How to figure Compression Ratio - D-series.org

Go Back   D-series.org » D-series Knowledge Factory » DIY Forum

D-Series.org is the premier Honda All Forum on the internet. Registered Users do not see the above ads.
Reply
 
LinkBack Thread Tools Display Modes
Old 12-19-2014, 05:41 PM   #1 (permalink)
DIY Guru
 
BogusSVO's Avatar
 
iTrader: (4)
Join Date: Dec 2014
Location: North Gulf coast Al/Fl
Posts: 637
Rep Power: 13 BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!
BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!
iTrader Score: 4 reviews
Send a message via Yahoo to BogusSVO
Question How to figure Compression Ratio

How to figure Compression Ratio





I have noticed very few know what their real compression ratio (CR) is. Most think since they have 9.0:1 pistons, that they have a 9.0:1 CR engine. The pistons in the engine are only one part of the formula. Several other things can affect CR, such as having the head and/or block milled, over sized valves, even a basic valve job can and will change CR.

The basic formula to figure compression ratio is fairly simple, but getting the volumes needed for the formula will take a few pieces of specialized equipment.

The formula is V1+V2+V3+V4+V5/V1+V2+V3+V4

Now,

V1 = Combustion chamber volume
V2= Head gasket compressed volume
V3= Piston volume, either a + or – depending on design
V4= Piston to deck clearance volume
V5= Swept volume of the cylinder

Now it is the time to start filling in the volumes to work the formula.

I am going to start with V5 or swept volume of one cylinder.
To find this there is another formula that needs to be worked.
The formula is for finding Cubic inch displacement or CID
Since most have a 2.0l 4G63T engine, that is the base engine I will work with.

The formula for CID is
Pi x R sq x S x C

Pi = 3.141
R = Radius of the cylinder bore or half of the diameter squared
S= Stroke of the crank
C= the number of cylinders of the engine

The bore of the 4G63 is 85mm and the stroke is 88mm

To convert from mm to inches multiply by .03937

85mm bore x .03937 = 3.346 inches
88mm stroke x .03937 =3.465 inches

Now to figure R squared

3.346/2= 1.673

1.673 x 1.673 = 2.799

Now to figure CID

3.141 x 2.799 x 3.465 x 1 = 30.463 CI

Now to convert back into metric measurement

30.463 ci x 16.387cc = 499.197cc

V5 = 499.197cc
The same formula is used to figure Head Gasket compressed volume.
I am going to us a Fel-Pro Composite 9627PT
The Fel-Pro has a bore dia, of 3.445 and a compressed thickness of .039

3.445/2= 1.7225
1.7225 x 1.7225 =2.967

3.141 x 2.967 x .039 = .363

.363ci x 16.387 = 5.948cc

V2= 5.948cc


Sometimes the manufacture will publish the compressed HG volume.

Now the two most difficult volumes have been figured, the rest will go rather quickly.

Piston to deck clearance is fairly simple, the 4G63 is called a “Zero” deck engine, meaning the top of the pistons is flush with the deck of the block.

If the block has been surfaced, the pistons may protrude above the block deck by a few thousands.

This still need to be measured.

https://www.d-series.org/forums/engin...clearance.html


Now on to the pistons, V3

Wiseco pistons are a common choice in builds.
http://www.wiseco.com/Catalogs/ProTr...eteCatalog.pdf

page 64 and 65

K559M85 6bolt 17cc dish (8.3CR)
K560M85 6Bolt 10cc dish (9.0CR)
K625M855 6Bolt 14cc dish (8.5CR)

Now on to the head, It is commonly advertised that the 4G63 cylinder head is 47cc.

47cc may be what the engineer who designed the head wanted, but in real life it may be larger or smaller than that. Starting with the foundry that cast the head blank.



Now let’s look how all this works together.

I have four short blocks in the shop I measured.

(SB1)The first one is a 6 bolt, stock rod, STD bore , 63DT pistons.
The block has been milled, the piston is .001 below the deck and has a 21cc volume, this includes the piston dish.

(SB2)The second block is a 6 bolt, Manley Turbo tuff rods, Manley pistons, Part number 6625M885 (.020 over), the block has been decked and the pistons protrude above the deck .003 Dish volume of the pistons is 16 cc

(SB3)The third is a 7 bolt, stock rod, STD bore with 63DTF1 pistons, The block has been milled, the pistons are .002 below the deck, The volume of this combo is 14cc

(SB4)The fourth is a 7 bolt with EVO pistons, E9K1, rods are unknown, the block has been belt surfaced, the pistons sit .060 below the deck, the volume on this combo is 15cc ( This engine was done at another shop)


Now so you do not have to do the math longhand, I would suggest downloading an engine calculator.

This is the one I use.
Download Virtual Engine Calculator by Challenger Engine Software

Now we need some head info that contains the combustion chamber volume.

Now lets figure some real world compression.

The bore and stroke is simple enough, along with the gasket bore.

Stroke is 88 mm = 3.465
Bore is 85mm = 3.346
Gasket bore is 3.445 (felpro 9627PT)

Since I have cc’ed the short block,SB1, we will use that number in the “Dome cc’s” slot, so that is 21cc

Now in the “Gsk + Deck” slot, Just use the HG thickness, since the volume above the piston to the deck was figured when the short block was cc’ed
HG Thickness= .039

Now we need the head spec.

This head has a thickness of 5.191 and is 46cc

Input it all in and you end up with a CR of 7.55:1

So this shows that the engine has even less compression than what is stated. Even after machine work, like block and head surfacing.

A Stock 6 bolt is stated to be 7.8:1 compression ratio

Let’s look at another at another combo.

This time we will use SB2 and head with 44.25cc
Same Felpro composite HG.

Now since the pistons are .003 above the deck, we will subtract that from the HG thickness, making the gasket thickness .036

Also this is a .020 or .50mm overbore block
So the bore has to change from 3.346 to a 3.366 bore

The wiseco piston PN 6625M855 is listed with a -14 dish, and is listed as 8.5:1 CR piston

In the block I measured a 16cc volume, the 2 extra cc’s is from the gap above the top ring and between the side of the piston and the cylinder bore.
When the math is run this combo works out to be 8.44:1
__________________
Quote:
this is probably the best noob weve ever had just pop in and actually be worth his weight
Quote:
BogusSVO nomination for newb of the year 2014, maybe lifetime honorary mention as well.
BogusSVO is offline   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 12-19-2014, 06:04 PM   #2 (permalink)
D-series post SLUT
 
iTrader: (14)
Join Date: Jan 2007
Location: Durham, NC
Posts: 2,638
Rep Power: 17 gearhead98 is hot as a volcano
gearhead98 is hot as a volcanogearhead98 is hot as a volcanogearhead98 is hot as a volcanogearhead98 is hot as a volcanogearhead98 is hot as a volcanogearhead98 is hot as a volcanogearhead98 is hot as a volcanogearhead98 is hot as a volcanogearhead98 is hot as a volcanogearhead98 is hot as a volcanogearhead98 is hot as a volcanogearhead98 is hot as a volcanogearhead98 is hot as a volcano
iTrader Score: 14 reviews
Default

Do you have a way of calculating the dynamic compression ratio?
__________________
98 VSM LX sedan - the all motor car - gone
98 VSM EX sedan - the nitrous car - gone
97 CGP LX sedan - the new boost project
06 CGP TSX - 6 speed DD
gearhead98 is offline   Reply With Quote Quick reply to this message
Old 12-21-2014, 04:12 PM   #3 (permalink)
DIY Guru
 
BogusSVO's Avatar
 
iTrader: (4)
Join Date: Dec 2014
Location: North Gulf coast Al/Fl
Posts: 637
Rep Power: 13 BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!
BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!
iTrader Score: 4 reviews
Send a message via Yahoo to BogusSVO
Default

That would take a computer program and a plot map to do.

Also would need flow rate of the head and a lobe map of the cam along with lb/min of turbo flow at every rpm of both engine and turbo.

I am not that smart....
__________________
Quote:
this is probably the best noob weve ever had just pop in and actually be worth his weight
Quote:
BogusSVO nomination for newb of the year 2014, maybe lifetime honorary mention as well.
BogusSVO is offline   Reply With Quote Quick reply to this message
 
Old 12-21-2014, 04:23 PM   #4 (permalink)
D-series PIMP
 
Mr.Fodo's Avatar
 
iTrader: (7)
Join Date: Oct 2011
Location: Florida
Posts: 1,055
Rep Power: 14 Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!
Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!
iTrader Score: 7 reviews
Default

Lol, I see where you understood dynamic, but N/A has a dynamic compression also... but exactly, the cam profile is one of the huge factors.

EDIT: Quickie Google search: http://ftlracing.com/dynamiccr.htm

Needs more digging for more understanding... I was reading about this a few years ago..
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
|
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

#
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
!
Quote:
Start there, if you still cant figure it out, you are not going to.
How
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
to act on this forum...

Last edited by Mr.Fodo; 12-21-2014 at 04:30 PM.
Mr.Fodo is offline   Reply With Quote Quick reply to this message
Old 12-21-2014, 04:29 PM   #5 (permalink)
DIY Guru
 
BogusSVO's Avatar
 
iTrader: (4)
Join Date: Dec 2014
Location: North Gulf coast Al/Fl
Posts: 637
Rep Power: 13 BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!
BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!
iTrader Score: 4 reviews
Send a message via Yahoo to BogusSVO
Default

Every engine has a dynamic compression, I am just used to dealing with more turbo engines than NA lol
__________________
Quote:
this is probably the best noob weve ever had just pop in and actually be worth his weight
Quote:
BogusSVO nomination for newb of the year 2014, maybe lifetime honorary mention as well.
BogusSVO is offline   Reply With Quote Quick reply to this message
Old 12-21-2014, 04:41 PM   #6 (permalink)
D-series PIMP
 
Mr.Fodo's Avatar
 
iTrader: (7)
Join Date: Oct 2011
Location: Florida
Posts: 1,055
Rep Power: 14 Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!
Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!Mr.Fodo is the fucking MAN!!!!
iTrader Score: 7 reviews
Default

Guess it just felt a bit funny that there was no separation...

Just trying to dot the i's, you get me?

__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
|
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

#
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
!
Quote:
Start there, if you still cant figure it out, you are not going to.
How
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
to act on this forum...
Mr.Fodo is offline   Reply With Quote Quick reply to this message
Old 12-21-2014, 04:50 PM   #7 (permalink)
DIY Guru
 
BogusSVO's Avatar
 
iTrader: (4)
Join Date: Dec 2014
Location: North Gulf coast Al/Fl
Posts: 637
Rep Power: 13 BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!
BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!BogusSVO is the fucking MAN!!!!
iTrader Score: 4 reviews
Send a message via Yahoo to BogusSVO
Default

I gotcha I gotcha..

Just dotting the Ts and crossing the Is...
__________________
Quote:
this is probably the best noob weve ever had just pop in and actually be worth his weight
Quote:
BogusSVO nomination for newb of the year 2014, maybe lifetime honorary mention as well.
BogusSVO is offline   Reply With Quote Quick reply to this message
Old 12-22-2014, 05:32 AM   #8 (permalink)
Member
 
SELF MADE's Avatar
 
iTrader: (0)
Join Date: Dec 2014
Location: Las Cruces, NM
Posts: 46
Rep Power: 0 SELF MADE is trying to make new friends
iTrader Score: 0 reviews
Default

Thanks for the formula. Should come handy when building a motor
SELF MADE is offline   Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the D-series.org forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


iconAll times are GMT -8. The time now is 03:25 AM. | Welcome to Forum, please register to access all of our features.