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Old 08-12-2019, 05:44 PM   #1
BCOWANWHEELS
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compression ratio MY ENGINE PIC,S.

anybody here real good at figuring out compression ratio on a 350 sbc........ I think I,am real close to race gas on my engine build............
thanks
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Old 08-12-2019, 07:46 PM   #2
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Re: compression ratio

First you need to figure out combustion chamber size, piston dish/dome, gasket thickness, overbore and anything I'm forgetting. No one can tell you the CR with no info.
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Old 08-12-2019, 08:29 PM   #3
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Re: compression ratio

.030 over bore, .125 dome pistons, .015 or .041 head gasket, I HAVE BOTH , 76 cc head, 0 decked............. I,AM TRYING TO GET HONEST 10-1 COMPRESSION
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Old 08-13-2019, 01:11 AM   #4
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Re: compression ratio

Knowbody
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Old 08-13-2019, 08:39 AM   #5
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Re: compression ratio

Oh no!
My calcs come out to 6.2 to 1.
I used this calculator.
Punch your info in and see what you get.
http://www.wallaceracing.com/cr_test2.php
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Old 08-13-2019, 08:51 AM   #6
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Re: compression ratio

http://www.csgnetwork.com/compcalc.html

will this do it? I thought some engine guy might just KNOW from memory.
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Old 08-13-2019, 10:17 AM   #7
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Re: compression ratio

need cc piston dome. .125 does'nt work unless it is 12.5 cc
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Old 08-13-2019, 12:55 PM   #8
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Re: compression ratio

I,ll get cc,s on pistons
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Old 08-13-2019, 08:49 PM   #9
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Re: compression ratio

piston info-
compression distance 1.56
head volume -3.5 cc,s
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Old 08-13-2019, 09:09 PM   #10
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Re: compression ratio

Is the CC number you list an average from measurements from the assembled heads or from a chart? I've found that some Chevy heads are not very close to the advertised CC's.
Are you shooting for 10:1 so you can run pump regular?
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Old 08-13-2019, 11:07 PM   #11
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Re: compression ratio

10-1 is a 93 oct eng....................76CCS ARE FROM HEADS CC,D
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Old 08-21-2019, 03:46 PM   #12
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Re: compression ratio

OK, THOUGHT THERE WAS SOME REAL MECHANICS HERE BUT GUESS I WAS WRONG.

THOUGHT THIS MIGHT HELP SOMEONE..................

Bore: (diameter) in. - 4.030
Stroke: in. - 3.48
Cylinder Head Volume: cc in. - 76CC
Effective Dome Volume: -3.5 (.125 DOME)
Use (-) for Dome . cc in.
Deck Clearance: in. -0
Compressed Gasket Thickness: in. -.039
Number of Cylinders: 8 - V8
Compression Ratio : 10.01 : 1
Total Displacement (in.3) : 355.12
Total Displacement cc's : 5821.64
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Old 08-21-2019, 07:03 PM   #13
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Re: compression ratio

I still get 9.2 to 1 like I did at the beginning.
What do you get and which calculator did you use?
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Old 08-21-2019, 09:49 PM   #14
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Re: compression ratio

Off of summits web site
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Old 08-21-2019, 10:01 PM   #15
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Re: compression ratio

Quote:
Originally Posted by BCOWANWHEELS View Post
Off of summits web site
And here I thought you knew something no one else did.
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Old 08-21-2019, 11:52 PM   #16
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Re: compression ratio

I used several web sites to calculate. All came to 10.1 to 1....
Perfect. I,am going to cc my intake and exh ports along with combustion chambers asap. The porting i did should help flow out some.. gotta order some .039 felpro h/gaskets tomorrow. Will have pic,s soon 4 ya,ll.
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Old 08-22-2019, 06:51 AM   #17
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Re: compression ratio

Quote:
Originally Posted by geezer#99 View Post
I still get 9.2 to 1 like I did at the beginning.
What do you get and which calculator did you use?
You are calculating for dished pistons. He has domed.
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Old 08-22-2019, 08:28 AM   #18
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Re: compression ratio

Quote:
Originally Posted by rpmerf View Post
You are calculating for dished pistons. He has domed.
No I didnít!
I assumed his numbers were correct but it seems he hasnít ccíd the heads yet!
I might be closer than he thinks!
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Old 08-22-2019, 11:31 AM   #19
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Re: compression ratio

guys my heads are 441,s and there 76 cc,s. there cut .010 but I unshrouded the 2.02 intake valves slightly to increase flow.
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Old 08-28-2019, 09:04 PM   #20
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Re: compression ratio

Cc,d my chambers, all was 75 to 77 cc,s. So 9.97 up to 10.19 compression with my combo. Perfect
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Old 08-28-2019, 09:19 PM   #21
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Re: compression ratio

A 2 cc variance in chamber volume is just ok for street use...

I like to keep them below 0.5....

Your compression ratio is around 10 to 1...too high for the gruel served up at most gas stations....try premium and add octane booster....

and watch the timing lead....

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Old 08-28-2019, 10:43 PM   #22
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Re: compression ratio

It will be fine for 93 real gas, no alky. I,AM NOT BUILDING A RACE ENGINE
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Old 08-29-2019, 09:09 PM   #23
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Re: compression ratio

Hey BC,

I like what your doing with your build, this is going to help you tremendously.

Check any info you may need here:

https://www.crankshaftcoalition.com/...ategory:Engine

I have flat tops in my stock engine with 76 cc heads. I can dial so much advance into it, most would call me ridiculous. With the domed pistons you will be into different territory.

The one thing that concerns me is you have as much as 2 cc of differences in each chamber. My instinct does not like that with a higher compression engine. Keep in my your dynamic compression is what will dictate true running compression with the cam selection you make.

My next build I want a bottom to mid range torque monster. With that in mind for a truck engine 2 topics came up with fellow engine buddies. Volumetric Efficiency, and Camshaft effective duration. A roller cam allows for more effective duration by design with less wear and tear.

I want the most out of the motor without all the hp hype. That just tears up a motor. Will like to see how your build turns out.
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Old 08-29-2019, 10:03 PM   #24
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Re: compression ratio

yea, this is the last flat tappet cam 4 me. roller from now on because of the poor quality oils now.
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Old 08-30-2019, 08:15 PM   #25
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Re: compression ratio

Heres some short block pic,s. ALL ARP FASTENERS , KING ROD N MAIN BEARINGS (THE BEST GOING NOW MADE IN ISREAL ) NEW FUEL PUMP, NEW MOTOR MOUNTS , MEW 8 INCH BALANCER NEW CLOYES DOUBLE ROLLER CHAIN N GEARSl aong with a howards reproduction lt1 350/370hp cam . SHOULD HAVE THE PAN ON IT BY TOMARROW EVENNING.
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