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How much should I shave off.
https://slantsix.org/forum/viewtopic.php?t=47978		 Page 1 of 1
Author:  Brussell [ Wed Feb 22, 2012 6:31 am ]
Post subject:  How much should I shave off.
How much should I shave off the head?

Will have a 350 holley, big exhaust and long runner intake manifold. Already done a ignition module and coil upgrade as well.

Should I find the max amount, and just go a little less? I am happy to run a high octane fuel.

Too my knowledge the 225 (67) is stock apart from what I have said.

What is the smallest my chambers can be before I would run into problems of needing new push rods etc.

It seems on this board that most people go to around 10:1 static compression, why not go the highest possible.

Would I need to change the cam?

Thanks for the help, I know it's alot of questions I am still doing searches and gathering info but you guys know these engines better than anyone.

Objective is: MORE POWER.
Author:  Doc [ Wed Feb 22, 2012 8:59 am ]
Post subject: 
A nice running "street performance" SL6 runs best when the Dynamic Compression Ratio (DCR) is in the 8.0 to 8.2 range. (pump gas)
You need to measure your combination of parts and calculate the DCR for your combo.

The hardest number to "find" is the cam's Intake Closing point (IC) but that is a "key value" to the DCR calculation.
Basically, you can run higher static compression if you run "bigger" cams (later IC point)
You can also run lower static compression with a "short" cam, and still have the needed 8.0 to 1 DCR... these are usually called "torquer" engine combinations.
DD
Author:  CNC-Dude [ Wed Feb 22, 2012 9:06 am ]
Post subject:  Re: How much should I shave off.
Quote:



What is the smallest my chambers can be before I would run into problems of needing new push rods etc.
It depends on what your pushrod geometry looks like before you begin. Many people assume that theirs is perfect to begin with, and there is a magic formula that tells them if you cut this much off the block or heads, you can get this length pushrod. All engines are made with production tolerances in most all areas, so without knowing where you are to start with, and can determine a baseline, you may be able to only cut as little as .030 from a head/block before you start to see a need to compensate. And thats also assuming the block or head hasn't already been cut previously. For instance, your engine could have been on the verge of being rejected or be on the low side of the tolerance scale as far as pushrod geometry goes, and you might cut .020-.030 off of your block or head and see valve tip scuffing issues, while another guy may cut .050 or more off of his combo and still not have any issues at all. You just have to see where you are before you start.
Author:  terrylittlejohn [ Wed Feb 22, 2012 3:21 pm ]
Post subject: 
if this is a work in progress, project, for compression increase start with .100" off the block, leave the head alone if it is straight.
you can shim the rocker shaft if you need to, when you get the cam you want more lift will give you a smaller base circle on the cam and give you more clearance you can play with.
you will have to run supreme gas and be very careful with total timing.
Author:  Brussell [ Wed Feb 22, 2012 7:48 pm ]
Post subject: 
Thanks for all the info and help! I will aim to get the DCR in 8 - 8.2 as Doc suggested. I'll pull the head and measure everything up when I get holidays in a month or so.

Thanks.
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