A while back I took some notes on turbo charging a carb
Turbo & Carb Placement
The longer the air fuel charge has to travel the more heat it picks up and also the more chances for the fuel to seperate form the air.
I was thinking a single 4bbl holley and have it bolt to the turbo with a 45 or 90 degree elbow that feeds the carb mix to the tubo... add a heat spacer to protect the carbs fuel source from boiling. But hot enough so the carb doesn't ice
This isn't the final Turbo orientation... but it gives you and Idea of what I was thinking of.
Turbo Manifold / Exhaust Routing
One thing that must be done is protection of all parts in the area from heat. So lots of heat shielding to the brake lines and trans and coolant lines is helpful
Also wrapping the turbo manifold and downpipe in key areas to protect the distributor and ignition parts... is a good idea, fully wrapping could be bad or good, excessive heat may damage the turbo, and can cause metal fatigue in turbo manifolds but loss of heat can lower the exhaust energy.
The downpipe for the turbo will need to be wrapped depending on where it routes to protect the oil pan from getting heated by the downpipe
Here is a SU carb on a Draw-Thru Setup, I like the way the manifold and turbo are situated with the turbo outlet facing upwards, I never figured the fuel would flow well upwards... I wanted my air/fuel charge to exit the turbo with the outlet facing down. Also water was injected in front of the carb instead of port injection.
Here is a Draw-Thru Setup, it uses a 4bbl 390 cfm double pumper on a rotary motor
Here is a list of some problems and links to possible solutions
DRAW THRU CARB
- Extreme vacuum condition if the turbo is at boost and throttle is closed could suck the oil out of the turbo bearings
- If oil gets into the air / fuel mix, it lowers your octane immediately, and pinging will start at lower boost pressures.
-FIX- Need turbo with a positive (Carbon) seal on the compressor side of the turbine
-FIX- Run a oil cooler before the oil inlet into the turbo.
This will cool the oil down and help it from being sucked through the seals or blown through the exhaust side (cooler oil is thicker).
Also makes the turbo run cooler and last longer.
- Restricting the intake to the turbo will lose compressor efficiency.
- Air-Fuel mixture must pass through the turbo
- Fuel must stay suspended in the intake charge
- Compressor turbine will throw the fuel against the turbo shell, causing a lean-out condition, thus turbo lag.
- Fuel is denser than air and tends to separate in the turbo and puddle up
- Turbo less efficient because it has to pump heavier mixture
When carb causes a pressure drop and the turbo tries to increase the pressure there is a loss in efficiency, which translates into a hotter mixture in the engine which limits the boost you can run and your power.
-FIX- Water / Alcohol Port Injection
-FIX- Avoid Extra Intake bends
- Heat needed to keep the carb from Icing
Air Charge Cooling
- Draw thru Intercooling, Not possible since intercoolers are dry flow
- Water / Alchohol Injection
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SMC
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RSR
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AQUAMIST
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ERL AQUAMIST
Turbo Cooling
Different turbos will use different methods of managing heat such as water or oil
- Oil coolers with fan
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B&M Oil Cooler
Oil Cooling
- Oil coolers with fan
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B&M Oil Cooler
Engine Cooling
- 160 Degree Thermostat
- Aluminum Radiator Dual fans with shroud
PCV System
???
VACUUM
On a draw through motor vacuum below the carb is giving the parts that operate off of ENGINE VACUUM false vacuum readings.
Vacuum below the carb 24"
Actual engine vacuum 14"
As you open the throttle vacuum is supposed to drop to allow the power valve to open... however...
Vacuum below the carb is 12"
Actual engine vacuum is 2"
Under actual engine vacuum the power valve should be open all or most of the way @ 2"
but because of the boost you get 12" so the valve doesn't open all the way or not at all and your mixture ends up being lean.
The POWER VALVE needs to be OPEN in order to RICHEN the fuel mixture, you do this by converting to a boost sensitive powervalve, which operates the power valve based on positive pressure, instead of negative pressure.
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