1971 sbc400 head casting mark - Page 2 - Chevelle Tech
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post #16 of 25 (permalink) Old Jul 23rd, 20, 3:16 PM Thread Starter
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What was meant with chosing 2 valve per piston and not the 4 valve type? You assume the 4 valve has more CC.

If i search pistons at summit i can chose almost any CC even minus (dome).

Who has a good calculator do determine CR? With input parameters like gasket thickness, stroke, combustion chamber CC etc...
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post #17 of 25 (permalink) Old Jul 23rd, 20, 3:17 PM Thread Starter
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and YES i agree i need to talk to an engine builder, but i want me to ask good questions to that guy
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post #18 of 25 (permalink) Old Jul 23rd, 20, 6:07 PM
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Re: 1971 sbc400 head casting mark

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Originally Posted by Bart Fransen View Post
What was meant with chosing 2 valve per piston and not the 4 valve type? You assume the 4 valve has more CC.

If i search pistons at summit i can chose almost any CC even minus (dome).

Who has a good calculator do determine CR? With input parameters like gasket thickness, stroke, combustion chamber CC etc...
I find all the calculators at Wallace Racing to be quite good.
Here's the Compression Ratio calculator:
Compression Ratio Calculator - Wallace Racing

Wallace Racing - Automotive Calculators
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post #19 of 25 (permalink) Old Jul 23rd, 20, 8:55 PM
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Re: 1971 sbc400 head casting mark

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Originally Posted by 1975TypeS-3 View Post
Back to your first question, I agree with those that say pull the valve cover to determine the actual casting number. However, I have had 4 sets of 493 castings over the last 25 years and all have had that same casting mark. I just pulled apart a 400 to rebuild three months ago and is also had one 493 head on it, with the same casting mark.

If they are 493 castings, they are good stock heads - heavy castings and about the best flowing heads of the early 1970's.

This guy knows............^^493

While were at it, Have You "Ever" Seen a Factory 5.560 400 Rod that weren't Numbered????
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Machined GM production heads
Oil pan modifications
Red Line Camshaft
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post #20 of 25 (permalink) Old Jul 24th, 20, 9:03 AM
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Re: 1971 sbc400 head casting mark

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This guy knows............^^493

While were at it, Have You "Ever" Seen a Factory 5.560 400 Rod that weren't Numbered????
Every standard bore 400 I have pulled apart had the rods marked! The fist one I did that still had the factory head gasket, I thought that was odd. After that it was "I have seen this before".
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post #21 of 25 (permalink) Old Jul 24th, 20, 10:15 AM
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Re: 1971 sbc400 head casting mark

If that engine is in solid condition as is I'd go with a cam change. Something like an Edelbrock Performer Plus that is designed for low compression stock engines. Increased lift and valve timing to improve mid range power with that type cam. A set of 1.6:1 rockers work well with that too if the head slots will clear. 300 Hp with a 400 small block seems like an easy task.
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post #22 of 25 (permalink) Old Jul 25th, 20, 2:32 AM Thread Starter
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If that engine is in solid condition as is I'd go with a cam change. Something like an Edelbrock Performer Plus that is designed for low compression stock engines. Increased lift and valve timing to improve mid range power with that type cam. A set of 1.6:1 rockers work well with that too if the head slots will clear. 300 Hp with a 400 small block seems like an easy task.
What is the stock rockers ratio? And why would it improve something
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post #23 of 25 (permalink) Old Jul 30th, 20, 7:24 PM
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Re: 1971 sbc400 head casting mark

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What is the stock rockers ratio? And why would it improve something
The stock ratio is on the small block rocker arm is 1.5 : 1. Bumping those up to a 1.6 : 1 would give a slight increase in lift and duration in the conservative camshaft, pretty much maximize the flow capable in those heads I'm thinking.
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post #24 of 25 (permalink) Old Aug 1st, 20, 12:19 AM
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Re: 1971 sbc400 head casting mark

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Originally Posted by Bart Fransen View Post
What was meant with chosing 2 valve per piston and not the 4 valve type? You assume the 4 valve has more CC.

If i search pistons at summit i can chose almost any CC even minus (dome).

Who has a good calculator do determine CR? With input parameters like gasket thickness, stroke, combustion chamber CC etc...
A piston that has 4 valve notches is a more common piston so there are more of them available for sale.They are usually the least expensive of a type.
But a piston with only 2 valve notches is the less common available piston and usually a little more money.
The reason a 2 valve piston is better is they don't have 2 valve notches sitting on their piston top that serve no purpose.
A piston only needs 2 valve notches to clear the valves,the other 2 notches are useless and only provide an area for extra carbon to buildup.They don't hurt anything but if compression ratio being higher is important to you because of the fuel you use then you only would want a piston that has 2 valve notches per piston.
Pistons with 2 valve notches have less CC area than a 4 notch piston.If you compute compression ratio the higher the CC the lower the compression will be.That is why a domed piston has a negative value for CC.

John
71 El Camino SS
406 SBC M21 3.31 12 bolt
"Quality is always remembered,long after the price is forgotten"
"I would rather have questions I can't answer than have answers I can't question" :R.Feynman
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post #25 of 25 (permalink) Old Aug 6th, 20, 1:12 PM Thread Starter
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Quote:
Originally Posted by tom3 View Post
Quote:
Originally Posted by Bart Fransen View Post
What is the stock rockers ratio? And why would it improve something
The stock ratio is on the small block rocker arm is 1.5 : 1. Bumping those up to a 1.6 : 1 would give a slight increase in lift and duration in the conservative camshaft, pretty much maximize the flow capable in those heads I'm thinking.
So it could be an alternative for a cam swap?
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