I've tore down my slant, I've grabbed a 60cc syringe and a piece of Lexan, and I crunched the numbers. Right now, my all stock 225 with .030" off the head in a rebuild currently has 7.9-8:1 compression. I would like to bump that into the 8.5-9 range, and if I did my math right that would mean shaving off about .050-.070" off the block. Using pump gas is a requirement since this is meant to be just a complete rebuild with some extras to free up some pep in the pedal, so I may err on the side of caution and go closer to 8.5:1. But now, I'm stuck with some reground camshaft choices from Oregon cam. The choices I've got:

#2106

210/214 @ .050”, 254/254 adv, .434”/.444” lift, 108 sep

Or:

#819

219/219 @ .050”, 264/264 adv, .437”/.437” lift, 110 sep

From what I've been reading they're pretty mild and I should be okay, but I want to make sure with my projected CR. I will be emailing Ken again to see if he recommends either or. This is really the first time I've done an actual build rather than a re-gasket, so I want to make sure I got my ducks in a row and be exact. The rest of my 72 Dart is a 904 trans, and a 3.23 gearing in the back. Super Six setup. Thank you!

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With Oregon cam, you can come up with your own specs... (mix and match lobes, lsa and advance)

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Determine the intake valve closing point with the cam grind you like and then use the info in the chart to calculate the engine's effective compression ratio.
Target an 8 to 1 effective compression ratio for 87 octane pump gas.
DD

I used the 818 grind which is 211 degrees @ 50 and .431 lift.

They didn't mention either of the two grinds you listed at the time. Either way, the 2106 is very close and the other is a little too hot for what I wanted. I only have 2.76 gears....

Cams are probably even worse than spark plugs and motor oil and headers. People lose an awful lot of sleep over differences they'll never see or feel. More importantly, the engine won't see or feel them either.

I have asked for intake valve closing ABDC. According to Ken, at 4 degrees advancing the cam with their current specs, the #2106 is 29 degrees with 104 degrees from centerline. The #829 @ 106 intake centerline will be 36 degrees.

Found an effective compression calculator (https://uempistons.com/p-28-effective-c ... lator.html), and according to that the #2106 gives me 7.908 ECR, #819 is 7.636 ECR. I can only assume the higher degrees of intake closing, the more air bleeds off and lowers compression. Either way it seems that I will be well within the range of pump gas.

I do realize I can order a custom grind from Oregon, but I want to keep it simple. This is the first time I've torn down this engine to this level and not just used stock replacement parts. Baby steps lol. Thank you for the help!

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