CAMSHAFT TIMING
Installing and Timing

By Martin Donnon
(c) Copyright Express Publications. Reproduced under expressed permission. No copying permitted

It's a logical part of dialing in a new set of cams, but timing them properly involves a few tricks for new players There comes a point in the modification 'life' of each and every car when you have just about exhausted all of the avenues of gaining extra power. This holds true particularly when every single bit of fruit has been bolted to the outside of the engine, and the cylinder heads and pistons haven't been touched. It's all too easy to run out of 'growth path' once the turbocharger of choice is bolted into place and the tuning has been carried out. A perfect example of this is Danny's own personal drive car, his 1805X. In true JMS style, it has been modified in an all-out bolt-on way to achieve the perfect drift balance. He was there when we had a good look at the Signal Drift 180 featured on these pages, so it was only natural that he should have a good look at the car's specification and take bits and pieces of its build to adapt to his own. There was nothing to be learnt from the turbocharger side of the equation, as Danny already had the stonking HKS 2835 external-wastegate kit complete with manifold hanging on the side of his 5R20; however, like all true enthusiasts he wanted more, lots more if at all possible.

Changing from the stock camshafts was obviously the next step, and in keeping with the advice received from Kida and Co at Signal, the straight-fit HKS 256 step 1 camshafts were selected. Previous research had been carried out, with numerous pieces of documentation from Japan and even some local users of these camshafts claiming that anything up to 30 additional engine kilowatts was available from their usage. Signal disagreed with this, stating that while 256 cams are a worthwhile addition, their true effect on total engine power would be more in the order of 15kW - interesting. THE BASICS There is much deep and dark art to installing and timing camshafts, or that's what those who fit them would have you believe. The whole science behind camshafts and their theory of operation can be fully explained with a protractor and elementary high-school mathematics.

 

Spinning at half engine speed, the camshaft(s) control the opening and closing events of the inlet and exhaust valves, the time at which these events happen, which in turn then has a big effect on the actual amount of cylinder ‘fill’ and therefore engine efficiency. It's in practice that camshaft selection starts to get a little more complicated. Although you may be changing the valve events on either inlet or exhaust by several degrees with a set of modified camshafts, the effect on the engine is to a large degree unknown without a touch of experience. Having seen similar installations in the past, and having carried them off successfully, is the mark that separates the men from the boys in the camshaft world.     There is also the small question of valve lift, as well as the actual timing of the camshaft event, which doesn't have any marked effect on the basic geometry, but does have a massive effect on cylinder fill. This is why on the flow bench, both inlet and exhaust valve lift are altered to check their effects on flow. Still, the dynamics of lift are a little outside this story. We need to stick to the basics of what is achieved for the average import enthusiast when bolting on a set of cam gears.

CONCEPT OF CAM GEARS Adjustable camshaft gears are a hot-ticket item at the moment, with many flocking towards them as the ultimate bolt-on accessory, but you really need to understand the principles before rushing out with money in hand. In many cases that we have witnessed, there is very little to gain, while others have shown an improvement that is reasonable in terms of dollars per kilowatt. With modern twin-cam engines, both the exhaust and inlet side of the camshaft timing can be altered independently. This is a far cry from the buried-cam pushrodders of the past that forced you to adjust both the inlet and exhaust timing together, as they were both ground on the same stick - no good. To change the all important lobe separation angle (LSA), you needed to change camshaft grinds. Any decent import gives a 'cam tweaker' the ability to change LSA to their heart's content, either opening or closing this crucial angle until the valve impact point (on a non-piston to valve clearance engine) is met. LSA is probably the single most crucial part of camshaft design, as it has some fairly severe effects on engine operation.

 

Opening up the LSA by moving both the inlet (retarded) and exhaust (advanced) will normally allow the engine to be more efficient in the lower rpm band. However, increasing the overlap between the two camshafts effects the cylinder filling index (a commonly referred to engineer's variable), robbing top-end power. Normally, manufacturers love to have a wide LSA (generally over 115 degrees) as it endows engines with beautifully stable, emissions-friendly idle characteristics. Look at systems like VTEC, Mivec and VVTiL to get the feel for this. Camshaft timing with any of these tends to close the LSA down with increasing rpm. The most common trick for the budding camshaft timer to try is decreasing the LSA to gain more top-end power. As a general rule of thumb, the inlet camshaft timing is advanced and the exhaust camshaft timing is retarded. It's by how much and how to quantify the results that causes the most confusion. HOW TO GO ABOUT IT Most cam gears, particularly the HKS type, are fairly easy things to install. The standard gears and any decent aftermarket unit will be dowelled, forcing you to install in the right direction, and marked either 'inlet' or 'exhaust'. Installation is a very, very difficult thing to get wrong.

You must then make sure that the inner adjustment ring is set to zero. Don't take it for granted that the bolts are tight either, as I've seen plenty of freshly installed gears that have slipped position and made the engine stop. Before doing anything else, once the cam gears are installed you need to get straight on the dyno and perform some power testing. Get the engine up to temperature and give it a couple of runs to get a baseline reading. In the case of an SR20DET, you are then in for a fair bit of work, removing the rocker cover to get at the gears to begin adjustment. Since this is a time-consuming exercise, we took some fairly substantial bites at adjustment to minimise the number of 'on/offs' that occur. Wanting to shut down the LSA in the quest for additional top-end power, we tried a couple of different settings, with the car being dynoed after each attempt. You need to remember that one degree on the cam gears is two degrees at the crankshaft, which tends to trick a lot of people - some who should know much better.

 

The rule of thumb: check and then double check. Our settings of two degrees advanced on the inlet camshaft and four degrees retarded were shown to be optimum for this particular engine, with a healthy gain of around 10kW. Be very careful; after each and every adjustment, turn the engine over by hand to ensure there is no interference between the pistons and valves. This can quickly make the whole task very expensive. Otherwise, on this particular engine, installation and tuning of the adjustable HKS gears on the HKS cams proved to be a good thing

 

(c) Copyright Express Publications. Reproduced under expressed permission. No copying permitted