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Old 01-13-2003, 01:35 PM   #1
madmike
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Big block Chevy valve sizes?

I'm in the process of thinking about rebuilding a 1972 402 rat engine for my truck. The motor I have ran ok when pulled, smoked and leaked oil, unknown mileage. I'd like to rebuild it, but I haven't torn it down yet. I'm looking to build an engine with around 9:1 compression, and to make a lot of torque at low rpm. Except for cam, intake, Qjet, and maybe headers, I'd like to stay pretty stock. My cylinder head casting number is 6272292, and the Mor-Tec website lists this as an open chamber oval port head. Does anyone know what the intake and exhaust valve sizes are? head cc's? Would this be a good head for the kind of engine I want to build? Thanks for your opinions.
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Old 01-13-2003, 03:42 PM
Posted in reply to madmike's post "Big block Chevy valve sizes?"
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Mr.Chevy4x4
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Re: Big block Chevy valve sizes?

Are they 2.19 and 1.88's, or are they the small valve heads?



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Old 01-13-2003, 06:30 PM
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Re: Big block Chevy valve sizes?

They are probably 2.06/1.72's. They can be enlarged to 2.19/1.88's. I would spend the $ to go bigger.
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Old 01-13-2003, 08:37 PM   #4
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Re: Big block Chevy valve sizes?

Bulding an engine for low RPM torque you want small valves and intake runners because it will build velocity which will make for the good low RPM torque he is looking to achieve.
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Old 01-14-2003, 11:54 AM   #5
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Re: Big block Chevy valve sizes?

I don't know if they are small valve heads or not, that's why I posted this, in hopes someone might know. I really don't want to disassemble the engine until I figure out if I'm gonna use it or not. From what I've been able to read, they're probably 2.06/1.72's, which as 4X4HIGH correctly said, would be better for building bottom end torque.
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Old 01-14-2003, 01:18 PM   #6
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Re: Big block Chevy valve sizes?

I have seen a test in one of the hot rod magazines that proved the oposite. They took a 454 with a very mild cam and small valve heads and dynoed it. They then swapped the heads for a stock set of big valve heads with the same combustion chamber and cam and the motor made quite a bit more low end torque with the big valves. I think that with the low lift the bigger valves allow so much more flow that it outweighs the velocity improvement of smaller valves.



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Old 01-14-2003, 01:30 PM   #7
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Re: Big block Chevy valve sizes?

*I think* the 292 heads are small valve heads with the small valves. I'll look tonight and see if tat casting is listed in the books I have.

IMHO as for the magazine test, if the camshaft was changed I don't think that's a fair comparison with respect to head flow characteristics.
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Old 01-14-2003, 01:57 PM   #8
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Re: Big block Chevy valve sizes?

nvrenuf, thanks for checking.
Mr.Chevy4x4, I hadn't thought of it that way, that's a possibility I suppose.
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Old 01-14-2003, 03:15 PM
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Re: Big block Chevy valve sizes?

Okay here is the formula for figuring maximum valve sizes. .52 * Bore in inches for the intake, and .80 * Intake valve in inches for exhaust. [img]/forums/images/graemlins/usaflag.gif[/img] [img]/forums/images/graemlins/burb.gif[/img] [img]/forums/images/graemlins/usaflag.gif[/img]
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Old 01-14-2003, 04:53 PM   #10
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Re: Big block Chevy valve sizes?

Where is this formula from? Seems pretty accurate for the engines I'm running too. I run a 427 with small port, small valve heads, GM marine cam (.500 lift, 218I & 228E @ .050)and have plenty of low end power.
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