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b20 head options

oemoilleaks

oemoilleaks

Member
Joined
Mar 26, 2017
Location
SoCAL
I'm in the process of building a big bore b20 and I realized that I haven't figured out what I'm doing about the head.

I know that there really isn't much that can be done except porting, polishing, and increasing the valve size. How large can I go on valves without making the car un-streetable?

The rest of the build is as follows:

The plan is IPD big-bore kit for a 6bolt crank.
Forged rods
R grind cam
123 ignition
high rev lifters
dual valve springs.
Weber DCOE 45's (choked to 40s)
 
If you have a fuel injected head or the later carbureted head with 44mm intakes, then you can go to 38mm exhaust and 46mm intakes.

You might be able to use the same sized valves on an early carbureted B20 head, but you might have to open up the combustion chamber.

Be aware that new seats will need to be installed to accommodate the larger valves.

FYI, the camshaft and compression are bigger factors that will determine how streetable your engine will be.
 
If you’re going to be porting, and you have the ability to weld cast, adding material around the exhaust short side radius really is a good way to get things breathing better. It’s a giant task, but it can be worth it. Otherwise just cleaning out the casting finish is all you want to do.
 
planetman said:
If you have a fuel injected head or the later carbureted head with 44mm intakes, then you can go to 38mm exhaust and 46mm intakes.

You might be able to use the same sized valves on an early carbureted B20 head, but you might have to open up the combustion chamber.

Be aware that new seats will need to be installed to accommodate the larger valves.

FYI, the camshaft and compression are bigger factors that will determine how streetable your engine will be.
Click to expand...

It's a 74 b20f FI head. The PO put some screws in there to block off the injection ports and convert it back to carburetion, but then couldn't get it to pass smog in 76 so it sat in a field.

What were the valve sizes for the earlier carb'd heads?

As far as compression goes, is 11:1 too aggressive? Is it even possible? Or should I shoot for a more modest 10.5:1?
 
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cwdodson88 said:
If you?re going to be porting, and you have the ability to weld cast, adding material around the exhaust short side radius really is a good way to get things breathing better. It?s a giant task, but it can be worth it. Otherwise just cleaning out the casting finish is all you want to do.
Click to expand...

I am going to be match porting the intake runners and cleaning out casting, as well as doing a three angle grind.

I'm not sure I completely understand what you mean by adding material, or where you're adding it.

This is the first engine I'll have ever built from the ground up.
 
The R-sport head I was lucky enough to snag on eBay many years ago has valves that practically touch each other. You can *barely* fit a fingernail between the intake and exhaust valves.

This puts the valves pretty close to the sides of the chamber (shrouding) - so I carefully matched those sides of the chamber to the B21 sized bores on my B20 block - which gave them a little more breathing room.

I think I've seen some Swedish made heads with even larger valves - they use offset drillings in the valve guides to move the valves slightly farther away from each other, so they can be slightly larger as well.

But again, as mentioned - increasing the valve size only does so much - the major limiting issue is the horrible crappy no-good exhaust port area. From my understanding, most people used to porting other types of heads can actually make this flow worse when they try their normal tricks of enlarging the bowl. Because in the Volvo head the exhaust has to make a SHARP turn - and increasing the bowl size above the port just makes the air a little less inclined to make that turn.

But there is some low hanging fruit on an injected head - for whatever reason Volvo put a restriction in just past the valve seat - a reduced diameter. For emissions? To gimp the HP a little in favor of longevity and reliability? Some sort of passive EGR? Who knows, but knocking that out makes some good gains. I know my R-Sport heads exhaust bowls and ports are wide open at that point, looks a lot different than the old stock F head I have laying about. But the bowls are not all that larger - just polished - they still make a fairly sharp turn toward the port. And the ports themselves are a bit larger as well.
 
There's the 90% percent rule for opening up below the seat..follow it, A port is hopeless if it is sewer sized and doesn't have any velocity after your cam peeters outout, Besides that how much time does a street car spend a 7k? Compression ratio depends on available fuel in your area) I run 100 low lead with my 12.1, quench, cam, fuel, timing control..how far are you willing to go....I'll admit I get tired of mixing fuels for it
 
JohnMc said:
The R-sport head I was lucky enough to snag on eBay many years ago has valves that practically touch each other. You can *barely* fit a fingernail between the intake and exhaust valves.

This puts the valves pretty close to the sides of the chamber (shrouding) - so I carefully matched those sides of the chamber to the B21 sized bores on my B20 block - which gave them a little more breathing room.

I think I've seen some Swedish made heads with even larger valves - they use offset drillings in the valve guides to move the valves slightly farther away from each other, so they can be slightly larger as well.

But again, as mentioned - increasing the valve size only does so much - the major limiting issue is the horrible crappy no-good exhaust port area. From my understanding, most people used to porting other types of heads can actually make this flow worse when they try their normal tricks of enlarging the bowl. Because in the Volvo head the exhaust has to make a SHARP turn - and increasing the bowl size above the port just makes the air a little less inclined to make that turn.

But there is some low hanging fruit on an injected head - for whatever reason Volvo put a restriction in just past the valve seat - a reduced diameter. For emissions? To gimp the HP a little in favor of longevity and reliability? Some sort of passive EGR? Who knows, but knocking that out makes some good gains. I know my R-Sport heads exhaust bowls and ports are wide open at that point, looks a lot different than the old stock F head I have laying about. But the bowls are not all that larger - just polished - they still make a fairly sharp turn toward the port. And the ports themselves are a bit larger as well.
Click to expand...

This is good information! This is what worries me about having my main concern about having this shop, who mostly doest porshe stuff, do the head.
 
freevolvos said:
There's the 90% percent rule for opening up below the seat..follow it, A port is hopeless if it is sewer sized and doesn't have any velocity after your cam peeters outout, Besides that how much time does a street car spend a 7k? Compression ratio depends on available fuel in your area) I run 100 low lead with my 12.1, quench, cam, fuel, timing control..how far are you willing to go....I'll admit I get tired of mixing fuels for it
Click to expand...

What's the 90% rule?
 
JohnMc said:
The R-sport head I was lucky enough to snag on eBay many years ago has valves that practically touch each other. You can *barely* fit a fingernail between the intake and exhaust valves.

This puts the valves pretty close to the sides of the chamber (shrouding) - so I carefully matched those sides of the chamber to the B21 sized bores on my B20 block - which gave them a little more breathing room.
Click to expand...

John, what cam are you running with that head?
 
I've run a Volvo 'R' grind in the past, I'm running an Isky VV81 currently. I was going to try a KG Trimning cam last time it was apart, but they had some several months long wait time, so I stuck the cheap and readily available Isky in.

It really kicks in around 3200-ish RPM and pulls strongly up past 7000 rpm. The most I ever rev it out is around 7500 rpm - it hasn't really dropped off terribly at that point, it's just more productive to move on to the next gear.

Annnnnd in totally unrelated news, I've done something to a piston again. Probably totally unrelated to revving the piss out of it frequently because it's so much fun to do.
 
JohnMc said:
I've run a Volvo 'R' grind in the past, I'm running an Isky VV81 currently. I was going to try a KG Trimning cam last time it was apart, but they had some several months long wait time, so I stuck the cheap and readily available Isky in.

It really kicks in around 3200-ish RPM and pulls strongly up past 7000 rpm. The most I ever rev it out is around 7500 rpm - it hasn't really dropped off terribly at that point, it's just more productive to move on to the next gear.

Annnnnd in totally unrelated news, I've done something to a piston again. Probably totally unrelated to revving the piss out of it frequently because it's so much fun to do.
Click to expand...

How many times has that thing been apart in the past two years?
That thing better be put together for Mountain Meat 2k19
 
Hasn't been apart at all in that time frame. It's actually been pretty reliable, compared to the wagon. I think I've had the engine out of it 3 times over 20 years?

It just started idling unevenly, diagnosed it as a compression leak in #3 that vents to the block. Which means something with a piston. 4 or 5 years ago it did the same thing and a small piece of the piston had flaked off, and was being held in place by the rings. I stuck it back together with a new set of B21A pistons (smaller dish than B21FT) and some B20E rods (the skinny B18 rods were making me nervous - some weird wear marks on the bearings where the big end has a skinny spot).

The LS turbo 245 should make it to MM '19.
 
Valve throat size not to exceed 90% of the valve diameter so for a 2.02 valve the ideal throat diameter would be 1.81.....don't concentrate on peak lift flow numbers say 500 lift the port flows 500 c.f.m. You only see this once per event, Instead focus on a port that flows well in mid lift, as the valve sees this twice per event..... A massive port with no velocity is no fun unless your road racing, a 30? back cut on the valves may help flow to..is there any flow data on this head?
 
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JohnMc said:
I've run a Volvo 'R' grind in the past, I'm running an Isky VV81 currently. I was going to try a KG Trimning cam last time it was apart, but they had some several months long wait time, so I stuck the cheap and readily available Isky in.

It really kicks in around 3200-ish RPM and pulls strongly up past 7000 rpm. The most I ever rev it out is around 7500 rpm - it hasn't really dropped off terribly at that point, it's just more productive to move on to the next gear.

Annnnnd in totally unrelated news, I've done something to a piston again. Probably totally unrelated to revving the piss out of it frequently because it's so much fun to do.
Click to expand...

Interesting.. That's for the ISKY cam?

The only reason I'm running the r-grind is because it came in the NOS ipd big bore kit I got off ebay a while back. And the seller claims it's an r-grind, but I have no way to know for sure. The other cam I have is a K cam that came out of the donor motor, but it looks pretty worn.

I would add the link but for some reason I can't find the permalink for the old auction.
 
Yeah, that's for the Isky. It's been a while, so the R grind wasn't as fresh in my mind, but IIRC it was pretty similar, but perhaps had a bit less low rpm torque, a bit more of an 'on cam' feeling as you passed that RPM threshold.

I didn't end up running the R cam for all that long, a lifter failed and took out a lobe. FWIW I run a high zinc/ZDDP oil additive (Lucas break-in oil) all the time now, double valve springs, large valve lifts (I have high ratio roller rockers) and high revs are hard on the lifters in a B20. From what I can tell, they're fairly casually oiled. Some oil leaking down past the lifters themselves (draining out of the valve cover - the lifters themselves are not directly oiled) and other than that, just crankcase windage/splattered
 
JohnMc said:
Hasn't been apart at all in that time frame. It's actually been pretty reliable, compared to the wagon. I think I've had the engine out of it 3 times over 20 years?

It just started idling unevenly, diagnosed it as a compression leak in #3 that vents to the block. Which means something with a piston. 4 or 5 years ago it did the same thing and a small piece of the piston had flaked off, and was being held in place by the rings. I stuck it back together with a new set of B21A pistons (smaller dish than B21FT) and some B20E rods (the skinny B18 rods were making me nervous - some weird wear marks on the bearings where the big end has a skinny spot).

The LS turbo 245 should make it to MM '19.
Click to expand...

I guess I read your thread and never actually recalled the years when it had the head off and the flaked piston.

Most excellent.
 
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