cc'ing heads

[pengulns2001]

hey what have you guys measured when cc'ing your heads, so far im getting around 9.2 does this seem right? ive measured it a few times with kerosene but i was expecting a little less than that, im looking to lower compression ratio by removing some material...

before you get carried away i know dont touch the squish area dont remove to much from between the intake and exhuast valves etc i plan on polishing the surfaces very well when im done so if anything it should be a bit stronger (and definatly more resistant to detonation and carbon build up)

if anyones interested in pictures i can post up what i have so far

[pengulns2001]

hey what have you guys measured when cc'ing your heads, so far im getting around 9.2 does this seem right? ive measured it a few times with kerosene but i was expecting a little less than that, im looking to lower compression ratio by removing some material...

before you get carried away i know dont touch the squish area dont remove to much from between the intake and exhuast valves etc i plan on polishing the surfaces very well when im done so if anything it should be a bit stronger (and definatly more resistant to detonation and carbon build up)

if anyones interested in pictures i can post up what i have so far

[DaveC]

It might help to say which motor youre measuring.

[Marshall Grice]

who says polishing the surface will make it stronger?

[pengulns2001]

f4i... i swear i said that somewhere but obviously i didnt http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif... i think its a pretty well known fact surface polishing stuff makes it stronger http://fsae.com/groupee_common/emoticons/icon_confused.gif

[Jersey Tom]

Polishing doesn't make anything stronger in terms of yield stress.. but it will increase the fatigue life of the part.

[Kamil S]

pengulns2001, I don't know if this would make sense, but it's sunday morning and i'm not feeling too smart. So anyway I guess you could try this simple calculation just for comparison with whatever you are getting:

f4i has Bore/Stroke of 67/42.5 mm, which means the displacement volume is

0.25*pi*(67^2)*42.5 = 149.84 cc (makes sense as 4*Ans gives 599.36 cc)

Stock CR = 12, so V_total = 12*V_combustion
V_total is V_displacement + V_combustion, so solving gives

V_combustion = 13.62 cc

From a theoretical standpoint at least, we never really had to CC the head, so I don't know if 9.2 seems realistic or not.

[John Bucknell]

Keeping in mind that the clearance volume consists both of the chamber volume and the volume contributed by the head gasket thickness and the top of the piston (which could be positive or negative depending on the shape of the piston crown and the piston drop - the depth below the deck face where the piston stops at TDC).

[UQ Turbo]

I actually got almost exactly 13:1 when cc'ing the f4i. This was done very accurately using a burette and the grease - smeared glass etc. (I got V_combustion = 12.476) I did a bit more reading though and the true compression ratio will be a little different. This is because the inlet valve is still open after BDC on the intake stroke and some gas will escape during the compression stroke. Hence, true dynamic compression ratio depends on valve timing as well as all your volumes and will be slightly lower than the measured static compression ratio.

So either I have screwed up the measurement, Honda is reporting a dynamic compresison ratio or Honda is boasting more power with a lower CR for marketing purposes...

Food for thought anyway!

UQTurbo

and yes, post some pics up!

[pengulns2001]

kamil i performed the same calculation, however what i actually need to know is the head volume, the combustion chamber includes piston area and gasket thickness...

i estimate my new compression ratio to be about 11.2:1 i really was not able to get much material out of the heads but they sure do look nice http://fsae.com/groupee_common/emoticons/icon_smile.gif