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Discussion Starter · #1 ·
If i pnp my head, do +1 valves and a 272 camshaft will i have to run a higher type of gas? I was just wondering because im not raising the compression or boosting.
WIll give rep.
 

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I wouldn't go to 1mm over on a stock compression motor (unless its for boost).

Higher gas then what? then 87? probably. that cam you can probably get away with 89. I run 91 octane on my high compression cam'd motor.
 

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Discussion Starter · #3 ·
I head that the +1 valves would help to create more power with the cam.
 

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the problem is the bore is only so big and the valves are pretty well shrouded from the get-go. You only make that problem worse when you go with bigger valves. Here is another thing, few people have EVER maxed out a honda head as far as theortical flow . . .

A quick formula from "back in the day".

Take the square area of the valve which is pi * radius^2

So for a typical non-vtec intake valve it measures 1.15" and you have two so 2.3" of total valve area.

3.141 x 1.15 = ~3.61 square inches

Multiply this by 100 and you get 361 cfm. In a perfect world where the port is maximized and professionally ported, the limit to cfm the head is capable of after overcoming the port is 361cfm based on simply the amount of valve area. Has anyone done this? Probably not, I haven't even come close. But mathematically speaking it is possible.

Sorry to go off on a tangent . . . :D
 

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the problem is the bore is only so big and the valves are pretty well shrouded from the get-go. You only make that problem worse when you go with bigger valves.
While this should be your creed if you have a SOHC VTEC head, the non vtec valves are a little closer together, and smaller. They don't really have a shrouding issue in stock form. (hence why people feel like they make better power with mods to nonvtec)
If he went 1mm over, it would be kinda like something equal to stock VTEC valves. Its just not worth the effort if your going to run stock compression. Im running a far more built motor, and my valves are still stock. When I do replace the valves, I will be maintaining the factory size valve for the intake valves. Since the exhaust valves are closer together (therefore farther from the cylinder walls) I may go slightly larger with those. (D-Series exhaust doesn't have the best flow anyway)
 

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Discussion Starter · #6 ·
its alright we all have are cosecants sometimes. Damn that was gay.
 

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I now run a 75.5mm bore and have +0,5mm exhaust valves. Should not make any extra issues with it atleast.
I would like to get a 78mm bore, as I think that would really get a lot out of this setup.
But there's a limited amount of money to spend at a given time, so this is what I ended up with.
 

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the problem is the bore is only so big and the valves are pretty well shrouded from the get-go. You only make that problem worse when you go with bigger valves. Here is another thing, few people have EVER maxed out a honda head as far as theortical flow . . .

A quick formula from "back in the day".

Take the square area of the valve which is pi * radius^2

So for a typical non-vtec intake valve it measures 1.15" and you have two so 2.3" of total valve area.

3.141 x 1.15 = ~3.61 square inches

Multiply this by 100 and you get 361 cfm. In a perfect world where the port is maximized and professionally ported, the limit to cfm the head is capable of after overcoming the port is 361cfm based on simply the amount of valve area. Has anyone done this? Probably not, I haven't even come close. But mathematically speaking it is possible.

Sorry to go off on a tangent . . . :D
So basically... It's a waste of time!
 

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While this should be your creed if you have a SOHC VTEC head, the non vtec valves are a little closer together, and smaller.
Maybe because I am used to inline sbf heads but my pm9 valves were all up on the side of the combustion chamber. I spent probably 10 minutes just in each chamber, with that and valve seat jump.
 

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So basically... It's a waste of time!
Unless you sleeve, NA D series don't really need bigger valves.

3mm bigger sleeves and Bisi "I think" went .5mm intake/1.0mm exhaust OS valves.

"Shrouded" in secretcy!
 
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