My heads are working fine but I took them off and dissassembled them so that I can port them. They are #416 305 heads and were rebuilt by a "reputable" machine shop about a year ago. The dude at the machine shop said the rebuild included cleaning, magnafluxing, and a 3 angle valve job (and he also threw in the word "umbrella"?).

So, my first question is: Can you physically see the 3 angles? All the valves only have 2 angles on them - or am I missing something like the seat is the 3rd angle? The heads were definitely clean and had new seals when I got them back; I'm just wondering if they skipped the valve job.

I noticed that the backs of all the intake valves are caked with carbon . Is this normal or do I have a carb problem or something? What would be the best way to clean it off?

Any tips on porting? I've read a couple articles and plan on gasket matching and smoothing with a pnematic die grinder. Thanks, Teddy Z '84 Z28

 

You should be able to see the angles if you look VERY close. If they are covered in carbon, use a green scotchbrite pad to shine them (WARNING: If you've gone this far, you may have to relap the valves to properly seal them)

p.s. all my tech tips will now come with a waiver.

 

umbrella is the type of seal on the valves, i doubt if you can see much of a 3 angle grind after it's been run for a year, to clean the carbon off the valves i use a wire brush in a bench grinder

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ICON Motorsports

1st & 3rd

 

what 305 do u have If its a 87 and up TPI why dont u get a set of used corvette heads 87'-91' have them ported and they will do wonders for your 305. Keep in mind these heads work 30% better on a 305 than 350.
Used corvette heads=$300.00-$400.00
Porting service=here in NY $250.00 a bargain.

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92' camaro
New 305 block TPI conversion, Flat top pistons,Bore over .30 Forged parts all around,Edelbrock intake,ported plennum,ported corvette alluminum heads, accel cam,52mm throttle bodie, SLP runners Home aid cold air induction, Air foil,ford SVO 19lb injectors,fuel regulator,cloys timing chain, comp alluminum roller rocker arms and pushrods MSD 8.5 mm wires, bosch plattinum plugs, hypertech cap & rotor and coil, Edelbrock TES headers, free flowing catalytic converter and a 3 inch force II flowmaster exhaust system, and a 3 inch cutout,Zoom multi friction clutch, T-5 tranny,billenstien shocks&struts.
Soon to come!!!
Procharger system 12lbs o boost.
New paint job(hawaiin orchid purple)Cast alluminum ZR1 rims w/ 275 tires.
Favorite quote: "where ever u go, there u are"

Other car;
1971 plymouth Duster
Mods:340,edelbrock victor jr. intake, 650 4 barrel holley, heddman headers,40 series dual flowmasters, cold air intake,4:10 gears, just got a new paint job and cragar rims with 315 tires in the back.
:Yeah its not a chevy but damn how many 71' dusters have u seen in the streets.

 

Yes, the valve seat is the third angle.

Umbrellas are the seals they use in place (or in addition to) the factory o-ring and shedder style seals. They are like a little rubber uh...... UMBRELLA that slides over the valve stem and keeps oil from splashing directly on the valve stem and sliding down the guide. They aren't super effective. I prefer the newer style positive seals that grab onto the valve guide boss and seal tightly against the valve stem- BUT ONLY ON THE INTAKE SIDE. Exhaust valves should NOT be sealed up tightly, or risk under lubricating them and burning a guide (personal experience).

Carbon on the back of the intakes is USUALLY a bad valve guide seal or the guide itself might be pretty far gone, in which case NO seal will seal it up well. In extreme cases, bad rings will allow oil to build up on the back of the intake valves (also personl experience). Some ammount of buildup on the intakes is unavoidable in a street motor, but if it's really caked up (more than a few hundredths deep) you have oil control problems.

 

Vortec 305- my brother just bought a set of aluminum 'Vette heads to put on a 305 we're dropping in his S-10 next year. I know the chambers are the right size (58cc) but I was worried about the larger 1.94 intake valve hitting the bore at higher lifts or just generall not performing well due to shrouding. Have you actually used a set of these on a 305? I'd love to hear your ideas about this if you have. Shoot me an email if you have a chance. Or look for my post about this in this forum. Thanks.

 

Thanks to everyone for your replies! I would get the vette heads but mine's an '84 - hopefully I'll have a 350 next year so I'd rather save my coin then dish out for better heads. Later!

 

The valve seat is where your three angles come into play. The valve should be cut at a 31* angle (I think! I don't do head work anymore, so I don't even remember the angles on a SBC!) and the sealing surface on the seat should be a 30*. The other 2 angles come from adjusting the seat face to make the contact pattern ideal. Like a 15* and a 60*. The larger and smaller angles are used to make the contact lower, or higher on the valve, or to make the cantact narrower or wider. Basically, they will end up with a band about half the width of the valve face, pretty much centered, or maybe slightly biased to the inside of the valve to allow for wear. The 1* "Interference angle" is there so that the valve and seat will "wear into each other" creating a better seal.

I hope this helps out a little!



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Working on:
'84 Z28 LG4 305 with 200,000 original miles!
Added dual elec fans.
145 MPH IROC Speedo
Building 430 HP 350 (ZZ430)
using primarily GMPP parts.
Short block sitting on a stand. (Man, those Fast-Burn heads sitting on it look good!)

Starting to look like the Kicker poster child!

ASE Certified Master Tech