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Old 10-11-2021, 04:13 PM   #1
blakemcelroy2000
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Default B20F Head porting valve guides

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.
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Old 10-11-2021, 04:17 PM   #2
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My R-Sport head has the guides ground flush with the port ceiling. FWIW.
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Old 10-11-2021, 07:53 PM   #3
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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.
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Old 10-11-2021, 08:19 PM   #4
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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.
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Old 10-14-2021, 06:37 PM   #5
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Any idea where I could find a cheap head to practice on? It could be warped, cracked, gouged. Doesn't matter to me.
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Old 10-14-2021, 07:47 PM   #6
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Any idea where I could find a cheap head to practice on? It could be warped, cracked, gouged. Doesn't matter to me.
I have some. How cheap is cheap?

Cameron
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Old 10-15-2021, 09:59 AM   #7
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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.
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Old 10-15-2021, 11:04 AM   #8
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I have some. How cheap is cheap?

Cameron
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Hey, is this Cameron from Swedish Relics? You rebuilt my M41 a couple years back. Cheap as in around $60 - $100, wouldn't need to have valves, guides, springs or rockers, and could be a real junk head as far as I care.
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Old 10-15-2021, 11:13 AM   #9
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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? Below the dotted line is where I would removed material.
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Old 10-15-2021, 12:05 PM   #10
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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.
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Old 10-15-2021, 12:10 PM   #11
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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.
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Old 10-15-2021, 12:51 PM   #12
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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.
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Old 10-15-2021, 01:04 PM   #13
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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?
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Old 10-15-2021, 01:34 PM   #14
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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.
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Old 10-15-2021, 01:38 PM   #15
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"Pencil them down", narrow down the guide that sticks out of the head as in a pencil point.
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Old 10-15-2021, 01:38 PM   #16
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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.
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Old 10-15-2021, 01:48 PM   #17
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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.
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Old 10-15-2021, 02:12 PM   #18
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Originally Posted by blakemcelroy2000 View Post
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.
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Old 10-15-2021, 02:42 PM   #19
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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.
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Old 10-15-2021, 02:59 PM   #20
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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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Old 10-15-2021, 03:41 PM   #21
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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.
The wizards agree with you; but, raising the floor is a lot more work as it involves filling the port floor with weld and then reshaping. I have seen photos where people have had steel tongues fabricated, welded to the exhaust flange and then inserted into the port to try and accomplish the same thing. I think member Canuck has posted pictures of ports where he has filled the floor for flow testing purposes. Phil Singher had also posted photos of B18 / B20s with filled ports (years ago and that may have been on the Sweedespeed forum).

Of course there was an over the top Swede who completely filled in the ports with weld and then machined in new ports where the central axis came in closer to a 45 deg angle relative to the valve stem. Obviously would have required custom manifolds; but, they didn't have photos of a completed engine, just the head with modified ports. I often wondered what they did with the water jackets and whether the head actually worked, or was just somebodies mantel piece.
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Old 10-15-2021, 03:56 PM   #22
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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.
Modest spraying of water / meth will cool the intake charge which can be effective in preventing detonation. That may have little effect on the actual temperature of the combustion gasses. As an observation, if the engine capacity is fixed increased horsepower generally comes from three things
- increasing the compression ratio
- increasing the RPM as long as the volumetric efficiency does not go in the toilet
- jamming more fuel and air into the cylinder (forced induction)

Since you appear to be planning on the FI approach, jamming more fuel and air into the cylinder must increase the amount of heat released on combustion to result in a power increase. Ergo your exhaust temperatures must go up. You need to figure out whether that is going to be a problem for you. If you spray enough water to drop the combustion temperature you are going to lose horsepower.

Last edited by 142 guy; 10-15-2021 at 04:02 PM..
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Old 10-15-2021, 04:49 PM   #23
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The wizards agree with you; but, raising the floor is a lot more work as it involves filling the port floor with weld and then reshaping. I have seen photos where people have had steel tongues fabricated, welded to the exhaust flange and then inserted into the port to try and accomplish the same thing. I think member Canuck has posted pictures of ports where he has filled the floor for flow testing purposes. Phil Singher had also posted photos of B18 / B20s with filled ports (years ago and that may have been on the Sweedespeed forum).

Of course there was an over the top Swede who completely filled in the ports with weld and then machined in new ports where the central axis came in closer to a 45 deg angle relative to the valve stem. Obviously would have required custom manifolds; but, they didn't have photos of a completed engine, just the head with modified ports. I often wondered what they did with the water jackets and whether the head actually worked, or was just somebodies mantel piece.
I was thinking about the welding "tongues" into the exhaust in order to simulate the floor of the port being welded, although Im not sure how you could keep gasses from getting shoved underneath the tongue. Also, from what Ive read, just welding the floor helps, but while you're at it you might as well widen the ports in the horizontal. Basically taking the normal "vertical rectangle" port shape and turning it sideways. Not really something I want to try since Ive got some really nice headers, and don't want to warp my head.
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Old 10-16-2021, 12:35 AM   #24
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Hey, is this Cameron from Swedish Relics? You rebuilt my M41 a couple years back. Cheap as in around $60 - $100, wouldn't need to have valves, guides, springs or rockers, and could be a real junk head as far as I care.
Yep. No longer at the same location (so don't swing by!), but I've got lots of heads you can choose from. Give a call and we can set a time.

Thanks,

Cam
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Old 10-16-2021, 07:15 AM   #25
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I had a talk with one of the leading Volvo B18/20 race engine builders in the US about removing the guide hump. He advised me to remove all of it for racing, and shorten the guide so it is flush with the new contour of the port. Culberro mentioned the same thing earlier.

A look at the guide length to be removed in the cutaway photo shows that at the most only about 10% or less will be trimmed off. Because of the the extra long length of the guide that Volvo engineers choose to use for long term durability a shortened one doesn't cause any problems in actual use.

Last edited by vintagewrench; 10-16-2021 at 07:29 AM..
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