Inlet runner lengh ?

[balldrick]

Im running a 250 engine with 2V head and triple SUs and have problems on hot days with feul vapourizing in bowls as there the old sort with bowl on side.Temps often reach 40+deg C here. im thinking of mounting the carbs obove the engine with 3 longer inlet runners,will this work?any info greatly apreceated.

 

[rbohm]

8) better to build a heat shield over the exhaust manifold.

 

[StrangeRanger]

The longer runners will lower the RPM at which the intake velocity is optimised. I don't know if this is something you want to do or not but it will happen.

Approximately:

L = (90 x 1100) / N

Where
L is the length of the inlet runner from mouth of the choke horn to valve face expressed in inches

n is the RPM at which maximum torque occurs

 

[xctasy]

With respect to your question, what you asking is not the core solution due to space issues with 2V's in any engine bay, be it XY,XA/XB or even a Cortina.


Heat soak is a serious problem with all non cross flow engines. It was the same with the CD 150 and CDS175 carbs on the Torana XU 1's and sportier Triumph I6's with 2.0 or 2.5 litre engines. You were fighting a loosing battle unless you could control air temperature and fuel temperature. This is why the sucessful fuel injection engines had return lines and external air inlets from the cool part of the engine bay, not Hemi E38 or XU1 pan cake filters

You've got a few options. The best is to keep the carbs as is, and rework each of the common side hung muck metal float bowls. You rework the feed line to a design showed in a book by David Vizard in 1988. The inlet has the float removed, and the seat removed. You use a restricted inlet via three Holley 2300/4150/4160 main jets, sized to the peak horsepower of the engine. Then scavange the float bowl via a steel ferule stand pipe and a small, cheap Facet, Carter or Bosch fuel pump. Sizing and how to do it are on page 167 of David Vizards Modifying Fords SOHC. That will totally fix the problem. Tank foam used in street stock racers to stop tank ruptue is used to stop fuel slosh, and each ferule is parked with its stop at the old float level.


The other option is getting three HIF 6, HIF7, or metric HIF 44's, and some biased O6 needles. The float bowls are integrated, and even closer to the touching the headers on most installations, but you can use the stock Marina 1750/2600/P76 2.6 phenolic spacers and move the carbs outwards. The advantage is the latter SU's are self compensating, and have a bimetalic strip to control fuel level, and flow about 25% more CFM than the earlier carbs, eclisping the 2" HD8's without having to run the bigger 125 thou jets.


Longer inlet runners that curve upwards are thing single most silly thing to do. Jag did it on the V12's, and the system never worked well from a fuel atomisation point or view, and created shocking fuel consumption. It's on par with the swan neck Webers used on BMC 1100'S and 1275'S and the Lynx side draft to Holley 4-bbl carb adaptor used in the TR8 race cars...a dead loss. With carbs, any gradual small or large radius turn creates fuel drop out and puddling, and you can never get them running right. Okay for an EFI Falcon, useless for triple carbs.

 

[Anlushac11]

I would run a heat shield as mentioned above but would also see about getting some Phenolic resin spacers to see about insulating the carbs from the intake.

Any chance of adding ducting to increase the air flow in/out of the engine compartment?

What about adding a cool can that you could add icewater to? Not practical for a daily driver so what about adding insulation to carbs and fuel line so they dont pickup underhood heat?

Make a little carb blanket? and run something over fuel line to insulate it?

PC's are now making use of heatpipe technology maybe incorporate something like that to pull heat off carbs or fuel line?

Or if ya wanna get really crazy add some peltier coolers.

 

[balldrick]

Thanks for the info guys.I have been looking at a few options,SU HIF44,Triple down draft webers,or going feul injection.Is there a big diference in performance between webers and feul injection?Im not worried about feul economy and price would probable be about the same.Do webbers suffer from het soak?

 

[L6]

Im running a 250 engine with 2V head and triple SUs and have problems on hot days with feul vapourizing in bowls as there the old sort with bowl on side.

I had a T2500 with twin SUs that routinely suffered from poor idle in heavy traffic on a hot day, and difficulty in starting the engine when hot.

The problem seemed to be fuel vaporisation so I fitted a bleed off at each carb with return line to the fuel tank. The scheme was to provide a means of bleeding off the vaporised fuel and also maintain a reasonable flow of cool fuel through the feed line even when the consumption was low at idle.

The idle problems disappeared completely and even when hot the engine started after two or three revolutions instead of flattening the battery.

There was little science to this; it was done as an act of desperation.

I cut the fuel line close to each carb and fitted a T with the middle leg facing upwards. Two hose barbs were filled with solder then a bleed hole drilled through the solder. The drill was one that I had for printed circuit boards and I think was .8mm. The modified hose barbs were then fitted into the upwards facing leg of each T. The bleed hoses were fitted to the hose barbs then joined together just behind the rear carb, and a single 6mm hose run back to the tank.

The size of the bleed hole was based entirely on the drill I had available but seemed to be quite satisfactory at allowing vapour to pass through quickly while providing enough resistance to liquid fuel to avoid starvation under full power.

 

[Lazy JW]

...
The size of the bleed hole was based entirely on the drill I had available but seemed to be quite satisfactory at allowing vapour to pass through quickly while providing enough resistance to liquid fuel to avoid starvation under full power.

Brilliant! I love it

The stock Ford 300 has similar problems in hot weather due to the carb sitting right on top of all that hot iron. Hmmmmmmm
Joe

 

[woodbutcher]

Sounds like the return line on our 6`s could be routed along the FEED line back to the tank area,and then use a "T" fitting to splice into the VENT tube that feeds back into the tank fill pipe.Neat,but not gaudy.
Leo

 

[Anonymous]

"With carbs, any gradual small or large radius turn creates fuel drop out and puddling, and you can never get them running right."


Well Dean, that statement would seem to mean that NONE of the manifolds on carbureted cars are acceptable, with the exception of nearly-straight runners from individual carburetor throats (which, we have observed, you prefer, and understandably so). Yes? No?

 

[rbohm]

"With carbs, any gradual small or large radius turn creates fuel drop out and puddling, and you can never get them running right."


Well Dean, that statement would seem to mean that NONE of the manifolds on carbureted cars are acceptable, with the exception of nearly-straight runners from individual carburetor throats (which, we have observed, you prefer, and understandably so). Yes? No?

8) to an extent that is true. the straighter the intake runner on a carbed engine, the better. but it also needs to be short. the problem is that fuel does not like to turn corners, air on the other hand doesnt care for the most part. there are ways to induce turbulance to keep the fuel mixture suspended, but that has its own problems. like restricting airflow, etc.

 

[Lazy JW]

...
Longer inlet runners that curve upwards are thing single most silly thing to do. Jag did it on the V12's, and the system never worked well from a fuel atomisation point or view, and created shocking fuel consumption...

I'm quite sure that this is correct in a performance engine that is trying to get maximum power per cube but I have data showing tractor engines with updraft carburetors achieving BSFC right at .50 hp/hr/lb of fuel. In my personal experience they run very well. These engines used hot-spot manifolds to better vaporize the fuel.
Joe

 

[Anonymous]

Dean is right about those first-generation Jag V-12s, and they weren't intended to be high-performance engines at that point, and they performed even worse than intended. Jag improved the engine with head mods and fuel injection with more direct manifolding. Now whether those first U-bend manifolds could have been rejiggered to work better, along the lines of your updraft tractor manifold, maybe so. I wonder why updraft carburetion fell out of favor. Seems like on a crossflow inline engine, updraft carburetion would be a good way to build a more compact engine and keep hood-lines low for style purposes. The manifolding would have about the same length and number of turns, whether updraft or downdraft. Maybe it was a safety issue, for containing possible fuel leaks.

 

[Harte3]

I wonder if any performance minded farmer ever made a mult-updraft manifold/carb set up for that old binder?

 

[Lazy JW]

They made some pretty big updraft carbs to feed those 500+ cubic inch engines. Of course they ran at slow speeds but those big pistons took a mighty big gulp every time.

Probably the main reason updrafts were used on tractors is the compactness factor needed to keep those engine hoods narrow and low for visibility. Try cultivating row-crops with your pickup and you will see what I mean.

Tractor carbs have a potential advantage for turbocharging as they are designed as "balanced" regarding air pressure, meaning that all of the air for float bowl venting, etc. is taken from inside the carb to keep dirty air out of the system. I "think" they could be turbocharged using a blow-through without using a hat. Just need a solid float.
Joe