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Author Topic:   305 or 350 Open Chamber Heads?
Whodat
Dirt Roller

Total posts: 17
posted May 04, 2004 09:42 PM  
Which would you choose, 305 or 350 open chamber heads, in a class limited to these type heads and why?

ruggs66
Dirt Maniac

Total posts: 193
posted May 05, 2004 11:56 AM  
what does the rest of your engine consist of?
pistons, camshaft, intake.....etc

& what RPM are you trying to turn it?



Raz_900
Dirt Forum Champ
Total posts: 635
posted May 05, 2004 12:06 PM  
If you can change valve sizes, run the 601 or 416 305 head with 1.94"/1.6" valves. With a .010" decking, they'll be around 50-52cc.

If you can't change valves, but can angle mill, angle cut the 76cc heads .125". That will get them down to 64cc or so.

The 305 heads will work better on lower rpm applications needing more bottom end power. With flattops, a 350 will be over 11:1 with 50ish cc heads.

As a general rule, each point of compression is worth 4% power EVERYWHERE. Each cc change will change the CR approx. .1 So you need a 10cc change to raise/lower CR 1 point.

Bigger valve heads will help high RPM power, but generally not help low-mid power nearly as much. In extreme cases, going to very large valves/ports with low CR will make the motor lose significant low-mid power and throttle response.

Whodat
Dirt Roller

Total posts: 17
posted May 05, 2004 09:42 PM  
Forged pistons - Speed Pro, 40 over, .450 lift cam by rule, 4 bbl Q-jet by rule, stock cast iron intake. cast iron exhaust.

Basically stock. We cannot angle mill the heads and the maximum valve size is 1.94/1.6.

So, all things equal, the 350 heads will benefit you more on larger tracks?

My engine builder says the 350 heads just flow better and dyno'd more hp vs. the 305 heads. I was just curious and wanted different opinions on the subject. Thanks fellas.

Raz_900
Dirt Forum Champ
Total posts: 635
posted May 06, 2004 12:28 PM  
If limited to 1.94/1.6 and stock intake & exhaust, you're not going to rev much past 6000 anyway. The .450" cam doesn't help matters either.

I'd go for as much compression as I could get. The difference between a 76cc head and 52 cc head will be over 2 full CR points and about 10% power increase across the board. Cam and gear it for 5800 rpm max and get ready to **** some doors off coming outta the turns.

    

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