shape or not?

skater · Post by **skater** » Wed Dec 21, 2011 5:07 pm

[quote="Aethelric"]Skater - it IS in the boot - just in case I get stopped.
Now done most of a tankful around town - getting 26-27mpg. I usually get 21-22.
I wonder why? Maybe the turbo is spinning faster?
I don't know if the saving will be as good on a long run where I usually get 28-30.
quote]

Could be the turbo spinning up a bit earlier giving a bit more torque at slightly lower revs, or something.
Surprised you're noticing such an mpg improvement but hey, make the most of it

Northern Bongolow · Post by **Northern Bongolow** » Thu Dec 22, 2011 2:22 am

more likely the internal baffle plates were blocking the outlet/throughflow, now its gone, back to good.

The Great Pretender · Post by **The Great Pretender** » Thu Dec 22, 2011 2:53 am

Northern Bongolow wrote:more likely the internal baffle plates were blocking the outlet/throughflow, now its gone, back to good.

Nope...........but as you know I have been around forever............

.................When I was at school with my mate Rudolf..........No not the reindeer, Mr Diesel, he explained it very simply as thermodynamic efficiency.
When you get all grown up you will realise that the turbo also does what most of the silencers do negating the need for the back box and more.
HP is then expended pumping exhaust gasses out.................

The Great Pretender · Post by **The Great Pretender** » Thu Dec 22, 2011 2:55 am

Bloody site is acting up again..................

Aethelric · Post by **Aethelric** » Mon Dec 26, 2011 3:52 pm

Update:-
One my next tank, the mpg dropped back down to its usual 21-22! (as far as I can estimate from the fuel gauge - I have used about a half tank) Bugger. But then I remembered that I had filled up at an Esso station for the first tank, and my usual Asda for the second tank. I had not believed all this talk about supermarket diesel being different to branded - but now I'm not so sure. I have just fitted the new backbox so next full tank will be from an Esso station and I'll see what transpires.

scanner · Post by **scanner** » Mon Dec 26, 2011 4:07 pm

Aethelric wrote:Update:-
One my next tank, the mpg dropped back down to its usual 21-22! (as far as I can estimate from the fuel gauge - I have used about a half tank) Bugger. But then I remembered that I had filled up at an Esso station for the first tank, and my usual Asda for the second tank. I had not believed all this talk about supermarket diesel being different to branded - but now I'm not so sure. I have just fitted the new backbox so next full tank will be from an Esso station and I'll see what transpires.

MPG cannot be estimated from the fuel gauge.

The ONLY way to calculate MPG is fill-up to fill-up making sure that each fill-up is to exactly the same point and that is not that easy with a Bongo, as even if you fill right to the neck it still keeps settling down for quite a while afterwards.

Aethelric · Post by **Aethelric** » Mon Dec 26, 2011 4:44 pm

It can be estimated quite accurately Scanner - I keep a close watch on that gauge, and I know quite well at what mileage (well kilometers really) that I expect it to pass through the three marks on the gauge. Around town is usually 118km and 240km for first and second marks. That is 22-23 mpg. On my last tank I first noticed it was 140km and 280km, which corresponds to 26-27mpg. When I filled up I could get the exact figure as you describe.

On a long run (for example from Scotland to Cornwall, which I do quite regularly) the km between marks is around 150km if I travel around 70mph or 165km if I keep it to 60mph. Most of that has been on Asda diesel.

Better fuel consumption

Better fuel consumption

Re: Better fuel consumption

Re: Better fuel consumption

Re: Better fuel consumption

Re: Better fuel consumption

Re: Better fuel consumption

Re: Better fuel consumption

Re: Better fuel consumption

Re: Better fuel consumption

Re: Better fuel consumption

Re: Better fuel consumption

Re: Better fuel consumption

Re: Better fuel consumption

Re: Better fuel consumption

Re: Better fuel consumption