7 replies to this topic

[prawny1]

Ihave noticed a few people asking about calculating compression ratios and stuff so i thought this might help.

Simple Engine Terminology.

Bore- diameter of the cylinder,
Stroke- distance the piston travels from the top to the bottom of the cylinder,
Capacity- total volume of all cylinders, expressed in ccm or litres (998ccm/0.998lt)
T.D.C.- Top dead centre- piston at top of cylinder (as far up the cylinder it will go),
B.D.C.- Bottom dead centre- piston at the bottom of cylinder (as far down the cylinder it will go)
A.T.D.C.- After top dead centre- piston moving up cylinder,
A.B.D.C.- After bottom dead centre- piston moving down cylinder,
B.T.D.C.- Before top dead centre- piston moving up cylinder,
B.B.D.C.- Before bottom dead centre- piston moving down cylinder,
LEAD- the number of degrees the valve opens B.T.D.C. or B.B.D.C.,
LAG- the number of degrees the valves remain open for A.T.D.C. or A.B.D.C.,
Overlap- the number of degrees both valves are open at the same time,
CR- Compression ratio- e.g. 9:1 formula, CR = SV plus CV devided by CV,
SV- Swept volume (capacity) of cylinder- formula = pie (not sure how its spelt) multiplied by the radius squared and then multiplied by the stroke,
C.V- volume of the combustion chamber,
To find out the cv of a standard engine or an engine that you know the C.R. and S.V. for, you just divide the swept volume of the cylinder by the compretion ratio minus 1,

If you could be bothered to read all that the fair play to you.

[ditz]

Cheers, i read it all but now im just confused by all the letters :saywhat:

[kada1980]

your aftc and abtc are round the wrong way but nice one.

[Jammy]

AFTC and ABTC?!?!

[Sprocket]

AFTC and ABTC?!?!

Second that

[kada1980]

Ok Ok too much red wine too early

ATDC and BTDC

picky gits!

you knew what i mean't F is right next to D on the keyboard and before you say it no i don't have big fingers :grin:

[Sprocket]

Ok Ok too much red wine too early

ATDC and BTDC

picky gits!

you knew what i mean't F is right next to D on the keyboard and before you say it no i don't have big fingers :grin:

Have you got a wireless key board, may be its time for new batteries :cheese: :grin: :grin:

[prawny1]

Sorry about the mistake, I saw what you mean when i read through it again sorry.