I looked up the front markings to my firebirds heads, they corresponded with the chevy 305 heads. So I am guessing around 150hp stock, but it came with an alluminum intake. Anyways, I can't find the stinking block numbers. So I put on the Performer RPM and brand new holley 750 vac sec, with a brand new pro form HEI. Do you guys think I upped the HP any in this combo. It originally had the sotck aluminum intake with a quadrajet and HEI stock. I know you can't tell me for sure, just asking for opinions.....thanks

BamaZ28

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1981 Pontiac FB originally V6, converted to SBC (HEI), Performer RPM, Holley 750 Vac Sec., Chrome Dress up, True Duals

 

I think carb might be a little big for a 305. You'd probably have better performance with a 600cfm or so.

-Dave C. '97 Z28

 

Usully. But as these cars get older and older there are more and more bastardized combos running around. 305 heads on a 350 short block is not uncommon- I've run into a few myself. Run the numbers off the back of the bellhousing and see what block it's got in it to be more sure.

Some 3rd gen cars (82-87) came with aluminum intakes under the stock computer controlled QJet carb. They were basically just aluminum versions of the junk cast iron 4bbl manifold used to save weight, not make power. My brother's 85 Z-28 with low-output LG-4 305 has such an intake on it and it came stock from the factory like that.

If it's basically a low output 305, you probably hurt performance more than you helped since that combo won't begin to make noticably more power until higher in the rev range- above what the super-wimp low output cam is capable of feeding. If it's a higher output 305 (like an L-69 HO 305) then you probably breathed some life into it, especially upstairs. Uncork the exhaust and it'll work even better.

 

Bama,

Did you get it running with the new HEI?

Bill B.