compression ratio - The 1947 - Present Chevrolet & GMC Truck Message Board Network

BCOWANWHEELS · 08-12-2019, 05:44 PM

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

franken · 08-12-2019, 07:46 PM

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.

BCOWANWHEELS · 08-12-2019, 08:29 PM

.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

BCOWANWHEELS · 08-13-2019, 01:11 AM

Knowbody

geezer#99 · 08-13-2019, 08:39 AM

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

RustyBucket · 08-13-2019, 08:51 AM

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

will this do it? I thought some engine guy might just KNOW from memory.

**kwmech** · 08-13-2019, 10:17 AM

need cc piston dome. .125 does'nt work unless it is 12.5 cc

BCOWANWHEELS · 08-13-2019, 12:55 PM

I,ll get cc,s on pistons

BCOWANWHEELS · 08-13-2019, 08:49 PM

piston info-
compression distance 1.56
head volume -3.5 cc,s

**HO455** · 08-13-2019, 09:09 PM

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?

BCOWANWHEELS · 08-13-2019, 11:07 PM

10-1 is a 93 oct eng....................76CCS ARE FROM HEADS CC,D

BCOWANWHEELS · 08-21-2019, 03:46 PM

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

geezer#99 · 08-21-2019, 07:03 PM

I still get 9.2 to 1 like I did at the beginning.
What do you get and which calculator did you use?

BCOWANWHEELS · 08-21-2019, 09:49 PM

Off of summits web site

**57taskforce** · 08-21-2019, 10:01 PM

Quote:

Originally Posted by BCOWANWHEELS

Off of summits web site

And here I thought you knew something no one else did.

BCOWANWHEELS · 08-21-2019, 11:52 PM

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.

rpmerf · 08-22-2019, 06:51 AM

Quote:

Originally Posted by geezer#99

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.

geezer#99 · 08-22-2019, 08:28 AM

Quote:

Originally Posted by rpmerf

You are calculating for dished pistons. He has domed.

No I didn’t!
I assumed his numbers were correct but it seems he hasn’t cc’d the heads yet!
I might be closer than he thinks!

BCOWANWHEELS · 08-22-2019, 11:31 AM

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.

BCOWANWHEELS · 08-28-2019, 09:04 PM

Cc,d my chambers, all was 75 to 77 cc,s. So 9.97 up to 10.19 compression with my combo. Perfect

**AussieinNC** · 08-28-2019, 09:19 PM

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....

BCOWANWHEELS · 08-28-2019, 10:43 PM

It will be fine for 93 real gas, no alky. I,AM NOT BUILDING A RACE ENGINE

toolboxchev · 08-29-2019, 09:09 PM

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.

BCOWANWHEELS · 08-29-2019, 10:03 PM

yea, this is the last flat tappet cam 4 me. roller from now on because of the poor quality oils now.

BCOWANWHEELS · 08-30-2019, 08:15 PM

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.

08-12-2019, 05:44 PM	#1
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	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 __________________ I BELIEVE IN JOHN 3:16 Last edited by BCOWANWHEELS; 08-30-2019 at 08:09 PM.

08-12-2019, 07:46 PM	#2
franken Registered User Join Date: Jun 2013 Location: Somewhere Posts: 3,154	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.

08-12-2019, 08:29 PM	#3
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	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 __________________ I BELIEVE IN JOHN 3:16

08-13-2019, 01:11 AM	#4
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	Re: compression ratio Knowbody __________________ I BELIEVE IN JOHN 3:16

08-13-2019, 08:39 AM	#5
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,785	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

08-13-2019, 08:51 AM	#6
RustyBucket Registered User Join Date: Jul 2009 Location: Space Coast, Fl. Posts: 1,055	Re: compression ratio http://www.csgnetwork.com/compcalc.html will this do it? I thought some engine guy might just KNOW from memory. __________________ Dad always said, "Son, WISH IN ONE HAND, and ......." -------------------------------------- -------------------------------------- Current toy trucks: '71 GMC 1500 SUPER CUSTOM short/step, orig. dk. blue, 350/700r, ps,pb, A/C '72 Blazer 2wd, ochre & white, 454, tremecTKO 500 5spd. ps, pb, A/C, tilt Last 10yrs of hobby vehicles, had a FEW more in the 50yrs. before these: '66 Plymouth Belvedere City of Miami cop car clone. '70 Nova 406"sb, 13.5-1, solid roller, Brodix, p.glide/t.brake, back halved, 9" Ford, spool 4.88, cage,ladder bar/coilover, 10.5 tire....... SOLD!! '67 C10 short/step side mount spare -- SOLD!! '72 Jimmy 2wd, 350/350, ps, pb, fun driver, lots of bondo & a shiny red paint job..... SOLD!! '69 Nova 350, 4spd, A/C, ps, p.b, ...SOLD!!

08-13-2019, 10:17 AM	#7
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,724	Re: compression ratio need cc piston dome. .125 does'nt work unless it is 12.5 cc

08-13-2019, 12:55 PM	#8
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	Re: compression ratio I,ll get cc,s on pistons __________________ I BELIEVE IN JOHN 3:16

08-13-2019, 08:49 PM	#9
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	Re: compression ratio piston info- compression distance 1.56 head volume -3.5 cc,s __________________ I BELIEVE IN JOHN 3:16

08-13-2019, 09:09 PM	#10
HO455 Post Whore Join Date: Feb 2016 Location: Portland Oregon Posts: 11,625	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? __________________ Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377

08-13-2019, 11:07 PM	#11
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	Re: compression ratio 10-1 is a 93 oct eng....................76CCS ARE FROM HEADS CC,D __________________ I BELIEVE IN JOHN 3:16

08-21-2019, 03:46 PM	#12
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	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 __________________ I BELIEVE IN JOHN 3:16 Last edited by BCOWANWHEELS; 08-21-2019 at 03:54 PM.

08-21-2019, 07:03 PM	#13
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,785	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?

08-21-2019, 09:49 PM	#14
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	Re: compression ratio Off of summits web site __________________ I BELIEVE IN JOHN 3:16

08-21-2019, 11:52 PM	#16
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	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. __________________ I BELIEVE IN JOHN 3:16



Register or Log In To remove these advertisements.

08-22-2019, 11:31 AM	#19
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	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. __________________ I BELIEVE IN JOHN 3:16

08-28-2019, 09:04 PM	#20
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	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 __________________ I BELIEVE IN JOHN 3:16

08-28-2019, 09:19 PM	#21
AussieinNC Moderator Join Date: Jun 2017 Location: Cherryville, NC Posts: 2,210	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.... __________________ Family and country before all others... 2006 Chevy Silverado (Daily Driver) 2012 Chevy Equinox

08-28-2019, 10:43 PM	#22
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	Re: compression ratio It will be fine for 93 real gas, no alky. I,AM NOT BUILDING A RACE ENGINE __________________ I BELIEVE IN JOHN 3:16

08-29-2019, 09:09 PM	#23
toolboxchev Registered User Join Date: Jul 2015 Location: 2nd left past the stump on a dirt road. Posts: 2,629	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.

08-29-2019, 10:03 PM	#24
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	Re: compression ratio yea, this is the last flat tappet cam 4 me. roller from now on because of the poor quality oils now. __________________ I BELIEVE IN JOHN 3:16

08-30-2019, 08:15 PM	#25
BCOWANWHEELS Registered User Join Date: Nov 2006 Location: KINGSPORT,TN. Posts: 3,035	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. Attached Images __________________ I BELIEVE IN JOHN 3:16 Last edited by BCOWANWHEELS; 08-30-2019 at 08:47 PM.

Register or Log In To remove these advertisements.