Are these Single point 'cooker-ring' mixers more snake-oil?

[CNG]

Adverse to the idea the constriction standard 'cooker-ring' type mixers put on the intake tract, I've always been sold on the BLOS mixer. Only BLOS is bulky, more awkward to install, and parts to maintain them no longer exist.

A good example of restriction are the 'cooker-rings' for any HS6 or HIF44 SU carb set-up. Despite being er... 44mm diam. these carb set-ups suffer mixers at 38mm. Thus WOT power suffers on both fuels. You're effectively making a 44mm carb a 38mm.

I've seen alternatives - all with the gas port centred in the venturi. Like one of those intake-fan 'doodads' that give you 20% more power and econamy, they smack of 'snake-oil'. Surely what these mixers do is put the self-same static restriction to the centre. Examples...

Snake Oil LPG Mixer 02.jpg (16.27 KiB) Viewed 4796 times

Snake Oil LPG Mixer 01.png (135.86 KiB) Viewed 4796 times

Why would they work any better? Surely to command the same venturi-effect you can't avoid the same restriction. Unless the restriction moves, ergo a BLOS? I would think they 'flow' worse than any standard cooker-ring? Am I missing something? Is there something magical, you know - in a mystical type way going on?

[Gilbertd]

I needed a 44mm mixer for a second Range Rover that I've just installed a Galileo system on but Mick at LPG supplies didn't have one, only 46mm which I know from experience is too big of one of these engines. However, he did have a BRC one the same as your second picture which he sent me to try. Works perfectly to the point that I'm thinking of getting a second one to replace the standard cooker ring on my car.

The idea that fitting a mixer will restrict the airflow is true and restrict power but only at, or very close to, wide open throttle. I suspect you'd need to put the car on a drag strip to notice any difference.

[CNG]

That's interesting. You're pulling a fair lump more air than anything I run, hence if 44mm is about right for your application, that kinda proves your point. Thus in my case, despite an HIF44 SU carb, any mixer - however shaped - must show a x-section at quite a bit less than 44mm. I'd be wasting time running your mixer.

More of AEB's omissions via poor documentation had me fitting a Leo in the finish. Knowing what I know now, I could have fitted a Galileo to a carb set-up.

Q1. Now you've bashed at both what are your thoughts?
Q2. Why do some cooker-rings have 2 x gas-supply ports?

[CNG]

Just seen these at:

https://forum.retro-rides.org/thread/20 ... comversion

Never seen such things but the post describes inserting add-on 'diffusers' into what are clearly stock Rover V8 Stromberg inlet parts.

Diffusers.jpg (244.97 KiB) Viewed 4764 times

If nothing else, It's neat.

[LPGC]

For a mixer system to work gas has to be sucked out of the pressure reducer at a rate proportionate to the airflow, for that to happen the mixer needs to give a vacuum signal to the reducer. Difficult to see that happening without the mixer giving some restriction to airflow but there are various design mixers and some designs will flow more air than others for the same proportionate signal.

If you're going to use a cooker ring type mixer usually the longer ones are better at that than the shorter ones because they'll remain more airflow/vacuum signal linear down to lower airflows.

Another common type is the shield type, at least the one pictured first in this thread looks like a shield design. I don't know if there's been any new developments but a cooker ring used to be expected to be a better compromise for linearity versus total airflow than a shield type.

Cooker ring mixer manufacturers used to imply/claim that their designs didn't really restrict airflow much, the shape of them designed to speed up airflow near the gas outlet openings, if airflow speed increases the density decreases (pressure decreases), same kind of effect to the shape of an aircraft wing. But of course shape also meant a narrowing which ultimately is going to cause a restriction to airflow. The shield design places an obvious restriction above the gas intake, airflow comes past the sides of it creating a bit of vacuum under the gas intake area.

I recently converted a 1972 V8 Chevy pickup, instead of fitting a mixer system I fitted an Impco gas carb setup. The gas carb is fed with gas under pressure and works a bit like an SU carb, the more airflow the more the carb throat is caused to open up but instead of this causing a tapered needle to lift to allow petrol to enter airflow as in an SU carb it causes a gas port to open so increased airflow causes increased gas flow into the engine. The gas carb principle need not be any more restrictive to airflow than (say) the metering flap in an old Bosch K Jetronic fuel injection system, it seems more signal linear and to have better airflow than a mixer setup. You can just about take one of these and fit it on any petrol engine within a wide size range and it will work nicely without any adjustment, but there are 2 easy adjusters for idle and full throttle mixture. I don't know if a CNG version would need to differ from an LPG version due to the different specific weights and stochiometric ratios but it could be that the LPG version would work for CNG if fed with a different pressure, and Mick at LPGautosupplies could probably tell you the answer to that question.

Remember in the 2 pics below the wide diameter pipe between reducer and gas carb has gas under slight pressure, not 'signal vacuum'.

20240927_160528.jpg (2.74 MiB) Viewed 4763 times

20240927_160537.jpg (2.73 MiB) Viewed 4763 times

The LPG switch can be seen in the pic below but the chrome T handle is also part of the LPG conversion. For running on LPG the handle needs to be pushed in, for running on petrol it is better to have the handle pulled out. The handle pulls a cable which pulls a cam type setup that forces the LPG carb diaphragm open, when it is open it presents no restriction to airflow so doesn't cause mixture from the petrol carb to be any richer than it would be without pulling it open, but even with the handle pushed in it will run happily on petrol just a bit richer. If the handle is pulled out when switched to LPG the engine won't run because the mixture will be far too rich.

20240927_160608.jpg (2.39 MiB) Viewed 4763 times

No thought has to be put in regards how to set it up so it will start on gas with the gas carb setup, it just will start on gas with no drama.

This pickup was fitted with an aftermarket (and smaller than original) petrol carb, driving on petrol it had/has a bit of a flat spot just above idle. Driving on gas it runs perfect. The only change I made to any settings were a slight turn of the idle mixture adjustment screw, it originally smelled a bit rich and turning the screw in increased idle speed.

[CNG]

Love that Impco carb set-up. I'd dismissed those things as 'fork-lift only offerings' - not hefty enough for even low-power engines. Er, got htat wrong then?.. yonder Chevy must be gas hungry.

The Yanks like their CNG fork-lifts and Zambonis so I reckon a CNG Impco is available. Yours is a neat solution and provides what a BLOS does via different means.

BTW: My BLOS has a piston lifter thus on petrol it's not an obtruction to my SU. Unfortuenatley via magnets or a solenoid or a bowden cable I've never been able to work out how to lift the piston on an SU. I've seen this:

SU Piston lift.png (541.01 KiB) Viewed 4754 times

My solution: Because petrol is in use every 1000+ miles - an emergency fuel - I've biased the improvement over getting the scewdriver out - removed the piston. Runs far better.

The gas-carb isn't going to be open-loop or is it? I can't see how you'd shoehorn say a Leo into there. Maybe you can? It's been done before. Could you put a stepper in the gas line much the same? The Volvo Necam system had a distributor but in essence it is a stepper motor much like the Leo but with gas above atmosphere.

You do do some unusual stuff! I'm curious on how you came to fit a gas-carb to what most would see as a shoo-in for 'bung a Leo/ Galileo on'. Or even a candidate for a BLOS if you get such things? Was it something your customer requested?

[LPGC]

Q2. - 2 x Ports on a mixer are likely 1 x gas feed and 1 x connection for an idle air port. On some engines the throttle is completely closed when the driver lifts completely off the accelerator but the engine gets idle air through a pipe that bypasses the throttle, the pipe probably has an electronically controlled valve to control airflow so electronics can control the idle speed. When not LPG converted the input end of the pipe may connect close to the air-filter, the output end straight into the vacuum side of the throttle, but with such setup using a mixer system the engine wouldn't be able to idle on LPG because there'd be no airflow through the mixer. On such setup we'd connect the input end of the idle air pipe to the lower port (closest to the throttle) of the mixer, so any idle air flows through the mixer venturi.

[CNG]

Q2. Thanks Simon. I like to know this stuff. I had it was something to do with balancing the feed to twin carbs.

[Gilbertd]

Hmm, missed a few posts here, so back to the beginning. The car I have just converted is near identical to mine, both are '98, 4.0litre GEMS equipped P38s (there's a difference in VIN number of just over 400). Both have an OMVL R90E, mine has one of the newer ones with the two small 6mm adjusters, the other a brand new old stock, older version. The GEMS system uses 5-0V lambda sensors but mine has an additional boss in one downpipe with a 0-1V sensor fitted solely to drive the Leonardo.

As for the difference between the Leo and the Galileo, I don't like the Galileo software, the only version I have managed to find doesn't have the nice graphical display of the stepper position, just a numerical reading, difficult to read when the laptop is in the passenger footwell for testing purposes. Although it isn't possible to set different stepper limits for idle and out of idle throttle positions, I have noticed that at idle, the stepper will always stop 10 steps below the maximum but will go to maximum at out of idle (if it needs to). Fuel consumption is worse on the Galileo equipped car but I suspect this is down to it using one of the 5-0V sensors as they are known to stop giving an output at idle. The petrol ECU recognises this and goes open loop but the Galileo sees it as lean so it will run rich at idle. I intend fitting another boss and using a 0-1V sensor the same as on the Leo equipped car. With the Galileo you can't simply Tee the purple wire into the existing sensor output either as that applies a voltage which is sent to the petrol ECU and buggers up running on petrol, it has to be intercepted as the manual shows. Knowing what I now know, I'd have fitted a Leo but as I already had the Galileo, I used it. Plus I've managed to fit the slim, square AEB119B in a convenient place where the chunky Leonardo switch wouldn't easily go.

The difference in mixer size between an injected car and a carb equipped car will be down to the lack of a venturi on an injected car, just a throttle body. Without the venturi provided by the mixer, there wouldn't be any 'suck' (or signal as Simon prefers to call it) but with a carb there is already a venturi there so as long as the mixer is close enough, you'll still get the suck required and can get away with a larger mixer. On the P38 with a 46mm mixer, it will idle fine after the idle bleed screw has been opened slightly but will go lean as the throttle is opened. With a 44mm mixer the output of the vaporiser can be set for it to idle with the bleed screw closed and it will still keep the stepper opening the same when the throttle is opened.

Impco systems are designed not only for small engines, but for big Yank V8s too. With the bulk of Italian systems being rated for up to 190bhp (and Italian bhp at that, so probably 150 in real money), they aren't man enough for a 6 litre V8. Hence Impco being the preferred choice for a larger engine. However, they are also bloody expensive compared with an Italian system so I've never got involved with them except for sorting out a wiring problem on one fitted to a Rolls Royce.

[LPGC]

I'll start this post by acknowledging Gilbert's post above, I agree with those points.

Sometimes placing a mixer right on top of a carb can cause airflow through the carb to be more central through the carb and cause the carb to give different mixture, often richer but depending on the specific carb.

Seems my last post and CNG's last post crossed..

Love that Impco carb set-up. I'd dismissed those things as 'fork-lift only offerings' - not hefty enough for even low-power engines. Er, got htat wrong then?.. yonder Chevy must be gas hungry.

The Yanks like their CNG fork-lifts and Zambonis so I reckon a CNG Impco is available. Yours is a neat solution and provides what a BLOS does via different means.

BTW: My BLOS has a piston lifter thus on petrol it's not an obtruction to my SU. Unfortuenatley via magnets or a solenoid or a bowden cable I've never been able to work out how to lift the piston on an SU. I've seen this:

SU Piston lift.png

My solution: Because petrol is in use every 1000+ miles - an emergency fuel - I've biased the improvement over getting the scewdriver out - removed the piston. Runs far better.

The gas-carb isn't going to be open-loop or is it? I can't see how you'd shoehorn say a Leo into there. Maybe you can? It's been done before. Could you put a stepper in the gas line much the same? The Volvo Necam system had a distributor but in essence it is a stepper motor much like the Leo but with gas above atmosphere.

You do do some unusual stuff! I'm curious on how you came to fit a gas-carb to what most would see as a shoo-in for 'bung a Leo/ Galileo on'. Or even a candidate for a BLOS if you get such things? Was it something your customer requested?

Impco make setups for everything from forklifts up to large V8 engines and there's some overlap on which parts will suit which size / power engines. I.e. Instead of making one set of parts suitable for 3>5L engines and another set for 5>7L engines it's more a case of one set of parts suiting 4>6L, another set suiting 5>7L. If you were converting, say, a 5L engine you could use either of the 2 gas carbs just mentioned, maybe expect the 5>7L version to have higher flow potential in case you threw a big cam in the engine etc, maybe expect the 4>6L version to have better idle mixture out of the box.

The owner gave me the impression he liked simple setups, something that would just work and turnkey without starting on petrol etc, the Impco was more expensive but ticked all the boxes, I did tell him a mixer setup would be cheaper and gave him the option but he let me decide and I went with what I thought the better system. Imho the Impco is better than a mixer/Blos full stop but especially for open loop setups and where cost isn't a high priority. I may yet even fit one on my boat and remove the petrol tank.

I have seen closed loop Impco setups with American made closed loop controllers, I don't think you could use a Leonardo/Gallileo with one, the owner wouldn't've preferred the additional electronics anyway, this install is open loop.

[Pinger]

Wouldn't a simple solution be a twin choke set up with a small and larger mixer, the larger one only being deployed above a specific speed/load threshold? The reason twin choke carbs were developed was to give good low speed manners without sacrificing top end power - the topic of this thread.

[Gilbertd]

What, like this https://lpgautosupplies.co.uk/shop/lpg- ... gas-97080/ you mean?

[LPGC]

I've fitted a fair few 'twin vanturi' mixers but only on carbs with twin venturis. I think I remember the last one, fitted it on a Ford Essex V6 in an ex-ambulance a few years ago.

I believe a possible complication with twin venturi LPG mixers fed from a single reducer, on a twin venturi carb that has throttle open on one venturi before the other... is that if air is only being drawn through one venturi there won't be any vacuum signal from the other venturi which is just effectively open to atmosphere, the venturi that is seeing airflow will have signal but due to the Y connector it may suck gas / air from the reducer / from the other venturi that is open to atmosphere. As said, would only apply if one venturi opened before the other.

[Pinger]

I've fitted a fair few 'twin vanturi' mixers but only on carbs with twin venturis. I think I remember the last one, fitted it on a Ford Essex V6 in an ex-ambulance a few years ago.

I believe a possible complication with twin venturi LPG mixers fed from a single reducer, on a twin venturi carb that has throttle open on one venturi before the other... is that if air is only being drawn through one venturi there won't be any vacuum signal from that venturi, the venturi that is seeing airflow will have signal but due to the Y connector it may suck gas from the reducer or from the other venturi that is open to atmosphere. As said, would only apply if one venturi opened before the other.

Good point I'd overlooked. If there was a suitable one available, would a one-way check valve in the line to the mixer in the secondary venturim downstream of the Y solve that?

[LPGC]

Not sure how well that could work in application. We're talking very small pressure differences so any such check valve would need to be very sensitive, also not affect flow in case of it being able to open to different extents otherwise it would act much like the inline adjuster being twiddled to various extents which could give kind of random mixture under load.

Going back to what I said in my last post a twin venturi petrol carb with throttle that opens on one venturi before the other isn't affected in the same way because the fuel supply is from the float bowl that is always full to the same level regardless of fuel use by either/both venturi, but fuelling from a single LPG reducer is affected by draw from either/both venturis and signal/draw from one venturi affects LPG flow on both and the reducer's gas output for given signal isn't entirely linear either... Unless you have 2 x LPG reducers and at least the reducer connected to the venturi that opens last is set with zero idle bypass.

Even if the throttle acts at the same time on both venturis there's an added complication even if the venturis are the same size, worse if the venturis are different sizes.

[Pinger]

Yep, you're right about a possible check valve.

2 x LPG reducers and at least the reducer connected to the venturi that opens last is set with zero idle bypass.

And yes, it would take the complication of an additional reducer (set-up as you say) to work,
The devil is in the detail - as it ever was.

[LPGC]

A potential problem with the 2 reducer idea (if we're trying to get around throttle opening on one venturi before the other) is that there will be a throttle opening at which the 2nd venturi is very slightly open, not enough to cause enough signal to make the 2nd reducer output any gas because both a mixer venturi and reducer are not totally linear in response. So we might think we could get around that with the single reducer idea again, but then we're up against the same problems we were up against in the first place when we decided it would be better to fit 2 reducers... and fitting a Y between a mixer/venturi with signal and one without signal will mean some air is drawn from the venturi without signal to the gas output of the venturi that does have signal having the effect of leaning the mixture unless compensated for probably by increasing reducer sensitivity, but increasing reducer sensitivity has the effect of richening mixture especially when both venturis are flowing air and creating signal.

I don't think I ever handed a vehicle back to a customer having left 2x reducers fitted because I fitted a single LPG mixer with 2 x venturis but I have tried it as an experiment.

Done plenty vehicles with 1 x reducer and 2 separate carbs, like on old Rover V8s with twin carbs. They usually run OK because both carbs have a single venturi and both have close to the same airflow because both cylinder banks draw close to the same amount of air so both mixers create close to the same signal. Always expected and often got setup issues fitting a single mixer with 2 x venturis on a single carb with 2 x venturis, especially on carbs with 2 different sized venturis. It seems almost asking too much of a mixer manufacturer to match mixer venturi sizes to carb venturi sizes when the venturi sizes are all different because there may not be an ideal combination of sizes, especially considering the reducers are not linear in terms of signal versus gas output. I've seen myself holding a carefully machined mixer thinking looks a nice bit of kit but wish the venturis were different sizes, not much I can do about that and this is the only mixer designed to suit this specific model carb.

[Pinger]

A potential problem with the 2 reducer idea (if we're trying to get around throttle opening on one venturi before the other) is that there will be a throttle opening at which the 2nd venturi is very slightly open, not enough to cause enough signal to make the 2nd reducer output any gas because both a mixer venturi and reducer are not totally linear in response. So we might think we could get around that with the single reducer idea again, but then we're up against the same problems we were up against in the first place when we decided it would be better to fit 2 reducers... and fitting a Y between a mixer/venturi with signal and one without signal will mean some air is drawn from the venturi without signal to the gas output of the venturi that does have signal having the effect of leaning the mixture unless compensated for probably by increasing reducer sensitivity, but increasing reducer sensitivity has the effect of richening mixture especially when both venturis are flowing air and creating signal.

Maybe, a way around that would be in the scenario you describe go straight to a larger second butterfly opening while simultaneously reducing the opening on the primary? Probably possible with mechanical linkage - with much trial and error to avoid a flat spot in the transition.(I'm wondering if progressive twin choke carbs don't do that to some degree for the same reason). FBW could be programmed to do it better but the complications keep on coming. Is the juice worth the squeeze?

I don't think I ever handed a vehicle back to a customer having left 2x reducers fitted because I fitted a single LPG mixer with 2 x venturis but I have tried it as an experiment.

Done plenty vehicles with 1 x reducer and 2 separate carbs, like on old Rover V8s with twin carbs. They usually run OK because both carbs have a single venturi and both have close to the same airflow because both cylinder banks draw close to the same amount of air so both mixers create close to the same signal. Always expected and often got setup issues fitting a single mixer with 2 x venturis on a single carb with 2 x venturis, especially on carbs with 2 different sized venturis. It seems almost asking too much of a mixer manufacturer to match mixer venturi sizes to carb venturi sizes when the venturi sizes are all different because there may not be an ideal combination of sizes, especially considering the reducers are not linear in terms of signal versus gas output. I've seen myself holding a carefully machined mixer thinking looks a nice bit of kit but wish the venturis were different sizes, not much I can do about that and this is the only mixer designed to suit this specific model carb.

If we view an OEM twin choke carb fitment as an admission that the engine couldn't be made to work as intended with a single choke carb then a single mixer is going to be compromised in the way a single choke carb would have been.

When you were discussing the IMPCO 'carb' earlier you mentioned LPG for your boat. Is LPG 'a thing' at harbours or would you be arriving with a bottle and decanting it?

[LPGC]

I certainly wouldn't assume LPG would be available at a harbour but I expect it is available at a minority. At a lot of harbours if they do sell fuel it's only diesel, not even petrol available. A lot of ski boats run on LPG but they are usually at ski clubs that have their own lakeside LPG refuelling facilities, though I have sold a pump to a ski club. If I convert my boat to LPG I would be expecting to use one of my LPG pumps to refuel it.

The problem with modifying the throttle (in case a carb has 2 venturis that the throttle opens on at different positions) is that it then affects the petrol carb too.

I think in most cases they probably could fit a carb with a single venturi and get the engine to run well on it, but they fit carbs with multiple venturis to allow better throttle control and better atomisation of the petrol so giving better fuel economy etc. With LPG we don't need to worry about atomisation because the LPG is already in vapour form before it gets to the mixer / gas carb / injectors.

[Pinger]

I certainly wouldn't assume LPG would be available at a harbour but I expect it is available at a minority. At a lot of harbours if they do sell fuel it's only diesel, not even petrol available. A lot of ski boats run on LPG but they are usually at ski clubs that have their own lakeside LPG refuelling facilities, though I have sold a pump to a ski club. If I convert my boat to LPG I would be expecting to use one of my LPG pumps to refuel it.

Is that V8 powered boats on LPG? LPG I'd guess is a safe fuel for boats - less of a fire hazard than petrol

The problem with modifying the throttle (in case a carb has 2 venturis that the throttle opens on at different positions) is that it then affects the petrol carb too.

Right enough - but for the things I have in mind, it's only the twin venturi concept I'd be looking to use and never a carb on petrol unless just for cold start.

I think in most cases they probably could fit a carb with a single venturi and get the engine to run well on it, but they fit carbs with multiple venturis to allow better throttle control and better atomisation of the petrol so giving better fuel economy etc. With LPG we don't need to worry about atomisation because the LPG is already in vapour form before it gets to the mixer / gas carb / injectors.

Good point. Oh the vagaries of carbs come (unexpectedly) back to mind. It's been a while...