My Compression - Needs Working Out!

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Sep 13, 2007 | 09:09 AM

dan_t

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Burning Brakes

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From: BC

My Compression - Needs Working Out!

Please can only help with working out my compression please, my engine is as follows.

1985 Block - TPI forged pistons
1987 Aluminum Heads
Felpro 1010 Head Gaskets

Sep 14, 2007 | 06:08 AM

dan_t

Thread Starter

Burning Brakes

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From: BC

anyone supply me with the information to work it out myself?

Bore
Stroke
I belive that Iron Heads were 76cc?
and Alloy 54cc?

Sep 14, 2007 | 08:59 AM

AGENT 86

Team Owner

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From: Summerland B.C. Canada

4.00" bore
3.48" stroke
58 cc head chamber
.039" head gasket
Your going to have to find out the piston info, as in - volume or + volume, dish, flat dome.
You can assume the piston to be in the hole by about .025"
Are you using one of the free calculators on the web ??

Sep 14, 2007 | 10:30 AM

dan_t

Thread Starter

Burning Brakes

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From: BC

just trying to find out as best I can. I have been using a calculator on the web but don't have all the information.
http://www.csgnetwork.com/compcalc.html

The pistons are standard 1985 pistons - not sure as to the spec?

Sep 14, 2007 | 11:00 AM

CFI-EFI

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From: The Top of Utah

Quote:

Originally Posted by AGENT 86

You don't need all that info if you are making changes to a stock engine. If it is a 1985, the iron heads are 76 cc. The stock head gasket is .021" compressed. The 1987 aluminum heads are 58 cc. It is easy enough to calculate the volume of the old head gasket. You can do the same for the new gasket, if it isn't listed in the specs for the gasket. Convert the bore and stroke dimensions from inches to centimeters and figure the swept volume in cc. The 1985 has a 9.0:1 compression ratio. With that information you can calculate the clearance volume, that is the sum of all the volumes above the piston, valve notches and all. Then alter the clearance volume to reflect the changes you are making. Reduce it by the (76 - 58 =) 18 cc difference in the heads and add in the additional volume of the 1010 gasket over the volume of the stock gasket. Then, with your new, altered, clearance volume, you can re-figure the compression ratio using the new parts you propose. Simple enough?

RACE ON!!!

Sep 14, 2007 | 11:04 AM

dan_t

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Burning Brakes

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From: BC

Im sorry but you've really lost me there

Sep 14, 2007 | 11:41 AM

CFI-EFI

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From: The Top of Utah

What part don't you understand?

RACE ON!!!

Sep 14, 2007 | 11:52 AM

dan_t

Thread Starter

Burning Brakes

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From: BC

I seem to have worked it out as a hike from 9.0:1 up to 10.5:1
I beleive that sounds about right

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Sep 14, 2007 | 06:54 PM

CFI-EFI

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From: The Top of Utah

Better check your math. Just quickly, in my head, I think you are off a half a ratio or more.

RACE ON!!!

Sep 15, 2007 | 08:54 AM

#10

dan_t

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Burning Brakes

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From: BC

fancy having a go at working it out for me?

Sep 15, 2007 | 11:29 AM

#11

ineVETTEable

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From: Muskego Wisconsin

Sep 15, 2007 | 01:29 PM

#12

CFI-EFI

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From: The Top of Utah

Quote:

Originally Posted by dan_t

fancy having a go at working it out for me?

I'll HELP you with it. This requires no skills more advanced than grade school arithmetic; add, subtract, multiply, and divide. As I asked, previously, after I explained the whole process, "What part don't you understand?". Don't take this as in insult, I need to know what we are starting with. Do you know what compression ratio is?

RACE ON!!!

Sep 17, 2007 | 05:59 AM

#13

dan_t

Thread Starter

Burning Brakes

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From: BC

I've checked this in a few places and i think i'm fairly accurate

Sep 17, 2007 | 02:50 PM

#14

CFI-EFI

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From: The Top of Utah

As long as you're happy.

RACE ON!!!

Sep 18, 2007 | 04:33 AM

#15

dan_t

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Burning Brakes

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From: BC

well as long as the calcuators that I'm using are correct then yeah. I have input data to with my known information and some random information to creat the original known CR.

A change in both headgasket thickness and head CC's gave me the figure I quote.

These are the only two variables so I don't see how I can be going wrong.