782 porting advise--valve guides

I have a 782 head at the machine shop right now getting cleaned up and pressure tested to make sure it's even a good candidate to work on before I get started. If it passes, what should I do about the valve guides? Should I have the shop press them flush with the bosses, do the work on the head and then have them press new guides in? Should I have them remove the guides and then do the head? Should I have them install NEW guides and then work the head and shorten the guides so they don't protrude?

I dug through old threads and have found a few "well some people say..." sort of stuff but no direct source. Something about possibly causing some sort of instability with the valves if you lose the little bit of guide poking through, and another something about how it probably affects flow so little that it doesn't matter.

While I'm making a thread, what other things should I have the shop do or check before I start to work over the head?

Thoughts?

If you are replacing the guides then just get in there and port.

Most shops wont push them out if the guides are not being replaced. Ask the shop that is going to work on your head.

In the grand sceme of it all, guides are cheap and if you are building a head, spent the extra bucks to make it all new.

Should I trim down the new guides so they don't stick out in to the bowl area so much, or should I just do the port work with the old guides in place and then have new guides pressed in and leave it at that?

I leave the guides full length for valve stem support. The small but the guide intrudes into the port is negliable.

Don't forget to have the machine shop do a back cut and polish on the valves too. The valves in the 8 valve head are pretty porky. Anything you can do to streamline the valve helps.

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Originally Posted by ajakeski

In the grand sceme of it all, guides are cheap and if you are building a head, spent the extra bucks to make it all new.

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Unless there is a real issue with the guides, most shops prefer to just reline a guide that is worn... Relining is cheaper and less traumatic on the head.

Ditto on leaving the guide protruding into the chamber for support.

Thanks guys. I'll have them check the guides for wear and just leave them in place if they're ok.

A good valve job helps flow more than shorter guides and good tight guides preserve the narrow precise angle (high flow) sealing surfaces of that good valve job because the valve doesn't crash imprecisely back onto the seat, it comes back down where it is supposed to. Read up on back cutting our valves; then put your time and money into good tight guides and then that enables precisely cut seats, that last, and . . . good flow.

I want to expand on the topic of porting for newbies. My plan was to just smooth out all these sharp edges in the bowl smooth out the step going to the guides. Not looking to hog the ports out. I think I would do more harm than good. I also planned on just smoothing out the combustion chamber. Is this a good place to start for porting a head?
http://i272.photobucket.com/albums/j...psk23u53x8.jpg

Quote:

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Originally Posted by thedon809

I want to expand on the topic of porting for newbies. My plan was to just smooth out all these sharp edges in the bowl smooth out the step going to the guides. Not looking to hog the ports out. I think I would do more harm than good. I also planned on just smoothing out the combustion chamber. Is this a good place to start for porting a head?

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If your looking for the basics, concentrate on short turn radius. Lots of work can be done there. Low flow area but very sensitive to changes. Best is to use a flame shaped rotary file on these areas, followed by sanding rolls. A bit of work can be done around exhaust guides without removing them. Wouldn't worry so much about areas you highlighted, but they can be smoothed out if it will make you feel better. Un-shroud the valves opposite side of spark plug hole. Don't gouge up the seats when doing so. If you have any old valves, you can install them to protect the seat while un-shrouding. If you want to do any port work, work to straighten out the ports, not just hogging them out in an effort to make them bigger. As Andy mentioned, back-cut the valves if using stock valves.
Todd

Thank you for the tips. When you talk about the short turn radius, im assuming you mean this part that's circled. It doesn't look like there is that much to mess with on the intake side. Kind of a straight shot. The exhaust side has more meat in that area.
http://i272.photobucket.com/albums/j...psvkiznb9n.jpg
http://i272.photobucket.com/albums/j...pssg0gpxi5.jpg

You have the correct area. Actually there is quite a bit you can remove on the intake short turn. That area that is covered in carbon is hiding a bunch of sharp machined edges. Remove the sharp edges where the machined throat meets the cast port all the way around to the long turn. On the exhaust, don't get carried away cutting down the floor or you'll wind up with a terrible flowing exhaust port (like the 655 head). Of course be aware of that small waterjacket on the roof of the exhaust just past the exhaust guide. Don't take anywhere near that much material out of either floor or roof or you'll have a paperweight.
20 some years ago, my first few heads actually turned out pretty decent making small improvements. Then as I got more aggressive with the carbide rotary files, I took a step backwards on the flowbench. Sometimes, you need to fail before you can go forward (lol). I spent a fair amount of money and time learning what worked and what didn't on these heads. I still flowbench every cylinder head I complete. I pretty much know what they will flow, but the end user knows precisely what their actual head flows.
If you just want to improve yours a bit, stay conservative. Remember it is far easier to remove material than to have to replace it. If you want to really get into these cylinder heads, practice on scrap heads before you port the one you want to run on your vehicle. Like anything else, your first effort will not be anywhere as good as your 2nd, 10th, 50th, etc.
The illustrated cutaway below shows the 655/445 head. Notice the changes to the short turn radius the factory made to improve flow. Think about that carefully as your cutting down the floors on your swirl head!
Good luck!
Todd

Quote:

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Originally Posted by 4 l-bodies

You have the correct area. Actually there is quite a bit you can remove on the intake short turn. That area that is covered in carbon is hiding a bunch of sharp machined edges. Remove the sharp edges where the machined throat meets the cast port all the way around to the long turn. On the exhaust, don't get carried away cutting down the floor or you'll wind up with a terrible flowing exhaust port (like the 655 head). Of course be aware of that small waterjacket on the roof of the exhaust just past the exhaust guide. Don't take anywhere near that much material out of either floor or roof or you'll have a paperweight.
20 some years ago, my first few heads actually turned out pretty decent making small improvements. Then as I got more aggressive with the carbide rotary files, I took a step backwards on the flowbench. Sometimes, you need to fail before you can go forward (lol). I spent a fair amount of money and time learning what worked and what didn't on these heads. I still flowbench every cylinder head I complete. I pretty much know what they will flow, but the end user knows precisely what their actual head flows.
If you just want to improve yours a bit, stay conservative. Remember it is far easier to remove material than to have to replace it. If you want to really get into these cylinder heads, practice on scrap heads before you port the one you want to run on your vehicle. Like anything else, your first effort will not be anywhere as good as your 2nd, 10th, 50th, etc.
The illustrated cutaway below shows the 655/445 head. Notice the changes to the short turn radius the factory made to improve flow. Think about that carefully as your cutting down the floors on your swirl head!
Good luck!
Todd

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Excellent information Todd!

Yeah that is what I'm going to do. Basically smooth out the edges in the throat and around the guides. Removing the smallest amount of material possible. I don't want to mess with the ports themselves for fear of screwing it up.