Air Filtration
To ensure your engine lasts for any length of time you will need effective air filtration, and that means paper filters. Oiled cotton filters flow quite well but are poor at filtration. Foam usually does very poorly at both. Paper is the best at filtration but needs a big surface area to maintain sufficient flow; large paper elements are the best all-round choice. When using IR type manifolds the quick-gulp flow characteristics that require relatively high capacity carbs will also dictate higher capacity filters. Small individual filters on each carb are unlikely to be big enough. It's probably better to duct all the intakes together into a common airbox and use a single BIG paper element. Also keep in mind that at low speeds a long duration cam might spit back a bit of fuel, so try to keep the filter far enough away from the carb inlet that the element doesnt get wet. Realistically I know that space limitations make all this difficult, but if you can set up a good filter system you'll maximise both horsepower and engine life.
Fuel Pumps
Obviously an adequate fuel supply is essential, but that doesn't necessarily mean swapping out the stock pump. These were used successfully at Bathurst on fairly high output engines so they can't be all that feeble. If you think you'll need more flow a small block Chev pump is a direct replacement. I tend to favour mechanical pumps for reasons of quietness and reliability, but an electric pump is fine too so long as the pressure and flow ratings are suitable. SU's in particular don't like any more than a couple of psi fuel pressure and will dribble and puke if overpressurized, so use the appropriate regulator. And don't forget to use a good quality filter.
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| This small-block Chev Carter pump (pn M4685) bolts straight up and has enough volume for even very high output engines. Cheap too.. |
If you're building a quickish car, it will pay to work out the fuel
requirements of the engine to ensure an adequate supply. Many instances
of top end power loss have been cured through increasing the fuel supply; on the other
hand there are many moderately powered cars around with fuel systems that would
be more at home on a 1200hp Pro Stocker. Engine design software will show
how much fuel is required, or you can use the following rules-of-thumb:
Normally aspirated engines need a minimum of 8usgph for every 100hp; round
this up to 10usgph/100hp for a safety margin. I've used US gallons as the unit
here because most of this hardware is US made. Adjust or convert as required.
People often talk about adding pressure to allow for acceleration g-forces, but realistically these will be negligible for most full-bodied Holden six powered cars. It works out that for every 1G of acceleration and 3ft of horizontal line length you need to add 1psi. For example, if the car accelerates at 1.5g and the distance from the pickup to the forwardmost end of the fuel line is 9ft you'd need to add 4.5psi to the pump pressure. Provided the regulator (if used) is mounted near the front of the fuel line there is no need to increase its setting to counteract G forces, only the rear mounted pump setting is affected. Keep in mind that g-forces will also have a siphon effect on return lines; specifically it can artificially reduce the regulators pressure while under acceleration. It's possible (though unlikely) that it will be necessary to use a check-valved vent to negate the siphon effect with some systems.