more valvetrain questions

[Str8sixfan]

So I've seen enough videos, tech articles about getting heads machined that I see the pattern of the recommendation where they say "make sure you mark which rocker goes with which cylinder and install in the exact same location". That recommendation makes sense, that one rocker might wear different than the next with a pushrod, yada yada yada.

But I want to know exactly how particular is that best practice?

Because I had a set of heads rebuilt, and what came with it was a box of the stock rockers. But with no idea of which came with what head/cylinder, what am I risking here re-using the stock? I'm buying new push rods anyway, and adjustment is inherent anyway. Do I really need to scrap these and buy a fresh set?

[ZephyrEFI]

I would think something like that is moot because you're assembling a new head/block combination.

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[Str8sixfan]

That makes some sense. Curious if anyone else would second that notion?

[rock4451]

Run them and don’t lose a wink of sleep over it. I’ve never ever set my rockers aside in a pattern so I know which went where. Just install them correctly and you’ll be grand.

[Str8sixfan]

I just recently learned that the commonly referenced E7 heads mean E = 80s, 7 = 7... meaning first year EFI heads (I know I'm not breaking new ground here, just adding context).

So since I have a 78 Fairmont with a 302, what are the specs on Intake and Exhaust valve size as well as combustion chamber size for whatever D heads I have? I'm mostly more concerned about the combustion chamber size, so I can do a compression calculator to figure out what GT40P heads I have might do to the compression

[Jack Hidley]

I don't have data on the 78 Fairmont, but the 79 Mustang 5.0l had 69cc chambers with a 0.047" thick gasket in 49 states and 1.78"/1.45" valves. 8.4:1 CR in 49 states.

[gmatt]

couple charts may helphttp://sbftech.com/index.php?action=...ach=3603;image

http://sbftech.com/index.php?action=...ach=1315;image

[Str8sixfan]

Thank you both!

I want to say the 78 dealer brochure said the Fairmont 302 had an 8.1:1 compression ratio, but I now need to go hunt that down to fact check.

[gmatt]

I have found this website to be very informative: https://www.automobile-catalog.com/auta_details1.php

[gmatt]

I have found this website to be very informative: https://www.automobile-catalog.com/auta_details1.php

That's weird, just checked my link and it goes to a BMW. The page I copied was '78 Fairmont. Anyway, poke around over there, they have a page for almost every car

[bwguardian]

The GT40p heads will add about a point in compression ratio. My GT40p heads measured right at 59cc combustion chambers. I had fresh from the machine shop heads that I used the stock rocker arms, push rods, and roller lifters without any issues...

[mcb82gt]

The GT40p heads will add about a point in compression ratio. ...

Are you saying 8.8 to 8.9, or 8.8 to 9.8?

[bwguardian]

Are you saying 8.8 to 8.9, or 8.8 to 9.8?

A point, not a tenth of a point...so the later. The 80's 5.0 was rated at 8.4:1 for most applications.