big cam vs. low boost
big cam vs. low boost Ok so as Bob states a big cam will bleed of boost. So only being able to make 4lbs with a P1, 6" crank and 3.85 blower pullies, would it be beneficial to put a smaller cam in to get more boost? My current cam is an old MTI R1 on a 116 lsa. I believe it is a 232/236 duration.
So my question is smaller cam more boost? I am putting a MMS crank pulley and 3.4" blower pulley on in spring. I am really looking for a solid 10lbs of boost next time around.
So my question is smaller cam more boost? I am putting a MMS crank pulley and 3.4" blower pulley on in spring. I am really looking for a solid 10lbs of boost next time around.
Teching In
Joined: Jan 2008
Posts: 35
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The only way you bleed off boost is by the engine demanding more air than the blower is providing. The cam can kinda do it by allowing the engine to take in more air at higher rpm. The higher rpm from the larger lift and duration will demand more air and if the blower cant keep up, it wont make as much boost. You should reach your power level earlier though since the volumetric effeciency increases from the bigger cams. An example would be my old SR20 engine in my 240sx. The stock turbo was a T25. Had the ability to push 15psi but it wasnt able to sustain that pressure above 5500rpm because the engine was demanding more air than the turbo was able to put out so the pressure would drop. It would hit 15psi by 3200rpm and fall to 10-12psi just after 5500rpm. But then i put a larger 2871R turbo on and i could hold 18-20psi all the way to 7500rpm. Its kinda a battle between airflow and engine demand. You gotta kinda remember, manifold pressure is kinda like backpressure from what the blower is able to flow and the engine is able to take in. Im sure im not totally accurate at what im trying to explain but i hope you get the idea.
