compression ratio again

[benno440]

having trouble understanding how to work this out.
the comp ration calculator asks for stroke is the the stroke of the crank?

so i have 80cc stealth heads
.040 cometic gasket
0 deck height
26.7 valve reliefed kb pistons
4.25 stroker crank
7.1 rod
.30 bore so 4.250"

what would my compression be at?

 

[RustyRatRod]

Your bore is probably 4.350. That would be .030 over 440.

Using that and all the other variables I get 9.836. Stroke doesn't figure into static compression. Only dynamic.

 

[MikeyT]

^ Rusty gets an apple for info today!

Mike

 

[RustyRatRod]

benno, double check that piston head cc. That's a huge amount. What part number is that piston?

 

[Meep-Meep]

Actually stroke does figure in. The basic formula is swept volume plus unswept volume divided by unswept volume. Here is doing it long hand.....

Use the cylinder volume formula to get the swept volume. Bore^2 x .7854 = 4.35^2 x .7854 = 14.86. 14.86 x 4.25" = 63.16 CI per cylinder (x 8 = 505 CI incidentally). Convert the 63.16 to CC's = 63.16 x 16.3872 = 1035 cc's. Now you are dealing with apples and apples. Add the 1035cc to the chamber volume then divide by chamber volume.

So the question is are the gasket bores round? If they are you can figure the volume of just the gasket with the above formula but use the .040" as the stroke. What is 26.7? The volume in cc's of the valve reliefs? Assuming so this will get added to the chamber volume. 80+26.7+gasket = unswept volume. Gasket volume, assuming the bore is at 4.35", which it probably isn't, is 9.74 cc's. Total chamber volume is 116.44 cc's. Add that to the cylinder = 1151.44 cc's. Now divide that by 116.44 and you have your static compression ratio of 9.88:1

 

[RustyRatRod]

Stroke aint counted in the calculator at the United engine web site. Only for dynamic compression. I should have clarified. It simply depends which formula and which calculator you use.

 

[Meep-Meep]

Who ever writes the program for the calculators must have stroke in there somewhere. Rod length doesn't matter for static but you can't calculate the volume of a cylinder without knowing the area and the length. And you can't calc compression without knowing the chamber volume and the cylinder volume.

 

[RustyRatRod]

Hush up. Stroke aint on that calculator. Yer tryin to make all this way too complicated. I'm too stupid for all that longhand. lol

 

[Meep-Meep]

Well, I know y'all aint stupid and that long hand is so simple even I can do it. Calculator; scmalculator...

http://en.wikipedia.org/wiki/Compression_ratio

"The compression ratio of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity. It is a fundamental specification for many common combustion engines.

In a piston engine, it is the ratio between the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke, and the volume of the combustion chamber when the piston is at the top of its stroke.[1]"

 

[RustyRatRod]

I know I know.......I was yankin yer chain genius. lol But the dang united engine calculator dont say nuffin bowt stroke till dynamic. LMAO

 

[benno440]

benno, double check that piston head cc. That's a huge amount. What part number is that piston?

part no. is Icon IC842-030

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Actually stroke does figure in. The basic formula is swept volume plus unswept volume divided by unswept volume. Here is doing it long hand.....

Use the cylinder volume formula to get the swept volume. Bore^2 x .7854 = 4.35^2 x .7854 = 14.86. 14.86 x 4.25" = 63.16 CI per cylinder (x 8 = 505 CI incidentally). Convert the 63.16 to CC's = 63.16 x 16.3872 = 1035 cc's. Now you are dealing with apples and apples. Add the 1035cc to the chamber volume then divide by chamber volume.

So the question is are the gasket bores round? If they are you can figure the volume of just the gasket with the above formula but use the .040" as the stroke. What is 26.7? The volume in cc's of the valve reliefs? Assuming so this will get added to the chamber volume. 80+26.7+gasket = unswept volume. Gasket volume, assuming the bore is at 4.35", which it probably isn't, is 9.74 cc's. Total chamber volume is 116.44 cc's. Add that to the cylinder = 1151.44 cc's. Now divide that by 116.44 and you have your static compression ratio of 9.88:1

they are almost round slight oblong shape

 

[benno440]

i was told with my setup i could make around 600hp, with this amount of comp ratio what does it mean? is it low? will i lose power? should i aim to get the compression up a bit and whats the easiest way to do this without changing the bottom end and is it even worth changing.

it is no race car but i would be happy with 550hp or more

 

[RustyRatRod]

You're over thinkin again. Sling her together and have fun.

 

[benno440]

You're over thinkin again. Sling her together and have fun.

righto cheers

 

[IQ52]

I know I know.......I was yankin yer chain genius. lol But the dang united engine calculator dont say nuffin bowt stroke till dynamic. LMAO

Roberto..........stroke...............or rod length?

 

[GrabberOrange69]

i was told with my setup i could make around 600hp, with this amount of comp ratio what does it mean? is it low? will i lose power? should i aim to get the compression up a bit and whats the easiest way to do this without changing the bottom end and is it even worth changing.

it is no race car but i would be happy with 550hp or more

I think this compression ratio is low for the intended purpose. I'd think you'd like 10.5 plus.

 

[benno440]

meh i could just supercharger it now i guess haha

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I think this compression ratio is low for the intended purpose. I'd think you'd like 10.5 plus.

yeh well i told muscle motors who did the kit for me that i wanted about 11:1 i dont know why this has happened, i am going to enjoy the car for now, but whats the go with compression this low? will i notcie any differences? and whats easiest way to raise it? that would be new heads with lower cc's?

 

[GrabberOrange69]

meh i could just supercharger it now i guess haha

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yeh well i told muscle motors who did the kit for me that i wanted about 11:1 i dont know why this has happened, i am going to enjoy the car for now, but whats the go with compression this low? will i notcie any differences? and whats easiest way to raise it? that would be new heads with lower cc's?

Easiest way to increase your compression from what you have here is to go for some steel shim head gaskets (only use with iron heads). For every approx .035" reduction you'll gain a point of compression.

This should get you another half a point: http://www.summitracing.com/parts/dcc-4286754?seid=srese1&gclid=COPVnsrn_bYCFelxQgodyWAAng Oops - just noticed you had stealth heads...try these: http://www.netgaskets.com/COMETIC_Head_Gasket_CHRYS_361_383_413_440_4_35_p/cometic%20c5460-a.htm

On a 350ci engine every point of compression is worth 30 horsepower. Your throttle response will be crisper, idle speed lower, torque higher with more compression...

 

[benno440]

Easiest way to increase your compression from what you have here is to go for some steel shim head gaskets (only use with iron heads). For every approx .035" reduction you'll gain a point of compression.

This should get you another half a point: http://www.summitracing.com/parts/dcc-4286754?seid=srese1&gclid=COPVnsrn_bYCFelxQgodyWAAng Oops - just noticed you had stealth heads...try these: http://www.netgaskets.com/COMETIC_Head_Gasket_CHRYS_361_383_413_440_4_35_p/cometic%20c5460-a.htm

On a 350ci engine every point of compression is worth 30 horsepower. Your throttle response will be crisper, idle speed lower, torque higher with more compression...

i already have .040 compressed thickness cometic head gaskets on with 0 deck height

 

[GrabberOrange69]

i already have .040 compressed thickness cometic head gaskets on with 0 deck height

That's why you want the .027 compressed Cometic gasket. Looks like you'd at least raise your compression 1/3 of a point. Easiest way to get there....