Shaving 2tc head

**Pattey21** · 23-02-2011, 09:34 PM

Gday all,

this is my first EVER tech thread so please be kind if all is not 100% and just correct rather than rage.

A while ago when i was re-building my head i looked up the differences between 2tc and 2t-b heads. The 2tc has a static compression ratio of 8.5:1 and the 2tb has a 9.4:1.

From what i researched both engines used the same block and pistons so i assumed that the 2tc head had a slightly larger cylinder head cubic capacity than the 2tb. Later after doing the shaving and putting the head back on the car i realised it was due to the emissions on the 2tc head but it worked just the same.

To work out static compression the formula is;

(per piston)

cylinder head capacity (when piston is at tdc)+ cylinder block capacity/ cylinder head capacity (when piston is a tdc)

This will give you the static compression ratio.

The standard head cubic capacity is 63cc however the top of the piston enters the cylinder head chamber @ TDC hence why this is significant to the formula.

To work out how much you need to shave off the head to give you a certain staic compression ratio you need to know how many cc's are in the cylinder head

now 1 millilitre is equivilent to 1 cubic centremetre.

To measure head cc's in millilitres whack in the valves and a spark plug. Get your mum's measuring cups or go down to supercheap and get a syringe for $5. You will need a standard piston to correct actual cc's in head when pston @TDC.

Obviously the head needs to be off the car in the shed, upside down, level on a bench secured.

fill the measuring device with 63ml of water and squirt into the head. With the head gasket on top of the head, push the piston down onto the head to get rid of the excess water and then remove.

This will give you reasonably accurately the cc's or ml's in the head standard. apply this to the above equation and that will give you your current static compression ratio.

Now you can adjust your cylinder head cc's to change you compresison ratio.

eg

47cc(cylinder head) +397cc (cylinder block)/47cc (cylinder head) = approx 9.4:1

Now simply add those cc's to the cylinder head chamber and however short the fluid level is from the top of the cylinder head is how much neads to be shaved approximately.

You can mark this better using a dye in the water eg food colouring.

Anyway thats my two bits.

Cheers
Patrick

**NME308** · 23-02-2011, 11:46 PM

Hi there Patrick,
It sounds like you had fun getting into the details of your engine build! I hope it goes well for you.

I would like to see a bit more accuracy in the measurements. A flat piece of perspex on the head with small hole and the use of highly accurate burette (which do not cost a bomb anyhow) will give better chamber cc results. You need to know the exact cc's of your own particular cylinder head chambers.
The liquid could do well to be either alcohol with a dye or a very fine llightweight oil as water's surface tension can be an issue.
The method of placing head gasket on the head and pushing piston into the chamber I believe will not give very accurate TDC chamber volume as there are too many variables... For pistons with material protruding from the top of the bore it is a little more complex to measure than those which can have the perspex and burette technique applied. Piston specifications from the manufacturer and commonly available internet calculators will give adequate results and also take the varying head gasket thicknesses available into consideration very easily.
I do like your method of tipping in the final cc's worth of dyed liquid into the chamber to mark the amount to be milled - rather resourseful!

Cheers,
Jason