Iron 302 heads....aka doorstops

These things are cheap.....probably harder to sell than E7TE heads. I picked up a rebuilt pair for 30 bucks. 1969 302 heads with 58cc chamber, hardened seats, new valves, and knurled guides. "Why on earth would you bother to trade 2 small bills for enough cast iron to wrench your back? seems dangerous." Lol...would be a fair question for a normal person, but I needed something to experiment with due to the fact that I watched one too many of David Vizards power tech 10 series. It was one where they ported old junk heads, and I love junk. I love it so much that I built something called a "Floating pressure drop" flow bench. It has a manometer (I had to research what that was) that you can build out of 1/4" clear plastic tubing and fill with windex. The picture explains it better than I can. One end is just vented, and the other end is plumbed to some 1/4" copper tubing that runs through a hollowed out spark plug. The spark plug gets installed in the test head, and the head sits on top of a 4" x 2" fernco style ABS connector with the lettering on the end very carefully razorbladded off. See pic. shop vac pipe in the 2" side. Block up the head, turn on the vac, make sure you got no leaks (put in exhaust valve with checker spring and tape over the port so the vac cant suck it open) see pic. You can now measure the drop in water inches at each valve opening increment, make changes to your port, and see what happens. I have nearly completed porting the old iron heads, and they are almost ready to be tested on a real flow bench.......but finding anyone who does it has proven fruitless.


So what did I learn about these heads and what they like? They seem to like de-shrouding, bowls blended, valve guide shaped to point at spark plug, about a 60/40 bias in material removed from the sides of the throat adjacent to the valve stem....60% on the cylinder wall side. Remove enough material from the roof on both sides of the guide boss, 60% on the 60 side and 40 on the other until your finger can glide through there without getting crowded.....well, at least my skinny finger.....almost nothing taken from the intake runner. All it got was about .040 smoothed off the top 3/4" of the pushrod pinch point. The true bottleneck in these heads, or any head, is the hole the valve closes off. Bigger valve, bigger hole......but that ups the cost, and do you really want to go there? Also, if you try this at home, dont mess with smoothing, shaping, or improving in any way the quench side of the chamber adjacent to the intake valve. (see final pic) Due to how the air wants to flow through the valve, this region is a place of less flow and needs to stay that way so the path of more and better flow gets followed. By the way, I cc'd the chamber in the pic, and it went from 58 to 60. Two cc's is a small price to pay for the increase in air flow, and there is also milling......


According to some of what I read, .25 -.375" is needed do fully deshroud an intake valve, and probably .25 minimally on the exhaust. In a 4" bore, .37+1.78+.040+1.45+.25 = 3.89. Simply adding bigger valves will begin to trade a less pinchy pinch point for some shrouding, and since we only got 3 inches of the bore to fill, it can be done reasonably with tiny valves plus a little more duration on the camshaft if you want to go fast. If you just want to go a little faster, leave in the tiny valves. Since the intake port didnt get hogged out, the speed of the mixture will be beneficial. There is also no need for an intake with big ports......but longer ones will help.


On the exhaust, the thermactor bumps got removed, valve guide trimmed down, and bowl blended. the exhaust port on these heads is noticably biased to the cylinder wall side of the port, and since the bump was placed over there, removal of it makes that bias more pronounced. I do not know if that is a bad thing, but it is good that the bump is gone. The valve gets deshrouded in the chamber, and David Vizard also highly recommends putting in something he calls a scavenging plateau. It is like a ramp from the quench side of the chamber that meets the exhast valve seat so gasses can escape all the way up to the moment the valve shuts (see final pic).
He also recommends the corner on the edge of the exhaust valve face be rounded to aid in gasses turning that corner to go down the exhaust port.


Yes....I am digging up 50 year old speed secrets, playing with 50 year old parts, but always gaining more understanding of what fills cylinders, tradeoffs involved in doing it, and the roles of supporting parts. Maybe I got too much time on my hands, but I get a thrill from making old junk perform above average. If anyone else plays with this stuff, let me know what you do.

 

this should be more..."off topic" than "technical"...LOL

 

Never mind the man behind the curtain, if it isn't shiny/new he isn't interested...

It's good tech, back in day(before the shiny, lightweight stuff) some of the local corner carvers were porting 289/302 heads, kept them ahead or at least even with the Chevies with better flowing heads.

A few years back one guy I know, working part time at a machine shop, tried to port E6SE(high swirl) heads. That didn't end well. Major improvements required removing too much material, broke into water passages.

 

Yeah, all the tech I can supply was marginal 30 years ago, but to me it is brand new. I will say this though, and it may have relevance. Comparing the performance of two ports "at lift" numbers may be deceptive in this way: The lift at .20 for one port may be exactly the same for another ports .21, and they might both follow the same curve......but one lags behind 10-15 thousands lift. On paper one looks much better, but in reality they may be nearly identical.

Another thing I will add is this: If someone is building a 302, and they are not going to push it over 5800 RPM, the above heads, in my opinion, would easily handle that and more with the right cam. Would the job get done better by some heads with 170cc ports? Maybe not.....but the 170cc port heads dont need to be messed with and are just as or more economical as iron that needs rebuilding and port work. If you need to fill a larger cylinder than one on a 302, or supply the air to get to 6500-7000+ RPM, by all means get a bigger head. Reving that high might require more expensive valve train parts too though if you want it to last.

 

oh, I forgot to mention, back cut the intake valve slightly to get rid of that ridge just above the sealing surface. I have not priced a 3 angle valve seat grind, but that is supposed to be a big plus too.

 

hope you know I'm joking with you.
I know I have no interest in the subject matter but I love your passion for any project you take on.

......

 

I know mister....and I dont expect anything to do with doorstops will translate to an LS...so in your case it is truly off topic. hahahah.....always enjoy when you chime in though sir!

 

I saw that on YouTube. Its very interesting to me also and iv ported a few sets of heads myself. I wish I had the knowledge he has. But, one thing I can say at least here in Central Mo. You can buy heads that flow better for the money it costs to build a set of heads like that. I did a set of GT40 iron heads a few years ago and they came out really nice with minimal porting and a 5 angle valve job and I had them decked also. I had more in them then they were worth. For whatever reason machine work is insanely high now.

 

I have a set of GT40 heads on my car currently. I am tempted to pull them off and do the chamber work as they are only bowl blended and milled .040. The heads I am experimenting on did not get solid improvements until the chamber work was done. I was surprised at how much rounding off the chamber edges along the sparkplug side helped the intake valve. De shrouding only added a little until that was done. I need another set of stock junk to figure out the value of that step by itself.

The only step that most online porters do that I am not convinced is a big plus is cutting back the pushrod tube....and it could be that this step is only fruitless when NOT increasing valve size over stock. Also, I have not done the multi-angle seat grind, which may also result in a gain at that spot. It is interesting how some areas are not a problem until other areas get improved, and also how work done to certain areas cancels out improvements made elsewhere. Maximizing a stock head without doing anything that makes it go backwards seems a bit tricky and intriguing. If just what happens in the intake port and valve is this fussy, its no wonder that the choices to make on either side of the valve seem endless.

 

Thanks for posting this information, I find it interesting and think about working a set of iron heads sometimes but I understand that I could actually do more harm than good.

 

The stuff you're doing/talking about is before we had puters and all these fancy machines to tell us what to do. You actually had to be a mechanic or think out of the box. Smokey was the master of that and proved it many times.
Now it's just buy something new and shiny off the shelf and it'll make HP. Prostock in the early days was something to watch.

 

Those type of mods may be considered old school, and yes there are more off the shelf performance options available, but there is some satisfaction in taking iron factory junk and making it the best it can be. I am still running 1970 351 Windsor heads on the Comet with larger Chevy valves and mild port on the exhaust.

 

Was this mod a big improvement over what it replaced?

 

My current project, 71 block, 72 460PI heads all going in a 68 Cougar. C-4 trans and 9" rearend.

 

It is hard to say. I already had the heads sitting around from awhile back, and I put them in the car at the same time as a newly rebuilt 5.0 h.o. short block, so there is no way to compare. However, in the 80's before all the SBF head options, I pulled the D0oe heads from my 70 Mustang (351w), had screw in studs & guide plates installed with the Chevy valves, and spent many hours porting/polishing those heads. After reinstalling them on the same engine, it was a noticeable improvement in the performance. Today, if I was starting from scratch and did not have any cylinder head money, I would probably just use GT40 heads and invest some time on the exhaust side. Way back then, there were machine shops that would do the Chevy valves/studs/plates for about $300.