stavros

I have fitted JUN stage 2 cams and adjustable cam gears on my WRX 1998.
Please advice on how to tune the cam gears and what will be the effect on the ignition timing.
Also I have trouble measuring the ignition timing advance with the timing light. Please advice.

p1mark

im not familiar with the cams or the specific gears, but if they are like any other adjustable cam gears you need special kit. i.e a degree disc, a DTI with a probe that will allow you to measure when the piston is at TDC and the valve bucket is fully compressed. this DTI ideally needs to be on some sort of bracket that you can bolt to the block.

obviously you need to know the figures you want to set them at first.

you need to find an accurate TDC @ no.1 cyl . best way to do this is not rely on any marks, but put a DTI with a long probe down the plug hole. find the high point and then put your degree disc on the end of the crank, lining the TDC mark up with a feature or pointer on the block.

if you dont have access to a DTI that will get down the plug hole, the other way is get a spark plug, take the electrode out and put an ally bung in the end that will collide with the piston before it reaches TDC. wind the crank CW, take a reading when the piston stops, wind it back ACW and take another reading, then set the TDC mark on the disc in the middle of these 2 points. dont forget to take it out before you start turning the crank to set the cams up though.

if your figures you want are qouted in just an angle, then these will be IMOP and EMOP figures (inlet / exhasust max opening position) the IMOP will be a ATDC reading, the EMOP a BTDC reading. this is the most popular way but some manufacturers qoute a set amount of lift at a specified crank angle. in this case you have to use the DTI to determine lift amount at that angle. this is a little more accurate, but more of a pain to set up. if you let me know how the figures are gven to you can advise this seperately.

once you have found TDC, put the DTI onto the top of the bucket of either an inlet or exhaust valve on the appropriate cylinder. turn the engine till that valve is fully open. it can be difficult to find the exact MOP because of a dwell across the lobe peak, but if you take a measurment either side of the lobe peak at a small but equal amount of lift, then take an average of the 2 you will get an accurate MOP.

once you know where the cam is and how far you need to move it, undo the adjuster retaining bolts and alter the timing. it is easier to do this by turning the crank (the cams will stay still) if you have vernier gears, look at the amount you are moving it there, if not you will need to look at the degree disc to see. bolt the cam up when you are done.

dont forget that 1 cam degree is equal to 2 crank degrees.

do the other 3 cams the same then turn the engine over a few times and re-check.

it sounds complicated and its difficult to write down, but its not that bad a job.

it wont have any effect on the ignition timing i think on a scoob, unless the cam sensor is timed in, but someone with more scoob related knowledge will hopefully confirm this.

stavros

Thanks mate,

If you have experience, what will be the effect on performance by advancing or retarding the intake or the exhaust?

On HONDA when we advancing the intake, the ignition timing is changed and we have to readjust it by turning the distributor, on SUBARU the timing ramains the same when we adjusting the cams?

p1mark

as i said, i am not sure about the ignition timing. if the cam sensor senses position as well as just being a prox switch, then it may well adjust timing via the ecu but i dont think it does. please dont take my word though.

as for the valve timing, its not something you should mess with unless you are sure. there is a general rule of thumb about which way to go with the cams from the standard timing but it is so dependant on many things. if you are running a lot more lift/duration then valve/piston clearance will be less at the same crank angle than o.e. if you then start moving the cams around it will effect this even more so. advance one and retard the other and your valve/valve clearance may be marginal. best find out what cam timing someone with similiar spec to you is running then set them at that IMO. the only true way to find out what advancing and retarding each cam does is to run the engine on a Dyno and make your changes between each run. obviously you need access to a proper dyno, not a RR.

sorry i cant be more specific.

Pavlo

there will be no change to the ignition timing.