Some camshaft data

[EricH]

I was wondering about the duration and timing of the stock camshafts... Most of the documented values are seat-to-seat with unspecified valve lash, so not always directly comparable.

So I set up a degree wheel, put a dial indicator on the valve face, shimmed the valve for zero clearance (that is, the valve is never fully seated in the head and its position is always determined by the cam lobe) and then measured the timing events at .050" lift.

US-spec carbed 1500, cam taken out of a well-used '79 motor:
-4/40, lift .358", duration 216 degrees at .050"

New in box euro 1500 cam:
7/47, lift .386", duration 234 degrees at .050"

There's a negative sign for the US-spec cam.... Really! The exhaust valve passes through .050" as it closes at 4 degrees before TDC, while the intake valve doesn't pass through .050" as it opens until 4 degrees after TDC.... No meaningful overlap at all... And not surprising that it's really easy to get a smooth idle with that cam :bored: Back when PBS still supported the Fiat SOHC motor, they reported that the "stock" cam had 18/62 timing. That's seat-to-seat, with 22 degrees of crank rotation going into the first .050" of lift.

Next I'll try a stock US FI cam (this is specced at 12/52 but with some oddball valve lash so not directly comparable) and a stray 1300 cam.

 

[Ulix]

Cool

I am looking forward to the results.

 

[EricH]

I am looking forward to the results.

I don't know if you remember, but some years back you sent me an Excel spreadsheet with a whole bunch of camshaft profile measurements.... I still have it, and hope to eventually getting around to consolidating all the data into a single master table for the wiki.

 

[rx1900]

Cool

Hi Eric. Way to go !!!

In case you dont have this info, I have both the factory shop manual (from Fiat USA for 79-82 US models) and a factory parts manual. BOTH say that both the 1500 carbed and FI engines took the same camshaft. But with Fiat...who knows. It will be interesting to see what you find as reality !!

For what is is worth, specs as follows:
Cam lift (without play) 9.2mm (0.362") intake, 9.25mm (0.364")exhaust
Cam timing (measured with valve clearances of .60mm(.024") intake and .65mm (.027") exhaust) of 12-52-52-12

Given that perhaps your used cam is a little worn, your lift measurement is pretty close to the above.

I have a used stock cam here from an '81 FI. There seems to be no numbers or markings on it that I can see. But there is a "37" written in white ink on the end of the cam (the tranny end). Don't know if that means anything.

That 1500 euro cam looks very promising. I think PBS always claimed that increased lift was more important than increased duration. I have a PBS SX! cam now. I'll see if I can find the specs on it, but I actually think it is pretty close to the euro 1500 cam.

Looking forward to your findings. Keep up the good work.

Cheers, Doug

PS: by the way, what was the story on those "oversized" valve seats from IAP ?

 

[EricH]

PS: by the way, what was the story on those "oversized" valve seats from IAP ?

Turns out that my machinist was confident that he could source appropriate seats - the SOHC valve seats are fairly standard he says. I have still haven't turned the head over to him yet though... some other family stuff going on.

 

[EricH]

Another cam measurement

I've been away for the entire month of September and then some, helping my mother close down her house in Maine and then catching up with everything else that I didn't get done during that time :bored: but finally I'm back in North Carolina with my shop and my tools and the cars :grouphug:

So I just tried the same set of measurements (exact same setup, down to the same shims in the same cam buckets) on a new-in-box Faza 35/75 camshaft. Results at .050" lift are 12/50, 50/12, lift .378"