Enjoy the new compression calculator:

http://www.c-speedracing.com/howto/c.../compcalc.html


Please report any bugs you may encounter. Thanks.

 

pretty interesting

 

How do I know what piston to select on that calculator?

 

Easy:

pr3 USDM b16a
p30 JDM b16a
p61 b17a
pr4 b18a/b
p72-A0 USDM b18C1
p72-00 JDM b18C1
p73-A0 USDM b18c5
p73-00 JDM B18C5
p3f b20b
phk B20Z
pct B16B

 

This is very nice.
One question...how do I account for milling the head?

 

It says at the top that it can't take into account a milled head.

 

Hmm crescent the calculations seem a little of to me, says that I'm running 10.8:1 CR in my B16A w/over bore CTR pistons. Should be more around 11.2:1 from what I've figured (if we factored in my head being milled 4 thousandths is actually closer to 11.6:1 or so.). Not bad though, although Jim's drag and drop CR calculator is a little easier for the newbies to use.

 

9.397510354203335

 

Kewl! I got it bookmarked.

 

That is one of the issues i'm concerned about specifically for the CTR pistons.. because i don't have a means to verify that the piston dome displacement is correct.

Refer to the other thread in the ITR forum pertaining to this matter.

 

G3-TEG,

Few months ago, a fellow H-T member helped me in calculating my CR.
I tried using your site as a comparison and the CR that I got was off by more than 1.0 point. The only difference between the two is the head milling, but I don't think head milling will make that much of a difference. Take a look and tell me what you think?


B18B block bore= 81.5mm (honed to RW bore), stroke = 89 mm

B18B Head Volume (Combustion Chamber Volume) 45 cc

Endyn Rollerwave High Compression Piston Volume +7.45 cc

Head Gasket 0.024" or 0.6mm

Deck Height = (Milled Amount off the Head - Stock Deck Clearance)=
(0.889mm - 0.76mm) = 0.129mm

------------------------
Swept Volume - [(81.5 x 81.5 x pi ) / 100] x [89 /10] = 1857.1 cc
Piston Dome Displacement - 7.45 cc x 4 = 29.8 cc
Combustion chamber Volume - 45 cc x 4 = 180.0 cc

Headgasket Volume (incl. piston to deck height)
[(81.5 x 81.5 x pi)/100] x [(0.6 - 0.129)/10] = 9.8 cc

If you use a 0.8mm (0.030") or 1mm (0.039") thick headgasket (eg. Toda
headgasket) instead of a stock 0.6mm (0.024") headgasket, the Headgasket
Volume = 14.0 cc and 18.2 cc respectively.

------------------------
Plug in the numbers to the equation:

Compression Ratio = (volume at BDC) / (volume at TDC) =

(Swept Volume - Piston Dome Displ. + Comb. Chamber Volume + Headgasket
Volume (incl. piston to deck height)) / (Comb. Chamber Volume +
Headgasket Volume (incl. piston to deck height) - Piston dome
displacement)

A. With Stock Headgasket

CR = (1857.1 - 29.8 + 180 + 9.8) / (180 + 9.8 - 29.8)

= 2017.1 /160 = 12.6:1


B. 0.8mm Headgasket

CR = (1857.1 -29.8 + 180 + 14.0)/(180 + 14 -29.8)

= 2021.3/164.2 = 12.3:1


C. 1mm Headgasket

CR = (1857.1 - 29.8 + 180 + 18.2) /(180 + 18.2 - 29.8)

= 2025.5/168.4 = 12.0:1

 

Project-X


There are few errors in your (or someone elses) calculations.

Right off the bat, you introduced error in the equation for finding VOLUME in a cylinder.

You were using: [81.5 x 81.5 x pi
Which is incorrect. Volume of a cylinder is: pi * RADIUS * RADIUS (or simply - pi * r^2)

Also, you are introducing further errors in your round off. To be most accurate you need to at least carry up to 8 significant digits and round at the very end to the 100ths decimal place.

Also, you are using 0.6mm as the stock headgasket thickness where as it really is 0.7366mm (or 0.029")

I didn't go through your entire calculations, but i'm sure those are what is causing the errors you are seeing.

HTH

 

Damn.. Looks like I'm back taking Algebra II/Trig in high school.

 

Ok.. here's some results that I got:

B18b block and head
7.45 piston dome displacement
0.024" headgasket thickness
-0.05078" piston-to-deck height (negative because of head milling)

Compression = 12.5908


Using a 0.8mm headgasket (0.031496...") = 12.3103cr
Using a 1.0mm headgasket (0.039370...") = 12.0300cr
Using OEM headgasket (0.029000") = 12.4022cr

Cool?

 

Excellent. Thanks.
Does the 12.5908 account for head milling? If so, how much head milling?

Also, I've found another calculation in my archive. Does this make sense for a head that's not milled?


Compression Ratio = (Volume at BDC) / (Volume at TDC) =

[Swept Volume - Piston Dome Displ. + Comb. Chamber Volume + Headgasket Volume (including Piston to Deck Height)] / [Comb. Chamber Volume +
Headgasket Volume (including Piston to Deck Height Clearance) - Piston Dome Displacement]

The Parts:

Endyn RW High Compression Pistons: (Piston Dome Displacement +7.45 cc, bore 81.5mm)

B18B Head Volume 45.5 cc

B18B Block honed to 81.5mm bore, 89mm stroke

Deck Height : 0.127 mm (0.005")

Headgasket Thickness: 0.76 mm (0.030")

Metric Conversions:
1 inch = 25.4 mm

1mm = 0.1 cm

----

Swept Volume - [(81.5 x 81.5 x pi )/ 100] x (89/10) = 1856 cc

Piston Dome Displacement - +7.45 cc x 4 = 29.8 cc

Combustion Chamber Volume - 45.5 cc x 4 = 182 cc

Headgasket Volume (incl. piston to deck height) -
[(81.5 x 81.5 x pi) /100] x [(0.76 + 0.127) / 10] = 18.5 cc

Compression Ratio =

(1856 - 29.8 + 182 + 18.5) / (182 + 18.5 - 29.8)

= 2026.7 / 170.7 = 11.87 CR


One thing I've noticed that in this calculation it uses 45.5 cc for the combuster chamber volume whereas you use 45 cc. Why is there a 0.5 cc difference?

 

Ok before we continue further about your compression..

You are using the wrong formula to calculate volume in a cylinder

Formula is: RADUIS * RADUIS * pi

You are using the DIAMETER * DIAMETER * pi which is totally incorrect.