81 replies to this topic

[speedster]

Best Compression ration for ITBs? Running with Eagle Chrome-Moly crank and rods.

 

 

 

[J4EY D]

I think most of us are at 11:1 CR. Achieved by either skimming the head 1mm or fitting new pistons, either z22yh ones or wiseco

Edited by J4EY D, 02 July 2013 - 09:48 AM.

[Nev]

11:1 seems quite low, has anyone gone into the 12:1 or 13:1 ? Maybe Vocky ?

[speedster]

11:1 seems quite low, has anyone gone into the 12:1 or 13:1 ? Maybe Vocky ?

 

Knock or ping might be an issue at higher compression ratios. That's what I trying to figure out. General rule is the higher the compression ratio the higher the fuel octane value. The octane rating of tells you how much the fuel can be compressed before it spontaneously ignites. Spontaneous combustion results in ping or knock and is not good for the engine. No idea what 97 octane translates into compression wise but I sure there is some formula out there somewhere.

 

I think vocky is running with custom [color=rgb(40,40,40);font-family:helvetica, arial, sans-serif;]Wiseco pistons @ 11.5 CR, he's best to confirm that though.[/color]

[Rosssco]

I don't know what the 'best' CR for the Z22SE, but 11:1 isn't really that high nowadays, especially if you have a good engine control and monitoring.

 

Many OEM engines run substantially higher than this (the GT86 is something like 12.5:1 I saw recently), just that the Z22SE with its standard 10:1 was probably designed to run in places outside Europe with their generally poorer quality fuel.

[slindborg]

Go for diesel numbers.

[J4EY D]

11:1 seems quite low, has anyone gone into the 12:1 or 13:1 ? Maybe Vocky ?

 
I think vocky is running with custom [color=rgb(40,40,40);][font="helvetica;"]Wiseco pistons @ 11.5 CR, he's best to confirm that though.[/color][/font]

Vocky used to be running 11:1 wiseco pistons but not anymore. He's built a new mental 2.5 engine.

His old block with wiseco pistons and everything is now in my Vx

[techieboy]

I think vocky is running with custom [color=#282828;][font="helvetica, arial, sans-serif;"]Wiseco pistons @ 11.5 CR, he's best to confirm that though.[/color][/font]

I think I read he was out of the country this week, so you might not get an instant response.

[J4EY D]

Yep he's in Germany at the moment, so is a bit slower on the forum than usual.

His build thread is here, the pistons he used should be listed on here somewhere around page 31-32

http://www.z22se.co....ld.2994/page-31

[2-20]

I think Alanoo has gone above 12:1.

 

Don't forget that the cams play a role.

The true CR will depend on when the valves close

[slindborg]

and the air temperature, and the engine temperature, and the revs, and the throttle opening, and the volumetric efficiency, and the ambient air pressure and many many more things

[speedster]

flux capacitor 

[speedster]

Yep he's in Germany at the moment, so is a bit slower on the forum than usual.

His build thread is here, the pistons he used should be listed on here somewhere around page 31-32

http://www.z22se.co....ld.2994/page-31

Great read. Photos have me drooling.

[speedster]

I think Alanoo has gone above 12:1.

 

Don't forget that the cams play a role.

The true CR will depend on when the valves close

ohhh... how's his engine breathing? ITBs?

[Nev]

To give you a frame of reference, my theoretical dynamic compression ratio (at sea level) with 20 degree air is calculated at 13.7:1 when I run 21 PSI of boost. However with the inevitable losses due to leakages and other dynamics this will drop in real terms, however I would hope that it is still around the 13:1 mark.

 

Most modern motorbikes will run at around 14:1 on normal pump fuel and race engines can even reach 17:1 with mega responsive ECUs that can detect knock on each separate cylinder and control a closed loop system fast enough, obviously with mega high octane rated fuel.

Edited by Nev, 02 July 2013 - 03:54 PM.

[speedster]

To give you a frame of reference, my theoretical dynamic compression ratio (at sea level) with 20 degree air is calculated at 13.7:1 when I run 21 PSI of boost. However with the inevitable losses due to leakages and other dynamics this will drop in real terms, however I would hope that it is still around the 13:1 mark.

 

Most modern motorbikes will run at around 14:1 on normal pump fuel and race engines can even reach 17:1 with mega responsive ECUs that can detect knock on each separate cylinder and control a closed loop system fast enough, obviously with mega high octane rated fuel.

As your boosted I assume your running an intercooler? And does it have any part to play in preventing knock?

[speedster]

Compression Ration =

Cylinder vol. + clearance vol. + piston Comp. vol. + gasket vol. + chamber vol. divided by Clearance vol. + piston vol. + gasket vol. + chamber vol.

[color=rgb(0,0,0);font-family:Verdana;font-size:11px;]Read more: http://www.carcraft..../#ixzz2XuApUP9u[/color]

 

[Boombang]

And massively depends on cams, cam timing etc.

[slindborg]

 

Compression Ration =

Cylinder vol. + clearance vol. + piston Comp. vol. + gasket vol. + chamber vol. divided by Clearance vol. + piston vol. + gasket vol. + chamber vol.

[color=rgb(0,0,0);font-family:Verdana;font-size:11px;]Read more: http://www.carcraft..../#ixzz2XuApUP9u[/color]

 

 

 

yes thats static CR... Which should be HUUUUUUUUGE and have lairy cams

[Exmantaa]

And massively depends on cams, cam timing etc.

 

     If you run hotter cams you can go higher in static CR. (Valves close later which lowers the dynamic CR back to suitable value for your fuel....)