42 DCNF's on a Mopar 440

[enigma57]

I know a guy or two working on a similar project.......
Rare casting to start with.

Nick, how's your workload in the coming months? Sure would like to have you do the machine work on my Inglese DCNF casting if you can work it in.

Best regards,

Harry

Working through a mountain of work at the moment. I have you covered just need to get caught up first. I have you on my list.

Thanks, Nick! No rush. I will be helping my son build the engine for his '92 Camaro as we can find the time to get together every few weekends over the next several months. Very limited space beneath the hood and we are having to be creative in packaging a one off induction system without butchering his hood (want to retain original hood and external appearance). He's dead set on EFI (can't talk him into a carburetted system), so I am modifying the bejavvers out of a vintage Hilborn stack injector base plate and we will be contacting Scott for his recommendations on setting up a computerized engine management system for the 427 stroker engine. First order of business is to clearance the block for the rotating assembly, though.

Best regards,

Harry

[enigma57]

Regarding the airflow capacity of the 42 DCNF carburettor and its ability to support engines of various displacement...... That is dependent upon choke (main venturi) size, number of carbs and most importantly...... Whether the intake is a plenum design or an isolated runner design.

The Weber 42 DCNF, when fitted to a V-8 engine with IR intake...... (4) 2bbl carbs, each throttle bore supplying a single isolated runner and cylinder...... Will support a 4.9 litre Maserati to 6,000 RPMs when fitted with 34mm chokes and that is the way the OEM setup was configured. When fitted to the 5.3 litre Aston Martin, the 42 DCNF was fitted with 36mm chokes and would support that engine to 6,000 RPMs redline, as well. That is as large a choke size as you should run on a 42mm throttle bore in order to maintain proper fuel metering and drivability from off idle to redline. There was also a 44 DCNF fitted to a few cars and Ducati motorcycles as OEM equipment and a 38mm choke size could be fitted to support either a larger engine displacement than the 325 cu.in. Aston Martin or the same sized engine to higher RPMs in sets of (4) carbs on IR intake.

When fitted to intake manifolding having a common plenum feeding several cylinders rather than an isolated runner intake, the 42 DCNF will support much more displacement, however. A 32mm choke size equates to 1.25984 inches and a single 42 DCNF fitted with 32mm chokes will flow around 360 cfm (2bbl rating @ 3.0" depression) or 315.5 cfm (4bbl rating @ 1.5" depression).

So at 4bbl rating, (2) 42 DCNF carbs will flow around 631 cfm at wide open throttle and (3) of them will flow around 946.5 cfm at WOT. What we will do with Grant's 440 MOPAR is set up the (3) 42 DCNF carbs so that the (2) end carbs which we will move inward a bit...... Will be situated very closely to being centered directly above the paired intake port runner groupings at each end in order to provide more even fuel distribution than the present carb pad location would allow...... And these will be primaries opening simultaneously. The center carb will be utilized as a mechanical secondary on progressive linkage for increased airflow under hard acceleration and will phase in progressively when engine speeds exceed the flow capacity of the (2) primaries. In the case of Grant's 440, the primaries would support the engine to around 4,800 RPMs, so we will begin phasing in the secondary at 3,500 - 3,800 RPMs to carry the engine to designed redline of around 5,300 - 5,500 RPMs (its a near stock build otherwise, with a mild cam upgrade).

Best regards,

Harry

[Caprimaniac]

Thanks for this info, Harry.

I knew the two throttles should be somewhere at 300 CFM. What you lay out there, should be be a great setup as far as I sse it.

I need to look into some of the weber data on the 48 IDA (IDF) for SBF and compare it to the data for The 4.9 Maserati V8. There has been much talk about the webers not supplying enough air on SBF (and FE) setups. (Assuming choke sizes and carb type beeing compareable.) I suspect some of the rant about too small chokes might be BS....

[user-9613590]

Just remember that those carbs are designed to work throttle/cylinder so if used throttle/several cylinders the tuning may (would!) be nightmare!

[enigma57]

Point well taken, Morgo! These carbs can be recalibrated to work on plenum style intake manifolding, however there are substantial jetting and setup changes required. On same sized engines as they may have been fitted previously on IR intake, emulsion tubes must be changed out in most cases and specific E-tubes utilized. Choke size will be substantially smaller, with idle (slow running) jets and main jets increased by quite a bit. Pump shot and air correctors adjusted as needed. The other thing is that there are limits as to how small of a choke size will work well on on a given throttle bore size. So unless smaller bore carbs are fitted, fewer carbs will be needed on plenum intake to provide the necessary airflow.

Best regards,

Harry

[enigma57]

Thanks for this info, Harry.

I knew the two throttles should be somewhere at 300 CFM. What you lay out there, should be be a great setup as far as I sse it.

I need to look into some of the weber data on the 48 IDA (IDF) for SBF and compare it to the data for The 4.9 Maserati V8. There has been much talk about the webers not supplying enough air on SBF (and FE) setups. (Assuming choke sizes and carb type being comparable.) I suspect some of the rant about too small chokes might be BS....

As I recall, the 48 IDAs when fitted to 5.0 litre (302) Ford V-8s in the 1960s on IR intake generally used 37mm chokes. Those engines were redlined at 7,000 RPMs and more on road race circuits, so there is plenty of airflow available with the larger Webers to support a small block Ford, Caprimaniac.

With a 48mm throttle bore, I wouldn't go larger than 40mm or 42mm chokes, as larger would be difficult to tune, manage fuel metering and maintain drivability...... But they should support a 347 (stroked 302) or even a 408 (stroked 351) small block Ford so long as CSA of the port runners is sized properly.

As the longer stroke small block engines will generally reach redline at lower RPMs due to the increased leverage provided by the longer 'arm' (need to do that in order to keep piston speeds within reasonable limits for sustained high speed running anyway)...... I see no reason why 48 IDA or IDF Webers on IR intake would not be up to the task.

With a 427 FE engine in a Cobra, 42mm chokes will carry the engine to 6,500 RPM shift points on IR intake, but that is pushing the envelope with 48s. There were larger IDA style carbs available from Berg and others which would work on the larger big block stroker engines in the 500 cu. in. displacement range, but they would require correspondingly larger runner CSA in their intake design to allow the larger engines to breathe when fitted with the Berg 58s or 60s.

Hope this helps,

Harry

[Grant007]

Hi Everyone, I have been emailing back and forth with Harry and I really wasnt aware of this thread continuing like it has and I was shocked today when I called back in and saw it all, thank you all so much for all your input and a Huge Thank you to Harry for his time and knowledgeable input with my Project, I have a huge Fascination for these old DNCF carbs and love them and am hell bent on getting a set on My 440, I feel Harry has researched the use of them immensly and will go head with the suggestions he has helped me with and modify the Offy Tri manifold and also try a Chrysler/Eldenbrock Tri Mani as well (if hood clearance will allow) as I really want to install the Air inlet Trumpets as I feel they look so good on these DNF's.
I have many sets, infact I have colected I think 5 x sets of 3, some from the Essex engines and also Maserati's too, I will get them out this evening and take a picture of them to add to this thread
Let the cutting and fabrication begin on the Offy and I will keep this thread updated accordingly.
Would anyone happen to know the Height of a Holley 4144 which is the new/the same design as the original centre carb used on the original 6 pack set up on a Mopar, this will greatly help me with my Height Calcs for hood clearance please, the height/measurement I need is from the base of the Carb to the top of the Carb
Thank you again everyone for their comments
Grant

[af2]

Grant, 3.250" base to air cleaner base.

[Grant007]

Grant, 3.250" base to air cleaner base.

Hi Adam,Bless you and thank you for that sport

[Grant007]

I know a guy or two working on a similar project.......
Rare casting to start with.

Was there ever a "4 x dncf" inlet like this this ever fabricated for a Mopar V8 like this either 383 or 440 does anyone know?
Grant

[Caprimaniac]

[quote="enigma57
As I recall, the 48 IDAs when fitted to 5.0 litre (302) Ford V-8s in the 1960s on IR intake generally used 37mm chokes. Those engines were redlined at 7,000 RPMs and more on road race circuits, so there is plenty of airflow available with the larger Webers to support a small block Ford, Caprimaniac.

With a 48mm throttle bore, I wouldn't go larger than 40mm or 42mm chokes, as larger would be difficult to tune, manage fuel metering and maintain drivability...... But they should support a 347 (stroked 302) or even a 408 (stroked 351) small block Ford so long as CSA of the port runners is sized properly.

As the longer stroke small block engines will generally reach redline at lower RPMs due to the increased leverage provided by the longer 'arm' (need to do that in order to keep piston speeds within reasonable limits for sustained high speed running anyway)...... I see no reason why 48 IDA or IDF Webers on IR intake would not be up to the task.

With a 427 FE engine in a Cobra, 42mm chokes will carry the engine to 6,500 RPM shift points on IR intake, but that is pushing the envelope with 48s. There were larger IDA style carbs available from Berg and others which would work on the larger big block stroker engines in the 500 cu. in. displacement range, but they would require correspondingly larger runner CSA in their intake design to allow the larger engines to breathe when fitted with the Berg 58s or 60s.

Hope this helps,

Harry[/quote]
E'llo, Harry.

I'm, running 40DCNF's on an Essex V6 (500ccm cyl) and they have 32 or 34mm chokes. Im' turning it past 7000, but I'll bet they'd like 36 chokes.

Had my 306 on 48 IDF's and 37 chokes, and it ran good. I got some New chokes polished to 40,5mm and they ran great on a 347 up to 8000 rpm. I'm building a New 306 and need to figure if it'll like the 40,5's better than the 37's.....Leaning toward a more street- friendly engine, I'm betting on the 37's. But you never know..... With this cam I used to go to 8000 on this engine as well.

+ 400 cui and +6500 is more or less the limit for the 48's, then. I seem to remember some whining about the 48's beeing too small for lower cui engines, but I'll have to check the Archives.

Do you know of anywhere With good Weber flow- data?

[SMITHBERGRACING]

Flow info? I have a flow bench and flow carbs as well. I'm willing to make a fixture to do this if somebody needs or wants this done.

[SMITHBERGRACING]

Does anybody happen to know what the bore spacing on one of these Weber DCNF's is?

[enigma57]

Hi, Nick! Bore spacing for the Weber DCNF carburettor is 48mm center to center. Mounting stud holes front to rear are 52mm on center. Mounting stud holes left to right are 85mm on center.

Jenvey in the UK manufacture individual EFI throttle bodies to replace various Weber carburettors and their pdf drawing are a good resource for carb mounting pad dimensions. Pull up Jenvey's webpage for DCNF throttle bodies......

http://www.jenvey.co.uk/home/twin-throt ... dcnf-tc45i

Then go to the "PDF Drawing (27,24 KB)" and you will find the dimensions there (use lower image marked 'Engine End').

Best regards,

Harry

[enigma57]

E'llo, Harry.

I'm, running 40DCNF's on an Essex V6 (500ccm cyl) and they have 32 or 34mm chokes. Im' turning it past 7000, but I'll bet they'd like 36 chokes.

Had my 306 on 48 IDF's and 37 chokes, and it ran good. I got some New chokes polished to 40,5mm and they ran great on a 347 up to 8000 rpm. I'm building a New 306 and need to figure if it'll like the 40,5's better than the 37's.....Leaning toward a more street- friendly engine, I'm betting on the 37's. But you never know..... With this cam I used to go to 8000 on this engine as well.

+ 400 cui and +6500 is more or less the limit for the 48's, then. I seem to remember some whining about the 48's beeing too small for lower cui engines, but I'll have to check the Archives.

Do you know of anywhere With good Weber flow- data?

Hi, Caprimaniac! Yes, the DCNF carbs were designed for IR intake on engines having individual cylinder displacement near 500cc. With 40mm throttle bores, 32mm chokes fall spot on with Weber's recommended 1.25:1 bore to choke ratio. Fitted to IR intake with 40mm throttle bores on an engine of that size, 34mm chokes are at the ragged edge of manageable fuel metering for a street driven engine that must have good drivability from off idle through the entire operating range.

With your 302 (5 litre) V-8, I believe you will find your present 48 IDA carbs with 37mm chokes to be as large as you will need on the street. As you state your goal to be a more street - friendly engine, no need to turn 8,000 RPMs. Depending upon vehicle weight and gearing, you may want to revise cam specs / valve timing to a grind that will give more low and mid-range torque, possibly limit redline to 6,500 RPMs or so on the street? Just a thought.

Happy Motoring,

Harry