Blower cams
 

We are always talking about cams for NA builds, but what about with forced induction?

Take a look at this, and let me know your opinions.

Lunati has a 250/255 112 LSA .630 lift cam, that is labeled a "supercharger" cam. Lets take a look at this cam, compared to a Crane 244/256 114 LSA, "651" that many like for supercharged engines, and is labeled a supercharger cam.

First, lets look at the exhaust timing events.

Exhaust valve opens at 61.5, and closes at 13.5 on the Lunati.

Exhaust valve opens at 67, and closes at 9 on the Crane 651.

Both exhaust lobes, have nearly identical .050 duration. Lunati at 255, and crane at 256. But look how different the exhaust timing events are. Anyone have any thoughts on WHY, and how that would affect things?

Where do the intakes open on each as a comparison to the exhaust closing?

IO 15, IC at 55 on the lunati.

IO 13, IC at 51 on the crane.

Of course the crane is sporting 6* less duration on the intake side.

Is it maybe due to better flowing exhaust ports on aftermarket heads? Just a guess but 651 been around for years and possible was more toylored towards GMs chits exh port. Any thoughts? Just throwing this out there.

Did you compare it with the SR Crane I sent you last week.

From the research I've done on even split (single pattern) cams (my whipple 500efi's have them)... the increased intake duration, or lack of favored exhaust for that matter, the more efficient the exhaust port/exhaust in general, the less exhaust duration desired vs intake. My theory is you want to limit intake blow thru as much as possible to take advantage of the blowers efficiency but have enough to clean the cylinder.

Blower engines in general do not require near the exhaust scavenging due to positive pressure on the back side of the intake valve. In affect the blower induces the clean fill to a much larger extent and not need the overlap

Efficiency is everything but again I think when were looking at two blower shelf cams with a noticeable difference in exh valve timing events. Exhaust port flow and what exhaust is being used for the particular build would come into play. Just getting back to OP.

Why they look are nearly identical but are quite different ?

Lunati is ground with 2* Advance . So being on a 112LSA, this puts ICL at 110* and ECL 114*
Crane ground with a 5* Advance. So, being on a 114LSA, this puts ICL at 109* and ECL at 119*

Could very well be. I honestly don't know without researching it so will have to look up what most blower cams have for specs. If you get a chance MT post the specs of the sci one merc used.