3.4 Cast Iron Heads port/polish

[mikewzman]

Sure would like to hear from anyone that has done a port /polish on the cast iron heads? There is a "bump" in the front of the intake ports. From what I have read, your not supposed to mess with this too much. Has any one ever removed it and seen what happens to the engine performance? Do the aluminum heads have this same bump? Are there any good links from someone that has actually done a port/polish on the iron heads?

Any help would be greatly appreciated.

Thanks.

[neo71665]

Thats the sharkfin. From what I understand in theory if you plan on running boost of some sort it could be removed with no ill effects. Otherwise leave it in there as it helps out in the lower or mid range RPMs.

[Superdave]

the aluminium heads are completely different and flow like 50% more stock

like neo said, for the iron heads, leave the fin for N/A and cut it out for boost.

[34blazer]

ive done a full port & polish on the irons and i left the hump in there, just trimmed down a little. with N/A the port flows 10% more than without it. the downside is the port volume is significantly less and the port will stall faster. the bowls are terrible and need some tlc, the short side radius needs lots of work as well

[mikewzman]

Thanks 34blazer. Have you run across any sites that have any details about porting the cast iron heads. I was curious about what you said that removing the fin acutally makes the port flow less causing a stall. Where did you find this info? I really would like to understand more why the fin is there in the first place. It just seems completely counter to good flow principles. In my thinking, the more open, the better the flow. I read somewhere that the fin was there to cause turbulance to help in mixing the fuel/air better before it gets to the valve. Wouldn't better injectors that atomizes the fuel better work just as well (if they make such a thing). Then the fin could come out. I am really wanting to hack the thing out of there, but until I have done my home work I really can't. There's no way to put it back once its gone.

I know the Al heads are completely different, but do they have the fin also?

[34blazer]

i found a book years ago covering some of the more popular v6 engines at the time. its old but it covers the first gen 660 fairly well.

http://www.amazon.com/V-6-Performance-Pat-Ganahl/dp/093147213X/ref=sr_1_2?ie=UTF8&s=books&qid=1231993509&sr=1-2

removing the fin will cause the port to lose some velocity, thats why the engineers developed that, to keep velocity. and the fact that the ports sit low has an adverse effect. when i just took a carbide to blend the bowls and remove the casting rough, the port gained 40 cfm. so the intake flowed ~135 at .480" lift before and ~170 at .480. after that i studied the ports and did some serious grinding and sanding. the throat around the valve seats really needs some serious blending; if you port match, be careful with how you blend in where the port wall bends around the head bolt boss. if you are really serious about doing work to these, study the ports before you do any grinding.

the Aluminum heads dont have the fin

[SappySE107]

You gained 40cfm from a bowl blend? That is insane.

[34blazer]

You gained 40cfm from a bowl blend? That is insane.

i was pretty amazed myself i havent had them flowed since i did the rest of the porting/polishing

[ForcedFirebird]

I'm curious to see how mine flow.

I really like your approach on the guide area there, 34blazer

[ForcedFirebird]

You gained 40cfm from a bowl blend? That is insane.

Iron head rule

[34blazer]

I'm curious to see how mine flow.

I really like your approach on the guide area there, 34blazer

Thanks

[mikewzman]

Thanks again 34blazer. This is a lot of help. Another question. I've done a lot of studying on head porting/polishing, but this is my first. I noticed you removed the flat area completely from the valve guide. I was told to leave a little of it flat, but from a flow stand point I like what you did. Just curious, if you read or from experience know if its OK to take the valve guide down that much.

Thanks for the pictures and the link to the book. Great stuff.

[34blazer]

Thanks again 34blazer. This is a lot of help. Another question. I've done a lot of studying on head porting/polishing, but this is my first. I noticed you removed the flat area completely from the valve guide. I was told to leave a little of it flat, but from a flow stand point I like what you did. Just curious, if you read or from experience know if its OK to take the valve guide down that much.

Thanks for the pictures and the link to the book. Great stuff.

you can take it down to where i have mine or you can leave a little meat on there. those bowls are really small in terms of volume. and the port walls are really wavy. theres more than enough of the guide that can support the valve stem. i made sure of that before i started grinding away. i also asked Jim at Weber racing to make sure. Weber racing reworks the buick GN 3.8 heads to rival those of Champion irons. these heads were my first P&P job , but with enough reasearch on the techniques it helped out alot.