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

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Robert Troy
69 slant 6 OD4 Barracuda conv
68 383-S 4 speed convertible

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

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Part of Tyrde-Browne Racing

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.

OK, didn't expect that.
I should be able to do it if I pull the radiator and attach the degree wheel.

Thanks,
Bob

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Robert Troy
69 slant 6 OD4 Barracuda conv
68 383-S 4 speed convertible

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

This will make you rethink cam choices.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

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.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.

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

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

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Part of Tyrde-Browne Racing