1 more head Q?

[tracy]

WELL I ALSO GOT A SHOT AT A PAIR OF 14102193. WITH A FRESH 3 ANGLE JOB ON THEM??????????OR.....OR.ON MY OTHE HEADS (185)WOULD THE 70 CC BE THAT BAD?? ON A 350 IF WE UPPED THE VALVES? WOULDN'T COMPRESSION MAKE UP FOR IT?

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72 CHEYENNE 3/4 TON 4X4...14 bolt full float rear.4.10 gear and 350/350/np205 has a little needs a lot!

[Fast68Chevy]

cam duratin and valve face size also affects compression ratio directly, reasons why include longer duration holding intake valves open longer so more air gets sucke dinto the cylinders, and larger valve head diameters beinf self explanatory in that being that they are larger means more air can get past them in same amount of time as a can with small valve. The intenal combustion engine is just a big air pump, more air that you can get or pack into the cylinders AND also get out of it then the better stronger and more efficient it wil run, getting valves opened up sooner(depends on cam grind and cam timing) after the TDC of the exhaust stroke and longer you can keep them open beofre TDC of the compression stroke then the stronger it will kaboom and push down on piston head. but if you cant get that burned fuel misture out just as efficiently then you will end up with contaminated intake air fuel mixture charge which is bad thing. thats why there are 1.6" exhaust valves. sometimes larger in serious drag racing applications.

intake runner size volumes are different in different castings of heads too, unchangeable unless you start doing some careful porting to enlarge them so that they will allow more volume air flow, do not smooth the walls of the runner, only smooth exhaust ones. port matching intake runners in the heads and in the intake would be awesome if you enlarge valves also.

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Randy- Lincoln, IL
randy@ccaonline.com 2177353230
*many GM parts bought, traded, or sold -am parting out: '81 Cutlass Supreme Brougham

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[This message has been edited by Fast68Chevy (edited May 11, 2002).]

[tom hand]

The last heads you listed are 87 up 350 and I have no specs on them tho I wouldn't think I would want them. That is also the year they started with center bolts on the valve covers. The first ones you listed you said were small valves so I wouldn't use them on a 350 unless you got the valves to a least 1.94's. Cam duration and valve size has no effect on compression ratio. The only things that effect compression ratio are deck height,bore size,compressed head gasket thickness,chamber size,and piston.[dish,dome, or flattop]etc. Cam duration and valve size can effect cylinder pressurebut that is a different animal.

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72 GMC Sierra SWB almost finished---- 84 Softail
Olive Branch MS

[bigjimzlll]

Tom you had me worried for a moment..cam duration plays a major part in compression..a static compression of 10 to 1 could very easily have a dynamic compression ratio of 8 to 1...the longer the duration will allow pressure to escape durring overlap. there is a very could calcualor for figuring out dynamic comp. ratio..if anyone wants it i'll email it to you

[69 longhorn]

Yup, its wild stuff! Static comp ratio is not affected by cam dur & overlap......but pressure/dynamic ratio is affected.....69

[tom hand]

bigjimzlll I will agree with what you just said but dynamic compression ratio is a relitively new term. It is just another way of saying cylinder pressure.The static compression ratio is what you measure on an engine stand with a burette and graduated cylinder. It's a simple mathematical comparison between the volume above the piston at the bottom and top of its travel. So a 10 to 1 motor will still be a 10 to 1 motor regardless of what cam you put in there. Dynamic compression ratio is what really counts in a engine because it determines the actual cylinder pressure. I am an old timer so I still use the old terms. I guess all I was saying was the actual compression ratio is set in stone when you build the motor and cannot be changed unless you change parts. The dynamic compression ratio or cylinder pressure is determined by a number of things and is very hard to measure with any chart[tho I would like to see it, never too old to learn something new]The only real way to measure cylinder pressure or dynamic compression is to put a compression guage in the cylinder after you build the motor. Not trying to start any thing, just an old timer that needs to learn all these newfangled terms.


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72 GMC Sierra SWB almost finished---- 84 Softail
Olive Branch MS