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rftroy
4 BBL ''Hyper-Pak''
Joined: 24 Dec 2005
Posts: 32
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Post subject:
Milling head. Please check my math.
(Tue Feb 07, 2012 12:00 pm)
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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
_________________
Robert Troy
69 slant 6 OD4 Barracuda conv
68 383-S 4 speed convertible
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Fopar
6 Pack Dart
Joined: 02 Nov 2002
Posts: 1866
Location: Eugene, Oregon
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Post subject:
(Tue Feb 07, 2012 1:07 pm)
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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_________________  
Part of Tyrde-Browne Racing |
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Doc
Guru
Joined: 14 Oct 2002
Posts: 4978
Location: Working in Silicon Valley, USA
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Post subject:
(Tue Feb 07, 2012 1:13 pm)
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| Quote: | ...but I am going to assume Intake ABC closing of 50 deg...
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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
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/6 Matt
TBI Slant 6
Joined: 09 Jan 2010
Posts: 177
Location: Burke County, North Carolina
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Post subject:
(Tue Feb 07, 2012 1:39 pm)
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| Doc wrote: | | Quote: | ...but I am going to assume Intake ABC closing of 50 deg...
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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._________________ 1970 Dodge Dart Swinger 225 slant, 3 speed auto. 1973 Factory spec electronic ignition upgrade, 1-7/8" exaust with a turbo muffler of unkown make. Otherwise stock.
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rftroy
4 BBL ''Hyper-Pak''
Joined: 24 Dec 2005
Posts: 32
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Post subject:
(Tue Feb 07, 2012 2:04 pm)
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| Doc wrote: | | Quote: | ...but I am going to assume Intake ABC closing of 50 deg...
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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
_________________
Robert Troy
69 slant 6 OD4 Barracuda conv
68 383-S 4 speed convertible
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Doc
Guru
Joined: 14 Oct 2002
Posts: 4978
Location: Working in Silicon Valley, USA
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Post subject:
(Tue Feb 07, 2012 3:52 pm)
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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
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sandy in BC
Board Sponsor & SL6 Racer
Joined: 08 Nov 2002
Posts: 4599
Location: Burton BC canada
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Post subject:
(Tue Feb 07, 2012 6:19 pm)
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| This will make you rethink cam choices. |
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65CrewCabPW
EFI Slant 6
Joined: 15 Jun 2008
Posts: 350
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Post subject:
(Thu Feb 09, 2012 12:53 am)
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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.
_________________
'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.
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raycycled
3 Deuce Webber
Joined: 03 May 2011
Posts: 62
Location: Sydney Ausralia
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Post subject:
(Sun Mar 18, 2012 2:31 pm)
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| 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
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Ceej
SSRN National Champion
Joined: 31 Mar 2003
Posts: 6332
Location: Oregon
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Post subject:
(Sun Mar 18, 2012 5:10 pm)
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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_________________ 
Tyrde-Browne Racing
I'm off to find myself. If I should return before I get back, keep me here. |
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