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Old 05-07-2012, 03:58 AM   #1
CaliMeatWagon
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Default NA Build, Compression Questions

On a 16v head how far can you shave it to increase the compression ratio.
How far can it be shave with out having to increase the depth of the valve reliefs?
Also I'm curious to same question with an 8v head.
This is on a 1991 745 B230F

Thank you for any advice/experience you have to offer regarding my question.
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Old 05-07-2012, 03:46 PM   #2
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Come on peoples. I know there is a good portion of the members here who have built NA motors and I know some of who had to run higher compression. How about a little helpful advice for some future competition?
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Old 05-07-2012, 03:56 PM   #3
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Who do you know on here that has built a high compression 16v engine? Maybe ask them, I can't think of anyone.
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Old 05-07-2012, 06:00 PM   #4
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Any amount you shave will increase the compression, or you could just install a thinner HG.

The maximum amount to shave is listed in the greenbooks, I know at least with the 8v head, people go past that amount with no ill effects except that now you need to degree your cam correctly to compensate for the change.

Just google compression calculator and plug in a few different numbers to see how the compression changes.
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Old 05-07-2012, 06:04 PM   #5
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Quote:
Originally Posted by Poik View Post
Who do you know on here that has built a high compression 16v engine? Maybe ask them, I can't think of anyone.
You can't?
Think just a little harder.

Here's a hint:


The things in the background ought to be a hint.
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Old 05-07-2012, 06:17 PM   #6
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John! How doin'? I didn't know you were into NA motors, those things sure are pertty!
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Old 05-07-2012, 06:29 PM   #7
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Quote:
Originally Posted by CaliMeatwagon View Post
John! How doin'? I didn't know you were into NA motors, those things sure are pertty!
Only been building hi-po n.a. since 1978....Those full circle steel billet cams I made for Knox Motorsport and for that matter the long rod--LIGHT piston stuff I do are really the outgrowth of doing n.a stuff for years..Every Saab which has ever won a round of Group 2 National Championship rally, and 2 that won the whole Group 2 title all were either built by me or full of the parts I supplied them.

So as for straight milling a 16v, the limiting deal is the outside edge of the valves, particularly the intake valves start getting awfully close to the cylinder walls as the height of the head goes down...Be a real bummer to bang the valves into the top of the block..

So I can't say how many mm, somebody is just going to have to set the head in the machine and start carving off aluminum...

I will say that even with pump gas you without a doubt can tolerate over 11.0 to 11.5:1 with zero deck pistons and say a 032 thick gasket...

With longer duration cams you can go higher static.

8v head, a friend over in Mill Valley carved 1,6 or 1,7mm off no problem, and with a K can that motor is NICE He has some cheesy headers and 2 1/2" exhaust and it pulls and actually revs pretty damn good.. You know Al Kun aka megulon-7?
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Old 05-07-2012, 06:36 PM   #8
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Normal Aspirated 16v porn:


Little bumps:


Some compression:


around 240 bhp on 48 DCOEs


The green B23 16v should be a bit more torque--on 48 ITBs
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Old 05-07-2012, 06:43 PM   #9
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see thats what I was curious about. I noticed that the valve reliefs are pretty deep. How far deep did you have to mill them and how much did you mill the head. I looked on greenbook and it said for a 16V min was 1mm. I'm mainly curious as to how far past that. Also where did you get the pistons?
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Old 05-07-2012, 07:15 PM   #10
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Quote:
Originally Posted by CaliMeatwagon View Post
see thats what I was curious about. I noticed that the valve reliefs are pretty deep. How far deep did you have to mill them and how much did you mill the head. I looked on greenbook and it said for a 16V min was 1mm. I'm mainly curious as to how far past that. Also where did you get the pistons?
He more than likely sells them.
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Old 05-07-2012, 08:31 PM   #11
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Well in that case how much?
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