Hello TGo Pros,
!) Is ther enough meat on the deck of iron Vortec heads to flat mill the from 64cc to 56ccc withjout hitting the outer edge of the intake valve, to retain enough compression for use on a 305?

2) Anyone know the math, if .030" or .040" off the deck is enough to get down to 56cc chamber volume?

'88 IROC-Z Vert TBI 305 5 speed

-Retain the stock 5 speed
-used roller camshaft-Ramjet/Ht383 196*-207*/.460"-.480" (w/1.6 rckrs) -109* LSA
-One piece Fel-Pro oil pan gasket
-Vortec heads machined for higher lift w/ LT1 springs
-on-hand 700 mech. sec. Holley
-Hedman shorty headers w/Y pipe
-3" Magnaflow exhaust
-non-computer HEI
-Mallory fuel reg
-Summit TFS Super 23 175 58cc Aluminum heads unfortunately NOT in budget.
-weekend use
Thanks in advance you guys.

 

I can't answer it directly, nut I see no problems, its been done before.
IMO I would just pick up a set of 059 Vortec heads that all ready are 58cc and flow just as well.

 

6thou per cc I believe?
Someone correct me if Im wrong.

Dont see why you couldnt, went from 76 to 64 and still room for more. Not a lot but some.

 

I thought those 059 vortecs had a different chamber design entirely?

 

My understanding is the chamber is more like the 081 heads, but its potential is greater.
I asked this before on here and thats what was posted to me.
Milling is a option, but wasn't recommended and I do not remember why!

 

The Vortec (062 or 906) chamber is quite a bit different from 081. 081 has a traditional "bathtub" sort of deal, while the Vortec chamber is sort of heart-shaped. You can look at them on eBay; the world's largest archive of photos of things that are for sale. Amazing how much picture info is posted there. Not much point in posting about "understanding" when it's that easy to just look at a picture.

.006" per cc is the "rule of thumb" for milling SBC heads. It goes up the farther you go, as the volume you lose is determined by the chamber cross-sectional area at the point you are cutting the metal from, and the chamber gets smaller as you cut more metal, meaning it takes progressively more .001"s for each add'l cc. To get from 64cc nominal to 56cc would therefore mean something in the range of .050" - 054". That's nearly 1/16". I suspect you'd stand a pretty good chance of scrapping some heads.

Personally I'd advise some other plan. Maybe take a look at the 305 "Vortec" heads. I don't have the slightest ideal whether they're "as good as" the 350 ones, but at least they'll bolt up and work.

 

Taken from this
https://www.thirdgen.org/forums/tbi/...bi-vortec.html

Flow numbers in case you don't want to through it all.

Lift-----Intake----Exhaust
.050------36-------28
.100------68-------47
.200-----128------103
.300-----179------138
.400-----205------152
.500-----221------163
.600-----225------165