any experience on camshaft regrind and compression ratio?

Just in the process of rebuilding the engine on my 400i (gen1). As we've already gone into so much work I am considering tweaking the camshafts and compression ratio.

Any experience on this?

 

Replying to my own thread... As a last resort I'll give a try to the 412 profiles (and add the blowout pop-up valve). Can anyone confirm what are the 412 diagrams on the user manual. I've had a rapid look at the online copy in www.f400register.com, but the intake figure is not clearly scanned (16° or 18°).

 

Roger: I am the other "R. Emin"... Raphaël's blue 365 is working great and he is not likely to play with the camshafts as the engine had already been upgraded in the 90s with close to 400hp. Mine is the yellow one with the variable pitch th400, hopefully it will be back in the road this year.

The Cat Cams profiles are for the "carbed" engine. Mine is equipped with k-jets and these do not play well with valve overlaps. On Erwin's scan the opening figure seems 16°, which would be consistent: -4° for aperture +4°for closure compared to the 400i gen 1 (16° vs 20° and 48° vs 44°). This being said I would feel more comfortable if someone who has an original copy of the manual could confirm these two figures:

1) "Too much overlap, or too late of intake valve closure will cause reversion, which will wreck havoc with fuel mixture, due to pressure pulses fooling the K-Jetronic into thinking the real flow is different than it actually is." (abstract from https://www.ferrarichat.com/forum/threads/performance-cam-regrinding.2788/#post-33983)

2) Too much reversion may also blow out the rubber "plenum" of the k-jet.

I suspect the 412 is at the limit of what k-jet can accept as the two I've inspected are equipped with some sort of pop-up valve just like the Porsche guy did in order to save the plenum in case of too much back pressure. Judging by the way it startups I would say the 412 auto-trans seems to have higher stall converter than the 400i, which could help with aggressive camshaft (=a less stable idle).

All in all if someone could confirm the owner book is stating 16°, that would be great!

 

Just received an answer from Techniprofil (our local equivalent to WebCam): the 412 and 400i profiles are just the same, it's just the inlet timing that is advanced by 4 degrees (open 4° earlier and closes 4° earlier). This produces a bit more of overlap as the inlet valves opens sooner while exhaust is still open, and also slightly increase compression ratio as chamber is closed earlier.

This seems consistent with the documentation : boring the cylinder from 81mm (400i) to 82mm (412) only increases the compression ratio from 8.8/1 to 9.1/1 while the 412 is rated to 9.6/1. So the larger piston alone does not explain the better compression ratio, but the advanced timing could do the trick.

Time to discuss this with my mechanic!

 

Not sure 400i gen2 benefited from the subtle refinements that can be seen in the 412: stronger starter (with Ferrari Emblem unlike the previous Iskra), shorter rear axle ratio, higher stall converter and modified airbox. So maybe the 400i gen2 was just in between in terms of timing (i.e not the full 4°)?

Just quoting Techniprofile :

"le diagramme ECH entre les moteurs "400 i" et "400 i génération 2 ou 412" sont identiques en temps d'ouverture et calage.
Le diagramme ADM entre les moteurs "400 i" et "400 i génération 2 ou 412" sont identiques en temps d'ouverture mais le calage dans le moteur est différent.
L'autre différence qu'il peut éventuellement y avoir entre les profils de ces 2 moteurs, se situe au niveau des levées mais il n'y a pas d'information à ce sujet"

Basically aperture and timing are the same for the exhaust. Aperture again is the same for inlet, but timing is different. At the end of the message they say that there is no information about lift. Based on their analysis the only adjustment is on inlet timing and maybe lift.

We know lift is not going to be vastly different as the pistons do have the same valve recess: the 412 is basically using the 400 2nd oversized pistons (82mm pistons were already quoted in the 400i manual, a few years before the 412 hit the market).

I've just made a search on FerrariChat forum about 4° and Camshaft... Identical camshafts profiles with varying timing seemed to be quite usual back then: in the 308/328 forum, there are numerous comments regarding the service manual: the document states that in order to comply with US rules, the inlet camshaft should have 4° less timing compared to the "euro" spec.

All in all the 412 looks like a "euro" spec 400 with 2nd oversize pistons.