Well, I felt like posting about my setup, heres the story.
I have a rayjay turbo with a .86 A/R exhaust turbine. The turbo is comparable to a T-04 B, it will support at most 400 horsepower. My carburetor is a Carter AFB, around 5-600 cfm. I am using a stock 79 intake manifold and have a custom 3 inch exhaust from the turbo back.

One common misconception is that you can't run high amounts of boost with a draw through setup. THIS IS COMPLETELY WRONG. In fact, if you were to run a blow through setup with NO intercooler, it would be more dangerous than running a draw through at the same amount of boost. I ran 18 psi through my engine with no problems (only once, want my engine to last). The reason for this is that, when the fuel/air mixture gets compressed, it actually causes the intake temp to drop. Compressing fuel takes heat from the air. So, if you ran 15 psi on a NON intercooled, blow through setup, your intake temp would be higher than a draw through running 15psi.

The plusses to draw through are better drivability than blow through, its inexpensive, it's compact, and it just plain looks cool (i will have to take pictures of my car and post them). The increased drivability is due to the carburetor being mounted before the turbo, so the carburetor, when the turbo kicks in, thinks that the engine is bigger. You dont have to pressurize the carburetor because its just getting sucked on.

The drawbacks are that you can't intercool it (if you were to do that, then the fuel would get stuck in the intercooler, and only air would come our the other side of the intercooler). Also, it gets poorer fuel economy (the fuel tends to puddle inside the turbo). You dont use a blow off valve, so you dont get that cool sound.

I ran a 13.8 in the quarter with 190 hp to the wheels. I am currently tearing down the engine to street port it.

 

so, your are puting an air/fuel mix into a red hot turbo, and don't see a problem with that?

 

Have you ever seen the COMPRESSOR side of the turbo get red hot? The exhaust side is what gets red hot, the compressor side stays much cooler.

 

it's okay coldy. He's just trying to build his post count and wants to sound smart. You know, to make a good first impression

 

Cool, I've only seen drawthrough setups in books and old magazines. Are there any problems with icing during the colder months when running a drawthrough setup?

 

no, it just seems like a bad idea to me
air--check
fuel vapor--check
compresion--check
only need a little spark to go bad in a hurry

 

Drawthrough works kinda ok. There is no way to intercool it of course.

 

B_U_L_L_S_H_I_T

When you compress ANYTHING it gets hot. End of story, laws of physics.

 

Just a guess here, but I think this is what he meant by it. The fuel coming from the carb is cooler than the air. So when the fuel and air are combined when compressed the fuel absorbs some of the heat from the air, making the air temp cooler. In a blowthrough, just the air is compressed and heated going through the turbo, so an intercooler is normally used to cool it down.

 

Yes icing is horrible until the engine warms up.

 

Okay, whatever you say. I am only in school for mechanical engineering. Go tell my physics professor that hes full of ****.

 

That is Exactly what i meant. It works kind of like water injection or alcohol injection.

 

Have you had any problems starting the car? I heard it's sometimes a bitch to start because the fuel has to go through the turbo before the engine.

 

Yes, I would be interested in this too. I thought about doing this, just because it is a little easyer than a blowthrough setup (don't have to boost prep the carb).

 

Ok ok. I was a bit harsh, sorry. How does the fuel cool the intake mixture? Is it significantly cooler or justt a liitle bit cooler?

If I'm ever wrong I'd like to know. I think in this case I may have just misread something.

 

Starting the car is a bitch only because i dont have my choke hooked up. When i open the hood and manually close the choke, it fires right up.

 

Thats cool.

If you think about it, fuel could cool the air down. Whenever you compress a fuel, it cools down A LOT. Take propane for example. It is actually cold enough in compressed form to give you frostbite almost immediately. Sure, it is a in a gaseous form at room temperature, but that has nothing to do with it. When its compressed its in a liquid form. So its technically the same difference.

 

Isnt this what happens inside your engine normally?? Last time i compression tested a piston engine (an old MG B, which has low compression compared to modern day engines), it was putting out 165 psi on each cylinder. 165psi compressionHow could 90 psi compression from the rotor, plus 15psi from the turbo, cause the fuel to spontaneously combust? And, if it's such a bad idea, why were they using it in FORMULA 1 cars in the 70's?
Oh yeah, Fuel injected cars's fuel pumps operate anywhere from 30-70 psi. Well, we have compressed fuel in the fuel lines spanning the length of the car. If it was so unsafe, there wouldnt be fuel injected cars.
By the way, detonation isnt a problem unless you go too lean, your timing is too advanced, etc.

Draw through was abandoned because
1-you cant intercool it (this is the main reason)
2-it has worse turbo lag (the turbo has a carburetor or throttle body to suck through)
3-poorer fuel economy compared to blow through (not by much though)

 

I know all the math behind the compressing anything. I can explain it to you all if you want.

 

No need to explain. Those compression numbers for the MG B are quite high compared to most cars. An Escort does 120 psi on a compression check (I know because I did it). 100-130 psi is fairly common. To get a compression number of 160+ psi is not normal in any late 70's to early 90's cars. You need in excess of 10.5:1 compression to do that. A diesel will have numbers of over 200 psi since they run VERY high compression, about 17:1 or something like that.

 

The reason that propane or any liquid for that gets really cold when you fill up the propane tank is because it is losing pressure (and sometimes converting back to a gas). Its like air conditioning, you take room-temp compressed fluid, and let it expand. It gets cold, then you use it to absorb the heat in the room. Then plumb it out of the room, compress it, it heats up, then cool it back down.

There is some cooling effect that gasoline will have on a drawthrough, because it is undergoing a state change from a liquid to a gas. Compressing the air/fuel heats it up, which makes the fuel quickly vaporize, cooling the mixture off to a degree. Thus making it better than blowthrough non-intercooled as far as intake heat is concerned (the fuel introduced after the turbo in a blowthrough dosen't have the time to absorb much heat from the compressed air , and doens't vaporize as quickly)

That being said, gasoline doesn't have a very high specific heat of vaporization: it doesn't absorb much heat when converting from a liquid to a gas. So the comparing of gasoline to methonol or water injection is poor at best. A blowthrough with even a marginal intercooler will out-perform a blowthrough, and at the same time not suffer from hard starting due to icing.

 

The reason that propane or any liquid for that gets really cold when you fill up the propane tank is because it is losing pressure (and sometimes converting back to a gas). Its like air conditioning, you take room-temp compressed fluid, and let it expand. It gets cold, then you use it to absorb the heat in the room. Then plumb it out of the room, compress it, it heats up, then cool it back down.

There is some cooling effect that gasoline will have on a drawthrough, because it is undergoing a state change from a liquid to a gas. Compressing the air/fuel heats it up, which makes the fuel quickly vaporize, cooling the mixture off to a degree. Thus making it better than blowthrough non-intercooled as far as intake heat is concerned (the fuel introduced after the turbo in a blowthrough dosen't have the time to absorb much heat from the compressed air , and doens't vaporize as quickly)

That being said, gasoline doesn't have a very high specific heat of vaporization: it doesn't absorb much heat when converting from a liquid to a gas. So the comparing of gasoline to methonol or water injection is poor at best. A blowthrough with even a marginal intercooler will out-perform a blowthrough, and at the same time not suffer from hard starting due to icing.The reason that propane or any liquid for that gets really cold when you fill up the propane tank is because it is losing pressure (and sometimes converting back to a gas). Its like air conditioning, you take room-temp compressed fluid, and let it expand. It gets cold, then you use it to absorb the heat in the room. Then plumb it out of the room, compress it, it heats up, then cool it back down.

There is some cooling effect that gasoline will have on a drawthrough, because it is undergoing a state change from a liquid to a gas. Compressing the air/fuel heats it up, which makes the fuel quickly vaporize, cooling the mixture off to a degree. Thus making it better than blowthrough non-intercooled as far as intake heat is concerned (the fuel introduced after the turbo in a blowthrough dosen't have the time to absorb much heat from the compressed air , and doens't vaporize as quickly)

That being said, gasoline doesn't have a very high specific heat of vaporization: it doesn't absorb much heat when converting from a liquid to a gas. So the comparing of gasoline to methonol or water injection is poor at best. A blowthrough with even a marginal intercooler will out-perform a blowthrough, and at the same time not suffer from hard starting due to icing.

 

The reason that propane or any liquid for that gets really cold when you fill up the propane tank is because it is losing pressure (and sometimes converting back to a gas). Its like air conditioning, you take room-temp compressed fluid, and let it expand. It gets cold, then you use it to absorb the heat in the room. Then plumb it out of the room, compress it, it heats up, then cool it back down.

There is some cooling effect that gasoline will have on a drawthrough, because it is undergoing a state change from a liquid to a gas. Compressing the air/fuel heats it up, which makes the fuel quickly vaporize, cooling the mixture off to a degree. Thus making it better than blowthrough non-intercooled as far as intake heat is concerned (the fuel introduced after the turbo in a blowthrough dosen't have the time to absorb much heat from the compressed air , and doens't vaporize as quickly)

That being said, gasoline doesn't have a very high specific heat of vaporization: it doesn't absorb much heat when converting from a liquid to a gas. So the comparing of gasoline to methonol or water injection is poor at best. A blowthrough with even a marginal intercooler will out-perform a blowthrough, and at the same time not suffer from hard starting due to icing.The reason that propane or any liquid for that gets really cold when you fill up the propane tank is because it is losing pressure (and sometimes converting back to a gas). Its like air conditioning, you take room-temp compressed fluid, and let it expand. It gets cold, then you use it to absorb the heat in the room. Then plumb it out of the room, compress it, it heats up, then cool it back down.

There is some cooling effect that gasoline will have on a drawthrough, because it is undergoing a state change from a liquid to a gas. Compressing the air/fuel heats it up, which makes the fuel quickly vaporize, cooling the mixture off to a degree. Thus making it better than blowthrough non-intercooled as far as intake heat is concerned (the fuel introduced after the turbo in a blowthrough dosen't have the time to absorb much heat from the compressed air , and doens't vaporize as quickly)

That being said, gasoline doesn't have a very high specific heat of vaporization: it doesn't absorb much heat when converting from a liquid to a gas. So the comparing of gasoline to methonol or water injection is poor at best. A blowthrough with even a marginal intercooler will out-perform a blowthrough, and at the same time not suffer from hard starting due to icing.

 

Boost prepping the carb is a lot easier than trying to fabricate the the custom intake from the carb to the turbo to the manifold IMO.

 

wow, clicked the submit button too many times??
anyways, thats sounds kinda cool, i'm doin a draw through supercharger