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Squish Clearance/Compressed HG Thickness
http://4g61t.org/forum/viewtopic.php?f=6&t=15811		 Page 1 of 1
Author:  Pazzesco [ Sat Nov 12, 2005 4:56 pm ]
Post subject:  Squish Clearance/Compressed HG Thickness
What are the factory squish clearances on the 4g64 and 4g63? What is the compressed thickness of the factory (or other) HGs?

Thanks!
Author:  unior [ Sat Nov 12, 2005 8:52 pm ]
Post subject: 
why do you wanna know? the HKS 1.6mm HG supposedly raises compression from 7.8:1 to 8.3:1 according to this site:

http://www.2kracing.com/index.php/cPath/476_494
Author:  Pazzesco [ Sat Nov 12, 2005 11:44 pm ]
Post subject: 
Just curious to see if anyone would know off hand, I can take some measurments I guess. I like to build engines that take advantage of tight squish clearances, and the many benefits that come with it.

That being said, if any of you know feel free to pipe up!
Author:  Slaphead [ Sun Nov 13, 2005 4:43 am ]
Post subject: 
The question is - how are you going to measure it? Difference in height between top of block and top of head possibly, or maybe the gap between head and block interfaces? As soon as you untorque those head bolts/studs then any crush on the gasket will be relieved.

May i ask what are the benefits of "tight squish clearances"?
Author:  adamrx7 [ Sun Nov 13, 2005 11:27 am ]
Post subject: 
more efficiant<sp

I'd say the gasket starts off at around .050 and compresses to around .035 to .040
Author:  xlr8 [ Sun Nov 13, 2005 10:47 pm ]
Post subject: 
There are plenty of resources that will tell you what "squish" and for that matter what "quench" does in a given motor. Google search that stuff.

From memory you want about 0.045" clearance to take good advantage. However IMO squish isn't going to be so important with the 4G6x DOHC heads since they run a "pent-roof" style combustion chamber (unlike say a 8v EFI 4G15 motor with its kidney shaped chambers where squish is extremely important). The head does however sport a pair of quench pads that if you get the clearances right will give you a bit of artificial-octane.
Author:  Pazzesco [ Mon Nov 14, 2005 12:18 am ]
Post subject: 
Quote:
The question is - how are you going to measure it? Difference in height between top of block and top of head possibly, or maybe the gap between head and block interfaces? As soon as you untorque those head bolts/studs then any crush on the gasket will be relieved.

May i ask what are the benefits of "tight squish clearances"?
I agree with the post above, google and ye shall learn :wink: As far a compressed HG height, the manufacturer of the gasket should be able to tell you.

As far a quench goes, the dual cam mistu heads dont have much quench area, or quench pads as some might say (most 4+ valve per cyl heads really dont due to the space constrainsts that come with puting that many valves in there :wink:), which is why heads of this nature usually make better use of tumble (in most cases) instead of siwrl.... EGH... tangent, sorry. Yeah the 4g15 would make great use, lost of quench pad, much like the volvo heads I know and love.
Author:  Slaphead [ Mon Nov 14, 2005 7:39 am ]
Post subject: 
The question still remains - how are you going to measure it :wink: ? I seriously doubt that without some proper measuring equipment (you might want to google that) one would be able to see the difference between 35 and 45 thou. If i remember my 61T block and pistons correctly, the chances of someone getting a nice flat surface on each part (block/piston) to line up properly whilst the piston is actually dead flat... add a bit of oil and there goes a couple of thou..
Unless running a competitive engine i seriously doubt that one would be able to tell the difference. Your thoughts?
Author:  Pazzesco [ Mon Nov 14, 2005 3:41 pm ]
Post subject: 
Quote:
The question still remains - how are you going to measure it :wink: ? I seriously doubt that without some proper measuring equipment (you might want to google that) one would be able to see the difference between 35 and 45 thou. If i remember my 61T block and pistons correctly, the chances of someone getting a nice flat surface on each part (block/piston) to line up properly whilst the piston is actually dead flat... add a bit of oil and there goes a couple of thou..
This isn’t rocket science...

The real way to measure and do so accurately without fancy equipment that mfg's have, is to measure from crank cl to the midpoint of the cams' cl after the head has been toured down... it works like a charm and its not difficult to do. As an example, Elring says they're gaskets compress to 45-47 range, people who use elring (and have measured) have reported numbers in that range.
Quote:
Unless running a competitive engine i seriously doubt that one would be able to tell the difference. Your thoughts?
This couldn’t be further from the truth, tight squish, in a nutshell, improves efficiency in MANY ways, it helps make tuning easier, which makes squeezing more power from the engine easier (that’s tip of the iceberg too). Also, when building an engine why the heck would you not want to make it more efficient (pleasant side effect: more "competitive" if that’s what you're concerned about).

The whole point is, after many calls to Mitsubishi, I still don’t have an answer for either of the questions I stated at the beginning of this thread, so I thought asking here might be worthwhile.... and it has. (thanks for the info adamrx7 and unior!)
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