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B20F Head porting valve guides

Joined
Oct 18, 2017
Location
Portland OR
Hey all. Ive been reading up on here about the truly horrible design of the exhaust port ceiling on B18/B20 heads. I saws some guides on removing the "hump" around where the exhaust valve guide comes through the ceiling. None of the posts however mentioned anything about what should be done with the valve guide. Should it be removed, the ceiling ground, then a stock length guide reinstalled? Or should a shorter valve guide (like an intake valve guide) be installed in its place to limit its protrusion into the flow? Or can the guide simply be left in the head, and ground down smooth with the rest of the ceiling, and then the ground side of the guide de-burred? Any disadvantage to running shorter guides? Thanks.
 
My R-Sport head has the guides ground flush with the port ceiling. FWIW.

Seen any evidence of premature guide wear? Just wondering if shortening the guides (which in turn shortens the surface that actually holds the valve straight) can cause them to put out more torque on the guide and impart more wear.
 
I've probably put 35K on it? No clue how much use was on it prior to it landing in my hands. It was on some sort of 'racecar' in it's prior life, IIRC from the eBay auction.

But really, there's not much side to side force on the valve, especially on that end (the rockers might nudge the tips a bit). And with the overall length of the guides, a little tiny bit off the end shouldn't make any difference. It would be what, less than 1/4 inch?

I have no real way of knowing if my head was like that from Volvo, or someone else had messed with it since then, for that matter.
 
I've done a lot of port work on many British cars. The one that I've done a lot of work on is the Austin Healey 100-4 cyl head for cars for vintage racing. I got a junk head and cross cut it at the valve guide holes to see how much metal I could take out, they have a big hump at the exhaust like the Volvo heads. Keep the stock guides but pencil them down at the port so you can keep the stock guide.
 
I've done a lot of port work on many British cars. The one that I've done a lot of work on is the Austin Healey 100-4 cyl head for cars for vintage racing. I got a junk head and cross cut it at the valve guide holes to see how much metal I could take out, they have a big hump at the exhaust like the Volvo heads. Keep the stock guides but pencil them down at the port so you can keep the stock guide.

What do you mean by "pencil them down?" To remove the hump in the exhaust ceiling without removing the valve guides, the guides would have to be ground down flush to the ceiling of the port. Do you mean remove the valve guides and cut/taper them outside of the head and then reinstall?
B20-exhaust-port-Markup.jpg
Below the dotted line is where I would removed material.
 
I calculated the exposed length of the guide, made a line where I wanted to taper from. Then buffed down the exposed length lengthwise to the angle I wanted. Really didnt take off too much. Left a decent wall thickness on the guides, then had them pressed in to depth. Did the same to the intakes, they were slightly different.
 
Those guides are so long that it doesn't matter what you do.

Grinding down the guides is usually easier than: removing the guides, porting the head, profiling the guides, and then reinstalling them, then having a new valve job done.

On full rebuilds I remove the guide then port the head, since I'll be installing new guides and doing the VJ anyways.
 
For what it's worth, with air cooled VW's and Vanagons, people who have been porting heads for 40 years always install new guides, and then blend them in on the intake side and do additional porting if wanted. On the exhaust side we usually left the guides factory length, but taped the OD at the end before installing. On exhaust valves, the heat is transferred away from the valve head from the seat but also the guide. That's why you see sodium filled stems on the exhaust valves of a lot of turbo motors. The Sodium actually melts and helps heat move up the stem and into the guides. In my opinion, The main cause of concern with running a shorter guide is not increased valve on guide wear, but thermal capacity on the exhaust side.
 
For what it's worth, with air cooled VW's and Vanagons, people who have been porting heads for 40 years always install new guides, and then blend them in on the intake side and do additional porting if wanted. On the exhaust side we usually left the guides factory length, but taped the OD at the end before installing. On exhaust valves, the heat is transferred away from the valve head from the seat but also the guide. That's why you see sodium filled stems on the exhaust valves of a lot of turbo motors. The Sodium actually melts and helps heat move up the stem and into the guides. In my opinion, The main cause of concern with running a shorter guide is not increased valve on guide wear, but thermal capacity on the exhaust side.

Ah, makes sense. A you can see from the picture though, only the side of the guide away from the valve will get ground down, and Im guessing by only 3/8th of an inch, while the valve side of the guide will barely lose length at all. This wouldn't cause a noticeable difference in heat transfer, would it? This is all planned for a future supercharged FI build, so maybe I should look for sodium filled valves. Any source for those for B20s?
 
Gary does runs of 8v valves, I had him add some to the last run, but I just went with material change. So SS intakes, inconel exhaust. Should be more than enough for a pretty wild b20.
 
"Pencil them down", narrow down the guide that sticks out of the head as in a pencil point.
 
Gary does runs of 8v valves, I had him add some to the last run, but I just went with material change. So SS intakes, inconel exhaust. Should be more than enough for a pretty wild b20.

Are stock valves not stainless steel? I recently had hardened seats, new guides, and new valves installed. Not looking to get the head sent in to get any work done and would rather just open up the restriction in the exhaust and maybe smooth/polish both exhaust and intake. I would be fine getting stainless valves and lapping them in as Ill be changing the valve springs and retainers too.
 
Are stock valves not stainless steel? I recently had hardened seats, new guides, and new valves installed. Not looking to get the head sent in to get any work done and would rather just open up the restriction in the exhaust and maybe smooth/polish both exhaust and intake. I would be fine getting stainless valves and lapping them in as Ill be changing the valve springs and retainers too.

Unless you got bronze guides installed, do not run stainless steel valves.

Stock valves are actually really high quality. Even the new stock replacements are better than the cheaper SS valves that are out there.
 
Unless you got bronze guides installed, do not run stainless steel valves.

Stock valves are actually really high quality. Even the new stock replacements are better than the cheaper SS valves that are out there.

Ah, good to know. Im hoping to run water-meth injection at high boost, as well as sequential spark through the use of MegaSquirt and a CAS in place of the dizzy, so that'll hopefully keep exhaust valve temps low enough. I may try to polish the portion of exhaust valve that isn't in contact with the guide to hopefully help it reflect some heat.
 
Isn't it a good idea to raise the floor a bit as well? I believe I recall seeing that somewhere over the years of reading forums and such.

I've seen that too. Also a picture on here relatively recently, I think.

I'm watching this thread with interest as it applies to my NA late carb head.
 
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