Thread: Porting the 305 chevy heads

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The stock 1982 305 chevy heads flow 58cc. To do a porting job, how much can you safetly open it up to increade air flow?

Do the bowl work for blending. Allow the valve job to finish off the blend. In other words, don't hog out a bunch so the cutter can finish the area with it's 3 angles. In most cases, shouldn't have to touch the intake ports because most intake manifolds will be slightly under sized compared to the opening of the head. Exhaust can always be touched up on the exit side. Standard 305 heads don't have much material to play with. Be careful, conservative, etc. What's it going on? What is the use? These heads are shy on big flow numbers but they can be improved.

Thes will be going on a stroked 305 chevy engine. Need compression of 10.5.1 and want to keep the stock heads. Will be using dished pistons and hope to put out 350 HP and same with torque.

Interesting....Keep it conservative and let the rest of your combo work. You can achieve it.

Originally Posted by chevy 37

The stock 1982 305 chevy heads flow 58cc. To do a porting job, how much can you safetly open it up to increade air flow?

They don't flow 58 cc's that happens to be the combustion chamber size.

Eric Just had my fingers type what my mind had wrong. You know us old geezer,we don't think right anymore at least I don't.

You will not get that CR with anything but a street or low RPM cam,if you are not using domed pistons,due to small bore and ICP of 'BIG' cams.
The heads list as 58cc but do vary so do a cc job if you want to know for sure.
The intake runners flow somewhere around 170cc. There are about three of the 305 heads that make decent hotrod (NOT FULL RACING) heads.The 416,601,and one other that I can't remember.
Most people don't know but the 416 and 601 intake runners are the same as some 350 heads. These heads are medium thickness and will handle a pretty good pocket port.
A .020" shave make get you around 9.5:1 CR but I wouldn't go more than .020" myself. And of course you could deck the block and mabe reach 10.1.

Yep,,,Denny has directed you to the best place to read up on these heads. Some of those guys are getting decent numbers out of the 305 heads with a little work. By the way,,,a cam with over 465 lift may get you in trouble with these heads without machine work.

I am running 416's on my 350. Work well with the bowl work etc I mentioned before. I have 3 prs of matched 601's that one out of every pair has cracked thru the water jacket from the middle exhaust valves. Be forewarned, they flow very well just making me nervous about the integrity of these 601 casting's. Maybe it's my karma.

Originally Posted by FAYLUR

You will not get that CR with anything but a street or low RPM cam,if you are not using domed pistons,due to small bore and ICP of 'BIG' cams.
The heads list as 58cc but do vary so do a cc job if you want to know for sure.
The intake runners flow somewhere around 170cc. There are about three of the 305 heads that make decent hotrod (NOT FULL RACING) heads.The 416,601,and one other that I can't remember.
Most people don't know but the 416 and 601 intake runners are the same as some 350 heads. These heads are medium thickness and will handle a pretty good pocket port.
A .020" shave make get you around 9.5:1 CR but I wouldn't go more than .020" myself. And of course you could deck the block and mabe reach 10.1.

Again they don't flow around 170 cc's that would be a port volume.
The port volume for a 305 head is no where near 170 cc's.
It is much closer to 150 cc's.

The 305 will be bored .040 over. Cam selection is a the same as my 305 which is .462-.469 110 degree lobe sep. 218/224 duration @.050. Your probably right on a CR of no more than 10.1. Going to be running a 650 Demon carb with a duel plane intake. We want this motor to hit its torque and HP curve around 4800 rpm's. Don't know if it's possible with that mild of cam but will have to see. DENNY Thanks for the info on that site.

Originally Posted by chevy 37

The 305 will be bored .040 over. Cam selection is a the same as my 305 which is .462-.469 110 degree lobe sep. 218/224 duration @.050. Your probably right on a CR of no more than 10.1. Going to be running a 650 Demon carb with a duel plane intake. We want this motor to hit its torque and HP curve around 4800 rpm's. Don't know if it's possible with that mild of cam but will have to see. DENNY Thanks for the info on that site.

The carb. might be a little large.
It might work better with a 500 CFM carb.

Originally Posted by erik erikson

Again they don't flow around 170 cc's that would be a port volume.
The port volume for a 305 head is no where near 170 cc's.
It is much closer to 150 cc's.

Your right Eric,,,,my goof. They flow very similiar to some 350 heads from 2500-5500 depending on differant factors.But the port volume for 416 heads is more than 150. But let him and others check with the "Head specialists" and they will see,,,I'll not argue the point anymore,thanks.

Waddaya mean "Oh No!" To quote Tim Allen, "MORE POWER! AARRGGHH ARRGGHHH!!!"

Originally Posted by FAYLUR

Your right Eric,,,,my goof. They flow very similiar to some 350 heads from 2500-5500 depending on differant factors.But the port volume for 416 heads is more than 150. But let him and others check with the "Head specialists" and they will see,,,I'll not argue the point anymore,thanks.

You don't flow heads at 2500 to 5500.
They are "flowed" on a "flow bench".
I am a "Head specialist".
I am not trying to "toot my own horn" but I am a little knowleable with cylinder heads.
Try www.e-squared-engineering.com
A 461 heads port volume is only 155cc give or take a couple cc's.
A common 882 open chamber head has a port volume of 151 cc.
I am not going to argue the point any more either.
If you don't believe me buy a chemist berret and cc away.