Slant Six Forum
https://slantsix.org/forum/

Milling head. Please check my math.
https://slantsix.org/forum/viewtopic.php?t=47843		 Page 1 of 1
Author:  rftroy [ Tue Feb 07, 2012 11:00 am ]
Post subject:  Milling head. Please check my math.
I'm preparing a new head and would like to have my calculations checked before I have the shop remove material.

- The engine is a 225 overbored .040" to 3.440"
- Stock rods, assume length of 6.699"
- Measured deck heights of #1 and #6 cylinders. -0.186" and -0.185" respectively, +/- .001
- Installed exhaust seats and did valve job, then measured chamber volume of #1 = 58cc; volume of #6 = 56cc
- I have a stock replacement TRW cam. I don't know the exact specs of the cam (lost records), but I am going to assume Intake ABC closing of 50 deg.
- I measured the used, compressed Felpro head gasket. It is .040" thick.

I calculate that installing the head as is, and using 56cc and -0.185" deck, to be conservative (conservative meaning I don't want knock), the static C.R. is 7.96. Using the rb racing online calculator, I get a dynamic of 7.04 at SL.


If I go for 9.0 static, dynamic of 7.94, I calculate a chamber volume of 44.3cc.
To reduce from 56cc to 44cc I would need to remove 0.076" from the head.

This is definitely a time when I want to measure twice and cut once, so please let me know if my math is wrong.

Thanks,
Robert
Author:  Fopar [ Tue Feb 07, 2012 12:07 pm ]
Post subject: 
Other than the cam, mine in the Dart has the same dimentions, and I had 0.100 off the head and it gave me a 42cc chamber with 9.1 static compression.
I run "cat pee" regular and have no pinging.


Richard
Author:  Doc [ Tue Feb 07, 2012 12:13 pm ]
Post subject: 
Quote:
...but I am going to assume Intake ABC closing of 50 deg...
Stock cams usually have a IC in the 30 - 45 degree range...
To do the job right, mock-up the cam and find the true Intake Closing point.
DD
Author:  /6 Matt [ Tue Feb 07, 2012 12:39 pm ]
Post subject: 
Quote:
Quote:
...but I am going to assume Intake ABC closing of 50 deg...
Stock cams usually have a IC in the 30 - 45 degree range...
To do the job right, mock-up the cam and find the true Intake Closing point.
DD
Agreed. This isn't the time for guesswork.
Author:  rftroy [ Tue Feb 07, 2012 1:04 pm ]
Post subject: 
Quote:
Quote:
...but I am going to assume Intake ABC closing of 50 deg...
Stock cams usually have a IC in the 30 - 45 degree range...
To do the job right, mock-up the cam and find the true Intake Closing point.
DD
OK, didn't expect that.
I should be able to do it if I pull the radiator and attach the degree wheel.

Thanks,
Bob
Author:  Doc [ Tue Feb 07, 2012 2:52 pm ]
Post subject: 
Yes... you really need to know the IC point, to get an accurate DCR number.

Example, I entered all your info. (58 cc head), including the 50 degree IC point, into the KB calculator and got a 7.795 static CR and 6.892 DCR
Changed the 50 degree IC point to 30 degrees and get a 7.472 DCR.
The intake valve closing point has a big effect on the DCR number.
DD
Author:  sandy in BC [ Tue Feb 07, 2012 5:19 pm ]
Post subject: 
This will make you rethink cam choices.
Author:  65CrewCabPW [ Wed Feb 08, 2012 11:53 pm ]
Post subject: 
I took mine down .115 to get to a static 10.5:1, which got me down to, if I remember right, a 42cc chamber.

I probably should have kept going and upped it to 11 or 12, but i got tired of the bill rising.
Author:  raycycled [ Sun Mar 18, 2012 2:31 pm ]
Post subject: 
I'm assuming that with all this upping the compression you are using a high Octane fuel to match? about to clean up the head on our replacement motor was going to take 0.070" just to get back to clean metal this is only a part time motor so I can rework the original motor with the works, but what is the optimium amount to shave off a head to run on 95-97 octane fuels? RAY
Author:  ceej [ Sun Mar 18, 2012 5:10 pm ]
Post subject: 
What is your chamber volume, deck, overbore, crushed gasket thickness, Fire ring diameter, cam selection and stroke Ray?

The question can't be answered without the above parameters.

CJ
Page 1 of 1 All times are UTC-08:00
Powered by phpBB® Forum Software © phpBB Limited
https://www.phpbb.com/