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in this class im racing in i have to pull 17 inches of vacum. im going to have to have a mild cam to be able to pull vacum and i got two sets of heads one set is some 300 horse double humps with 202 valves by the way the engine is a 350 but a man told me to use my set of 58 cc 305 heads to get my compression up and there was no need for the large valves because of the mild cam so he was saying the 305 heads would be better for me what do you guys think
 

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mudracer101 said:
in this class im racing in i have to pull 17 inches of vacum. im going to have to have a mild cam to be able to pull vacum and i got two sets of heads one set is some 300 horse double humps with 202 valves by the way the engine is a 350 but a man told me to use my set of 58 cc 305 heads to get my compression up and there was no need for the large valves because of the mild cam so he was saying the 305 heads would be better for me what do you guys think
Oh boy, you don't necessarily need a mild cam, though that will work. But what you can do is what the factory did with the LT1 and 4 which is a cam with fairly long duration combined with a lot of degrees in the Lobe Separation Angle (LSA). This cuts down or eliminates the overlap but can allow for a late closing intake. This will raise the manifold vacuum since there won't be communication between the intake and exhaust during what is a typical overlap period, yet keeps the intake open fairly late which takes advantage of high speed ram effects of the incoming mixture. But keep in mind you can't go totally nuts with late closing of the intake as this causes reversion.

The use of 305 heads would get intake flow speeds up early which will take advantage of the long LSA, but they will run out of breath sooner than a larger port.

Something to keep in mind when it comes to cam timing, lift, port and valve sizes. Which is;too small of ports and valves respond best to more cam timing and not to more lift or valve size. This is so because the port maxes out earlier than the capacity of the the valve's curtain (open) area. So increasing curtain area with a larger valve or more lift has little to no effect on flow. So the solution to more flow is to hold the valve open longer. This combination then can be advantageous in keeping the port velocity high which is good for sharp throttle response especially on a short track, yet you can get decent top end power with a long cam of moderate lift with lots of LSA. Keeping the lift a half inch or less allows the use of milder springs which greatly reduces wear and tear on the valve train.

I recommend you get on the tech line of some of the country's cam grinders and discuss your rule constraints with them.

Bogie
 

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Just becareful with the piston, because using 58CC heads on a 350sbc with flat top piston will get you 11:1 compression. Keep your timming down if you hear pinging. Better use high octain gas. :smash:
 
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