CHANGING LOBE SEPERATION

[buddy rawls]

if the motor was needing later exhaust activity and you were running the 106 LSA set-up with good success, then the earlier exhaust of the 108 may not be a good thing. It will definitely be letting cylinder pressure escape a little earlier and may not be working the overlap as nicely. However, if the timing events were needing to calculate closer to a 110 or 112 LSA, then the change from the 106 to 108 will helping out, but a 110 might have been a far better choice. But it goes beyond LSA; its actually a timing event issue. LSA changes are what gets seen during the grinding or checking process. LSA is not a true design criteria. It is manufacturing or checking criteria. The real story is the timing event changes. the LSA is an end item, after the design.

I do not subscribe to the assumptions about advacing or retarding or LSA chenges, etc etc without knowing info about the motor. the Exh to Int is crucial, as is the availability of flow and cross-section versus the displaced cylinder volume. In short is the motor intake restricted or less restrictive, is it exh restricted or not, etc etc?

[piston guy]

I think it's hard to apply generalities to lsa. Some engines are far more sensitive that others. Some engines thrive on wide lsa's. others won't get out of their own way.

[Krooser]

Good question… maybe someone can give me am opinion on this cam.

Limited mod type dirt track car. 4412 2 bbl Mopar 367 ci. Mopar J heads. '69 340 iron intake. 12-1 compression. Stock 6.123 rods. Cast crank… external balance. HEI ignition. Maybe 6500-6800 RPM's.

The cam is from a different project than this modified… it's a Hughes stock roller regrind. .510 lift w/1.5's (.544 w/ 1.6's). 228 duration in/ex @ .050. Intake opens 4 degrees BTC exhaust 50 degrees BBC. Intake closes 44 degrees ABC exhaust closes 2 degrees BTC. Lobe separation 113 degrees[/i][/b].Installed centerline 110 degrees.

Seems to me this cam would be a little mild for this deal… but I've heard guys actually having good luck with some of these 'short' cams especially with the stock iron take and heads.