Fuel Cost Germany Trip

Chat about the 25 Years Anniversary meet (May 2010) at Mammut Park Germany here!

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HarryMann
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Re: Fuel Cost Germany Trip

Post by HarryMann »

Without knowing what your bus weighs, comparisons are a bit meaningless..

Well yes true, it does have an affect, but for long distance crusing, provided the tyres are up to pressure and not knobblies, the type of body, wing mirrors and appendages will dominate fuel consumtion above 45 or so mph... we all tend to run fairly heavy when touring abroad, which is what most of these posts are referring too, certainly we're all 2t or over. Also it wasn't a particularly hilly drive, although the last section to Mammut were pleasant, but quite slow A type roads with lots of villages (slow, slow, quick, quick, slow) where weight would predominate.

As for your Silverbullet at 3600 rpm, here some figures I've extracted from a set of SFC curves I derived for the subaruvanagon forum a good few years ago, for the EJ22, using an SFC polar published in an SAE paper. We can maybe make a few adjustments based on improvements to the engine in later (Post 1990) models and to transmission and running-gear inefficiences (or simply assume they cancel out) and also speculate on speedo/tyres etc later too... but for now...

The bottom line is:
BHP(flywheel); RPM; MPH; MPG

30 3600 80 38.517
40 3600 80 31.028
45 3600 80 28.504
50 3600 80 26.347
60 3600 80 22.680
70 3600 80 19.895
80 3600 80 17.777
90 4000 80 15.760

So it looks like at 3600 rpm, only less than 45 BHP can get anywhere near 30 mpg at 80mph for this engine...

The question then is, can a T25 (however sleek) attain 80 mph on 42 BHP (at the flywheel), that is, maybe from somewhat less than 40 HP at the wheels?

If we consider the power output of various new models as road tested or specced by VW, and their tested/quoted top-speeds, model for model, we should then have a good plot of required flywheel power against speed and maybe can then draw some conclusions.

Personally though, I'd say 80 mph from 40 BHP or less is not possible, more like 70 would be my instinct, but reserve that big differences would apply to body style, tyre tread, Syncro or not, as well as weight.

As a guide, the aerodynamic drag alone approx. doubles from 56 mph to 80 mph, which might be half or more of the total at 56 mph, thus perhaps being three-quarters at 80 mph

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Re: Fuel Cost Germany Trip

Post by silverbullet »

OK...I'm always a bit catious when it comes to SAE data - septics say horsepower and we say PS (DIN) the difference getting on for about a third! What they call 300 hp is more like 200 PS DIN... Are these figures for specific fuel consumption worked out for stoichometric (check spelling - it's been a while) ratios?
Never mind the US short gallon!
A modern (read late 80's Japanese design) sequential efi engine will cruise at significantly higher air/fuel ratios than stioch, but I don't need to tell you that :mrgreen:
I may have been a bit over optomistic when I said at 80mph :oops: Probably more like legal +5 at best...
The Microbru uses the tallest standard diff ratio and 5th gear with rear tyres that are a shade small (255/40/17, could do with being 45 section really) so at say 70 mph is pulling about 3500 which is just over the peak torque rpm for the EJ22 or about as efficient as it's going to get :D
There's a lot of intelligent debate going on here at the moment - who's going to wade in with the toilet humour?
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90 SA Microbus supercharged wbx/UN1 project

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Re: Fuel Cost Germany Trip

Post by syncropaddy »

HarryMann wrote:
Without knowing what your bus weighs, comparisons are a bit meaningless..
certainly we're all 2t or over.

Are we? A DoKa would need another 400kgs to bring it up to 2 tonne

The fastest Diesel Syncro top speed is quoted by VW at 122 KM/h or 75.8 mph which on 185/14 tyres and a standard set of gearbox ratios equates to 4600 RPM or thereabouts which is what VW say is the limit for a JX. The fastest speed I attained on the German trip was 134 km/h (on a GPS)with a taller final drive than standard and larger tyres and a roof tent. The rev-counter was indicating between 3900 and 4000
Last edited by syncropaddy on 17 May 2010, 17:18, edited 1 time in total.
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Re: Fuel Cost Germany Trip

Post by HarryMann »

OK, well, the SAE reference was to the society that the paper was delivered to, not the HP rating.

The HP figures were derived from SFC loops of Torque Vs rpm with the sfc loops
In most cases, the difference in DIN HP and SAE is so negligible that the two numbers are interchangeable and engineers don't use the formula to find the actual difference.

The difference varies of course, but usually about 1.5%

30 3500 70.000 34.25
40 3500 70.000 27.39
45 3500 70.000 24.94
50 3500 70.000 23.22
60 3500 70.000 19.93
70 3500 70.000 17.45
80 3500 70.000 15.60



So can 70 mph be held with about 37.5 hp, or minus losses less than 35? It's certainly more likely than 80 from 42 or so.

One question of course, is have you calibrated your speedo against a GPS or timed against the M-way poles lately? Over a reasonable few miles... It's possible it could be reading high

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Re: Fuel Cost Germany Trip

Post by Aidan »

According to my gear calculator Ian's bus at 3600 on 185R14C would be doing 74 mph, if on 205/70/14 then knock off another 2mph

I'm pulling a true 60mph (gps/sat nav - dash indicated 64mph) at just under 3300rpm running 205R14C which is as fast as I generally cruise with short blasts of 65-70mph for overtaking the wagons, and showing 14-15inHG vacuum with a gentle right foot on cruise on the level at 3300, 10inHg on a gentle climb keeping speed fairly constant

I'll give the disi another few degrees of advance (Already running 3 degrees more than standard) and see what difference it makes, but looks like maybe the MV too clever for it's own good sometimes but at least it never runs lean so shouldn't burn out a piston and is able to adjust itself back to petrol pretty readily, takes about 15-30 seconds after switch over from gas at speed to get itself back in the room properly

if the idle vacuum doesn't improve with more advance then I think it's suggesting the engine is pretty tired, though it runs and revs well, I'll do another compression test and see if it's changed much in the last three years since I've been running it fully; it came with a TUV compression test record which was a year old and 5-10% better than I recorded when I got it, I think it had had a head off and the compression test was done after that work to show it had been done right - still weeps a nats out of one of the head stud nuts

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Re: Fuel Cost Germany Trip

Post by HarryMann »

BHP(DIN Flywheel) RPM MPH MPG
37.8 3600 74.000 30.000

The mixture would be whatever Subaru engine management determined, these were original test-bed figures for the early series EJ22 engines, produced by Subaru. The mixture would be varying as a functional of throttle opening which again would be set by the torque at given rpm.

Of course, there is a lot of translation & cross-plotting from one rather small zeroxed polar, and then I might have made a mistake somewhere.

But I'm failry confident for two reasons; I've extracted meaningful data from iffy small graphs a lot over the years; by inspection, the curves I originally derived look OK to me, that is they have the right shapes, stack up in an expected way, and the mumbers didn't shock me.

I know the consumptions look a fair bit higher than one might expect, but then, perhaps that's the point... there's no free lunch!

The missing link is of course the required power, and I've seen a few attempts at estimating this theoretically (and know how dubious this can be, if not normalised (pulled into agreement) with actual road-test data). I'll have a go from actual roadtests, if I can acquire enough examples.

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Re: Fuel Cost Germany Trip

Post by HarryMann »

This is from Subaruvanagon forum, for a 2WD with EJ22. I am not sure how it was derived, possibly with SFCs from the set of curves I put up a year or two earlier, but no idea where the drags came from.

Image

This is in US gallons, so at 70mph gives 18.5 (US) ~= 22.2 Imperial MPG

So going back to some of the figures above, (3500 rpm; 70 mph) points at about 55 BHP..

So roughly supports my guess on required power, although I certainly wouldn't stamp this subaruvanagon mpg plot a gold seal, without knowing a lot more.. I suspect it was built using a vehicle drag programme I've seen knocking about, pretty well entirely theoretical

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Re: Fuel Cost Germany Trip

Post by HarryMann »

Andrew

Are we? A DoKa would need another 400kgs to bring it up to 2 tonne

The fastest Diesel Syncro top speed is quoted by VW at 122 KM/h or 75.8 mph which on 185/14 tyres and a standard set of gearbox ratios equates to 4600 RPM or thereabouts which is what VW say is the limit for a JX.

My Doka weighs about 1780 kg empty, and is easily 2t when 'on tour'

So whatver the JX flywheel power is at 4600 rpm - gives us one data point at 75.8 mph - what bodystyle was that for (a delivery van?)

So 68 BHP >> 75.8 MPH
Does anyone have similar (offficial) top speeds for 1600 NA, KY?, DJ, MV and DG for various bodystyles?

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Re: Fuel Cost Germany Trip

Post by syncropaddy »

For the JX, VW quote the max power is 70bhp at 4500rpm.

"The fastest Diesel Syncro top speed is quoted by VW at 122 KM/h or 75.8 mph which on 185/14 tyres and a standard set of gearbox ratios equates to 4600 RPM or thereabouts which is what VW say is the limit for a JX."

"The fastest Diesel 16" Syncro top speed is quoted by VW at 116 KM/h or 72.1 mph which on 205/16 tyres and a standard set of gearbox ratios equates to 4400 RPM

This data is for the van body. The DoKas and SiKas are slower.

n/a 1.6 diesel - 50 bhp @ 4200 rpm
n/a 1.7 diesel - 57 bhp @ 4500 rpm

DJ 2.1 petrol - 112 bhp @ 4800 rpm (without cat)

"The fastest Petrol Syncro top speed is quoted by VW at 142 KM/h or 88.2 mph with a 2.1DJ

"The fastest Petrol 16" Syncro top speed is quoted by VW at 140 KM/h or 87 mph with a 2.1DJ

I dont have the ratio figures for the petrol data
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Re: Fuel Cost Germany Trip

Post by HarryMann »

Thanks Andrew, now we need the quoted top speeds for 1600 na and 1700 na if possible?

Maybe Bolze has more comprehensive data, partic. Syncro/2WD speeds as well

But already we can see the sort of power to do over 70 mph, but we need a nice speed power polar and the more points, the better...

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Re: Fuel Cost Germany Trip

Post by HarryMann »

OK, I've built a total drag polar for Syncro kasten wagens and 2WD buses... (which will permit some v.interesting numbers when crossed with engine data)

I would though still like to know the official top speeds of a 2.1 DJ 'bus' (Caravelle) AND same for a 2.1 MV bus

Anyone :?:

and any other official speeds anyone has, partic for 1.7 KY diesels

PS. Thanks Christoph, those were very useful numbers you sent...

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Re: Fuel Cost Germany Trip

Post by HarryMann »

Click image to see the full-size and resolution

NB. Initial analysis for 2WD buses

Image

Image

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Re: Fuel Cost Germany Trip

Post by syncropaddy »

HarryMann wrote: I would though still like to know the official top speeds of a 2.1 DJ 'bus' (Caravelle) AND same for a 2.1 MV bus

Anyone :?:

and any other official speeds anyone has, partic for 1.7 KY diesels

Speeds for 2WD Caravelle/Kombi/Van

82kw Petrol Engine = 150 km/h
70Kw Petrol Engine = 135 km/h

37Kw Diesel Engine = 103 km/h
42Kw Diesel Engine = 115 km/h
51Kw Diesel Engine = 127 km/h
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Re: Fuel Cost Germany Trip

Post by axeman »

[quote="HarryMann

[quote]Are we? A DoKa would need another 400kgs to bring it up to 2 tonne


as for the weight of our vans, i had to do a dump run full of hard core, standard doka (mv), vindic back, full tank of petrol. and me.

loaded up with hard core as i said, going in weight 2922kg. the van was heavey, riding with the front way up in the air. and the rear springs were very compressed. driving with this weight was fine from the engines point of veiw, but the breaking had to be thought about in advance, the coming out weight was 2020kg compleatly empty van no tools just five seats and me so

my weight 90kg

so including vindic and oil and fuel the weight my doka is around 1930kg.
just makes me wonder what are the weights of full blown campers? by adding 900kg it realy effects the way the van drives, and in reality 5 adults can weigh over 400kg, may have somthing to do with all the weight being from the middle of the van and going back. and in a camper the weight is more evenly spread over the whole van.

just my thoughts

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Re: Fuel Cost Germany Trip

Post by syncropaddy »

axeman wrote:Are we? A DoKa would need another 400kgs to bring it up to 2 tonne


loaded up with hard core as i said, going in weight 2922kg. the van was heavey, riding with the front way up in the air. and the rear springs were very compressed. driving with this weight was fine from the engines point of veiw, but the breaking had to be thought about in advance, the coming out weight was 2020kg compleatly empty van no tools just five seats and me so

my weight 90kg

so including vindic and oil and fuel the weight my doka is around 1930kg.
just makes me wonder what are the weights of full blown campers? by adding 900kg it realy effects the way the van drives, and in reality 5 adults can weigh over 400kg, may have somthing to do with all the weight being from the middle of the van and going back. and in a camper the weight is more evenly spread over the whole van.

just my thoughts

neil

Neil

VW quote a DoKa unladen weight as being 1595kgs incl driver and the gross vehicle weight as being 2500kgs. My van weighs in at 1680 in its present form without awning and roof tent so I think you may have a problem with your weigh bridge or you need to give your DoKa a good wash!
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