What all is done to the heads when you get a 3 angle valve job? How about porting (or is it the same thing)? I have a set of 66 BB heads 2.06/1.72 that I'm about to have worked on. I recently put new springs and roller tip rockers on them. Someone suggested putting larger valves in them, but I want to use the rockers and springs I just bought. Is it possible to go to larger valves and still use the what I have? I don't race the car, just shows and cruises. The heads needed worked on, so I thought I would do what I could to beef them up a little. thanks for any comments.
3 angle valve job???
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A 3 angle valve job is a good idea. it makes the flow through the seats a little smoother by making the seat blend better to the port and cumbustion chamber.
Porting is something else. I entails grinding and smoothing, by hand, the port areas of the head. It is usually quite expensive since it is all hand work.
Your rockers and springs should work with the larger valves but you will need to make sure the larger valves do not hit the pistons. Unless you are looking for higher RPM use of your engine, larger valves aren't really needed. Smaller valves will be better at lower RPM and build more torque. They increase the velocity of the fuel mixture and promote better mixing. Larger valves come in to play at higher RPM where the higher volumn of air and fuel are needed. At lower RPM they slow the filling of the cylinders and can actually decrease the amount of fuel going into the cylinder.
Hope this helps
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Pat Kelley
66 & 67 El Caminos
[This message has been edited by Pat Kelley (edited 08-08-99).]
[This message has been edited by Pat Kelley (edited 08-08-99).]
Porting is something else. I entails grinding and smoothing, by hand, the port areas of the head. It is usually quite expensive since it is all hand work.
Your rockers and springs should work with the larger valves but you will need to make sure the larger valves do not hit the pistons. Unless you are looking for higher RPM use of your engine, larger valves aren't really needed. Smaller valves will be better at lower RPM and build more torque. They increase the velocity of the fuel mixture and promote better mixing. Larger valves come in to play at higher RPM where the higher volumn of air and fuel are needed. At lower RPM they slow the filling of the cylinders and can actually decrease the amount of fuel going into the cylinder.
Hope this helps
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Pat Kelley
66 & 67 El Caminos
[This message has been edited by Pat Kelley (edited 08-08-99).]
[This message has been edited by Pat Kelley (edited 08-08-99).]
Rob, those early heads have the valve seats machined directly into the cast iron of the head. This will not do with unleaded gas. If you want to fix up your heads a little, have a good machine shop install the hardened seat inserts into the exhausts. Otherwise, all your work and expense may go to waste when the valves start pounding out the freshly machined soft iron exhaust seats. I have seen this on many rebuilt 60's engines that were done without installing the exhaust seats. This is really a loser and a well known problem. Also, the shop may recommend replacing the worn valve guides, this would be typical for a Chevy with a few miles on it. Be careful here, you want new valve guides with an outside diameter of 0.500" installed. Big blocks were originally manufactured with pressed in guides, some shops will still try to replace these. This is a loser because the new press-in guide will come out way off-center, causing bad problems with machining the valve seats. Most shops don't do this anymore but a few still try for some reason.
Main thing is, get some seats in the thing so you won't be doing the whole job again.
Tom
Main thing is, get some seats in the thing so you won't be doing the whole job again.
Tom
G
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·First let me say I don't agree with most of what was said here other than the post about leaving the valve size alone.
Fat seats are not as important as where the seat is. The seat width will widen as the motor runs, if you put the seat on the edge of the valve like a race prepared head, it will go away much faster than one moved more toward the middle. Fat or thicker exhaust valves or one with more "margin", is more desirable. I used larger diameter valve and trimmed them for the smaller applications. We also back cut all the valves at 30 degrees, helps flow in low velocity situations.
A good three-angle valve job is a thing of beauty and can help improve flow.
I don't like replacing seats, and here is why. There is very little room for error when working on early heads. They were never intended to have replacement seats. The area under the valve is thin; water is lurking close and hand. The exhaust seat operates at extreme temperature and unless the crush on the seat and the seat thickness is good, it will fall out and kill the bullet.
I run so much crush on these babies it's ridiculous, .008. You need to freeze the seat with dry ice then install it.
I had one disaster on early heads, dropped the seat out and blew a hole in a piston and cracked the block.
As for the guides, I use solid bronze replacement guides. I never had a set of heads that were so far out that I could not put the seat in.
I have seen the .500 guide installed, then a liner installed in that. What is that all about?
I have seen people drive the old guide out the wrong way, ugly.
If you look at the newer aftermarket heads you will see the difference in the seats, much thicker.
Maybe I'm gun shy about seats in early heads.
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Wally
Gold #67
67 malibu
[This message has been edited by Wally (edited 08-09-99).]
[This message has been edited by Wally (edited 08-09-99).]
Fat seats are not as important as where the seat is. The seat width will widen as the motor runs, if you put the seat on the edge of the valve like a race prepared head, it will go away much faster than one moved more toward the middle. Fat or thicker exhaust valves or one with more "margin", is more desirable. I used larger diameter valve and trimmed them for the smaller applications. We also back cut all the valves at 30 degrees, helps flow in low velocity situations.
A good three-angle valve job is a thing of beauty and can help improve flow.
I don't like replacing seats, and here is why. There is very little room for error when working on early heads. They were never intended to have replacement seats. The area under the valve is thin; water is lurking close and hand. The exhaust seat operates at extreme temperature and unless the crush on the seat and the seat thickness is good, it will fall out and kill the bullet.
I run so much crush on these babies it's ridiculous, .008. You need to freeze the seat with dry ice then install it.
I had one disaster on early heads, dropped the seat out and blew a hole in a piston and cracked the block.
As for the guides, I use solid bronze replacement guides. I never had a set of heads that were so far out that I could not put the seat in.
I have seen the .500 guide installed, then a liner installed in that. What is that all about?
I have seen people drive the old guide out the wrong way, ugly.
If you look at the newer aftermarket heads you will see the difference in the seats, much thicker.
Maybe I'm gun shy about seats in early heads.
------------------
Wally
Gold #67
67 malibu
[This message has been edited by Wally (edited 08-09-99).]
[This message has been edited by Wally (edited 08-09-99).]
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