Status on High Performance 4-barrel Carbs

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Marc
Posts: 73
Joined: Mon Apr 23, 2012 8:54 am

Status on High Performance 4-barrel Carbs

Post by Marc »

Hi Guys,

I will dedicate in particular this topic first to Martin (NL), however everybody is welcome to share information of course!

Martin has a page protouring.nl with his 71 Camaro. Also he advertised on this forum and shared his experience on SBC : with a OHG-450 dual fuel and then technocarb straight LPG … this was ~10 years ago.
It seems the Technocarb set up gave satisfaction, delivering the power expected. Then he removed all the stuff and converted back to gazoline with a EFI system.

Meanwhile we are now 2020 and my search on the web let me discover that :
- Technocarb does not produce any more the 4 barrel kit due to low commercial success
- Another propane kit builder closed in Australia (I fogot the name?)
- Sjak Brak in the Nederland left the LPG business
- OHG-450 mixer is also not available anymore
- There was a Kurt in the Netherland that wanted to develop a powerfull mixer but no signs?
- Gas research kits are not commonly used due to the price
- Some guys in pro-touring are going back to gazoline
-...

Today it seems there is less possibilities than 10 years ago.

What is happening?
For us propoane Gays I think it is intersting to make a status of the current possibilities and evolution of legislations?

Martin, as one of the few people from Europe sharing on internet your knowledge of the carburated propane conversions for powerfull 4 barrel V8, can you also share your point of view based on the past and current situation?


Thanks,

Marc

BigBlockMopar
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Re: Status on High Performance 4-barrel Carbs

Post by BigBlockMopar »

(I think you might want to edit a worfd in your post somewhere near the last couple of lines ;) )


Here in the Netherlands, LPG is only interesting to use on American cars when the car is used often. AND, only because 1 liter of (compressed) LPG is about 1€ cheaper than 1 Liter of gasoline.
On an occassional good weather, weekend driver, the costs of doing a LPG-conversion doesn't weigh up against the 'easy' mods like gasoline EFI.

I still daily drive my '73 Dart with a Impco 425. I know power is decreasing fast from 4000rpm and up because of this.
I have an OHG450 carb laying around, but not a matching vaporiser.
'Only' way to improve the current propane-system is to install another 425 carb (and manifold), or just go to LPG-injection (vapour or liquid).
EFI alone adds a whole level of complexity to an engine. After that, vapour injection is still 'fairly managable', while liquid propane injection comes with another set of modifications to the fuelsystem that add even more costs.
https://www.bigblockmopar.com
'73 Dodge Dart - 360ci - 11.3:1cr
MegaSquirt + HEI 7-pin timing control - Edelbrock AirGap - Cold Air Intake
IMPCO E / 425 mixer - A518 OD-trans - 3.55 gears - 225/50/17" tires.

C3H8
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Re: Status on High Performance 4-barrel Carbs

Post by C3H8 »

First a comment on the 450 mixer. You can use it with IMPCO vapourizers. The only difference using the IMPCO E or L is the secondary spring has to be changed from the blue spring (neg. 1.5" WC) to the orange spring (neg .5" WC).

As for the availability of equipment. Simply put it comes down to supply and demand. Yes there are millions of older cars around the world but only a certain number of these people want to consider propane. Most owners of older cars are usually trying to remain as original as possible other then maybe some engine modifications. Installing a propane tank, vapourizer and mixer is beyond their plans of rebuilding an older vehicle. It adds significant costs, beyond appearance, for vehicles driven limited amounts each year. Because of this the companies that produced the adaptors and auxiliary equipment to complete a conversion have moved onto other products or just went out of business further limiting the consumers choices.

The propane market is still there in specific areas of the world for newer vehicles but at significant cost penalties. In addition the proliferation of new electric options is cutting into the alternative fuel market. The number of hybrid options is increasing every year. Strangely enough these could probably use propane or NG as an alternative fuel but it is unlikely due to the current cost of EFI conversion equipment

storm
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Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: Status on High Performance 4-barrel Carbs

Post by storm »

C3H8 wrote:
Mon Jan 13, 2020 3:42 pm
Most owners of older cars are usually trying to remain as original as possible other then maybe some engine modifications. Installing a propane tank, vapourizer and mixer is beyond their plans of rebuilding an older vehicle. It adds significant costs, beyond appearance, for vehicles driven limited amounts each year.
This is the major issue. Originality of older classics is a big thing and propane tanks take up a lot of space in locations that, in many cases, is extremely inconvenient. I never completed the conversion on my VC Brock (European guys the early Australian Commodore was based on the Opel Rekord of the last 70s early 80s) purely because of the fact I would have lost approximately 1/3 of the boot space. There is a company in New Zealand that makes a brilliant tank that could easily be used in the space of a regular petrol tank but the cost of getting it bracketed and the valves put in a safe place is prohibitive on older cars purely because the demand for these simply isn't there. If a "group buy" could be organised for each vehicle that requires special modifications and setting up you would need at least 500 orders to make it viable.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

Marc
Posts: 73
Joined: Mon Apr 23, 2012 8:54 am

Re: Status on High Performance 4-barrel Carbs

Post by Marc »

I agree, it all make sense. Another aspect is that these american V8 carb cars are becoming older and older so fewer cars are running, with a ever larger budged need for restauration (that adds to keep them as original as possible) and on top of that maybe in some part of the world there is a decrease in old car enthusiasts as generation X is not so much moved by old cars….
This, in addition to the previous explanations, makes it clear that propane conversion kits for such cars is certainly not a market in expansion and we see a difference from 2005 to 2020.

I also agree that EFI adds complexity to the car so I don't understand why some owners of old american muscle cars are turning to gazoline EFI system neither. marketing maybe?

Personely, this is only me, I like the simple, economic, green aspect of LPG on my old camaro. I would not spent more time and money for a vpaor injection system, and I am not yet ready to convert back to gazoline so let's make this forum live for a long time still :-)

storm
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Location: NSW, Australia

Re: Status on High Performance 4-barrel Carbs

Post by storm »

Marc wrote:
Tue Jan 14, 2020 3:57 pm
and on top of that maybe in some part of the world there is a decrease in old car enthusiasts as generation X is not so much moved by old cars….
That's not really the case in Australia. it's the baby Boomers and Gen X (of which I am one) who are keeping the older cars going. In Australia Gen Y, and now the Millennials, are the ones who must have the latest "and greatest". In Australia Gen X remember what a recession is, Gen Y and Millennials have never been through one. It is not economically viable to purchase a new car every 5-10 years here and buying a 2nd hand modern car is often fraught with the hassles of fixing the problems someone else didn't fix.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

51geezer
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Location: Vancouver

Re: Status on High Performance 4-barrel Carbs

Post by 51geezer »

I'm learning as I go with my gasoline to propane conversion, so...

I was also concerned about the 425 cfm rating of the Impco being inadequate for my V8. I don't want two carbs on that weird siamesed dual-carb intake, although the thought of using the factory-style 427 FE 8V manifold is intriguing.

My plan is to increase displacement from 352" to 410-416" and the compression ratio from 8:1 to 10.5:1 (or as high as 12:1 if I want expensive pistons). My thinking is that the Impco 425 will be adequate for my build because the 352 4V used a 450 cfm Holley and it is rumoured that some 428s used one as well. Similar to the D0PF-9510-U. My targets are 275-300 hp and 4500 max rpm. The reasons for my project are the high price of alcohol-free gasoline and the fact that even the most expensive pump gas is incompatible with the old-tech materials in the fuel system. (Some say that the alcohol is not the problem but it is some other additive, maybe MTBE.)

Do I have the solution?

storm
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Location: NSW, Australia

Re: Status on High Performance 4-barrel Carbs

Post by storm »

Impco 425 mixers flow approximately 460 cfm. Using the formula CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456 you can work out what you need.
If your engine is 416 ci, your max rpm is 4500, and your VE is 85% you'll need approximately 460.41666666666 etc cfm. If your VE is higher, e.g. 90%, you'll need 487.5 cfm.

Alcohol is part of the prblem not the whole problem. Water gets in and mixes with the alcohol and this causes issues with the old metals.
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: Status on High Performance 4-barrel Carbs

Post by Tom68 »

storm wrote:
Tue Jan 28, 2020 8:51 pm
Impco 425 mixers flow approximately 460 cfm. Using the formula CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456 you can work out what you need.
If your engine is 416 ci, your max rpm is 4500, and your VE is 85% you'll need approximately 460.41666666666 etc cfm. If your VE is higher, e.g. 90%, you'll need 487.5 cfm.

Alcohol is part of the prblem not the whole problem. Water gets in and mixes with the alcohol and this causes issues with the old metals.
That's a terrible carb sizing formula and on top of that Impco carbs were flowed at 2" of pressure drop, Holley 4 Barrels flowed at 1.5" pressure drop and Holley 2 barrels flowed at 3'' drop.

C3H8
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Re: Status on High Performance 4-barrel Carbs

Post by C3H8 »

There are two ways supplied by IMPCO for CFM calculations. The calculation storm supplied or a chart that IMPCO made up to forgo the calculation. According to the chart storms formula pretty well matches the chart. IMPCO does suggest rounding up the CI for over the road vehicles. In this case the chart has 400 CID and then goes to 450 CID. At 400 CID at 4500 RPM the chart specifies 448 CFM. The 450 CID indicates a maximum CFM of 499 at 4500. This is not the only basis of selecting the carb though. The manual makes the following recommendation.

"
The type of service the engine provides is another necessary consideration in selecting the appropriate carburetor (or mixer). An engine which is never operated at wide open throttle provides the best performance and service using carburetion, such as lift trucks and some passenger car applications. These engines have a degree of under carburetion, are easier to start and will develop the low end torque required suited for this type of service. Engines used in high rpm ranges can be equipped with carburetors delivering somewhat over the air-low capacity dictated by the engine’s air-flow requirement and the larger capacity carburetor will be able to respond to maximum air-flow requirements."

Let's be realistic. How long is an engine going to remain at maximum RPM and WOT. In most cases a few seconds or less. Unless your operating a racing vehicle with your foot constantly asking for max RPM most of us drive only occasionally at WOT. I have seen many conversions that operated sluggishly at low RPM because the owner figured the bigger the mixer the better the performance. This is not true with IMPCO mixers since they lift the gas valve based on airflow. Too big of a mixer slows the lifting of the gas valve causing lean operation when accelerating from a stop. You have to ask yourself. Will I be happier with great reaction off the line or will I be happier with great acceleration from midrange to WOT. From what you have described the 425 is very close to the ideal mixer for you unless you decide to modify the engine to achieve a higher RPM.

The one thing I would change on the mixer is to remove the restrictor plate inside the vapour inlet of the mixer. The plate reduces the flow on propane. Normally it is only removed on NG, however removing it on propane may help the volume on propane at WOT.

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

Re: Status on High Performance 4-barrel Carbs

Post by Tom68 »

C3H8 wrote:
Wed Jan 29, 2020 1:40 am
There are two ways supplied by IMPCO for CFM calculations. The calculation storm supplied or a chart that IMPCO made up to forgo the calculation. According to the chart storms formula pretty well matches the chart. IMPCO does suggest rounding up the CI for over the road vehicles. In this case the chart has 400 CID and then goes to 450 CID. At 400 CID at 4500 RPM the chart specifies 448 CFM. The 450 CID indicates a maximum CFM of 499 at 4500. This is not the only basis of selecting the carb though. The manual makes the following recommendation.

"
The type of service the engine provides is another necessary consideration in selecting the appropriate carburetor (or mixer). An engine which is never operated at wide open throttle provides the best performance and service using carburetion, such as lift trucks and some passenger car applications. These engines have a degree of under carburetion, are easier to start and will develop the low end torque required suited for this type of service. Engines used in high rpm ranges can be equipped with carburetors delivering somewhat over the air-low capacity dictated by the engine’s air-flow requirement and the larger capacity carburetor will be able to respond to maximum air-flow requirements."

Let's be realistic. How long is an engine going to remain at maximum RPM and WOT. In most cases a few seconds or less. Unless your operating a racing vehicle with your foot constantly asking for max RPM most of us drive only occasionally at WOT. I have seen many conversions that operated sluggishly at low RPM because the owner figured the bigger the mixer the better the performance. This is not true with IMPCO mixers since they lift the gas valve based on airflow. Too big of a mixer slows the lifting of the gas valve causing lean operation when accelerating from a stop. You have to ask yourself. Will I be happier with great reaction off the line or will I be happier with great acceleration from midrange to WOT. From what you have described the 425 is very close to the ideal mixer for you unless you decide to modify the engine to achieve a higher RPM.

The one thing I would change on the mixer is to remove the restrictor plate inside the vapour inlet of the mixer. The plate reduces the flow on propane. Normally it is only removed on NG, however removing it on propane may help the volume on propane at WOT.
Under carburetted is always more practical, I'm surprised it's that big a deal on variable venturi carbies though, no doubt it is when Impco tunes them as such.

We get the CA 225 down here for our 3.8 litre Commodores, seems that would over carburetted compared to my 300A on a 327.

I know one thing when my 327 was a petrol motor and had a mild cam blowing through a single 2" exhaust system, a Holley EconoMaster 465 stifled it, a 600 vac secondaries was considerably better, and an 850 double pumper was a little better again but obviously more than it needed, it drove fine with all three carbies, you just didn't use W.O.T to kick the powerglide down with the DP, had it been vac sec it would've been fine.

P.S the 327 I built in 1983, still running the short motor untouched, it currently has a 650 spreadbore double pumper with a 300A flowing though the primaries and a separate air filter on the secondaries running on Petrol, centrifugal advance locked out but with 15 degrees of vac advance plumbed direct into the manifold, runs like a dream.

storm
Posts: 796
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: Status on High Performance 4-barrel Carbs

Post by storm »

Tom68 wrote:
Wed Jan 29, 2020 1:12 am
storm wrote:
Tue Jan 28, 2020 8:51 pm
Impco 425 mixers flow approximately 460 cfm. Using the formula CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456 you can work out what you need.
If your engine is 416 ci, your max rpm is 4500, and your VE is 85% you'll need approximately 460.41666666666 etc cfm. If your VE is higher, e.g. 90%, you'll need 487.5 cfm.

Alcohol is part of the prblem not the whole problem. Water gets in and mixes with the alcohol and this causes issues with the old metals.
That's a terrible carb sizing formula and on top of that Impco carbs were flowed at 2" of pressure drop, Holley 4 Barrels flowed at 1.5" pressure drop and Holley 2 barrels flowed at 3'' drop.
Terrible or not it is the industry standard formula and works regardless of pressure drop. Many, not all, EFI "single barrel" Throttle Bodies are flowed at 3" but when it is all said and done the pressure drop the item is flowed at means very little until the thing becomes a restriction and limits the revs an engine can pull.
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: Status on High Performance 4-barrel Carbs

Post by Tom68 »

storm wrote:
Wed Jan 29, 2020 10:20 pm
Tom68 wrote:
Wed Jan 29, 2020 1:12 am
storm wrote:
Tue Jan 28, 2020 8:51 pm
Impco 425 mixers flow approximately 460 cfm. Using the formula CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456 you can work out what you need.
If your engine is 416 ci, your max rpm is 4500, and your VE is 85% you'll need approximately 460.41666666666 etc cfm. If your VE is higher, e.g. 90%, you'll need 487.5 cfm.

Alcohol is part of the prblem not the whole problem. Water gets in and mixes with the alcohol and this causes issues with the old metals.
That's a terrible carb sizing formula and on top of that Impco carbs were flowed at 2" of pressure drop, Holley 4 Barrels flowed at 1.5" pressure drop and Holley 2 barrels flowed at 3'' drop.
Terrible or not it is the industry standard formula and works regardless of pressure drop. Many, not all, EFI "single barrel" Throttle Bodies are flowed at 3" but when it is all said and done the pressure drop the item is flowed at means very little until the thing becomes a restriction and limits the revs an engine can pull.
It means an awful lot if you're chasing performance, you don't get 1.5" of vacuum at wot peak torque or at peak horsepower, so a 600 holley on a 300 cubic inch engine never gets to flow 600cfm. Yet the calculation is for carb size from engine speed and capacity has no allowance for vacuum, it is what goes through the motor unrestricted.

My old Impco book has a horsepower rating for each mixer, seems logical if I build a 300hp engine and would like access to that 300hp, I'd use their chart to see my mixer options.

I see Impco has a 2" and 1.5" rating for some of their mixers now, look at the airflow difference and remember you'll have virtually no manifold vacuum at wot.

I've rang Holley before for carb sizing for a Cleveland going into a street driven Cobra, where I was going to use an 850 they recommended a 950, I was expecting them to recommend a 750. Obviously they don't use the formulae that's published in the old HP books and S A Design books.

I know this threads about what's available but it's also got performance in the title, everybody that's sized off that formula know it leaves an engine seriously under carb'd.

storm
Posts: 796
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: Status on High Performance 4-barrel Carbs

Post by storm »

Tom68 wrote:
Thu Jan 30, 2020 2:17 am
It means an awful lot if you're chasing performance, you don't get 1.5" of vacuum at wot peak torque or at peak horsepower, so a 600 holley on a 300 cubic inch engine never gets to flow 600cfm. Yet the calculation is for carb size from engine speed and capacity has no allowance for vacuum, it is what goes through the motor unrestricted.

My old Impco book has a horsepower rating for each mixer, seems logical if I build a 300hp engine and would like access to that 300hp, I'd use their chart to see my mixer options.

I see Impco has a 2" and 1.5" rating for some of their mixers now, look at the airflow difference and remember you'll have virtually no manifold vacuum at wot.

I've rang Holley before for carb sizing for a Cleveland going into a street driven Cobra, where I was going to use an 850 they recommended a 950, I was expecting them to recommend a 750. Obviously they don't use the formulae that's published in the old HP books and S A Design books.

I know this threads about what's available but it's also got performance in the title, everybody that's sized off that formula know it leaves an engine seriously under carb'd.
You've somehow managed to seriously screw up the intention of that formula and have taken it as far away from the reason I posted it as you can. As C3H8 pointed out the formula I posted is close to IMPCOs recommendations, enough said really.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

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