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Old 01-26-2008, 07:41 PM
chevy350_Camd's Avatar
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Compression Ratio ?

Does anybody know this compression ratio?.

Vortec Heads with 62cc chamber with 2.00 and 1.55 valves and 210 cc intake runners, 78 cc exhaust. This is on a 350 with a stock bottom.

Other Combinations Include a edelbrock Rpm manifold, a 282 and 292 cam with 4.66 and 4.88 lifts

Thank you for any comments

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Old 01-26-2008, 11:41 PM
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Hi,
Click on the link below.
Just on top of the car brands is a
compression calculator link.
Rich

http://www.campbellenterprises.com/keith.htm
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Old 01-27-2008, 12:24 AM
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Quote:
Originally Posted by chevy350_Camd
Does anybody know this compression ratio?.

Vortec Heads with 62cc chamber with 2.00 and 1.55 valves and 210 cc intake runners, 78 cc exhaust. This is on a 350 with a stock bottom.

Other Combinations Include a edelbrock Rpm manifold, a 282 and 292 cam with 4.66 and 4.88 lifts

Thank you for any comments
Here is a useful comment

A 350 with a "stock" bottom end can mean anything inasfar as actual volumes are concerned.


You need to know the deck height, compression height, compressed gasket thickness, piston dome,(or dish), actual bore and stroke. .030 overbore is alot when it comes to calculating CR.

Don't assume that your deck height is zero, many new replacement pistons have less compression height than stock to compensate for a decked block. Don't assume that a piston has no dish...even valve reliefs in pistons can drop static CR a good amount, rendering your calculations useless.

Many stock motors deviate significantly from the advertised specs.

CC your heads, measure your current deck height and CC your piston dish or dome. You can make your own CC'ing equipment with a 100 cc burette from your local scientific supply and some clay and a 4x4" piece of plexiglass. Use some alchohol with food coloring in it, or water with a little bit of dish soap ...with those materials the surface tension is less and it is easier to get an accurate measurement.

Valve size, intake runners and intake manifolds have no bearing on static CR. Cam timing/ duration has an effect on dynamic CR, which is sometimes a better judge of how a motor will perform.

Here is a link to a whole page of calculators.
http://www.wallaceracing.com/Calculators.htm

Those should come in real handy in your listed occupation as an engine builder.

Have fun,
Mikey
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Old 01-27-2008, 12:27 AM
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Quote:
Originally Posted by chevy350_Camd
Does anybody know this compression ratio?.

Vortec Heads with 62cc chamber with 2.00 and 1.55 valves and 210 cc intake runners, 78 cc exhaust. This is on a 350 with a stock bottom.

Other Combinations Include a edelbrock Rpm manifold, a 282 and 292 cam with 4.66 and 4.88 lifts

Thank you for any comments
Please ask these questions in this forum, not the engines forum. Once you garner some knowledge and ask questions that aren't vague, move on to the engines. I will copy my reply to one of your posts that ended up in the dump:

re: Whats is this motor best at ?

--------------------------------------------------------------------------------

This one is destined to land in the dump if A. The kid doesn't figure out what he is doing wrong. Stretching the truth isn't acceptable.
B. Your questions are too vague. This is a total waste of everyone's time. Use the search engine for what if questions. We have very knowledgeable people in the engine forums that take their time to address questions, assuming the person asking them needs help. Don't run them off wasting their time, we need them here. Youngsters are welcome here, use some common sense, use the search engines first, ask questions second, anything you garner from using the search engine info will make you that more knowledgeable and you will also learn how to ask a question that can be answered properly.
Dan

I've taken your defense twice with others on this site because of your age, pay attention, listen, listen and then listen more. Jon is also starting a site called "youngrodders" , you may be one of the oldtimers on there when it rolls.
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Old 01-27-2008, 02:18 AM
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Here´s a good learning page and it includes the math to do it yourself.
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Old 01-27-2008, 02:26 AM
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Quote:
Originally Posted by chevy350_Camd
Does anybody know this compression ratio?.

Vortec Heads with 62cc chamber with 2.00 and 1.55 valves and 210 cc intake runners, 78 cc exhaust. This is on a 350 with a stock bottom.

Other Combinations Include a edelbrock Rpm manifold, a 282 and 292 cam with 4.66 and 4.88 lifts

Thank you for any comments
i have noticed your posts recently, so i will waste a few minutes of my time to answer your question:
vortec heads are worth 2 extra points, the 2.00 and 1.55 valves are worth 1/2 point. then you have to square the 210 cc intake runners (210 x 210=44100) that will give you 6.11341 points. then you have to figure the square root of the 78cc exhaust ports (78*78=0.6084) that minuses you 3.1418 of a point. assuming zero deck that gives you 19.62341 static compression. now figuring your 282-292 cam, if that is advertized duration that will drop your dynamic compression to 5.443625-1. if the cam is 282-292 at .050 lift then your compression will drop to 3.11791. this will kill your bottom end torque but you will make great horspower at 18,000 RPM with no detonation problems. of course if you turbo it at 60LBS boost the 3.11 compression won't be a problem. NOW:

do like dinger said, you can read 100s of pages on this sight and learn something, there are lots of knowledgeable people here. we all will wecome a young gearhead, but if you keep asking silly questions with vague information eventually the troll hunters will come out of the woodwork. the choice is yours, either read and learn and become one of us gearheads or get trolled out.
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Old 01-27-2008, 07:08 AM
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i think im over compressed !
who wants to help me ???????
i was playing with this
http://www.campbellenterprises.com/R...o%20calculator
and my compression its like 15.x:1
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Old 01-27-2008, 07:31 AM
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Thanks, Im sorry

Im sorry im so vague about everything but dont know what my deck height is on the block. I know its a 1980 block with 8 to 1 cr stock. The bore is 4.000 and stroke is 3.48. With hypreutectic pistons that are stock with valve reliefs. The Vortec Heads are 62cc chambers while my smog heads are 76cc could you give me a ball park figure, thank you.
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Old 01-27-2008, 07:44 AM
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You can calculate here... http://www.turbofast.com.au/Tfcomp.html
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Old 01-28-2008, 12:27 PM
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Hi,
Stock deck height for chevy. big & small is 0.25"
but this can vary, so you need to measure.

search button, "How to measure deck height"
then down to "Measuring piston below deck"

I only know the thickness of the Fel-Pro sbc
composite gaskets of .039 & .041 & have 4.166
bores.
Hope this helps some,
Rich
PS I think you need to read more, look around the net
for places like carcraft, that have some dicscent articals
about autos
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Old 01-28-2008, 07:10 PM
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I did a bit of reverse engineering and some quick internet research to arrive at some kind of answer for you. You can take what I have here and modify it if anything is not accurate.

Here are the basic numbers you need to know to arrive at your static compression ratio:

* Cylinder head volume (yours = ?)

* Piston head volume (yours = ?) Note: This is the size of the dish on your piston or in the case of flat-tops, valve reliefs

* Head gasket compressed thickness (yours = ?)

* Head gasket Bore (yours = ?) Note: This isn't critical for this example, but you need to know it if you want an exact number.

* Cylinder bore diameter (yours = 4.000")

* Deck clearance (yours = .025") Note: This is assuming your block has never been machined (decked) in the aftermarket and that your block doesn't vary too much.

* Stroke (yours = 3.480")

Now to fill in the blanks for your stock 1980 SBC. I don't know anything specific for this engine, so I went to Mortec and scanned through the 1980's heads, and most of them seem to be 76 CCs. Piston head volume is another question mark for me, so I assumed flat-tops with 7 CC valve reliefs, which is a number I've seen on a few aftermarket pistons and while it's most likely wrong, it will get us close in this example. Head gasket is, again, unknown, so we'll use the common aftermaket size of .039". For gasket bore, I used a size of 4.130" which is the size of the head gasket I'll be using on my current build. So now the numbers look like this (bold numbers are my estimated figures):

* Cylinder head volume: 76 CC
* Piston head volume: 7 CC
* Head gasket compressed thickness: .039
* Head gasket Bore: 4.130"
* Cylinder bore diameter: 4.000"
* Deck clearance: .025"
* Stroke: 3.48"

I plugged all of this into this calculator, which is only one of many spread over the internet: http://www.kb-silvolite.com/calc.php?action=comp

With those numbers, I got a static compression ratio of 8.413 to one. If the actual compression of your engine is 8.0 to one as you think it is, then perhaps the dish on the pistons is greater, or the head gasket used in the factory is thicker... who knows? However, we can use this number for our example.

There are only three numbers (maybe just one) there that would change if you swapped to vortec heads: Cylinder head volume and the head gasket thickness and bore. Assuming you used the same head gasket so those numbers don't change, and changed only the heads, just change the 76 to 62. Now you have a compression ratio of 9.668 to one. You gained more than two points of compression.

Now, if you can find the exact numbers to replace my estimates above, you can find the exact change in compression ratio that you will see by using the vortec heads. Maybe some of the folks here, who have common knowledge of this year SBC 350, will contribute them.
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Old 01-28-2008, 07:21 PM
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Hi cool post Arcuden
i used your step by step example to calculate my 350 TPI engine compression.
i came up with this :
just what i was after !!!
thanx a lot
im assuming that the pistons have 7 cc eyebrows but not sure

Is there any instrument to measure or calculate compression of the engine
with the engine running ?
like a dyno or something but for compression ?
thanx !

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Old 01-28-2008, 10:14 PM
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Calderone, you're welcome.

I looked at your numbers in your screenshot, and I noticed you input your cylinder bore at 4.137". Is that a typo or did you somehow modify your block to take that kind of bore size? I was under the impression that 60 thousandths over-bore is cutting it close for a 350 SBC (which would be 4.060 for that field).
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Old 01-28-2008, 10:19 PM
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argggggggg LOL

it was 4.03056"
i forgot the numbers !!!!!
will try again with that
thanx ! heehe
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Old 01-28-2008, 10:22 PM
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Now its all good !
better than the 9.5:1 stock compression !!!
what you think ?

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