Optimising Cam Timing

[simonb 0]

I just have a quick question regarding the cam timing on a std 1.9 engine. From everyones experience in this area, do the standard timing holes indicate the "Optimum" timing for the engine? i.e is this the point that produces best performance or has anybody tried advancing the cam timing to obtain better off the line times?

 

Basically, mine is set to standard at the moment and I have read an article that suggests that a 10 degree advance of the cam (s degrees on the crank) should produce a better results as I would ideally like to shift the torque curve of the engine lower down the rev range. Currently the engine really starts to pull at around 3000 rpm but some 19's I have been in seem to develop the power much lower down and so I am wondering if cam timing is the issue.

 

My car is healthy and is putting out 190 accross all cylinders, ignition timing and fueling are fine too.

 

Any ideas?

 

Thanks

Edited March 22, 2006 by simonb

[j_turnell 137 3 Cars]

If its a standard engine then use the standard cam timing it will run like crap otherwise, you may be able to get gains from advancing the ignition timing whilst running super unleaded but leave the cam timing alone. If however you get a different cam, kent, piper etc then yes a vernier is benficial in setting up the cam timing and you should see gains.

[jack biscuit 0]

Hello there people.. going on from this i inherited a piper 270bp cam and a vernier timing wheel. they've gone into my 1.6 to have a looksee as i've rebuilt the top end. just are there any pointers anyone might give me, as you can guess i'm sure i will be experimenting anyway but any personal nuggets are always appreciated..

 

i thank you please

 

Heheh.. thread hijacker..!

 

soz simon, no really, soz like!

Edited March 22, 2006 by jack biscuit

[Ahl 4]

If however you get a different cam, kent, piper etc then yes a vernier is benficial in setting up the cam timing and you should see gains.

Why would a Kent or Piper cam be anymore liable to swinging the cam timing than the standard cam, which is as lumpy (if not more) then most sports cams anyway?

[pug_ham 245 3 Cars]

If the Piper 270 is a regrind you will need the vernier pulley as using the standard pulley will be out & you will loose power.

Regardless of the amount of change in cam profile these give the standard cam timing holes are usually wrong. I had to advance my cam 7' iirc when I built my engine up to get full valve lift at the right time.

Graham.

[Rob_the_Sparky 10]

Advice I got from my local engine builder was that all cams will be out due to the difficulties of aligning the pulley to the lobes. Only way to get it spot on is a vernier cam and a rolling road or to use a micrometer on the cam lobes but that only gets it to the theoritical optimum. Rolling road is the better method.

 

Rob

[jack biscuit 0]

Thanks Graham and Rob, I'll bear this in mind..

 

The cam was taken off a 1.9, and isn't very old. It was advanced 10 - 11 degs as it was fitted there..

 

We'll see what happens in this 1.6 lump..

 

Cheers again!

[M3Evo 0]

Advice I got from my local engine builder was that all cams will be out due to the difficulties of aligning the pulley to the lobes. Only way to get it spot on is a vernier cam and a rolling road or to use a micrometer on the cam lobes but that only gets it to the theoritical optimum. Rolling road is the better method.

 

Rob

 

I could just about understand that for a re-grind, but starting from scratch, surely the blank would have the keyway cut already and everything can be easily referenced to that.

[Rippthrough 98]

I could just about understand that for a re-grind, but starting from scratch, surely the blank would have the keyway cut already and everything can be easily referenced to that.

 

 

Yeah, but then how would they sell their shiny, overpriced pulleys to eh?

 

/cynical mode

[Rob_the_Sparky 10]

Guy I was chatting to had no vested interest in selling me anything and had MANY years experience building and tuning engines...

[Rippthrough 98]

Guy I was chatting to had no vested interest in selling me anything and had MANY years experience building and tuning engines...

 

 

But some of the cam makers do

[pug_ham 245 3 Cars]

I could just about understand that for a re-grind, but starting from scratch, surely the blank would have the keyway cut already and everything can be easily referenced to that.

I agree it should be but I'd still check it with a DTI & make sure it is ok.

 

With the head skimmed after a rebuild even on a standard cam the timing will be slightly out as the distance has decreased so the original timing holes for the cam is wrong so with it skimmed as recommended by the cam manufacturer it could be even worse.

 

Graham.

[simonb 0]

So judging from this info; my head has had a 6 thou skim therefore the cam timing will now be too advance at the standard marks? is this correct? obviously 6 thou is next to nothing so would I really be noticing anything at all my retarding the cam?

[petert 601]

Skimming the head retards the cam timing. Ten degrees is a long way to swing any cam. Are you sure it wasn't a tooth out to begin with?

[simonb 0]

No it was spot on when I checked it again a couple of days ago. So if skimming retards the timing I guess that I will try a small advance of 2-3 degrees and see if there is any improvement. What are the effects on ignition timing if the cam is advanced? I am right in thinking that I must then retard the ignition timing by an equal amount?

 

Simon

[Craigb 2]

Bit of a side issue

 

From an optimum point for the Best cam timing , What is the effect on the torque or power curve of advancing or retarding the cam timing. Apart from a peak power loss?

[simonb 0]

my understanding (correct me if i'm wrong) is that advancing the cam shifts the power band lower down the rev range and retarding shifts it up. I think that there's only so far you can go though before advancing has a negative effect.

Edited March 24, 2006 by simonb