Fuel Consumption Test: Single vs Double Barrel Carburetor

[Greenpeace]

oooo... I used to get 12mpg out of the old flat head cussy back in the day.... until I got some avgas for it, well that's what they called it, went like the clappers, but the "economy" went to 9mpg....

Bob

When I used to drag race in the '80s and '90s, they would sell you a 20L drum of 100/130 Avgas at the track.
100 was the lean mixture octane rating, and 130 was the rich mixture octane rating.
IIRC, (at the track), they were charging about double the price of pump petrol (for the Avgas) at the time.
Even so, it was still a lot cheaper than C16.

The use of Avgas went the way of the dinosaurs (pardon the pun) in the automotive field due to its lead content.
Modern Avgas is still a leaded blend fuel in Australia.

 

[bob]

but fuel was "cheap"... at 3/6 to 4/- (35-40 cents) a gallon (4.5l), around £2.10.0 ($5) to fill Henry. Out of a weekly £12 ($24)you didn't want to fill it too often... then again, an LP vinyl was about the same price as a tankful !!
It was a long time ago, but I reckon that we were adding toluene.

Bob

 

[driven]

Top fuel these days burn about 7-8 Litres of nitromethane per SEC

 

[Greenpeace]

Top fuel these days burn about 7-8 Litres of nitromethane per SEC

The amount varies depending on the TF team setup, but between the start up, burnout and (now 1000 foot) pass, they use anywhere from 40 to 80L of fuel.
Under full power they are running on the cusp of hydrolock.
They burn more fuel per second than a fully loaded Boeing 747.

When I was a kid I used to buy the US published Hot Rod magazine.
In one issue there was a guy in California that had a street registered alcohol funny car.
It passed emissions because it was running on alcohol, but IIRC the owner said it got around 3 mpg on the street.
I don't think it was his daily drive.

 

[Wildebeest2]

Back in the '50's when I was an apprentice mechanic cum bowser boy for a mining company, the engineer decided that the fuel offered needed a bit of a sting. He ordered in a couple of 44's of I think it was Mobil [Vacuum Oil Co] fuel additive. It was my job when the underground tank got low I was to decant one of the 44's into the tank. My maths then and now were pretty poor. So the ratio of Mobil's finest could have been anyone's guess. What effect it had on the company's fleet with compressions of the day not much more than 7.55 / 1 ? Further to this. I wonder what effect it had on yours truly as he decanted this brew. I wonder what effect....ZZzzzzzzzzzzzz?

 

[GRAHAM WALLIS]

The amount varies depending on the TF team setup, but between the start up, burnout and (now 1000 foot) pass, they use anywhere from 40 to 80L of fuel.
Under full power they are running on the cusp of hydrolock.
They burn more fuel per second than a fully loaded Boeing 747.

When I was a kid I used to buy the US published Hot Rod magazine.
In one issue there was a guy in California that had a street registered alcohol funny car.
It passed emissions because it was running on alcohol, but IIRC the owner said it got around 3 mpg on the street.
I don't think it was his daily drive.

747 in take off?

 

[Greenpeace]

747 in take off?

General consensus seems to be that at cruising speed a fully loaded 747 consumes 1 US gallon per second, or 3.7L per second, or 5 US gallons per mile.
It's hard to find data on take-off consumption, obviously it will be significantly higher, but how much higher?

 

[GRAHAM WALLIS]

General consensus seems to be that at cruising speed a fully loaded 747 consumes 1 US gallon per second, or 3.7L per second, or 5 US gallons per mile.
It's hard to find data on take-off consumption, obviously it will be significantly higher, but how much higher?

Much higher I would say, just the increased noise says that.

 

[driven]

Start with a single barrel carby and end up with a 747. What a great thread

 

[Greenpeace]

Start with a single barrel carby and end up with a 747. What a great thread

On to Space-X.....................

 

[Wildebeest2]

How do you tune these carbies? You can change the jets I suppose but why would you? The manufacturer has spent loads of money to get the setup right. SU carbies are different, where you can adjust the needle, I think.

Graham. My reply is more of a memory exercise for me. The early type SU's mixture adjustment apart from selecting a needle, was via the jet holder at the carby base. Screwed in and out altered the mixture. The much later SU could be adjusted almost like a normal carb, an external screw in contact with the jet. Now if memory serves there was also an internal bi-metal device that compensated for temperature ?

 

[Greenpeace]

Graham. My reply is more of a memory exercise for me. The early type SU's mixture adjustment apart from selecting a needle, was via the jet holder at the carby base. Screwed in and out altered the mixture. The much later SU could be adjusted almost like a normal carb, an external screw in contact with the jet. Now if memory serves there was also an internal bi-metal device that compensated for temperature ?

The early SUs were the simplest of the lot, H and HS series.
You screw the jet holder clockwise to home, then unscrew it 12 flats (2 full turns).
The car will start and run fine at that, and the final mixture adjustment, if needed, is only minor from there, anti-clockwise for rich, clockwise for lean.

The later HDs had a diaphragm added at the base of the carb, so they have a mixture screw that lifts the jet up and down via a lever.
The easiest way to do the initial setting on these is take the dashpot and piston off the top, adjust the top of the jet so it is flush with the bridge, the turn the lever adjuster screw clockwise 2 1/2 turns.
Reassemble, and fine tune from there, clockwise is richer.

The later still HIFs also had the diaphragm in the base, and the bi-metallic "temperature compensator" that slots into the base of the jet. These carbs had a conventional idle mixture circuit added with a small adjusting screw.
This was a reverse idle circuit, so clockwise is rich not lean.

The early ones (H and HS) are what you see by far the most of in Australia, and they are dirt simple.
At most, they contain 2 small O rings (that you can buy anywhere), and a float chamber lid gasket (that you can make), the only other consumable item is the needle and seat.
Maintaining the correct float level is very important in these, as it correlates directly to the fuel level in the main jet.

 

[Wildebeest2]

The early SUs were the simplest of the lot, H and HS series.
You screw the jet holder clockwise to home, then unscrew it 12 flats (2 full turns).
The car will start and run fine at that, and the final mixture adjustment, if needed, is only minor from there, anti-clockwise for rich, clockwise for lean.

The later HDs had a diaphragm added at the base of the carb, so they have a mixture screw that lifts the jet up and down via a lever.
The easiest way to do the initial setting on these is take the dashpot and piston off the top, adjust the top of the jet so it is flush with the bridge, the turn the lever adjuster screw clockwise 2 1/2 turns.
Reassemble, and fine tune from there, clockwise is richer.

The later still HIFs also had the diaphragm in the base, and the bi-metallic "temperature compensator" that slots into the base of the jet. These carbs had a conventional idle mixture circuit added with a small adjusting screw.
This was a reverse idle circuit, so clockwise is rich not lean.

The early ones (H and HS) are what you see by far the most of in Australia, and they are dirt simple.
At most, they contain 2 small O rings (that you can buy anywhere), and a float chamber lid gasket (that you can make), the only other consumable item is the needle and seat.
Maintaining the correct float level is very important in these, as it correlates directly to the fuel level in the main jet.

Greenpeace. Thanks for rejuvenating my grey cells. Owners of early English sports cars would have made it a social occasion, on the weekend with their mates, tuning or otherwise their SU's. My past work experience with Volvo took in the early SU and later the HIF type. Along with the Stromberg they came off the Volvo "menu" when fuel injection was the go in the later models.
The Stromberg 175 on vehicles such as Rover, Triumph etc could be adjusted like the early SU. The Stromberg had a rubber diaphragm instead of a piston / dashpot. On the Volvos with Strombergs they were "tamper proof". Requiring tools for the setting of the jet height. A strange design feature of these carburetors is that the SU needle had to be centred in the jet. The Stromberg were spring loaded from centre. This caused them to wear over time. If I recall, the HIF type didn't like carby cleaner. It would affect any rubber O rings.

 

[Greenpeace]

Greenpeace. Thanks for rejuvenating my grey cells. Owners of early English sports cars would have made it a social occasion, on the weekend with their mates, tuning or otherwise their SU's. My past work experience with Volvo took in the early SU and later the HIF type. Along with the Stromberg they came off the Volvo "menu" when fuel injection was the go in the later models.
The Stromberg 175 on vehicles such as Rover, Triumph etc could be adjusted like the early SU. The Stromberg had a rubber diaphragm instead of a piston / dashpot. On the Volvos with Strombergs they were "tamper proof". Requiring tools for the setting of the jet height. A strange design feature of these carburetors is that the SU needle had to be centred in the jet. The Stromberg were spring loaded from centre. This caused them to wear over time. If I recall, the HIF type didn't like carby cleaner. It would affect any rubber O rings.

The HIFs and HDs don't like ethanol either.
E10 turns the original diaphragms etc into black goo.
Haven't had a lot to do with the CD Stombergs.
My brother had them on a 144S Volvo, and on his TR7s.
We put a 16V Dolomite Sprint engine into one of his TR7s, and found the twin HS6 SUs ran much better on it than the twin CD175 Strombergs (both sets were re-freshed carbs).
I had a Hillman with a single CD150 on it, but never had to touch it

I like my SUs, I have 4 vehicles at the moment running them, set and forget.
Other than to top up the damper oil, I haven't touched the H1 SU on my Harley in 15 years.

You would probably appreciate the simplicity of this bronze 1909 Schebler carby.
I had it fitted on a crank driven GM supercharger, hanging out the front of a 1924 Bean speedster.
The screw on the top (red line) adjusts the opening resistance of a leather air valve in the inlet snout. The L handle adjuster (blue line) has a tapered needle on the end of it that screws straight into the main (only) jet.
The total air flow is metered by a gate valve (green line).
I had it set up as a sidedraught, you can swap the gate valve and inlet snout around, and it becomes an updraught carburettor.

They came in several sizes, this one is the 1 1/2" BSP thread model, you can see it's size relative to the soft drink can in the photo, and it's bloody heavy too.
Altough I've never seen one, they also came in a 2" BSP thread size as well.

I should make a little stand for mine and sit it on the coffee table, it's just laying on a shelf in the shed at the moment.

 

[Ikenna351]

Update:

Shortly after I published the Single vs Double Barrel Carburettor Fuel Consumption Tests on 2.0 engine, I drove into the same Total Fuel station to buy petrol for my Z9 (phase II) 607 V6 of the same fuel quantity used for the tests on the 505 (25 litres). As I was about to start the car, it occurred to me that the car has same volume of loads (about 100 kg) in the boot just like in the 505 during the test, and I would be driving the car in same manner (mostly city drive, and on AC). So I decided to do same test on the Z9 and see how many km the 25 litres will cover. Note that the Z9 has zero rich running issues and all engine related systems in good perfect working conditions, including the engine itself. Of course, this is a different car to the previous test car (505) with more power, different transmission, final drive, car weight, demands on Alternator, etc. So, not necessarily a fair comparison, but just for the sake of it.

Below are the results of the 3 tests on both cars:

1. The 505 - 25 litres - Single Barrel Carburettor - 2.0 - 5MT: *119 km* .

2. The 505 - 25 litres - Double Barrel Carburettor - 2.0 - 5MT: *161 km* .

3. The Z9 607 V6 - 25 litres - EFI - 2.9 - 6MT: *134 km* .

So, from the above, the 505 with the 2.0 engine and Double Barrel Carburettor covered more distances/kilometres, given same quantity of fuel and similar other conditions. As weird as it sounds in the original report, both carburettors were making the engine run rich during the test (burning more fuel than they should - emitted black smoke on harder accelerations). So they both would have covered more distance or consumed less than they did in the tests if they were in best tunings or were good quality carburettors. I guess the power differences and weight differences between 505 2.0 and the 607 V6 could be the reason for the fuel consumption differences, considering also the quality of fuel that may likely not be the best, especially in Nigeria.

Ikenna351

 

[Whippet]

Hi.

I can see what you are trying to achieve but for me there are too many variables on the test methodology for the 505 outcome to have a lot of sigificance.

I wouldn't describe the Solex 34-34 Z1 as a double barrel carburetter, but as a primary/secondary staged carburetter, as they have separate butterflies for each stage, and they are not on a common shaft.

While I would expect the primary stage of a progressive carburetter to provide better control of the fuel metering. I would not anticipate a variation in the order of 35% additional distance between these two carburetters.

I wonder if there is another variable to the outcome? If the Solex 34-34-Z1 provided higher vaccum to the distributor, on cruise, this might provide additional ignition timing advance, which might also contribute to less fuel consumed?

Cheers.

 

[bob]

...........I wonder if there is another variable to the outcome? If the Solex 34-34-Z1 provided higher vaccum to the distributor, on cruise, this might provide additional ignition timing advance, which might also contribute to less fuel consumed?

Cheers.

Better breathing needs less pedal for the same amount of work, less pedal will lift the manifold vacuum.....

In my youth I swapped carbies around, cos we could... In general, the fuel economy was a little better with a larger throat area, within reason - getting carried away with 'bigger is better' messed up the 'drivability' introducing flat spots.

My ancient Standard 8 was quite happy running a twin barrel Stromberg ex flat top Ford V8, and gave better economy than it's original tiddly Zenith[?] way back when.

Bob

 

[Mike Tippett]

Pumping losses due to throttles are significant!

 

[GRAHAM WALLIS]

S

Update:

Shortly after I published the Single vs Double Barrel Carburettor Fuel Consumption Tests on 2.0 engine, I drove into the same Total Fuel station to buy petrol for my Z9 (phase II) 607 V6 of the same fuel quantity used for the tests on the 505 (25 litres). As I was about to start the car, it occurred to me that the car has same volume of loads (about 100 kg) in the boot just like in the 505 during the test, and I would be driving the car in same manner (mostly city drive, and on AC). So I decided to do same test on the Z9 and see how many km the 25 litres will cover. Note that the Z9 has zero rich running issues and all engine related systems in good perfect working conditions, including the engine itself. Of course, this is a different car to the previous test car (505) with more power, different transmission, final drive, car weight, demands on Alternator, etc. So, not necessarily a fair comparison, but just for the sake of it.

Below are the results of the 3 tests on both cars:

1. The 505 - 25 litres - Single Barrel Carburettor - 2.0 - 5MT: *119 km* .

2. The 505 - 25 litres - Double Barrel Carburettor - 2.0 - 5MT: *161 km* .

3. The Z9 607 V6 - 25 litres - EFI - 2.9 - 6MT: *134 km* .

So, from the above, the 505 with the 2.0 engine and Double Barrel Carburettor covered more distances/kilometres, given same quantity of fuel and similar other conditions. As weird as it sounds in the original report, both carburettors were making the engine run rich during the test (burning more fuel than they should - emitted black smoke on harder accelerations). So they both would have covered more distance or consumed less than they did in the tests if they were in best tunings or were good quality carburettors. I guess the power differences and weight differences between 505 2.0 and the 607 V6 could be the reason for the fuel consumption differences, considering also the quality of fuel that may likely not be the best, especially in Nigeria.

Ikenna351

Still woeful economy for the V6, 18.6 litres per hundred I have had up to 7 litres a hundred out of these engines. Is this all in heavy traffic?

 

[Ikenna351]

Hi.

I can see what you are trying to achieve but for me there are too many variables on the test methodology for the 505 outcome to have a lot of sigificance.

I wouldn't describe the Solex 34-34 Z1 as a double barrel carburetter, but as a primary/secondary staged carburetter, as they have separate butterflies for each stage, and they are not on a common shaft.

While I would expect the primary stage of a progressive carburetter to provide better control of the fuel metering. I would not anticipate a variation in the order of 35% additional distance between these two carburetters.

I wonder if there is another variable to the outcome? If the Solex 34-34-Z1 provided higher vaccum to the distributor, on cruise, this might provide additional ignition timing advance, which might also contribute to less fuel consumed?

Cheers.

The XN1A engine has magneto distributor which is more fuel efficient than the popular contact point used in earlier 504s and 505s. Of course, the consumption was still very high in the test, but performed better than I expected even with the bad quality of the new carburettor or tuning issue. Like I pointed out in the original report, even with the bad conditions the tests were carried out on, it still out-perform the single carburettor on same engine which reverse should be the case. The fuel quality they sell to us here in Nigeria is horrible, yet it did better than the EFI which is not a good comparison though, considering the weight, number of cylinders and power differences between both cars.

I disagree with your position that Solex 34-34 is not double barrel. I understand the design is different from common carburettors in majority of 504s and 505 sold in Europe, Australia and North America like the Solex 32-35. Attached is Peugeot workshop manual on 32-34 & 34-34 Carburettors.

The issue I have with the 34-34 is that it's not stable, probably because it's a new copied 34-34, not a genuine Solex product. I believe there are better made copied new 34-34 in the market, but it appeared I got the badly made ones. The first new 34-34 I bought in 2020 was worst than the current new one on the engine. The 2nd barrel butterfly wouldn't even open, and the auto choke would refuse to stay open. In fact, it was hell until I bought the 2nd new 34-34 from another source which is the current one on the engine and better, but still very unstable. You might tune it today and it will work perfectly fine, aside the black smoke on hard acceleration. The next day, it might start stalling the engine, as if it's overflowing (it does actually behave like it's overflowing). Next minute, it's working well again. It makes using AC very difficult, since you wouldn't know when the issue would start and the AC will be stalling the car at idle or once you stop accelerating while in motion. Again, it's possible it's happening because the carburettor may probably be the bad Chinese copy, even though there might be good Chinese ones. I have seen quite a few new 34-34 on AliExpress that looks like the genuine ones, but no feedback on them yet to confirm how good they work. I actually have another brand new 34-34 Z1 that is yet untouched and still in it's box. I bought it together with the current one on the engine. So, I assume the quality would be the same since they were both from the same seller. I probably may have need for it in future, but I am thinking of another carburettor model now.

Based on personal experience I had with Solex 32-35 MIMSA on my 504 GL (2.0) for years without headache and any of the issues the new 34-34 is giving, I ordered a used 32-35 MIMSA (manual choke) last week, unfortunately the seller sent me 33-35 TMIMA (auto choke) instead, even though I specifically requested for the MIMSA. I am yet to determine if he did it intentionally or not, but I plan to return the TMIMA not because I don't trust it's better than the 34-34, but I want to go back to what worked for me in the past, which was the MIMSA. I just want to stay away from auto choke carburettor for now.

The challenge I may have is fitting the 32-35 on the XN1A or 4-branched intake manifold meant for the 34-34 on the XN1A engine. The 32-35 can only fit in with one bolt off. So can't tell if I mount it on that manifold with only 3 bolts, if it won't create leak on the gasket between the carburettor and manifold? Notwithstanding, will try it and see, as soon as I lay my hands on a good used 32-35 MIMSA. I think someone in Nigeria is selling new 32-35 MIMSA, but I honestly want to avoid new carburettors for now, since their qualities are not guaranteed.

Ikenna351