308 QV ignition curve question

"Is it possible to change the Digiplex ignition in a USA Digiplex so that it follows the Euro advance curve..."

Found a post from some years back. Sadly, the short answer is, "No."

https://www.ferrarichat.com/forum/threads/ignition-advance-curve-qv-us-versus-base.356077/

 

Not so easily, but David Feinberg at: https://www.sarasotaitaliangarage.com can replace the guts of the Digiplex with a more modern solution (similar to the Microplex) and can give you almost any ignition curve that you like.

 

You need a Boxer, a TR, or a supercharger . It probably would "feel" a little bit peppier at the low end, but more for how it changes the behavior of the acc pedal motion vs airflow (i.e., from the idle position, a smaller motion of the accelerator pedal on the euro produces a bigger change in the engine operation, but you could get to a similar operating point by just pushing the US acc pedal further). The reason is that the idle timing on a euro 803A is 10 deg BTDC; consequently, the amount of air entering the engine at idle has to be set very low to get the 1000 RPM idle speed, and therefore, a small opening of the throttle plate makes a big percentage change in the amount of air entering the engine. On the US 805A, the idle timing is 3 deg ATDC so more air needs to enter the engine to get the 1000 RPM idle speed, and the same amount of acc pedal motion (i.e., the same amount of throttle plate motion) produces less of a percentage change in the amount of air entering the engine (vs the euro). The euro curve does have more advance (maybe 5 degree-ish) in the 2K~3K RPM range than the US curve so that would add some mid-range peppiness, too, but don't expect a night-and-day change. If you'd like to compare the advance curves, they are both in the 281/83 Mondial 8/QV WSM:

euro 803A - page D4 Fig 5/1

US 805A - page D5 Fig 6/1 (which they left off the 6 and 6/1 labels, but you can figure it out based on how 5 and 5/1 are labeled on page D4)

 

FWIW, adding advance at the low end was a common "shade tree" mod in the muscle car era to add grunt. Back then this was done simply by filling part of the slot in the centrifugal advance mechanism so that the weights (and the distributer cam) couldn't return to the fully retarded position. This changed the low end timing but had no effect on the max timing. IOW, let's say the factory spec was for 4 degrees before TDC at idle and 36 degrees at max advance. The mod to the slot might make the idle timing 10 degrees BTDC while keeping the 36 degrees max advance.

Later, performance distributer kits came with a selection of various cams/springs/'slot fillers', etc to adjust the timing curve without the shade tree method of finding something to block part of the slot though the intent/results were exactly the same.

IF it matters, the digiplex/microplex US timing curve will meet USA emission testing requirements; the Euro timing will not.

 

Yeah, but it doesn't feel as "peppy".

Actually, rainman ray recently had a video where he installed a Bully Dog electronic gizmo on his Diesel Pickup that just made the throttle control (not sure what's it's really called on a diesel) move more for a smaller acc. pedal motion.

 

I have driven 308's back to back with US and base Digiplexs. It is a very noticeable difference but would not say a lot is at bottom end. Mostly mid and top.

One reason I really like going to more compression during rebuilds. They are not sensitive to detonation and really respond well. My 328 is at 3.5L, of that I think 3mm was stroke and it is just shy of 11:1 and spins good tires very easily.

 

I have one of Rifledrivers 308 carburetored rebuilt engines that is stock except for compression and ignition. On the same dyno, it has almost identical HP and torque curves to a stock 4 valve 3.2 liter. In a 2700-pound car...that is pretty peppy. The compression increase, of course, makes torque and horsepower across the power band. There's no substitute for displacement, but compression is a close second at mid and low range.

 

"I have driven 308's back to back with US and base Digiplexs. It is a very noticeable difference but would not say a lot is at bottom end. Mostly mid and top."

FWIW...when I "tested" the US vs Euro curve on my 328 (Microplex)I noticed the low end first. On the same road surface (actually a large, empty parking lot), flooring the accelerator from an idle-RPM rolling start, with the US curve the car accelerated and did not lose traction at any time. The euro curve spun the tires when the RPM came up a bit. The euro curve also "barked" the tires at a WOT shift into second which it wouldn't do with the US curve. I repeated this "test" multiple times that morning and then permanently changed to the euro curve, where it's been the last 10+ years.

 

The microplex US vs Base curves are not a great big difference. It was a surprise to me how much difference there was in the digiplex system. Until really good anti detonation systems were available Ferrari has always been very conservative in both compression and advance. Even back to the 60's when we could buy real gas with real octane.