[KNanthrup]

Hey guys. It's winter and so I'm just tinkering in the garage when I get a chance. The other day I realized that I have an set of old iron heads that came on my crate engine. They're cast #33417369 and I really don't know much about them other than that they're 76cc ports and came on the block (#10066036) which is supposedly a 79-85 GM goodwrench engine, it has 4 bolt mains. But then when I look up the heads, it says they're from a 90+ GM goodwrench crate engine, so maybe the block is newer than I thought or maybe they just changed heads somewhere.

Anyways, I'm really not doing anything with them and I've got a grinder out there. I've been thinking that maybe just for fun I would try doing my own port job and try to widen out the runners to get some flow going. Maybe a little more machine work like screw in studs and whatnot and then toss them on the engine to see if I make more power than I am currently. I figure it might be a fun experience and possibly end up with some nice gains, plus I don't need the heads so if I screw up it's no loss. Anyways, I don't know much about head work but is it possible to make these old iron things flow pretty good with some porting? I figure as long as it's got a good chunk of iron to work with it seems like it would have as much potential as any.

My other choice would be to keep the #369 heads for backup and try to work with the #376450 heads that I have on it now. The #450 heads are from smaller sized SBC like 305 and below, but the shop that sold them to me said they could make good power. They're 64cc and have 2.02/1.60 valves with a back grind, plus a few small machine extras but no porting. Obviously these are high compression heads, do you guys think I have more potential or getting power out of these or the other heads? I've had a lot of people frown on these because they came off a 305 and below smallblock, whereas the #369's came off a 350 crate.

And don't worry, if I do decide to I will try to read up on self-port jobs, I know there's some good write-ups out there. Suggestions? Comments? I'd really appreciate input from thosewho are experienced.

p.s. i have absolutely zero money to spend, so don't tell me to switch to vortecs or ditch iron for aluminum. in good time it will happen but im working with what ive got for now

thanks guys!




By the way, I found some more info on my engine parts here. With the 64cc heads I have now, my compression is about 9.1:1, if I go back to the 76cc it will drop to 8.5:1.

Also, the #369 heads I want to port are using 1.94/1.50 valves. My #450's have been upgraded to 2.02/1.76.. so i don't know which to use now. It seems if I had enough meat to port on the #450's that with the larger valves and higher compression that I could make more power. I'm so confused!

Oh and I actually found the exact specs on my engine the way it came. Here's a link... this is the exact engine I had received, all the part #'s match. I am using a much larger cam and the #450 heads right now though..
www.paceparts.com/index.asp?PageAction=VIEWPROD&ProdID=24755

 

[Max Keith]

porting heads

The bowl area under your valves is the most critical part of your porting job. that is where the bulk of the gain will be regardless if you mess with the runners or not.

I would recommend finding a book on porting out SBC's as porting isnt just a matter of grinding out material.

You can mess up the flow of a set of heads by taking material out in the wrong places or as in the case of an often made mistake, opening up the bowls too much, causing fuel air flow stumble, and even worse, getting into a water jacket.

If I were in your shoes, I would do what I did to learn some about porting. Go down to your local auto salvage yard and pick up a set of junk heads to play with first, so you get the feel of what you are doing, and can see whats happening without trashing a good set of heads. This will give you 16 ports to destroy, by using a set of junkers first.
If you tell them you will bring them back when you are done grinding on them, most likely they will let you have them for nothing, or a couple bucks at the most.

 

[KNanthrup]

Thanks for the tips. I will certainly do this and I'm actually reading up on porting as we speak. I also ordered a port and polish kit which comes with a porting guide as well. I'm doing this more for a fun and learning experience with hopes that I may perhaps be able to even squeeze more power out of my setup. It's not crucial that I improve the heads, it would just be kind of a cool project with potential outcome.

I guess I'm looking more for tips on which heads to work with, or even whether these heads have any potential for making good power or not. I guess I should have the thing dynoed to see what kind of improvements I may get but I'm not sure if I'll get around to that. I suppose any stock heads have room for improvement. I was looking for flow numbers on these heads but was not able to find any. I read that the #369's are supposedly real similar to #882's and I did find some numbers on those.

 

[Max Keith]

Tieing up the loose ends

One thing you dont want to do is polish the intake runners or the bowl. Testing has shown that this will cause the fuel air mixture to come out of suspension and cause serious loss of power. Instead, you will want a more of a florentine finish in the intake runners. This all has to do with laminar air flow, and not being an aeronautical engineer, I really dont adiquately know how to explain it.
However, on the exhaust side, you cant ever get it smooth enough.
Since you dont have any fuel air mixture to contend with on the exhaust side, you can polish the daylights out of them. An added bonus to polishing the exhaust ports is that this will reduce all those neat little places carbon can build up and eventually inhibit the flow.

To do your main grinding, I would recommend a carbide rotory file. The ones I use are 1/2 inch in diameter and straight sided with a rounded nose, looking a lot like a round nosed bullit.

 

[68Velle]

Well if you could spend a little money, you could take them to a machine shop with a flow bench. Run them before any work, and then after.

 

[skooldaze]

Porting bits

One thing you dont want to do is polish the intake runners or the bowl. Testing has shown that this will cause the fuel air mixture to come out of suspension and cause serious loss of power. Instead, you will want a more of a florentine finish in the intake runners. This all has to do with laminar air flow, and not being an aeronautical engineer, I really dont adiquately know how to explain it.
However, on the exhaust side, you cant ever get it smooth enough.
Since you dont have any fuel air mixture to contend with on the exhaust side, you can polish the daylights out of them. An added bonus to polishing the exhaust ports is that this will reduce all those neat little places carbon can build up and eventually inhibit the flow.

To do your main grinding, I would recommend a carbide rotory file. The ones I use are 1/2 inch in diameter and straight sided with a rounded nose, looking a lot like a round nosed bullit.

When I did my porting I went to my local "Boeing" aircraft maker's "SURLPUS WAREHOUSE". They had file bits, drill bits, anything you wanted that would go through steel or cast iron like a hot butter knife! Depending on how "serious" your project is. A surplus warehouse like these can get you a whole load of bits for just a few bucks... I buy bits for around $4.00 a lb!!
Except specialty bits and they cost around $1-$3 a bit! Still cheap!!

 

[xntrik]

You are right, there are lots of good porting sites out there.
Get a grasp on how to do SBC heads,

Don't hog them out, just blend and smooth out what is there.

try to visualize how air moves. Contour the guides and smooth and polish everything. Make the short turn radius smooth. Blend in all lines and lumps.

They might not be as good as somebody elses, and maybe you ground too far in places..... Generally speaking, if you don't hit water you can't hardly ruin them.

I have seen first time DIY head porting that made my eyes bug out.. yikes..... and he put them on a 350 and it ran like gangbusters.....

Figure out which compression ratio will work for you. 9/1 for 87 octane is good. Gas is not going to be better quality or lower prices, ever....

Remember the experts' 80/20 rule of porting. The first 20 % of your time will yield 80 % of the airflow increase.

 

[machinestheman]

i just recently posted a thread of the same question and one reply contained this it was the most helpful
http://www.chevyhiperformance.com/techarticles/95518/

 

[xntrik]

here's his thread, there is some good stuff in it

http://www.hotrodders.com/forum/head-porting-76372.html

 

[machinestheman]

here's his thread, there is some good stuff in it

http://www.hotrodders.com/forum/head-porting-76372.html

just wanted to comment nice link