Ok guys help me out here. I'm in school for diesel tech and there's a guy here that thinks he can take an old n/a 7.3L Ford diesel and put a gaser intake n carb on on it bit yet still keep it a diesel.

We think he needs to go to the funny farm !
What yall think?

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ummmm.....NO, you cant do that . the diesel needs to be injected at just the right time to fire correctly there is no other timing to it. if you did put a carb on it, then fuel would flow all the time and cause a runaway! there is no way it would work!

 

i do not believe that is true. the valves in the engine tetermine when fuel and air enter the cumbustion chanmer. and the throttle stop in the carb would determine air flow. to little and it would die out due to a super rich mixture just like a gas engine. each cylinder sucks air/fuel in at a specific tim NOT ALL THE TIME!!! so it the carb is tuned correctly there is no reason it wouldnt work. old 6.9s and 7.3 idi's are injected into the manifold not the cylinders.

food for thought... if you take the multiport fuel injection off of a gasser truck and swith it to an old school holley intake/carb will it run? YEP and run well. not quite as efficient but it will run.

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also there would be no reason to ever change the cam timing on the engine??? this is what tells the valves to open when they do. that was an irrelivant fact in the above post. all engines need to be Injected/timed at the right moment to run properly

 

i didn't say anything about cam timing, there would be no timing for the fuel to go in or spark timing to time when the fuel burns is all i meant, therefore if the intake valve is open sucking fuel in the entire time it will run away if you even try to rev it up.

you are comparing an apple to a bannana yes they are fruit but not the same at all, a carb will not work on a diesel period. thats why they don't do it.....ever. a diesel has to have a precise fuel timing in order to run correctly, without that it will not run. and if it does you will have some serious damage.

try it with yours and see, put a throttle plate on there and start spraying fuel in and see what happens when you rev it up make sure to get a video too

to the op it won't work.

 

never said it would run well but with a throttle plate you can slow the air which cools fire. it would most likely idle great run decent in gear but rev to the moon and take a VERY long time to idle back down after you reved it up in neutral, but it WOULD idle run.

 

All diesels inject the fuel directly into the cylinder. When they are talking about idi it is a prechamber in the top of the cylinder where the fuel is injected but it is still the cylinder.

It would not work to just put a carb on it. It is like turbostang said it has to be precisely timed. If you just run it through a carb the cylinder would fill with fuel and air when the piston came up and hit a point where it could burn it would no matter where in the cranks rotation that was. The next problem with it is the fuel has to be atomized to burn right which would be one problem a carb would have.

The reason you can take multiport off a old gas truck and put a carb on it is because a gas engines ignition is timed by spark and a diesel is timed by fuel.

 

exactly^^ no way it will run might idle like s**t for about 10 seconds then load up and die if you don't lock it up with too much fuel. like i said, try it on your truck (take a video) and let us know what happens

 

interesting. at what compression does diesel ignite? ive been wrong a million times before probably am again. i just cant fathum how an engine can run away if it is getting anywere near close the amount of fuel it needs to run. atomization would suck no doubt.

to me fuel timing would be acomplished by valve timing. but if it ignites before tdc comp. the it no doubt would knock itself to death not RUNAWAY!

so you fill it full of air compress it some fill er full of fuel compress it some more then bang. if that s the case wouldnt it be going bang as the fuel is being injected?

here to learn like everone else.

 

It does go bang as its being injected. It doesn't in the injector lines because it has no oxygen and has not been atomized. I don't know if there is a exact compression ratio that it ignites there are many factors that go into that heat, how well the fuel has been atomized, cylinder pressure.

I can tell a story of experience of why not to dump small amount of diesel down the intake to get one to start. We had a old junk chevy with a 6.2 that would not start so we took out the can of diesel and dump a small amount in the intake a couple of cranks and a few loud pops and we had a busted piston.

 

it does go bang when the injectors open thats what causes the bang. when a diesel opens the injector it is already starting to burn it fires at what could be considered when the spark plug sparks. no fuel is in till then only sucking air and compressing it. then when the compression is just right and it is at the right time the injector opens and sprays in like i said already burning at this point.
diesel will not ignite if it isn't atomized good, and the compression is too low it will just fill it up untill there is enough heat from compression (friction) to ignite it.
a diesel will also run away if it is getting any amount of fuel over what it needs to idle, thats how they rev up not like a gasser where you have to allow the throttle blades to open creating less vaccuume. a diesel revs acording to how much fuel is injected (crudely said i know)
we are all here to help each other bud

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oh and as for your compression questions there are many variables that can play in here, how much boost, injection timing etc that it can vary widely, most high boost racers or pullers have a low compression ratio to allow for the extra boost, (and bigger camshafts to allow for valve reliefs )