ne evening in the latter part of the year 2001, I was trying to sort out some notes I had on various cam data. Comparing some figures I had from different sources, it quickly became evident that there was really no comprehensive set of data available, and the bits of information I had culled varied widely. There didn't seem to be any sort of standard for measurement, some of the cams were only measured in lift and duration, and had no reference as to base circle or checking clearances used.
At the same time, there was a huge aura of mystery surrounding something that was referred to as the "Euro 1608 Cam". Popular belief held that this was some sort of special performance cam, and this also seemed to be supported by a text written by a well known FIAT engine tuner, which claimed this particular cam had both a greater lift and duration than those of comparable FIAT twin cam motors of the period.
Not being able to reach any hard conclusions from the data I had, I set about making a measuring fixture from an old cam box, a degree wheel, and a dial indicator. After carefully recording measurements for each degree of cam rotation, I made a spreadsheet in Excel and used MS Graph to plot the profile of each cam I had available.
Then came the mission of collecting every cam I could get my hands on, finding the least worn of each type, cataloguing them by application and casting number, and plotting the grind of each cam. Below is a photograph showing some of the different types of cam configurations. Some FIAT cams have distributor drive gears cut on the exhaust cam, others have block mount distributors, hence no cam gears. Lancia Betas have gears on the intake cams, but the fuel injected models have eccentric slots milled into the exhaust cam end to drive the distributor. The Lancia Scorpion has a dowelled pulley mount on the end of the intake cam to drive an emissions air pump. There seemed to be an almost endless permutation of casting numbers, and not all had the same grind, but sometimes cams with totally different casting numbers shared a common grind.
Once the measurements and raw data had been collected, the task of data entry began. First came the point entry, creating a 360 column wide spreadsheet to hold values for each degree of cam rotation (two degrees of crank rotation). Each cell was then filled with the appropriate measurement, measured in thousandths of an inch. Once this was completed, the cams needed to be "timed". Referring to the original factory cam timing specifications, I found the lobe centers of each cam, then cut and pasted the graph data to match the lobe center. The result in each case was a graph taken from base circle, showing the ideal factory timing, and actual lift, duration and profile of each cam. Finally, I added horizontal lines to represent the standard FIAT checking clearance and a reasonable running clearance, and made up a legend key to identify the various cams.
So, you ask, what became of the mysterious "Euro 1608" cam? After acquiring three such cams through much begging, pleading, and bartering, and the generosity of a few good people, I degreed each of them. In every case, the grind matched IDENTICALLY to the most common grind across the FIAT TC range, referred to lovingly in the USA as the "U.S. Smog Grind". This profile has a duration of 238 degrees at a standard checking clearance, NOT the 273 degrees that the 1608 cam was rumored to have. At some later date, somebody pointed me towards a small footnote in one of the service manuals that stated that FIAT themselves, for some inexplicable reason, had deviated from the normal checking clearance when making up a specification chart for the 1608 cams. The higher numbers represented the same grind as a "normal" cam, but taken at a lower checking clearance, i.e. closer to base circle. The tuner who had mistakenly quoted the higher lift and longer duration of the 1608 cam eventually conceded that he had taken the figures from the original FIAT literature, rather than a comparative measurement.
There were a lot of other discrepancies between cams, quoted lifts and durations, mostly due to the fact that all the various manufacturers and vendors quoted the cams they offered with a checking clearance anywhere from FIAT's checking clearance of .032", to any one of a number of lower running clearances, or in some cases, even zero (base circle)!
Here are some graphs of factory FIAT cams for some applications, and some graphs showing comparisons between relevant cams.
Master Chart of Twin Cam Profiles
Twin Cam Plots
Twin Cam Plot Comparisons
PBS Engineering Cam Data
As I write this, in October of 2004, Graeme Wellington of Australia has just completed measuring several dozen more cams and putting the data into an Excel spreadsheet. Thank you Graeme! You can download it here:
A lso, David Beale in the UK has provided an Excel spreadsheet of various 16V Abarth cam profiles, here:
And somebody dug up this Berni Motori catalog page of 124-131 Abarth Rally cams. It was recently enough I should remember who it was, perhaps Volumex Spider owner Chuck Storry?
If I manage to find some time one day, perhaps I will try to make plots of Graeme's Data as well as David's. Meanwhile, if you'd like to degree some cams of your own, I do have fixtures now for measuring both SOHC and 8V Twin Cam items. You can contact me here.
Twin Cam and SOHC Fixtures
You'll want a crank degree wheel if you plan on tuning a TC. I made the following degree wheel for the FIAT_TC_Motors yahoo group members. You can download it here. Special thanks to Jeff at machinerycleanery.com for the initial wheel geometry.
Important: Select and save the image to your computer, then open it and print it out. If you try to print it directly from your browser, you may get a low resolution image. The degree wheel is a high resolution image and should come out razor-sharp. Attemping to print from the webpage may make some of the small text illegible.
The crank timing wheel uses the following legends:
- Intake valve duration is indicated in BLUE
- Exhaust valve duration is indicated in RED
- Overlap is indicated in YELLOW
- Timing advance is indicated in GREEN
- Stock settings are indicated by POINTERS
Stock settings used for this wheel are standard spec timing of 13/45 Inlet and 49/9 Exhaust.
Advance timing used is static:10 deg. BTDC, centrifugal 10 deg. between 1000-1600 RPM, 5 deg. per 1000 RPM up to maximum centrifual advance of 28 degrees crank at 5400 RPM. This is a fairly standard distributor curve for FIAT TC motors, but it should be noted that the stock timing for your particular motor may vary. At any rate, it is a simple matter to mark the wheel accordingly to suit your preferences.
Master Chart of Twin Cam Profiles
PBS Engineering Cam Data
