IT’S been said that there’s no such thing as bolt-on horsepower. I beg to differ. A blower is one of the best all-round bolt-on bits you would ever want to own. It is one of the easiest ways to improve a vehicle’s performance. There are three main gains aside from the cool factor and they start the moment you turn the key. A properly set up blown engine will fire instantly, generally before the engine has made one full revolution. This is because the blower is pushing the air/fuel mix straight into the cylinder, rather than waiting for the piston going down the bore to suck the mix in.
This article was first published in the May 2005 issue of Street Machine
Drop the car into gear and ease on the loud pedal and the next thing you’ll notice is the large increase in bottom-end grunt. Obviously the more overdrive on the blower, the better the initial pedal response. Finally, mash the loud pedal and you’ll see what all the ‘ooh-aah’ is about. Blowers make horsepower and lots more torque than a standard engine.
The amount of extra horsepower really depends on what your engine is like. On a 350 Chev, Weiand estimates an extra 100-120hp with one of its low-blow superchargers on an otherwise stock motor. Add a mild blower cam (something with a 112 lobe centre) and a larger carburettor, and you can expect a typical small-block to produce around 400 ponies.
Add a decent set of heads to the combination and you’re looking at a solid 450-475hp.
The biggest gains will really be in torque. Blowers turn streeters into tyre shredders — an engine making 280ft-lb can typically jump to 450ft-lb when blown, and that’s with a smallish blower at six to seven pounds of boost. Large blowers, like the 6/71, can push the same engine above 500ft-lb.
Under-bonnet blowers (low blowers like the Weiand 142 and 144, and B&M 174) are typically better suited to street cars as they develop their boost lower in the rev range than large-capacity blowers. Big blowers add to mid-range and top-end performance.
Because superchargers push the air/fuel mix into an engine, they’re well suited to stock motors — provided you don’t get greedy with how much boost you want to run or how hard you want to rev the engine.
Stock production heads can be terribly asthmatic, which is why a blower smartens up the performance of a standard engine. Stock engines are typically fitted with a cast crankshaft, two-bolt main caps, cast pistons and small camshafts, so trying to push more than six pounds of boost into them will ultimately cause detonation and engine failure.
Aside from the problems of trying to make stock engine components cope with more than six pounds of boost, factory fuel and ignition systems are rarely designed to cope with more than this and the two biggest killers of blown engines are excessive timing and inadequate fuel systems.
One of the most crucial aspects of any supercharger set-up is carburettor selection. Too little fuel can destroy your engine in moments. Blower carbs are specially designed for the job. Trying to run a blower without boost-referenced carbies is just asking for trouble. Boost-referencing is basically a way of ensuring enough fuel is added for the larger quantity of air the charger is forcing in, to prevent the engine from running lean.
There are several indicators of an engine running too lean. The first and obvious one is backfiring through the carbs under acceleration. Others include glowing red headers or the engine surging under acceleration.
The best way to check your fuel mixture is to read your sparkplugs. It does sound old school but it’s a very effective way of checking the tune of your engine. You want to see a medium to dark-tan colour rather than the white or pale-ash colour that indicates a lean fuel mix. Carburettors need to be boost-referenced so that an appropriate amount of fuel is supplied to the engine to match blower boost as your engine makes power. Trying to set up a carb without boost referencing is difficult and will result in poor economy and driveability at best, while in most cases it will kill your engine.
You can buy a blower carb from your local Holley dealer or have your standard Holley modified by one of the many carb specialists in Australia.
So you can see that a blower truly is a bolt-on route to more horsepower but there are traps for the unwary. Get the set-up right, though, and you won’t go back.