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Author:  nomad [ Thu Nov 15, 2012 10:44 pm ]
Post subject:  Shrinker

This post is a follow on to my earlier post on dynoing the Mopar engine in the Fuel systems forum.

We've talked about 93 octane low compression engines liking a mix of large and small droplets via the intermediate "piss and dribble" method.

We've also found that E85 likes less smaller bubbles in the emulsion. At least in what we are doing. Ex: same amount of emulsion air, just spread out over more and smaller emulsion jets.

Now, using the same principles do we think E85 would also like the additional "piss and dribble" circuit?

Just as a note. I have a 1050 Dominator E85 carb in the field on a 440 inch small block Ford the customer just loves. he drives it on the street.
He insisted it stay a 3 circuit and he couldn't be talked into a 2 circuit. It's got a idle tube in the mainwell, the mainwell is .193 top to bottom. Booster inserts are stock with 8 holes. I increased my gas intermidiate jetting by 30% to start and we jetted the main jets appropriately on our 357 dyno mule. To date it's the highest HP we've made on that engine. Lamda on our engine was in the .80 range.

That said. While the carb has done well, just one carb doesn't prove a lot.

Author:  shrinker [ Thu Nov 15, 2012 11:21 pm ]
Post subject:  Re: Shrinker

The reason the piss and dribble works in some conditions is its a method of getting the fuel into the engine in larger droplet form. AFR is one thing, droplet size is another. Consider it this way. On the molecular scale any time there is a collection of molecules its in the form of a liquid. Once the heat is high enough the liquids turn into gasses, thats when the individual molecules run free, thats when they can be oxidized (burnt), The larger size a droplet starts out at the longer it takes to boil away in the heat, so the atmosphere around the droplet changes in AFR as the droplet is boiling to gasses. The environment between liquid state molecules varies considerably, It goes from full rich beyond the flammable limit, to as lean as it can be under the circumstances in the zone near the middle of the droplets. This is where the AFR and the droplet mixture comes into play. The fuel from the boosters is one style, the t-slot is another, the piss and dribble is another. The task is to have enough fuel vaporized from the 'better circuits" to match the heat generation of the engine. Thats things like compression ratio, time of compression, exhaust recycling etc. In low compression engines if there isnt enough heat to deal with the AFR and gas the fuel load then you have to resort to some larger droplets to lean off the start of the burn but quickly obtain a safe burn at some time after ignition. When you consider street fuel it makes sense because they have large molecule structures to feed cats and those molecules are low octane. So you can stop some detonation by having larger droplets that are still in liquid form thus not burning. The light chemicals will boil from the droplets first, and give you the octane you need trapping the low octane heavies in liquid form. Its the blend of the droplet sizes that fits each engine that you find by experimentation.

Author:  shrinker [ Thu Nov 15, 2012 11:35 pm ]
Post subject:  Re: Shrinker

Now E85, its a simple alcohol molecule thats stuffed up by the inclusion of street grade fuel. The problems of droplet size are less important for the trapping of low octane junk but the specific heat needed is much greater, so in some situations fine drops will work best. If the engine doesn't produce enough heat to gas the Ethanol then finer drops should be needed. The danger with alcohols and fat drops is the initial burn around the plug is too lean, Bet you see that all the time, its the old white plug dark piston syndrome. Alcohols are bit funny to read though, because they sometimes dont crack the CO part of the molecule, when thats happening you dont make max potential power and you get a clean plug read because there is little or no carbon to see. You have to crack the CO to get a carbon read on a plug. If the engine has carbon on the piston, then you know your starting the burn incorrectly, basically the burn goes from lean to rich curing the cycle, the WB's read it at the end of the cycle so its no help, thats why we read plugs and use gas benches. Gas benches show the relationships of the gases and reveal all this stuff.
If you have a street car with 3 circuits the factors of exhaust blockages, (there not like race cars are they) forces CO2 or CO into the environment between the drops, If its CO you dont want to gas the droplet too much other wise the environment goes too rich early in the process, the overall mixture from the carby is one thing, whats happening where the air and oxygen is between the fuel molecules is how you have to think. If the exhaust retention is CO2 you now have a fire extinguisher gas present, so its more difficult to set the fire off, lots to think about isnt there.

Author:  shrinker [ Fri Nov 16, 2012 5:55 am ]
Post subject:  Re: Shrinker

As for if the E85 would like the piss and dribble circuit, its probably going to be more related to the flow rate interruption of the 3rd circuit feed tube. The feed tube stuffed into the main well idea of Holley's is going to cause the E85 which is thicker viscosity that straight gasoline to go turbulent flow at a lower HP level per barrel that a 3rd circuit done the right way like others do. Guess its a suck it and see situation.

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