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Intake manifolds for a Turbo engine. For more airflow, a higher flowing carb, intake, heads (ports and valves) and exhaust system is beneficial. Supercharging will increase power on a stock engine, but increasing the airflow capability of the engine will bring your blown engine to its full potential.
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Overview
#Top-hatted Carburetor on stock manifold
As far as designing a custom inlet manifold for a turbo, keep the path from carby to turbo as short and straight as possible (hopefully with no uphill stretches) from the turbo, out and up to the top of the manifold. It'll be impossible to avoid an uphill stretch there, just avoid unnecessary twists turns and uphill (or otherwise long) stretches. Use a log type inlet, with the log reaching further forward and back than the front and rear runners.
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Stock Manifold
Blow-through or draw-through systems can use the stock Intake Manifold.
Draw-through
Stock manifold with EFI throttle body (see $1200 EFI Turbo A12)
Blow-through with #Top-hatted Carburetor
Blow-through with #Boxed Carburetor
With pressure hose adapter
Stock Manifold cut and swapped sides
A15 Turbo using factory Twin Hitachi sidedraft manifold. Adapter runners bolt to a single Weber DCOE
Log Manifolds
A log manifold is a cylindrical plenum type with individual runners to each cylinder. Log manifolds can either be fed by an EFI throttle body or by a sidedraft carburetor. They can be used with either blow-through or draw-through systems.
Also See: EFI Manifold#Overview for more Log info
Generally, any EFI log manifold can be used with a turbo, you can even use them with a carburetor feeding the log.
Log Manifold
UM-1 Manifold
Ram plenum manifold
clyon's A-series Turbo Manifolds
This kind of stock manifold-runner is limited in horsepower. The turbo can force more air through it (for more HP) but the air temp will escalate, limiting the power to be made.
Corolla manifold adapted
Draw-through with very small plenum
With air horns (trumpets)
Far-side-mounted intercooler
A15 in Datsun 1000
EFI A14
Tuned Runner Length
For scavenge effect at 5000 RPM, the runners should be 20" long!
Optimum runner length vs RPM
Top-hatted Carburetor
Feeding the carburetor via a top hat was a popular OEM method. phunkdotaspok say the stock Hitachi can handle 10 psi with a good top-gasket seal. In an NA application, a warped top is not a problem, as there is no pressure in the float chamber. This only becomes important in boosted application.
Blow-through system feeding carb top-hat
Weber 32/36 Carburetor with custom top hat
Twin-sidedraft top hat
downdraft Dellorto carburetor on custom manifold
Good for 10psi
Twin Sidedraughts
Blow-through
Boxed Carburetor
Blow through works well. The main reason to use this over a draw-through is so an intercooler can be used. The boxed carburetor can take more boost than the top-hatted carburetor.
Boxing the carb allows a more or less stock carb to be used, the outside pressure balancing the inside pressure. Special non-crushable fuel floats are needed.
