I hope all that have read this thread has started at the beginning & read Greg`s link from his website and the other tuning info on the V6 which is very valuable to all of us. I hope I can provide a little insite on some cam info on these motors.
Before I get started, you will find on my website, (in the "How TO" section) if you scroll down far enough, you will find some info & comparisons of some Alfa V6 12V cam grinds. I will refer to those for lobe shapes & lifts to explain a bit on making these motors work as they should with different induction systems. But mainly EFI.
Questions about the cam timing of the cams speced by Autodelta might be best addressed after the basics on this specific motor`s cam needs are considered. Short duration/overlap does not mean weak cams.
These motors are difficult designs to build proper camshafts that work as the driver expects. As you know, everything has to happen from a cam timing event to make any power, and unlike the 4 cyl. Alfa`s we can`t change the lobe separation angles at will, to alter the engines breathing characteristics.
( lobe separation is a fuction of Lobe centers for the intake & exhaust for each cylinder. Add the two together & devide by 2. The result indicates the relative length of the power stroke & propensity for overlap. The same lobe design with LSAs of 114 will be low end biased (more torque) or if at 100 will be more effective at high RPM)
It all has to be designed into the cam by the builder before it is ground.
The cams can be tuned a minor amount (by advancing and retarding both cams a small amount, Just like you would a Chevrolet/Ford) to enhance the powerband towards more low end or high end performance. Alfa knew in it`s wisdom not to make the cam sprockets adjustable, otherwise most motors would have experienced bent valves from "improved timing".. We had to redesign the sprockets ourselves to make them adjustable for the race motors with big cams & cut down heads. Unfortunatly all the stock cams are biased to emission control design and not much comes from minor adjustments, although there is a good bit of "slop" in the drive units that allow a degree or two at the cam.
The 164"S" cam has a bit wider lobe separation angle (109.5 as opposed to the GTV6/Milano/164 cam`s 108). This is not bad, as the low end is enhanced by the cam timing (wider lobe separation angles) and the 1mm lift gives more intake charge. The intake lobe is basically the standard lobe expanded to give 1mm more lift and 7 degrees more duration at .050 lift. It is still not much lobe above .100 lift where duration means something. (where the valve is open & piston stroke is creating the best negative pressure)
The lift rate is a bit quicker than most of Alfa`s designs but not much, as quietness, long life (from material that isn`t that durable) and lack of maintaince for the Dealer`s, are the first considerations (& did I mention emissions?).
The "timing event numbers" published for the various stock cam fitments are based on published "off the seat" timing occurances.
Aftermarket cam builders in the USA use as a standard for "timing events", valve lift at .050 lift at "0" lash. (Not "off the seat" measurements.)
If you are "degreeing in" a set of cams, and have set lash at .015 you would note where the degree wheel is, at .035 lift)
Euro cam builders seem to have no standard, but but in general I find overall duration is given at .020(.5mm) and duration at .040(1mm lift). So comparing cams is really guesswork without full profile information.
Back to cam timing and the V6-12V. Except for the early 2.0 & 2.5 the motor has been fuel injected. The 3.0 built & sold in S.Africa was carbed with the same Delorto`s as the small motors. They look good, but nothing to drool over performance wise. As do the 4 cyl. Alfa`s the EFI alfas respond poorly to cams with much overlap. (spica too for that mater) as metering is based mainly on manifold air pressure which is severely disrupted by back pulses into the intake system caused by overlap. This happens with the same negative effect on carburetted vehicles at lower RPMs. But they were built before the "E" word controlled engine design.
To make a "hotter" street cam work on these motors, the amount of overlap has to be addressed first. This is a function of lobe design in the late ramp & early flank of the lobe. This is where deviation from the traditional designed Alfa lobes of the past, pays big dividends in terms of low end performance(torque) and emission compliance (we hope), yet can give amazing improvement in performance across the full RPM range, because of expanded duration in the middle & upper lobe flank & nose of both intake & exhaust..
As a "for instance" compare the 164 "S" and normal Milano/GTV6/164 to the RJR 28/744 cam profiled on the website. The LC`s on the website were those used, but lobe centers could be built engine specific as any of the cams can be. It is easy to see how opening & closing events do not exceed stock cam because of ramp rate. Yet large duration gains are made.
FYI the lift timing data for all of the intakes are pure
lobe lift for all. The Exhaust duration is given for the Alfa stock cams at the
lobe as well. The RJR 744 exhaust cam is given as "duration at valve" which is done to reference their flow capacity Exhaust lift & duration is a function of the 1.4 rocker arm ratio. For comparison the pure lift/duration profile for the 744 compared to the "S"/all exhaust is below:
lobe lift .273 (6.95mm)
"S" Exh. lift .252
.010 252
.020 234
228
.040 212
210
.050 204
204
.080 186
.100 177
174
.200 107
96
.250 60
24
These are hot street cams that work with the stock system and don`t still play within the emission tolerances..
I will pick up tomorrow at this point and hopefully get into the issues of lobe design as to intake track and the problem that really was difficult to overcome which was cam lobe design for the exhaust side what limits the motor`s RPM range & solution, and what seems to work well, and what it takes to fit high lift cams in the heads as it is far more difficult than the 4 cyl.
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