12a carburted DRAW THROUGH turbo
#1
Fabrineer
Thread Starter
12a carburted DRAW THROUGH turbo
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.
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.
#3
Yeah, shutup kid.
Originally posted by 97dohc
so, your are puting an air/fuel mix into a red hot turbo, and don't see a problem with that?
so, your are puting an air/fuel mix into a red hot turbo, and don't see a problem with that?
#6
Originally posted by pratch
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
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
air--check
fuel vapor--check
compresion--check
only need a little spark to go bad in a hurry
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#8
Re: 12a carburted DRAW THROUGH turbo
Originally posted by shm21284
, when the fuel/air mixture gets compressed, it actually causes the intake temp to drop.
, when the fuel/air mixture gets compressed, it actually causes the intake temp to drop.
When you compress ANYTHING it gets hot. End of story, laws of physics.
#9
Yeah, shutup kid.
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.
#10
Fabrineer
Thread Starter
Originally posted by Junia
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?
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?
#11
Fabrineer
Thread Starter
Re: Re: 12a carburted DRAW THROUGH turbo
Originally posted by nevarmore
B_U_L_L_S_H_I_T
When you compress ANYTHING it gets hot. End of story, laws of physics.
B_U_L_L_S_H_I_T
When you compress ANYTHING it gets hot. End of story, laws of physics.
#12
Fabrineer
Thread Starter
Originally posted by coldy13
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.
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.
#14
love the braaaap
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).
#15
Re: Re: Re: 12a carburted DRAW THROUGH turbo
Originally posted by shm21284
Okay, whatever you say. I am only in school for mechanical engineering. Go tell my physics professor that hes full of ****.
Okay, whatever you say. I am only in school for mechanical engineering. Go tell my physics professor that hes full of ****.
If I'm ever wrong I'd like to know. I think in this case I may have just misread something.
#17
love the braaaap
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.
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.
#18
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Originally posted by 97dohc
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
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
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)
#20
love the braaaap
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.
Last edited by 85rotarypower; 05-27-04 at 04:20 PM.
#21
Got Boost?
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.
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.
#22
Got Boost?
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.
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.
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.
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.
#23
Got Boost?
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.
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.
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.
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.
#24
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Originally posted by 85rotarypower
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).
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).