playing with the cam / valve timing.

[GeX]

howdy

after some advice here. my car has an 8v, OHC engine. It runs wasted spark and multipoint fuel injection. That is all controlled by a megasquirt ECU, so i can play with ignition advance and fueling to my hearts content.

The cam is stock. The head has been skimmed to 'max' markers on the head. I'm unsure what my CR is, but it is higher than it was before - that's for sure.

I have a vernier cam pulley which i've not yet fitted. I'm not sure how best to set one up. My engine is non-interference, so am not worried about any intimate valve on piston action.

Any tips for decieding if i should advance or retard the cam timing.. or should i not be playing about with this without a RR?

 

[Jonny69]

Well rumour has it that factory timing wheels can be anything up to 5 degrees out. That has always sounded like a lot to me and personally I think you'd really notice it and the engine would run like crap or struggle to start if it was that far out but I might be wrong.

Advancing the cam timing a few degrees from stock will push the power band up the rev range and you'll lose some bottom end but go to far and you'll start losing power again so it's your choice. Opposite happens when you retard the cam timing, you move the power band down the rev range..

Since it's on a vernier at the top of the engine you could just set it to stock and have a play. If it's like a Pinto you've got access to the vernier without even having to take the engine apart so why not

 

[ethos]

Advance till it pinks then back it off a bit?

 

[Wayn0r]

you would need a good knock sensor for that or your asking for trouble! or a stethoscope would work on the head of the engine.

 

[Dogbreath]

Advancing the cam timing a few degrees from stock will push the power band up the rev range and you'll lose some bottom end but go to far and you'll start losing power again so it's your choice. Opposite happens when you retard the cam timing, you move the power band down the rev range.

It's a bit counter-intuitive, but it works the other way around. Advancing tends to improve bottom end torque, retarding can give better top end power. Moving the cam timing tends to tilt the power curve, so whilst you may gain a little at one end, the area under the curve remains fairly static for small adjustments.

The first thing to do is make sure that the cam timing is set to the manufacturers values to provide a starting point (i.e. using a dial gauge to measure lift at TDC, or using protractor on crank to measure timing at full lift). Without spending time on a rolling road the chances of optimising the cam timing by guessing is pretty slim, but it might be worth swinging it a few degrees each way to see if a noticeable improvement can be made.