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11-21-2002, 03:19 PM
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compression and torque question
If a set of 305 High Output heads (55CC chamber 1.84/1.50 valves) were put on a 350, how much compression would you estimate it to have? The engine is a 1980 350 4 bolt main. My chilton book says it comes factory with 8.2 compression. Also, how much HP and TQ would this add? Thanks for any help!!
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11-21-2002, 04:26 PM
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You'll have nice low end torque but no high end rev.It'll be around 9.5:1
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11-21-2002, 06:32 PM
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I also found a set of 991 heads that came off of a 307 with 1.72/1.50 valves and 75cc chambers. Would this raise my torque rating a good bit, compared to 1.94/1.50 valves? Or are these valves too small for a 350??
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11-21-2002, 07:05 PM
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The smaller the valves, the more low RPM power is made due to higher volosity. Where the 991 would be lacking compared to the 305 heads is the compression ratio, the 75cc chamber was not very effiecent, and a aftermarket head gasket is thicker, so there would be a slight loss in compression ratio and the quench would be opened up more which makes it even less effiecent. The 305 heads with there smaller 60cc chambers will make real nice low end power and the added compression ratio will help even more, but if your running a stock cam, it`ll likely only run on 93 octane fuel. We`ve ran 305 heads on stock 350`s with factory dish top pistons with a real small low RPM power cam, and they`ll come out of the hole screaming, but dead on top end, so if Low RPM power is your goal and seems to be, the 305 head is the way to go.
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11-21-2002, 07:12 PM
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If I used the 307 heads and used a .015 head gasket, would that help on the compression end of things? I have a Comp. Cams Xtreme 4x4 cam with 250/258 duration, 206/214 @ 50, .432/.453 lift and 111 deg. lobe separation. I am looking for a set of heads to give me good low end power in the 1000-3000 range only. That is where almost all of my driving takes place. Thanks!
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11-22-2002, 04:26 AM
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OK, which would be better, 1.72 valves or 1.84 valves on a 350?
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11-22-2002, 04:31 AM
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Yes, it would be okay with the 307 heads and a thin gasket, but not as good as the 305 heads would due to compression ratio and combustion effientcy, which both play a role in torque output as well. it would run fine with the 307 heads and your cam on 87 octane fuel, which would be the only benefit over having to run 93 octane fuel with the 305 heads.
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11-22-2002, 04:40 AM
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I already have the 991 heads and would have to buy the 305 heads. So I guess I will use the 991's. Thanks for the help.!
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11-22-2002, 09:29 AM
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Another question. What would be a good cam grind to use with the 991 heads and a .015 head gasket. I also have a 278 duration cam with 222 @ 50 and a lift of .467 and a 110 lobe spearation. Would this cam be ok??
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