alfa 2600 camshaft timing with weber set up

[franco-veloce]

Hi All,

standard 20 degr + 10 degr (3.5mm ) extra advance gives 30 degr on camshaft timing

This is camshaft timing and has nothing to do with the cranckshaft timing .

for more info you can see on page 237 of the alfa romeo owner bible by Pat Braden

rgds Franco

[Sputnicker]

Franco,

Unfortunately, I don't have Pat Braden's book. I'm looking at the "Technical Characteristics and Principal Inspection Specifications" published for the 2600 by Alfa Romeo (green manual in English about 6mm thick) and it says the opening of the inlet valve...before TDC is 20°36' for the Spider and Sprint. (Interestingly, it's 33°20' for the Sedan.) These values are under the heading: "Angle values of the actual diagram of valve timing system with cold engine (clockwise rotation direction of the crankshaft seen from the front side." This seems like they are talking about degrees at the crankshaft rather than at the camshaft, but the language isn't completely clear.

The Piper camshaft specs provided earlier in this thread by Red Merlin has a value of 30° for a 2600 Sprint and has the following definition: "Timing = Valve timing figures measured in crank degrees." Duration is also measured in "crankshaft degrees."

In both documents, timing is expressed in degrees before TDC, which is normally measured at the crankshaft.

So I'm still confused about camshaft degrees versus crankshaft degrees. Since the crankshaft is turning at twice the speed of the cam, your 30° at the camshaft would be 60° at the crankshaft. That's twice the value of the Piper specs. That seems like too big a difference. It also seems like the critical issue is when the valves open relative to where the piston is. It doesn't seem right that the intake valve would be opening 60° before the piston reaches TDC (which equates to one third of the 180° exhaust stroke. Seems like you would be forcing a lot of exhaust gases out the open intake valve.

Can you share what the Braden Bible says for those of us who don't have a copy?

I don't care who is right, or who is wrong, I just want to be sure we are all looking at this correctly and there seems to be some conflicting data.

Thanks,

Barry

[DPeterson3]

Purely generic comment...

Every engine I've ever built has noted the cam timing with respect to the crank position. So, if a cam is listed as opening (or closing) at a certain degree point BTDC or ATDC, it is the crankshaft position that is being referenced.