joek84

how would one go about getting a turbo running on a carbed car. i know theres two setups, can someone explain, thanks

CRXdan

resgister on http://www.redpepperracing.com/forums
PM eldo, he is in the process of turboing his carbed 86 crx dx.
Hell help you out.

joek84

cool thanks, im already on there

093turbo16

iTrader: (2)

1: draw through, doesn't require a prepped carb, you draw the fuel and air through the turbo and then it goes into the motor. No intercooler or BOV

2: blow through, requires lots of carb work to "seal" the carb, and you can run an intercooler and a bov. It works just like a normal turbo setup with FI, just goes through the carb.

Loco Honkey

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 93turbo16 &raquo;</TD></TR><TR><TD CLASS="quote">2: blow through, requires lots of carb work to "seal" the carb, and you can run an intercooler and a bov. It works just like a normal turbo setup with FI, just goes through the carb. </TD></TR></TABLE>

Does not requre a lot of work. Just build a box around the carb that the charge pipe blows into. You'll also want an FMU and a fuel pump to increase fuel pressure, or the boost pressure will blow it back into the tank. BTW- FMUs were designed back in the '70's for just such an application.

No need for different carbs... stock carb in the stock location works fine.

Chip

Don't need an FMU, just a rising rate FPR.

/owner of JY turbo'ed, carb'ed 89 mustang with a stock motor and a T70

093turbo16

iTrader: (2)

To do it the right way, you need to seal of the fuel bowls and what not. It requires more work to the carb than the blow through does by convention.

Taken from here, for those who don't like links.

http://www.dune-buggy.com/turbo/carbureted.htm

Draw-Through: Generally speaking, there's 2 ways to use a carburetor with a turbo engine...draw-through or blow-through. The draw-through arrangement is where the carb is arranged first and the turbo then sucks air through the carb. This has the benefit that it doesn't require any special carb changes because the carb is just seeing more air flow through it. The main drawbacks are that the fuel-air mix must pass through the turbo. Since fuel is denser than air it will tend to separate in the turbo and puddle up. Don't expect instant off-idle throttle response. The turbo also becomes less efficient because it has to pump this heavier fuel mixture, and it is trying to do it's job after the carb has already caused a pressure drop. You basically have the carb causing a pressure drop and the turbo trying to increase the pressure. The efficiency losses translates into a hotter fuel-air mix in the engine which limits the boost you can run and your power.

Now here's the confusing part to me. The majority of the people with Carbureted Turbos run them in a draw-through arrangement and they say you get more power that way. Personally I don't agree with that thinking and some of my research has led me to believe otherwise. I tend to believe that the power difference they speak of is related to people not using fuel enrichment in a blow-through setup. I have not tried either so you should make your own decision and there are certainly plenty of engine builders who would argue the point.

In addition, In a draw-through system it is possible to create an extreme vacuum if the turbo is at boost and you shut the throttle. This vacuum will have a tendency to suck the oil out of the bearings. You will need to use a turbo with a positive seal on the compressor in a draw-through arrangement. Diesel turbos do not have this seal. I think most gasoline cars do have a positive oil seal but with the popularity of fuel injection on the newer cars I'm not positive.

Blow-Through: In a blow-through arrangement the turbo is going to blow pressurized air through the carb and then into the intake. This presents two problems: First, a carburetor does not understand pressure. Remember, a carburetor supplies fuel by creating a pressure drop across the venturi. If the carb sees a 2 PSI pressure drop across the venturi, it will supply that much fuel whether you are at 0 boost or 15 pounds of boost. This would cause the engine to run very lean at max boost, but it can be fixed with some form of fuel enrichment. The second problem you will encounter is that when you put pressurized air into the carb, it will make the fuel flow in ways that it is not suppose to flow. The pressure will try to crush the fuel float, it's going to want to blow fuel mix out the throttle shaft, or back into the fuel line. Don't be discouraged though these problems have all been overcome with varying degrees of success. The book Turbocharging by Hugh MacInnes covers a lot of the carburetor mods you can implement to have a successful blow-through turbo setup.

Carb Sealing: The entire carb must be sealed so it does not leak the pressurized air-fuel mix. I've heard that Dellorto carbs have ball bearings and mechanical seals so they may not need further sealing. On other carbs the throttle shaft rides inside a brass bushing, the leaking can be "fixed" by running a hose from the top of the carb where there is more pressure to a fitting that will pressurize the area around the shafts with "clean" air. Note: This method will leak clean air, but not leak the much more dangerous air-fuel mix. In a closed engine compartment, leaking fuel vapor is even more dangerous so please be careful. The metal plugs on the carb could blow out under the increased pressure. Use a punch and put several "dings" around the outside of the plugs to hold them in better. Others have used epoxy on the plugs.

Some have also set the entire carb inside an airtight box. You will then need to seal the opening for the throttle cable by using a sealed marine cable or a similar "trick".

Fuel Pressure: You will need to use an electric fuel pump and a boost sensing fuel pressure regulator to increase fuel pressure as boost pressure increases. Remember every pound of boost that comes out of the turbo is another pound of boost that the fuel pump must be able to overcome if it wants to push fuel into the carb. Read the "Fuel System" page for background on a turbo fuel pressure regulator. With a carb, you will not need a high pressure pump and regulator like you do in an EFI application, so a decent quality electric fuel pump and regulator should suffice.

Finland

Draw through scares me. Do I want an intercooler and pipes and turbo full of compressed air and fuel...nope...not me..

I'd do blow through, or nothing.

mrbsponge

see your other posts for pics from me as well and an explanation 2

joek84

yeah, i don't know why it posted twice, i only clicked the post button once