Head talk
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Intermediate
Joined: Dec 2022
Posts: 38
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From: Lakeside, ca
Head talk
Hello everyone. I have a ‘40ish UL project and I have two sets of heads, 8.2 & 9.3. I’m having a hard time finding information on these to determine which ones to run. My parts book says 8.2’s are high comp and the 9.3’s are mid. I have another book that says high compression were only made in aluminum and the numbers on the cast iron heads related to combustion chamber volume. This bike is going to be rode, not too hard and I just want reliable power. Thanks! Happy new year! Once my cases get back from the machine shop I’ll start a thread on it.
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Intermediate
Joined: Dec 2022
Posts: 38
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From: Lakeside, ca
I understand. The 8.2’s have two stroke marks and 9.3’s have one.
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Joined: Jun 2015
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From: Canada
What is your concern? Neither is high compression, just one is higher than the other. I would select the higher of the two and run that. To do it properly you should cc the head and piston / valve area to know what you actually have, you might find its not what any literature says it is. I've found that to be the case in a variety of different engines over the years. As a machine shop owner used to tell me, if you dont check, how do you know?
Thread Starter
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Intermediate
Joined: Dec 2022
Posts: 38
Likes: 14
From: Lakeside, ca
What is your concern? Neither is high compression, just one is higher than the other. I would select the higher of the two and run that. To do it properly you should cc the head and piston / valve area to know what you actually have, you might find its not what any literature says it is. I've found that to be the case in a variety of different engines over the years. As a machine shop owner used to tell me, if you dont check, how do you know?
Seasoned HDF Member
Joined: Jun 2015
Posts: 8,055
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From: Canada
I would run the aluminum heads if I had a set sitting there, my 80 came with them which is currently in pieces. One has 1 bar and the other 2 so I'll be cc'ing them and matching the chamber sizes.
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Intermediate
Joined: Dec 2022
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From: Lakeside, ca
both of my sets are cast iron. I’ve been looking for aluminum. The repops are $700ish.
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Thread Starter
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Intermediate
Joined: Dec 2022
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From: Lakeside, ca
that’s really where I’m leaning. Sell the cast and go aluminum. It makes more sense and I’m just finding excuses to be cheap.