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305 heads on a 350

  #1  
Old 10-26-2009, 09:26 PM
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Default 305 heads on a 350

I know this subject has been touched on quite a few times but i wanna ask again with my specifics. I have a gm performance parts 350 engine part #12499529 with these specs:

8.5:1 Compresion
Bore x Stroke: 4.00 x 3.48
76cc Cylinder Heads
Cam Duration: 222 deg int/ 222 deg ex
Cam Lift: .450 int / .460 ex

I have a set of 305 center bolt heads #14101081 off of a 90 tpi camaro. I want 2 put these heads on this engine. Is this possible with specs of this engine? Will I have to buy/ modify anything to make this work?

Thanks
Jeremy
 
  #2  
Old 10-26-2009, 09:46 PM
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Lets look at the heads that are currently on your engine:
Part # 14034808 - 1.94" Intake valve , 1.50" Exhaust Valve 76cc Combustion Chamber (one reference shows this as 1.84" on the intake valve...)
And then the 305 heads:
Part # 14101081 - 1.84" Intake Valve, 1.50" Exhaust Valve, 58cc Combustion Chamber
The -081 heads can be opened up to fit 1.94" intake valves and with some porting in the combustion chamber to unshroud the valves as well as in the intake/exhaust runners, they will out perform the cylinder heads. The -808 heads will flow better stock for stock (if they do have the 1.94" intake valves) and the -081 heads may increase your compression ratio too much for pump gas. If you were to open up the combustion chamber to somewhere around 65cc, you could keep the compression ratio in a manageable 9.5-10:1. The higher you go, the more precise you will have to be on fuel and spark control.
 
  #3  
Old 10-27-2009, 12:09 AM
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Ok cool thanks. I was worried about the compression ratio being to high. As for flow im not to concerned because its on my lifted k5 on 35s so it never sees rpms higher than 3 grand so flow and top end are not a big concern im just looking to cheaply boost torque and horsepower in the low range.

The heads i have on there are not in the best of shape so i was looking to jump to something else. Do you think i should get the ones i have on there rebuilt or should i have the 305 heads machined?

Thanks
Jeremy
 
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Old 10-27-2009, 06:59 AM
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If you are looking for a higher compression ratio, then you'll get there with the 305 heads, but they will need to be opened up some so you do not go too high. Opening them up to 65cc chambers will net you a 9.7:1 CR with everything else being the same. To really be comfortable, you should get below 9.5:1 which would be around a 67cc or a bit larger combustion chamber. If you were to stick with the 58cc combustion chambers, you would be around 10.5:1 CR which is not pump gas friendly unless you really feed the fuel to it to cool things down.
 
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