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Discussion Starter · #1 ·
Several years ago I picked up a pair of iron heads from a local wrecking yard. I don't know much about them other than someone wrote 96 Impala on them. No idea of mileage or why the car was scrapped. The thought was to work on them a little here and there and eventually have them ready to install on the wagon at the same time as a cam install. That plan has now changed due to a low oil pressure problem that popped up. DETAILS HERE. I'm now going to be building or rebuilding a complete engine for the wagon and need to get these heads ready to go on the new engine. I'm not in a hurry since the wagon rarely gets driven - especially in the winter - but I do want to keep it moving forward.
Why am starting with iron heads instead of aluminum? To be honest, I went back and forth a bunch of times and I'm still not convinced I made the right choice. The light weight and easy cutting of aluminum are big benefits. The iron seem to be easier and cheaper to find locally. They also have a reputation of being less picky about head gaskets and supposedly have redesigned ports that flow better.
I've done some searching to try to quantify the flow difference from the improved port design and the best I can find indicates that the aluminum heads flow 206 CFM on the intake and 161 CFM on the exhaust. The irons flow 226 CFM on the intake (which seems to match what I can find for stock Vortec intake flow). If anyone has better data, feel free to share.
What are my plans for this head build? Subject to change, but:
  • I currently have the press in rocker studs pulled and I'm going to machine for screw in studs.
  • I have VS2700 springs from Bullet on my shelf.
  • I also have a set of Comp self aligning ultra pro mag 1.6 rockers on the shelf.
  • I'll measure the clearance of the valves and install bronze guide liners as needed to bring any worn ones back to spec.
  • They will get a performance valve job for sure and I'll very likely install 1.60" exhaust valves. I haven't decided if I'll go to 2.02" intake valves.
  • The chambers will get work to unshroud the valves for improved flow. Unfortunately this drops the compression a bit which is opposite of the direction I want to go. So..
  • I may get the decks cut slightly to bump the compression back up.
  • The intake and exhaust ports will both get work to improve flow, but this part is still up in the air. I haven't decided if I'll just go into this blind and be conservative in my cutting while following the Vizard Vortec porting videos on YT - OR - if I'll build a simple floating depression flow bench so that I can measure my progress.
  • I might do ceramic coatings on the chambers, ports, and valves to minimize heat transfer, but again am undecided. The before and after dyno tests with completely coated engines seem to indicate there is not a lot of bang for the buck with the coatings.
I have barely started on this project, but I wanted to start posting pictures and commenting as I go, while things are still fresh in my mind.
 
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Discussion Starter · #2 ·
This is what I'm starting with. These crusty critters looked a lot better when I first brought them home. A couple years of sitting in the shop has them looking like garbage.

Machine Auto part Metal Gas Fashion accessory


You may notice one exhaust valve has already been removed. I had pulled it shortly after I got them to get some measurements. I managed not to lose the retainer, spring, or locks, but I haven't yet figured out what happened to the valve. I'm not planning to reuse them anyway, but it bugs me when I lose parts.
My first step was to pull the rest of the locks, retainers, springs, and seals. I built this valve spring compressor several years ago for a flathead twin I was working on. Turns out it works fine for LS and LT engines as well. I have one of the stamped steel lever type spring compressors that utilizes the rocker stud as a fulcrum and I HATE it. This C-clamp compressor works MUCH better.
Wood Window Rectangle Fixture Material property

Wood Gas Motor vehicle Engineering Auto part


The valves feel like there is very little clearance to the guides, but I still need to clean things up and actually measure to be sure.
The press in studs are getting replaced with screw in. The VS2700 springs hit 370 lbs at 1.2" compressed height which is well beyond the 280 lbs generally considered the limit for press in studs. Studs without a hex built into them are the easier way to go. With these, the press in studs get pulled, then tap the bosses to 7/16", and screw the new stud in. This is definitely better than press in studs, but is considered by many to be inferior to using the studs with a hex on them. The hex will seat against the stud boss and allow the stud to be tightened into the head with a higher torque. The GM studs seemed to have a good price from Summit, so I went with them. These do have the hex in the center and will require cutting down the stud boss to create a flat spot for the stud to seat and put the stud at the correct height.
I was going to use this tool from Summit to pull the rocker studs, but some YT videos seem to indicate they get marred up when used for this. I built a puller instead to pull the studs.
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What size is the LT1 you're rebuilding?
If it'll still be a 350, then why make the valves bigger than 2.00" intake & 1.56" exhaust?
Unless you plan on a larger engine?
 

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Discussion Starter · #4 ·
What size is the LT1 you're rebuilding?
If it'll still be a 350, then why make the valves bigger than 2.00" intake & 1.56" exhaust?
Unless you plan on a larger engine?
I’m not planning to stroke it, so it will be in the 350 to 360 range.
The 2.0/1.56 valves are a possibility and are capable of supporting the flow I’d like to see. Valve sizes are still up in the air.
 

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Best of luck to you, look forward to seeing the end results. I bought a spare engine and entered the planning stages of an engine build. Sadly some parts are currently unobtainable and will stay that way for some time. Decided to bag the wagon instead and get it painted.
 

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Discussion Starter · #8 ·
… if you're going to port the heads yourself, Vizard has some pretty good ideas for DIY flow testing in his book, not to mention where to port for maximum effectiveness.

David Vizard's How to Port & Flow Test Cylinder Heads (S-A Design): Vizard, David: 0884265645592: Amazon.com: Books
Some of his flow bench data can also be found here:
 
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Yep, good book. Unfortunately, those flow balls he uses are ridiculously expensive for what they are. Something like 150 and up range when I looked. I'm thinking to just get ball bearings in those sizes and tack weld a rod onto them :)
One of the more basic techniques he uses is a shop vac and a vacuum gauge. What you do is create a flow bench with some lumber and pvc pipe, and then take a small diameter copper tube - 1/8" or something like that - and put a 90 deg bend in the end. Hook it to the vacuum guage with some hose and start the air flowing through the port. Hold the end of the tube perpendicular to the port surface maybe 1/8" or less from the surface. Anywhere there is high vacuum, that means high velocity airflow at that spot in the port.

... And now I can't remember if you're supposed to grind away material where the vacuum is high or where the vacuum is low. I guess you're going to have to buy the book. This is going to bug me, I'll probably end up buying it myself to refresh my memory. Lost my copy two moves ago.
 
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Discussion Starter · #11 ·
Yep, good book. Unfortunately, those flow balls he uses are ridiculously expensive for what they are. Something like 150 and up range when I looked. I'm thinking to just get ball bearings in those sizes and tack weld a rod onto them :)
I was also planning to make my own flow balls. Haven’t put much thought into them yet. Whatever sphere I can find with an appropriate diameter will get glued or tacked to a piece of wire most likely.
 
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Open the ports, and raise the intake side as much as you can. There is plenty of iron there.
Probably last things I would do. Vizard's testing showed the port and the pinch area already flow way more than the valve area and should be focused on first. And in his 5 rules of porting, one of them is air is heavy. So more can be gained working the floors where air wants to lay.
 

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Discussion Starter · #14 · (Edited)
I bought this cutter from Summit to cut down the rocker stud bosses.
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It pilots in the stud holes and is meant to use free hand with a drill. I decided I didn’t trust myself to keep it straight as I cut down the boss. If the flat it creates is not perpendicular to the stud, the stud will contact on one side first and put a bending load on the stud. After thinking on it for a few days I made a fixture to keep the cutter located.
The bracket bolts to the intake manifold surface and an alignment pin slips into the stud hole. There is no point to the threads you can see on the pin, it is just what I had on hand the right size.
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Next the alignment plate and bushing get installed over the alignment pin and the plate is clamped tightly to the bracket.
Wood Gas Auto part Machine Metal


The pin and bushing can now be removed leaving the plate centered over the stud hole.
Wood Gas Tool Machine Composite material


The cutter drops into place.
Wood Gas Fixture Composite material Screw


Then the bushing goes back in to support the top of the cutter. With the pilot at the bottom and the bushing at the top, the cutter is very well supported and has no chance to get out of position.
Wood Gas Metal Auto part Machine


Ran out of time tonight, so I’ll try it out tomorrow.
 

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Probably last things I would do. Vizard's testing showed the port and the pinch area already flow way more than the valve area and should be focused on first. And in his 5 rules of porting, one of them is air is heavy. So more can be gained working the floors where air wants to lay.
To the best of my recollection from 20 years ago (and my notes), Mr. Vizard didn't borrow my heads for flow testing. If you look closely at the attached photo (linked above) it should be evident that the valve bowl and runner transition areas have had significant material removed to support the 2.02/1.60 valves, even if my amateurish photos don't show it in detail. One of the beauties of the iron head is that it allows more material removal than its aluminum brother. Those over in the Y-Body forums might take exception to that, and possibly get a painful twist in their thongs, but this is a B-Body forum.

The intake ports were raised because although apparently every other SBC head which has ever been in a hotrod magazine responds to weekend flow-bench testing in a way that may not show a benefit, GM's professional powertrain engineers established the restriction areas of the castings and raised the ports on the subsequent LT4 heads, and it was presumably not done to reduce power. This operation was done in conjunction with lowering the floor in the valve bowl end of the runner to ease that transition.

And before you ask, the runners of the intake plenum were raised accordingly to match, and gaskets "massaged" to fit.

As for head preparation, I also did the stud boss machining as well as the spring seat and guide preparation on my bench, without having to waste any of the valuable time of local automotive machinists.

http://www.wwdsltd.com/files/RockerStuds.jpg

 

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Discussion Starter · #16 ·
I got out to the shop for a few minutes during my lunch break. Measured the hex portion of the new studs so I knew how much to take off.
Watch Analog watch Clock Font Measuring instrument

I chucked the cutter into the drill so that the drill chuck would bottom on the alignment bushing at the correct depth (didn’t take a picture) and cut away. Went very well and I expect to finish them up this afternoon.
Wood Gas Auto part Engineering Machine
 
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Discussion Starter · #17 ·
To the best of my recollection from 20 years ago (and my notes), Mr. Vizard didn't borrow my heads for flow testing. If you look closely at the attached photo (linked above) it should be evident that the valve bowl and runner transition areas have had significant material removed to support the 2.02/1.60 valves, even if my amateurish photos don't show it in detail. One of the beauties of the iron head is that it allows more material removal than its aluminum brother. Those over in the Y-Body forums might take exception to that, and possibly get a painful twist in their thongs, but this is a B-Body forum.

The intake ports were raised because although apparently every other SBC head which has ever been in a hotrod magazine responds to weekend flow-bench testing in a way that may not show a benefit, GM's professional powertrain engineers established the restriction areas of the castings and raised the ports on the subsequent LT4 heads, and it was presumably not done to reduce power. This operation was done in conjunction with lowering the floor in the valve bowl end of the runner to ease that transition.

And before you ask, the runners of the intake plenum were raised accordingly to match, and gaskets "massaged" to fit.

As for head preparation, I also did the stud boss machining as well as the spring seat and guide preparation on my bench, without having to waste any of the valuable time of local automotive machinists.

http://www.wwdsltd.com/files/RockerStuds.jpg

What did you end up with for flow with the work you did?
 

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Discussion Starter · #19 ·
That's a loaded question. At what lift, and at what pressure differential. Every flow bench has settings.
I was deliberately vague since I don't know what data you recorded when you did your work. I'd really like the complete flow curve with flow at every 0.050 or 0.100" along with port volume before/after measurements. But even just peak flow before/after would be interesting.
Standard flow bench depression is 28" of water, I believe. If you did not use this standard or did not convert, then before/after measurements would still help us quantify your results.
 
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Discussion Starter · #20 ·
Finished cutting down the stud bosses.
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Next I believe I’ll attack some of the rough spots in the casting with the die grinder. I can’t put the alignment block between the stud bosses with this ridge in the way.
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