so , how far can i port my heads? im going eXtreme. is there any danger areas to watch for?? likely hood of hitting water/oil ways or anything?
cheers ant

 

You can overport the heads. That bump that is in the runner chould be smoothed out but don't completely get rid of it. Be ready for a few people on here to tell you go to the 3x00 top end.

 

why would you not get rid completely RS?? can you expand on overport?
ref 3x00 for others- yeah i know i could do that but ive a build in mind and this is the route ive taken ( for a great no. of reasons as well !). accept it. dont bother to try changing my mind ! ;-)
all help on iron head porting greatly appreciated
thanks RS

 

Here is what mine look like:


I bought them a while back when a member here parted out his motor. They need to be cleaned up a little. That "shark fin" at the bottom of the runner increases flow so the best thing to do is to like that.

 

ahhhh nice one, they look pretty good, i guess the fin is to guide flow around the valve stems? the biggest problem i see is the 90 degree bend in the flow - the 3x00 heads are much taller i see for beter flow-less of an angle, so i want to concentrate on the 'inside' of the corner to make it less of an angle.

 

You can do that with the MIM and UIM. Besides gasket matching the intakes the best thing that you could do is attack the inside bend of the runners to help the air flow better in that area as that is where it is the most restrictive.

 

dont take any offense to this, because none is meant by it.... but if you dont know much about porting, please dont try it. this is a very touchy area on an engine. ive bench flowed a good number of heads before and after modifications, and you can tell who is a novice and amature. most who do it their first time will get the following results: bigger ports, loss of flow and velocity. its not just as simple as "grinding out and making the opening bigger". there are certain bends and curves that, if integrity is lost, will compromise flow. you need to know a lot about the heads your working on, and porting in general. its best left to those who know how, again, dont take offense. i found out the same way, luckily i was in a class and it was a "junk head" so i didnt lose anything on it.

 

hey no probs dave, ive access to spare heads and i have a good understanding of flow and velocity and stuff, im quite tech minded, as i said before and as RS has confirmed my first main concern is that sharp bend and therefore getting at the inside of it. i know the importance of velocity, but heres a Q when do you sacrifce velocity for capacity ? im looking for big rpm's eventually and im sure i can get it from the ol iron's.......

 

I think that that requires alot of porting. Way more than I have done to mine.

 

well when i say that, thats the plan A for fun but i havnt decided on my cam yet, ill wait to see how the heads turn out first. my biggest concern was not finding a water/oil way. is there any blueprints kicking around? how likely and in what area is this likely?

 

Here is what I dont understand. From my understanding, the UIM/MIM is the biggest restriction in the intake. So why wouldnt you get a basic P&P done to the heads and then try to get the UIM/MIM flowing better.
I havent looked into this lately, but dont the heads already flow more than the intake?

 

The heads do flow much more than the intakes.

 

im not using stock intake, i know its pants.

 

You can't port the iron heads out much. Thin castings from the factory. Take out too much in one area and you risk craking the heads. Any porting you do should be done judiciously, or better yet with a flow bench. Best idea is just keep the stock shape, smooth out casting marks and polish it up with some rough grit foam polishing wheels. You might consider having it machined for larger valves (3400 valves) and having them back cut to improve flow.

 

now that sounds interesting, good thinking batman!! how much room is there? i believe the 34's have bigger bores so they would have the room for bigger valves. hmm ill look into that one ;-)

 

The newer iron heads had 1.72 intake, and 1.42 exhaust valves. 3100/3400 heads came with 1.76 intake and 1.42 exhaust valves.

 

oh, no difference then!! ill still look at other valve options mmmm stainless shiney shiney mmmmmm

 

after gasket matching the intake ports be careful not to feather too much of it away because you could get into the pushrod holes, also dont smooth out the intake ports too much, you want them fairly rough. I just did a set myself, but it was mild.

 

The iron heads have 1.6"/1.3" valves. 3400 valves w/ backcutting would be a nice improvement. While you're at it you might as well grab the beehive valvesprings and roller rockers off newer heads and throw them on. The rockers are only roller fulcrum, but still better than the stock stuff.

 

ill have a look at valve sizes as it seems people have different ideas, im guna get the crane springs matched to there cam and the rollers as well.

 

The early iron heads had small valves, the 'HO' mpfi heads had larger valves and the gm performance iron heads have 1.76"/1.42" valves. Matched springs are good, but beehive-type springs (3x00, LS1, comp's beehive springs) are a much better design. For a solid profile like you're planning on the LS1 springs would be a good match.

 

You want the intakes a little rough so the turbulance helps atomize the fuel/air mixture better- the exhaust you can make much smoother. Also, you could match the ports and send the heads out for extrude honing- save you a lot of Saturday nights with the dremel.

Finally, an old hot rodding tip: keep the intakes slightly smaller than the head intake opening and the head exhaust port slightly smaller than the exhaust manifold/header opening. This creates a slight vacuum as the gases pass through the head and helps with gas scavenging...

 

ok i may have skipped some stuff and being repetitive now, but heres what i saw and am going to comment on. 85 and up heads have 1.72intake/1.42exhaust valves. when you port these heads, do NOT grind down the "thermactor hump" when you look down in the port, youll see a lump in the middle of the port, its there for a reason. you machine it down a lil bit, but DONT get rid of it. and it is very true about leaving the intake a bit rough for atomization of the fuel. go ahead and gasket match the ports, good thing, as well as smoothing over any sharp edges before the valves.

 

Do you know that dragsters used to glue a paper clip in the vertical position in the center of the intake ports?

This has been discussed many times over.

Keeping the "shark fin" is a good idea both for atomization and for other characteristics (like above mentioned vacuum, swirl and velocity).

Good advice, DR.