14 replies to this topic

[speedster]

Quote from https://z22se.co.uk/...on-ratio.15750/

 

 

 

[color=rgb(20,20,20);font-family:'PT Sans', sans-serif;background-color:rgb(252,252,255);]20thou (0.5mm) will increase the 2.2 by 1/2 cycle raising from 10:1 upto 10.5:1[/color]
[color=rgb(20,20,20);font-family:'PT Sans', sans-serif;background-color:rgb(252,252,255);]40thou (1mm) will increase the 2.2 by one cycle raising from 10:1 upto 11:1[/color]
[color=rgb(20,20,20);font-family:'PT Sans', sans-serif;background-color:rgb(252,252,255);]60thou (1.5mm) will increase the 2.2 by one and 1/2 cycle raising from 10:1 upto 1!.5:1[/color]

[color=rgb(20,20,20);font-family:'PT Sans', sans-serif;background-color:rgb(252,252,255);]60 thou is the max from the head any more and the oiljet is compromised[/color]
[color=rgb(20,20,20);font-family:'PT Sans', sans-serif;background-color:rgb(252,252,255);]for additional increase in CR can be acheived through skimming[/color]
[color=rgb(20,20,20);font-family:'PT Sans', sans-serif;background-color:rgb(252,252,255);]upto 60 thou from the block face[/color]

 

 

Anybody know if the same wriggle room is applicable to a B207 SAAB head?

If you take 60thou off the block what's the CR? 12:1?

[Nev]

Do you happen to have the block and head on the bench? If so, you can measure it yourself quite easily.

Edited by Nev, 07 February 2015 - 06:18 PM.

[vocky]

I would not recommend taking more than 1mm off the head and would not recommend taking anything off the block.

 

'The Doc' was correct in the data, however the timing chain cannot take up the slack and you would need to 'vernier in' the cams and create a new manual adjusting chain tensioner with major skimming. Plus the pistons would probably need valve pockets.

[speedster]

Haven't split the engine yet

[speedster]

I would not recommend taking more than 1mm off the head and would not recommend taking anything off the block.

 

'The Doc' was correct in the data, however the timing chain cannot take up the slack and you would need to 'vernier in' the cams and create a new manual adjusting chain tensioner with major skimming. Plus the pistons would probably need valve pockets.

 

Thanks vocky. Looks like a custom set of pistons is the only way above 11:1 CR then.

[wizzard8]

i have a skimmed head already. so how much raise of cr makes sense with new pistons? i have catcams probably similar to stage 1 compcams (dont know really exactly) and rev atm 7200. i would like to raise rev limit up to 7600. valve shaft geometry is also modified already. i bought my engine already done..

[slindborg]

Why are you aiming at high cr?

[wizzard8]

atm my engine is good for rd 200hp.. heading for 215 hp i consider raising the rev limit which will need new pistons and rods. also considering itbs instead of my bilas intake. i guess higher revs demand highee cr to deliver in that region

[wizzard8]

tell me if i am wrong pls

[slindborg]

At higher revs you've past the peak volumetric efficiency of the engine but you want to keep the average as high as possible.... If you can't do that (ie shoddy cams, headwork, or p*ss poor intake like a dilbert one) then sure bang the static CR up but you'll be suffering lower down the rev range and the pistons will suffer higher temperature changes which might not be ideal. Ofcourse, that could all be wrong and so it, go for a 20:1 CR and run on diesel

[speedster]

Upping the static CR and to get the best results means your working with cam timing. These can help http://www.summitrac...ts/nal-88958613

 

 

 

[color=rgb(0,0,0);font-family:Tahoma, Arial, sans-serif;font-size:13.3333330154419px;]The cylinder pressure is a result of 5 things, the static compression ratio, cylinder head material (iron or aluminum), the closing point of the intake lobe, the altitude of operation of the engine and the final displacement of the engine.[/color]

 

[vocky]

atm my engine is good for rd 200hp.. heading for 215 hp i consider raising the rev limit which will need new pistons and rods. also considering itbs instead of my bilas intake. i guess higher revs demand highee cr to deliver in that region

The NA engine really does need 11:1 CR for decent power, you can either use z22yh pistons and rods or skim the head by 1mm.

 

Or skim the head 0.5mm and use the z22yh rods and pistons for 11.5:1 

 

Itb's should take your engine well into the 200's with decent CR 

 

Plus they sound     

[wizzard8]

my head is already skimmed by a 1mm.. using z22yh pistons is too much as I understand you right?

[vocky]

That would be fine, you can either use a thicker head gasket or have 12:1 CR 

 

Skimming 2mm from the cylinder head would be too much for the chain tensioner 

 

I am running 11.5:1 CR 

Edited by vocky, 08 February 2015 - 06:13 PM.

[Paulus H]

Vocky thanks for the info

 

Kindly, Paul