Camshaft Vs Crankshaft Degrees

[Saveit 0]

Hi there

 

How much is 1 degree on the camshaft in crankshaft degrees? I have made my own pulley to advance cam timing, and i have moved the little split about 1.5 mm which results in about 11 degree advance measured from center to the outer edge of the camshaft pulley. Now how much is this in converted to crankshaft degrees? Should perhaps say that its a 1.9 gti engine with an XU10 head on from a 306 xsi 8v. The head will be skimmed by 1.8 mm and i will use a Kent PT27 camshaft. So i want to be sure that the valves wont hit the pistons.

 

Stefan

Edited April 5, 2009 by Saveit

[Sandy 191]

1 cam degree is 2 crankshaft degrees.

[Saveit 0]

1 cam degree is 2 crankshaft degrees.

 

Measured where? On the inner or outer edge?

[Saveit 0]

Someone? Where, on the pulley, do you measure the degrees? On the edge or at the center where the key/split is?

[welshpug 1,662]

doesn't matter where, but its far more accurate around the edge

[Saveit 0]

Okay. So PeterT told me that if i skim the head by 1mm i should advance cam timing by 4 crankshaft degrees. I am planning on 1.8mm skim though. Furthermore if i then use an aggressive cam i should advance it a few degrees more. So i was planning on advancing it about 5-6 crankshaft degrees. That would be around 3 degrees on the camshaft pulley. So the 11 degrees i have made is a bit too much Glad i have a few pulleys more .

[ifcho 0]

Okay. So PeterT told me that if i skim the head by 1mm i should advance cam timing by 4 crankshaft degrees.

 

is this valid for 8v engines as well?

I have skimmed 3mm, so I should advance the cam with 12crank degrees?

[pug_ham 244 3 Cars]

Should perhaps say that its a 1.9 gti engine with an XU10 head on from a 306 xsi 8v.

 

is this valid for 8v engines as well?

I have skimmed 3mm, so I should advance the cam with 12crank degrees?

 

Stefan is asking about an 8v engine & imo its only applicable to an 8v engine with a skimmed head.

 

On an 8v the cam timing is going to be slightly out because of the skim but the 16v engines have two tensioners (one for for each side of the belt) meaning the standard timing pin holes will stay the same & any skim will be taken up by the tensioners keeping everything close to the same as standard.

 

Graham.

[Saveit 0]

PeterT wrote the following:

 

8V

1mm off the head needs approx. 4 deg. of advance (crank). If you also install a bigger cam at the same you need to advance it more. This could be 6-7 degrees depending on the cam grind.

 

I assemble the head/cam/belt first, then measure how much valve lift there is at TDC. I then work out how much the cam needs to be advanced to get the desired lift @TDC, in crankshaft degrees. Halve this figure for camshaft degrees.

 

The location pin is then removed from the pulley and the hole drilled oversize to accept an offset pin, turned to the required offset from above in camshaft degrees.

 

It's a little more tricky than a 16V offset woodruff key, but a fraction of the price of a vernier pulley.

 

Many folks skim a head, then loose what ever performance they've gained by the camshaft being retarded.

 

I can do exchange 8V pulleys if you tell me how much advance you want.

 

16V

Theoretically on a 16V, any deck or head skimming should be equalized because there's two pulleys. In reality, for a big skim (eg 1+mm off the block), this is not the case as it's not possible to pull enough tension on the inlet side. Thus most of the tension is taken up on the exhaust side, retarding the cam timing.