dangerous to run cc306 cam with a turbo?
08-23-2004, 08:41 AM
#1
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Join Date: Nov 2002
Posts: 1,074
dangerous to run cc306 cam with a turbo?
saw this at a website who sells turbo kits... (considering cc306 is 230/241 and 11lsa, it got me worried) am i gunna be ok running this cam for now?
Will a bigger cam make more power with a turbo?
Cam choice in turbo applications is critical. In many cases, a stock cam will work better than a typical "race cam" that would work well with an aspirated engine. What you want to avoid is the "intake and exhaust valve overlap". This is the time that the exhaust and intake valves are open at the same time. In aspirated engines, this theory facilitates the scavenging of all burnt exhaust gasses from the cylinder after the power stroke so that an "uncontaminated" and 100% burnable charge fills the cylinder on the next cycle which produces maximum power. Some of this condition can be tolerated with supercharged applications as it merely blows some of the boost out with the exhaust. However, on turbocharged applications (many people believe that the boost also is just blown out with the exhaust) however, the opposite is truer to the case. With exhaust pressures sometimes exceeding boost pressures, the exhaust can flow into the cylinder and into the intake manifold during this overlap time which contaminates the intake charge, decreases HP, and can cause pre-ignition as well. Also, most cam applications begin flow at .050" of valve lift. On forced induction systems, there can be substantial flow below this amount of lift because of the higher pressures behind the valves.
So, if in doubt go smaller on your cam rather than larger. Go wider on lobe separation angles (114 degrees is usually safe) Smaller on durations (stick around 220) and check with the cam manufacturer to make sure that it is a good "turbo" cam and not just a generic supercharger/turbo cam. A good option is to install a set of higher ratio roller rockers on your stock cam. Better pushrods and stiffer valve springs will help as well because boost and cylinder pressures will be way higher than stock. Stiffer springs will help close the valves against the pressure of incoming air and stronger pushrods will help open the exhaust valve against the increased cylinder pressures.
Will a bigger cam make more power with a turbo?
Cam choice in turbo applications is critical. In many cases, a stock cam will work better than a typical "race cam" that would work well with an aspirated engine. What you want to avoid is the "intake and exhaust valve overlap". This is the time that the exhaust and intake valves are open at the same time. In aspirated engines, this theory facilitates the scavenging of all burnt exhaust gasses from the cylinder after the power stroke so that an "uncontaminated" and 100% burnable charge fills the cylinder on the next cycle which produces maximum power. Some of this condition can be tolerated with supercharged applications as it merely blows some of the boost out with the exhaust. However, on turbocharged applications (many people believe that the boost also is just blown out with the exhaust) however, the opposite is truer to the case. With exhaust pressures sometimes exceeding boost pressures, the exhaust can flow into the cylinder and into the intake manifold during this overlap time which contaminates the intake charge, decreases HP, and can cause pre-ignition as well. Also, most cam applications begin flow at .050" of valve lift. On forced induction systems, there can be substantial flow below this amount of lift because of the higher pressures behind the valves.
So, if in doubt go smaller on your cam rather than larger. Go wider on lobe separation angles (114 degrees is usually safe) Smaller on durations (stick around 220) and check with the cam manufacturer to make sure that it is a good "turbo" cam and not just a generic supercharger/turbo cam. A good option is to install a set of higher ratio roller rockers on your stock cam. Better pushrods and stiffer valve springs will help as well because boost and cylinder pressures will be way higher than stock. Stiffer springs will help close the valves against the pressure of incoming air and stronger pushrods will help open the exhaust valve against the increased cylinder pressures.
08-23-2004, 11:01 AM
#2
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Location: cinci
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Re: dangerous to run cc306 cam with a turbo?
yea, i'd say go with a diff cam
that cam is more for an n/a application
also, at the top, you didn't tell us what lsa you want (it says 11_lsa)
114 would be good and yea, i'd reccommend talking to some cam guys at compcams or cmotorsports or whatever, they'd know what a good cam would be for whatever setup you're trying to do
that cam is more for an n/a application
also, at the top, you didn't tell us what lsa you want (it says 11_lsa)
114 would be good and yea, i'd reccommend talking to some cam guys at compcams or cmotorsports or whatever, they'd know what a good cam would be for whatever setup you're trying to do
08-23-2004, 11:09 AM
#3
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Join Date: Dec 2002
Location: Indiana
Posts: 1,810
Re: dangerous to run cc306 cam with a turbo?
general rule of thumb SO I'VE HEARD, is that 112 lsa will hold 4.5-10 lbs of boost comfortably. 114 lsa will hold 4.5-18 lbs of boost comfortably. thats just what i've heard for rules of thumb for street motors, like the average bolt on lt1 or head/cam lt1. there's probably better theory out somewhere, but this isn't a bad idea to follow. btw, cc306 seems to like high compression and natural asperation. i knew a guy running 11.5:1 on a stock bottom ended lt1 with stage 3 heads and cc306 that ran 11.7's on motor with 3.73's and 3200 stall. he says it could have gone faster. I'm sure u can spray this cam, but it doesn't sound like much of a boost cam
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