I found out the specs of my engine heads were. 1968 Chevy Camaro 350. 76 cc chambers/ intake flow 152 cfm/ exhaust flow- 93.2 cfm/ valve size 1.94--1.50/. What does this stuff mean and how would I use this info when upgrading new parts like cam, lifters, and rockers etc?
SBC 350 HEAD SPECS
- Thread starter franknitticutlass
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Ok, generally speaking, the combustion chamber size is one of the factors that will determine your compression ratio. So without knowing your head gasket thickness or piston type, I can guess that a 76cc chamber on a 350 will give you somewhere between a 8.5:1 and 9:1 compression ratio. Probably closer to 8.5:1.
Valve size... the larger the valves, the more air they flow. Most SBC performance heads have 2.02" intake and 1.60" exhaust valves.
Flow numbers - the ones you posted are missing valve lift information. When you get a set of heads flowed, they should give you a range of intake and exhaust cfm numbers from.1" valve lift thru .6" valve lift. So if you have a set of heads that produces peak intake airflow at .510" lift, then you should pick a cam with .510" lift.
I am going to post this now. Hopefully it doesn't get deleted again.
Valve size... the larger the valves, the more air they flow. Most SBC performance heads have 2.02" intake and 1.60" exhaust valves.
Flow numbers - the ones you posted are missing valve lift information. When you get a set of heads flowed, they should give you a range of intake and exhaust cfm numbers from.1" valve lift thru .6" valve lift. So if you have a set of heads that produces peak intake airflow at .510" lift, then you should pick a cam with .510" lift.
I am going to post this now. Hopefully it doesn't get deleted again.
Glad that worked. As far as you picking a cam and rockers, it depends on what you hope to accomplish. A mild cam might be a good match for those heads, as they sound relatively stock. If you are going for maximum power output, invest in another set of heads or have yours reworked. It is hard to make specific suggestions without knowing what you are trying to accomplish.
And like I said, I am being very general. This subject can easily fill a book.
And like I said, I am being very general. This subject can easily fill a book.
Well of course when most people upgrade. Im looking for more overall HP and speed. How could I determine my max lift for a cam? by my valve lift or exhaust? What do the numbers mean?
franknitticutlass said:
I'm not exactly sure what you were asking but I'll try to help. 79GP6.6L you did a good job of explaining that.
The maximun lift your cam can have right now is determined by the valve springs and the piston-to-valve clearance. The valve springs will only depress so far before all the coils touch each other or "stack up". The max cam lift should be at least .060" less than this or you could actually pull the rocker stug out of the engine among other very bad things. The P-V clearance is the minimun amount of clearance between the valve as it's moving down the cylinder opening to let the fresh air-fuel charge. The closest area is actually before the piston comes to the very top of the chanber to pull this charge in. The minimun clearance is differant for the intake and exhaust due to the heat of the exhaust but it's somewhere in the vicinity of .080"-.100" for the intake and .100"-.120" for the exhaust.
When looking at flow numbers, as 79GP6.6L said they will be listed at .100" - .600" lift at a certain vacuum rating. If your heads won't flow very well at higher rpm's then there's not much reason to get a .600" lift cam as the rpm and lift needed to fill these heads will be well under your engine speed. When looking at heads also look at both flow and velocity. Picture it like this. A 3" firehose will flow more water at a certain pressure than a 1/2" garden hose. That's flow. Unless you have a high rpm race motor, you don't need that much flow. Velocity is the amount of charge delivered. At the same pressure, the 1/2" hose will move more quality charge (think kinda like ram-air) rather than a slower moving charge.
Remember also when looking at heads and flow numbers. At peak lift, the valve is only there once for a small amount of time. At the mid-lift numbers, say from .200" - .400" lifts where the charge is actually MOVING it pass this point twice in the cycle. Once opening and once again while closing.
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