Technical Tips - Spark Plugs, Flywheels and cams

[Mondeo]

Interesting article :

 

SPARK PLUGS

We have had this one before, but readers are still asking about types of sparking plug and which are the best for power. Please note: muti-earth electrode plugs are not designed to increase power output. The only reason they are becoming popular is that the service intervals are getting so long that a normal plug wears out before the service is due. By having two or three electrodes, the spark can choose the shortest path to earth which means it moves about as they wear down - and therefore the service life is extended.

 

For power output, the real trick is finding the right grade of plug. Plugs with similar grades from different manufacturers are not exactly the same which is why some people find one brand of plug better than another in one particular engine. You have to experiment with each engine to see what it likes.

 

 

FLYWHEELS

Lighten and balance are words we often use, without stopping to explain exactly what we mean and why they're important. For instance, what are 'lightened' flywheels and why do they allow the engine to generate more power? Well for starters they do not affect the power output of the engine one way or another. Let's begin with why we have a flywheel in the first place; it's more than just somewhere to put the clutch and starter ring gear.

The flywheel effectively stores the energy acting on the crankshaft. It smooths out the pulses from the firing cylinders and reduces the tendency of the engine to rock on idle. It allows lazy gear shifting by keeping up engine rpm when the clutch is depressed and the throttle is closed during gear changes. This is fine on a family car but we look for something different. The down side of the heavy flywheel is that it takes energy to accelerate it, energy that could be better employed in accelerating the car. The way to think of it is that every gram taken off the flywheel is like one gram (multiplied by the overall gear ratio) taken off the car.

 

For example, reduce the flywheel weight by 1kg and with an overall gear ratio of 10.1 your car is effectively 10kg lighter. Note now that 1kg off the centre of the flywheel is not as effective as 1kg off the outside - now I'm sure you are getting the picture. The lighter flywheel also allows the engine to slow down quicker so gear changes can be made in a hurry. Generally speaking, for a competition engine you cannot have the flywheel (and clutch assembly) too light.

 

 

CAMSHAFTS

We get a lot of enquiries about camshaft specs where readers are trying to fathom out which camshaft to buy. Sadly the numbers given by manufacturers only give you a clue as to what performance you can expect from a camshaft. So much depends on what you do with rest of the engine, and the exhaust in particular.

As an example, I have seen a 300 degree camshaft in a Pinto regularly peak at 6,400rpm. But when the exhaust is swapped from a 4-2-1 to a 4-1 design, peak power shifts up towards the 8,000rpm mark. But this isn't a general rule, the lengths and design of the 4-1 system are critical.

 

If you get the lengths right you need not lose out on bottom end or mid-range power either. Generally it would appear that a 4-2-1 design will ultimately give you better results on a competition engine.

 

Going around the country on rolling road tours I regularly find that the best engines use 4-1 manifolds rather than 4-2-1 but that isn't always the case, there are plenty of Pintos making 200bhp on 4-2-1 systems.

 

From our own experience the exhaust has a major influence on how well the camshaft works - or doesn't work. On our Golf we tried a 300 degree cam which gained 2bhp on peak and lost power everywhere else. But then we refitted the stock cam and Magnex developed an exhaust manifold and system for us. The exhaust picked up some l2bhp on the stock cam but when we fit/ed our 300 degree camshaft we gained l4bhp on peak with improved mid-range. As with all engine mods you have to look at the overall pictures before you start making up general rules to apply to all engines.

 

from Demon Tweeks 2002

Edited July 10, 2003 by Saaber