Differences between 456 and 550 V12?

I've read that the 456 is a detuned version of the 550 V12, although I'm thinking it must be the other way around (550 is a pumped up 456). I have not been able to find any discussion of the actual differences anywhere online. Is it just cam timing and advance? Or something fancier like variable cam timing and variable intake tracts?

Are there any tech books that go into Ferrari engine details? The 456 I'm looking at needs a top end rebuild (poor compression and leak down), and it will be tempting to swap cams and such since the engine will be apart. TIA!

Jeff

 

A big difference is that the 550 has hydraulic tappets, and the 456 has shims to adjust valve play.
The heads are different because of that.

There are no variable cam timings or inlet tracks.

The 550 has a higher maximum allowable rev limit, and because of that probably stronger valve springs.

The valve timing is probably not too different, but a bit difficult to interprete because the cams for the 456 are specified at 0.5 mm play, but they have to be adjusted to 0.2 and 0.3 mm for in and outlet. So the real timing figures are quite a bit more aggressive as the specifacitions do suggest (240 degr in and 244 degr out)
For the 550 the figures provided are even harder to understand, because with hydraulic tappets one would expect the real timing figures with no play.
But the figures provided are so tame, that this does not fit for a sports car
( 226 degr in and 226 degr out), so they are probably specified with a play of x,x mm. One would expect for a highly tuned engine figures around 270 to 290 degrees.

As far as I can see, the inlet sides of the two engines are almost identical, i.e. air filtration, maf and throttle.
The exhaust headers are the same, the cats are different from shape, so is the rest of the exhaust, similar but shlightly different.

As a last point of difference there is the compression ratio, 10.6 vs 10.8.

Up to something like 5000 rpm, there is hardly any difference between the power of all the V12´s from 456 to 599. it is beyond this point where the differences start. The 599 continues from 5000 rpm as a straight line to over 7500 rpm with more than 600 Hp, and the 456 starts slowing down from 5000 rpm and gives up somewhat over 6000 rpm with 445 Hp.

My guess is that the main reason for the 550 having more power above 5000 rpm has to do with a more efficient exhaust system, a higher compr. ratio and maybe a somewhat more agressive cam although the manual tells a different story.

The exhaust system can easily be adressed by removing the muffler after the cats. This muffler can be replaced by two straight pipes for max power, or if you want a nicer sound with an x-pipe that give a bit less power. This adjustment may give you something between 10 and 30 Hp.

Another easy adjustment can be made by replacing the air filters by BMC filters. This will probably give you some 10 Hp extra.

 

Hans, what about the fuel system?
Any differences there?
Tks.

 

I am not sure what you mean, but the fuel injectors are the same for the 456 and 550.
ECU for some 456 GT´s and all the 456M GT is the same Bosch Motronic 5.2. as used for the 550.
The 456 GT with the Bosch Motronic 2.7, produces exactly the same power curve, so most likely it uses the same ignition and fuel tables as the 5.2 ECU version.