Dual carbs with propane?

Propane, Butane, LPG, GPL, C3H8, C4H10
jon_g9121
Posts: 15
Joined: Mon Dec 09, 2019 11:59 am

Dual carbs with propane?

Post by jon_g9121 »

My plan is to use 2 impco 125 carbs with a modified efi intake but Im not sure of the feasibility of it. Ive seen 2 mixers and 2 converters for the bigger V8s, but nothing on running 2 mixers with 1 regulator. Is there any reason it shouldn't work?

The second piece of the puzzle is finding a dual outlet fitting from the regulator for the 2 vapor hoses. All I can find are the single 90 and 180 degree outlets (like this,https://carbturbo.com/product/84-en-fitting/) . Anyone know where to look for them?

Thirdly, can I expect any power increase from this? Im thinking of it mostly so I dont have a huge hole in my hood, but getting more power out would make it a no brainer.

Parts I currently I have a ford 300, a model E and a impco 200

C3H8
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Re: Dual carbs with propane?

Post by C3H8 »

Dual mixers with a single regulator are fine. Just make sure the hose length is the same from the "Y' or "T" fitting is the same. As for the "Y" or "T" fitting. A "Y" is preferred. If you can't find a "Y" usually available in brass you can use 45 degree cast iron fittings or 90 degree as cast iron fittings are rounded inside reducing the restriction of the 90's you show. There heavier and that may require a bracket to support them.

jon_g9121
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Joined: Mon Dec 09, 2019 11:59 am

Re: Dual carbs with propane?

Post by jon_g9121 »

Great! I appreciate the info. Ill check out my local hardware stores for the Y fitting.

Do you have any opinion on the good-ideaness of it? I noticed ford treated the 6 cylinder like 2 3 bangers with the split exhaust manifolds and the divided intake and I was thinking 2 1bbl mixers would complement that. Of course, if its a waste of time, hooking up a 225 would be easier....

C3H8
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Re: Dual carbs with propane?

Post by C3H8 »

The Ford 300 CI engines were kind of unique with the dual intake system making this a difficult question to answer. The 300 CI Ford, a straight I6, is a fairly strong engine and had good torque. This engine had a longer stroke then most engines. Most engines today have bores and strokes quite similar, example 3.5" bore and 3.5" stroke. Typically a longer stroke improves torque but limits RPM. This also cause a problem with the 300 CI engine on propane. Early 300's had a different cam then late model 300's. Estimating the fuel consumption on 300's is complicated. For various reasons the fuel consumption varied greatly depending on the model year, and specific model ordered.

I don't believe a single 225 vs dual 125's will make a huge difference in power, however as we know improving airflow will help a little but to take full advantage you need to improve the exhaust also and preferably other things. Problem #2 on the newer computer controlled engines was adapting the timing perfectly for propane was challenging. The computer helped and hindered. The computer would adapt the timing to the limits it was programmed for but that did not mean the timing was optimized for propane. Since the computer had sensors such as knock sensors it could adapt the timing to take advantage of the higher octane, however the total available advance may have been limited by the maximum allowed by the programming.

I say all this because our success was limited on the 300. We converted thousands but it was also the engine we received the most complaints about on fuel consumption. Improving the fuel consumption was difficult and in a few cases, and only a few, we actually removed the equipment. The ones removed were on customers vehicles that did fewer km's then average resulting in minimal savings to the customers. All the others were satisfied but faced the reality that the payback would be longer.

We had similar issues with 390 CI V8's. This engine also had a longer stroke. Fortunately the 390 was phased out in the 70's or early 80's.

jon_g9121
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Joined: Mon Dec 09, 2019 11:59 am

Re: Dual carbs with propane?

Post by jon_g9121 »

Interesting. Are you saying that propane generally doesnt work well with long stroke engines or that mileage was just never very good? I would think that I long stroke would take advantage of propane's slower burn rate to impart more energy on the crankshaft, but thats just a theory. I know that these engines never got great mileage even with gasoline, Im guessing due to the high amounts of internal friction from the long stroke, timing gears, and 7-main bearing design.

Tom68
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Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: Dual carbs with propane?

Post by Tom68 »

Thought he meant poor mileage from timing restrictions with dual fuel and possibly from some odd camshaft designs.

Never gunna be revvers with the limited valve area for the capacity, but you need at least enough mixer area to fill the cylinders at 3500 rpm.

Can't see any need to seperate it into two banks on gas, that's more a gasoline carby thing. Two mixers on a common plenum gives the cylinders more area to pull from if the mixers are a bit small.

jon_g9121
Posts: 15
Joined: Mon Dec 09, 2019 11:59 am

Re: Dual carbs with propane?

Post by jon_g9121 »

Im RV cammed and computer free, so I dont have those restricting me.

Seems like the consensus is a single mixer for propane. I know the old school GM inline guys swear by dual or triple carbs for their sixes, and thats what got me thinking about it, but they dont have the benefit of dealing with perfectly vaporized fuel like we do. Either way, I think the impco 225 flows something like 215 hp and I cant imagine seeing a ford 300 requiring more than that. Only trouble now is finding a adapter to go from the efi throttle body to a 225....

storm
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Re: Dual carbs with propane?

Post by storm »

The 300 is virtually a square bore engine with a 4" bore and a 3.98" stroke. The stroke in the 300 is only 0.07" longer than the Ford 250 fitted to Falcons in Australia from the late 60s through to the late 80s and in the 1969 Mustang.

The design differences that cause such fuel inefficiency is in the head and intake. Ford Australia redesigned the head of the 250 and made it work well. The 300 was designed as and remained a truck engine with small ports for it size so it could deliver earth moving low RPM torque. The 300 was basically choked by its intake, head, and exhaust. They can be made to perform and free up some power and with an added side benefit free up some fuel economy but it takes alot of time and effort on the head a better intake and a large truck exhaust or headers. There was one particular car that won the Baja race with a 300 and it had alot of work done to the engine.

Having said all that the 300 is never going to provide "good" fuel economy on any fuel or any particular induction system.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

Tom68
Posts: 75
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: Dual carbs with propane?

Post by Tom68 »

jon_g9121 wrote:
Fri Mar 06, 2020 11:51 pm
Im RV cammed and computer free, so I dont have those restricting me.

Seems like the consensus is a single mixer for propane. I know the old school GM inline guys swear by dual or triple carbs for their sixes, and thats what got me thinking about it, but they dont have the benefit of dealing with perfectly vaporized fuel like we do. Either way, I think the impco 225 flows something like 215 hp and I cant imagine seeing a ford 300 requiring more than that. Only trouble now is finding a adapter to go from the efi throttle body to a 225....
RV cams good for low rpm power but might need some intake volume to help with economy.

225 might need to be on a 300hp motor to make 215 ?

C3H8
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Re: Dual carbs with propane?

Post by C3H8 »

HI everyone,
I was beginning to think we had all disappeared. Nice to see all the feedback. I'm going to clear up two things. The Ford 300 F150's in NA have a longer stroke then bore as far as my old memory can remember. I decided to look it up and storm is actually correct. The bore and stroke are almost identical. Not only that I carried this over to the 390 I mentioned and found out it has a wider bore and shorter stroke. Hate being wrong.

The second point I mentioned was mileage issues. For some reason the 300's pre 1980 got better mileage then the post 1980 models. Here comes the old memory again, but pre and post 1980 models on gas would get 18 to 20 mpg per imperial gallon. On propane the pre 80's typically achieved 15 to 16 MPG. The post 80's though dropped to 11 to 13 MPG. We never truly found out why the disparity between the decades. We tried many things to improve it but overall most of the tries only had marginal improvements. Timing changes made subtle differences until the computer versions entered the market. We tried various devices to lean out cruise mixtures including vacuum operated power valves with limited results. One customer even went to the trouble to change cams to improve the mileage. One thing was true though. The 300 was a tough hi torque engine that ran forever. The only mechanical issue we ever had was a build up of oil residue on the intake valves. IMPCO claimed their testing showed this was because the air speed at idle was very low on this engine.

Lastly to the original question. Gann made an adaptor specifically for this engine although I believe it used a 300 mixer. To use a 225 a hand made adaptor would have to be fashioned. I will try and locate the part number.

storm
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Location: NSW, Australia

Re: Dual carbs with propane?

Post by storm »

Gentlemen one manufacturers "RV cam" is another manufacturers stock replacement cam. It's like referring to stage 1 stage 2 stage 3 but it isn't really useful because there is no industry consensus on what makes a cam an RV or stage 1 etc. Do a search on "what does RV cam mean?" and you'll find as many different answers as people posting, its the internet so they all think they are experts but they can't all be correct. Much better off giving actual cam specs including, but not limited to duration, duration@0.050", LSA, LCA, (cam) lift, and total (valve) lift, to get an much more accurate picture of the type of cam and how useful it would be on any particular engine.

There are a variety of reasons to use multiple carbs or mixers
1. engine needs more airflow (not really the case with the 300).
2. multiple smaller carbs increase air velocity which aides in atomisation of liquid fuels. More velocity = better torque.
3. multiple, well placed, carbs decrease individual cylinder lean outs. On 6 cylinder engine 1 & 6 can run lean compared to 3 & 4 running liquid fuels because liquid fuels can, and do, drop out of suspension when they have to travel longer distances. Remember everything takes the path of least resistance.
4. multiple, well placed, carbs provide a "straight(er)" and more equal length path to the intake valve rather than making the air/fuel mix twist and turn through an intake. This increases air velocity.

The ideal setup for any engine would be an appropriately sized ITB (individual throttle body) or an individual runner into a plenum, the same size as the engine capacity, which enables equal air flow and velocity to all cylinders. With this engine I'd, personally, use either the oem manifold or an aftermarket 4 barrel type. With the oem manifold size the mixer(s) accordingly, with a 4 barrel manifold you could use a 425 but you will never use it to its full potential or you could fit a 225 and it would provide good air velocity which will help with torque production.

Using a calculator, which I know some people disagree with, a 300 running at 80% VE (and this is being kind) will use between 306 and 389 cfm at 4000 RPM, at 5000 RPM that jumps to between 382 and 486 cfm. Ask yourself how often, if ever, will you take the 300 over 4000 RPM?

The Impco 225 is rated to 237 HP, years ago the show Engine Power rebuilt a 300 did some sensible modifications to it and then put it on a dyno. It achieved 206 HP. The 2 episodes were called Old Skool Six. Realistically speaking a single 225 is fine for your 300. If you go multiple mixers I'd, personally, be very tempted to try 2 smaller mixers and take advantage of the improved air velocity but I wouldn't be expecting much from it with regards to fuel economy or higher power and torque figures.

EDIT: In the time it took me to write this up C3H8 posted again, I'm getting slow and I'm not even old ;)
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

jon_g9121
Posts: 15
Joined: Mon Dec 09, 2019 11:59 am

Re: Dual carbs with propane?

Post by jon_g9121 »

For reference, my cam is a isky 256. 450/450, 202@.050 and 112 lobe sep.

I think a important thing to remember with mileage is that its more about the whole truck than the engine. Replacing the 9 in axles with 8.8s and the granny 4 speeds with the mazda 5 speeds im sure helped with mileage. the bullnose body style probably had something to do with it too.

Ill have to second C3H8's comment about the dirty intake vavles. I had my head apart last month after about 1 year of daily driving on propane and they were disgusting. I had thought it had more to do with the lack of any solvent qualities of propane compared to gasoline. Ive since bought a catch can but Im not sure itll help.

Tom68
Posts: 75
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: Dual carbs with propane?

Post by Tom68 »

jon_g9121 wrote:
Mon Mar 09, 2020 12:03 pm
For reference, my cam is a isky 256. 450/450, 202@.050 and 112 lobe sep.

I think a important thing to remember with mileage is that its more about the whole truck than the engine. Replacing the 9 in axles with 8.8s and the granny 4 speeds with the mazda 5 speeds im sure helped with mileage. the bullnose body style probably had something to do with it too.

Ill have to second C3H8's comment about the dirty intake vavles. I had my head apart last month after about 1 year of daily driving on propane and they were disgusting. I had thought it had more to do with the lack of any solvent qualities of propane compared to gasoline. Ive since bought a catch can but Im not sure itll help.
Nice cam, 4 degrees advanced I'd imagine, did you check it ? Sounds like this could be one of those engines with retard built into the timing gears.

You mention a catch can, is it breathing oil into the intake?

storm
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Location: NSW, Australia

Re: Dual carbs with propane?

Post by storm »

jon_g9121 wrote:
Mon Mar 09, 2020 12:03 pm
For reference, my cam is a isky 256. 450/450, 202@.050 and 112 lobe sep.
I just looked that up and I think you have lobe separation (LSA) and Lobe Centreline Angle (LCA) mixed up. In all honesty I think the MILE-A-MOR or the Turbocycle-A are better alternatives. Why? Mile-a-mor is a single pattern fuel economy cam with a lower working rpm range from 1000-3800 rpm, the Turbocycle is a split (more duration and lift on the intake which should indicate to you how deficient the intake flow is on these things) pattern cam with a working rpm range of 1000-5000 rpm. Both of these work from 1000 rpm compared to the 256 cam which starts at 1500. Of course this is JMNSHO (Just My Not So Humble Opinion).
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

Tom68
Posts: 75
Joined: Mon Jun 18, 2018 2:46 am
Location: Australia

Re: Dual carbs with propane?

Post by Tom68 »

storm wrote:
Tue Mar 10, 2020 12:43 am
jon_g9121 wrote:
Mon Mar 09, 2020 12:03 pm
For reference, my cam is a isky 256. 450/450, 202@.050 and 112 lobe sep.
I just looked that up and I think you have lobe separation (LSA) and Lobe Centreline Angle (LCA) mixed up. In all honesty I think the MILE-A-MOR or the Turbocycle-A are better alternatives. Why? Mile-a-mor is a single pattern fuel economy cam with a lower working rpm range from 1000-3800 rpm, the Turbocycle is a split (more duration and lift on the intake which should indicate to you how deficient the intake flow is on these things) pattern cam with a working rpm range of 1000-5000 rpm. Both of these work from 1000 rpm compared to the 256 cam which starts at 1500. Of course this is JMNSHO (Just My Not So Humble Opinion).
112's a common lsa in that size cam.

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