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Old 05-23-2016, 12:42 PM   #26
JohnMc
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The main difference (besides incremental changes to the internal port castings) is the thickness. The F heads extend downward further, thus everything in the head sits slightly higher, and the combustion chambers in the head are deeper and have a higher volume.

This many decades on, F heads could have been shaved down by now, for someone wanting more pep. Heck, E heads can and have been shaved down too (like the WAY shaved down R head I got on eBay). So the main thing that really matters is the thickness of the head, measure between the top and bottom machines surfaces. Or measure the chamber volumes.

Other than that, there are some tell tale casting differences between E, F, and late F heads. Here's a link that has some pics: http://www.v-performance.com/article...ification.html

That part of the head is nice and visible even on a fully assembled engine.
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Old 05-23-2016, 12:52 PM   #27
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It appears that there were two different models of B20 fuel injection heads and I am looking for the one with the lowest compression ratio to use with this supercharger

One is referred to as the "E" and the other as the "F"?

What are the actual differences between the two and the compression ratios for each one?

How exactly can they be told apart?
The E head only came on the 70 1800 and some 71 142's so it's not likely you'll bump into one.

But to answer your question...

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Old 05-23-2016, 01:16 PM   #28
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Looks like a Nazi supercharger.
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Old 05-23-2016, 01:21 PM   #29
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Nvm
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Old 05-23-2016, 02:50 PM   #30
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Thanks to all for your responses and information.

The original 1968 B18 that was rebuilt is in the car w/a thick head gasket and the head on it, thanks to Redwood Chair's photo does in fact turn out to be an F.

This F head with the smaller B18 bore will lower the compression ratio below 1968 specs which will be good for the supercharger. I will cc the head before I put the blower on and find out exactly what the CR is.

Last edited by vintagewrench; 05-23-2016 at 02:56 PM..
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Old 05-23-2016, 03:03 PM   #31
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Looks like you're starting at 8.7:1 on a B20 bottom end.

http://www.k-jet.org/files/greenbook..._0_general.pdf
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Old 05-23-2016, 03:09 PM   #32
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Thick headgaskets and possibly 'mushroomed' combustion chamber walls are not good ways to control detonation.

This style of combustion chamber is designed to use /quench' or 'squish' to control detonation. That's where the flat sides of the combustion chamber that hang out over the pistons get *very* close to them at TDC. If they just get 'sort' of close, the air doesn't move out from between the closing surfaces very quickly. If they get very close, you'll get a very violent 'snap' as the air is squeezed out of the gap and into the chamber. This produces a lot of swirl and mixing and movement of the burning air/fuel (ignition occurs before TDC, this snap occurs right at TDC). That swirl helps promote a more complete and controlled burn, and helps keep chamber temps more even (prevents hot spots). Temps are more even throughout the chamber and piston crowns.

A piston to head clearance of down to .032 is what I've heard to aim for on a nice pushrod build. Any closer and there's a chance of things actually touching, from piston rock, piston expansion, rod stretch, etc. The effect diminishes and anything more than .045 - .05 or so and it's pretty much non-existent.

Spacing the head out away from the piston via a thick HG very directly hampers this part of the detonation resistance, and only gradually when the CR is way down does it recover and get better. And lower compression is not good for other reasons.
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Old 05-23-2016, 03:13 PM   #33
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Quote:
Originally Posted by vintagewrench View Post
This F head with the smaller B18 bore will lower the compression ratio below 1968 specs which will be good for the supercharger.
Unless the b18 was significantly overbored, that combination will be relatively low on torque, and be rather difficult to tune without spark control. The relatively low "squish" and the slightly mushroomed bores can cause adverse "quench" creating hot spots and wonkiness that makes tuning timing a pain. I was able to figure out that a B20 E head, coupled to a .040 overbored B18 did not have a significant "mushroom", although it may have been there, and my timing curve ended up behaving similar to a B21 turbo car.

Sourcing a B20 bottom end would be a way better solution if you can, or want to. I do understand the nostalgia that you are working with, but honestly either a b20 bottom to go with that head, or a b18 head with larger valves would make for a far better match up.
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Old 05-23-2016, 11:00 PM   #34
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Originally Posted by Redwood Chair View Post
The E head only came on the 70 1800 and some 71 142's so it's not likely you'll bump into one.
E heads were also used on the '71 1800.

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Old 05-24-2016, 12:16 PM   #35
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Once again thanks to all of you for all the information which is valued, but like most things mechanical there are more factors than you would first think of involved with this Holley carbureted Judson supercharger (boost of 6-7 psi) installation:

1. My business is rebuilding antique racing a road-driven engines (pre-1930) and since I also run a very busy vintage car website, theoldmotor.com this project is going to only use (for now) period speed equipment and a Bosch centrifugal advance points style distributor (re-curved) and no electronics. That way the build it can be covered on the website as retro project, and a friend who writes for Road & Track is also interested in covering it as a period-like piece.

2. The blower output capacity is sized to work on a 1800cc engine, and on a 2000cc motor it will be undersized and produce less horsepower and torque.

3. I had a Judson in the past (late-1970s) and installed it on a stock B18. It produced exceptional power, but could not handle even premium gas due to detonation, but would run great on racing gas. A standard carbureted B20 head was then installed (lowered the CR due to the smaller B18 bore) and it then preformed great on pump gas.

4. This car is going to be used like a shop truck in local traffic and some runs of up to 200-miles and has to be reliable.

5. It is first going to be installed on the completely rebuilt, original to the car, standard bore B18 with the new set Mahle cast pistons that are in it, and the "F" head that is on it now. This will give a good base line and with the lower compression ratio will handle the denotation issues and give a good base line to begin with.

After all of this is accomplished, a programable electronic distributor will likely be installed and the blower speed may be be stepped up a bit.

I have very little knowledge of electronic ignition - what Volvo distributor (so it will look stock) and programable electronic system would you recommend that could be setup later to be work on this engine?

Last edited by vintagewrench; 05-24-2016 at 12:29 PM..
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Old 05-24-2016, 12:19 PM   #36
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75 was the only year for a factory black box ignition on a B20.

Or fool with the advance counterweights in the dizzy, although that's an inexact science.

Last edited by Redwood Chair; 05-24-2016 at 12:25 PM.. Reason: advance counterweights
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Old 05-24-2016, 12:31 PM   #37
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Quote:
Originally Posted by Redwood Chair View Post
75 was the only year for a factory black box ignition on a B20.

Or fool with the advance counterweights in the dizzy, although that's an inexact science.
Thanks again!! What could I use to program the timing with this system?
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Old 05-24-2016, 12:35 PM   #38
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.

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Old 05-24-2016, 12:42 PM   #39
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its not about compression ratio, the reason for trying to steer away from the hybrid b18/b20 is the poorly managed burn characteristics that are directly correlated to oversized combustion chamber shape compared to bore. The burn management creates hot spots that lead to detonation (and no matter how much you finesse timing those hotspots are still there acting like glow plugs). After my experience with a boosted hybrid motor, and then building a proper b20 bottom end to go along with it. I would never do it again, or recommend that anyone do it. My new motor pulled harder at ~7psi than the hybrid did at 18psi.
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Old 05-24-2016, 12:51 PM   #40
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I could be wrong, but the blower crams X amount of air into the engine per revolution (positive displacement). Cramming it into 1800cc's worth of displacement just means it happens at a higher boost pressure. 2000cc's of displacement means the same amount of air at a lower pressure. Well, slightly more since the blower efficiency goes up as the output pressure goes down.

Net effect, cramming it into a smaller engine won't produce more HP. To indulge in some reducto absurdium, would it make even more hp on a 1600 cc engine? A 1000 cc engine? No.
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Old 05-24-2016, 12:59 PM   #41
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Something I would look into while rebuilding is the squish as well. I found on the 2130cc B20 in my 140, with a ported head it would ping at around 11* base timing with a stock Elring HG. Just swapping to a thinner .036" Cometic instead of the .049" compressed Elring, the pinging went away completely. Even at 17* base timing it was fine. Now on MS it can handle a good bit of timing without any pinging on 89* or 91*.

For the ignition, as Ken mentioned, 75 was the only year for a factory electronic on the B20 and tweaking the timing curve on the associated box hasn't been cracked yet. You can run just the dizzy and a MSD or the like though, did that for years on mine. Otherwise look into the 123 distributors. Programmable, drop-in ready, seem to have a decent rep from what I've seen so far, and relatively stock looking as well.
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Old 05-24-2016, 01:02 PM   #42
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Quote:
Originally Posted by cwdodson88 View Post
its not about compression ratio, the reason for trying to steer away from the hybrid b18/b20 is the poorly managed burn characteristics that are directly correlated to oversized combustion chamber shape compared to bore. The burn management creates hot spots that lead to detonation (and no matter how much you finesse timing those hotspots are still there acting like glow plugs). After my experience with a boosted hybrid motor, and then building a proper b20 bottom end to go along with it. I would never do it again, or recommend that anyone do it. My new motor pulled harder at ~7psi than the hybrid did at 18psi.
[QUOTE=gsellstr]Something I would look into while rebuilding is the squish as well. I found on the 2130cc B20 in my 140, with a ported head it would ping at around 11* base timing with a stock Elring HG. Just swapping to a thinner .036" Cometic instead of the .049" compressed Elring, the pinging went away completely. Even at 17* base timing it was fine. Now on MS it can handle a good bit of timing without any pinging on 89* or 91*.

For the ignition, as Ken mentioned, 75 was the only year for a factory electronic on the B20 and tweaking the timing curve on the associated box hasn't been cracked yet. You can run just the dizzy and a MSD or the like though, did that for years on mine. Otherwise look into the 123 distributors. Programmable, drop-in ready, seem to have a decent rep from what I've seen so far, and relatively stock looking as well.


Since a carbureted B20 head worked exceptionally well w/a B18 bore with my other blower, let me ask you and others this: What is the difference in the shape of the combustion chamber and the CR between it and that of a F head??

Last edited by vintagewrench; 05-24-2016 at 01:13 PM..
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Old 05-24-2016, 01:10 PM   #43
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9.3 minus 8.7 = .6

http://www.k-jet.org/files/greenbook..._0_general.pdf
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Old 05-24-2016, 01:45 PM   #44
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Since a carbureted B20 head worked exceptionally well w/a B18 bore with my other blower, let me ask you and others this: What is the difference in the shape of the combustion chamber and the CR between it and that of a F head??
Pretty sure that all b18/b20's use the same bathtub chamber shape, with a squish pad on the passenger side. The only differences are going to be how wide the combustion chamber is. I cant directly comment as to the difference between say an A head and and F head, but I can say that my NA form b18/b20 hybrid compared to my NA b18 was a dog until wound to 6-7k

You say it worked "exceptionally well" but have you driven a properly built b20 running boost? Have you compared a b18/b20 hybrid to a b20 with the same boost, timing, fuel consumption?
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Old 05-24-2016, 01:48 PM   #45
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Sorry, I can't really comment on chamber shape between them, only really played with the F heads.
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Old 05-24-2016, 01:54 PM   #46
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The issue would be if the combustion chamber is wider than the bore. That's just one more protruding edge in there.

On my PV's engine, I found an R-Sport head on eBay. Lots or really good aspects to it (huge valves, great worked ports, double valve springs, etc), but it had been shaved down to a ridiculous degree. To something like a 12:1 CR on a 2.0L bottom end, and I was putting it on top of a 2.1L (92.5mm bore) bottom end, so it would be even higher. But raising the head away from the piston to decrease CR would just make it more detonation prone, until the CR was finally low enough to counteract that. And low CR motors just aren't as peppy. My solution was to use some dished B21 pistons to lower the CR, and build it with a .036 squish. Net result is 155 - 160 HP at the wheels (calced from 1/4 mile speeds) and it runs just fine on pump 93 octane. Ping resistant enough that you can advance the power of the front end of the timing curve - no pinging but it starts making less power.
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Old 05-24-2016, 02:16 PM   #47
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Pretty sure that all b18/b20's use the same bathtub chamber shape, with a squish pad on the passenger side. The only differences are going to be how wide the combustion chamber is. I cant directly comment as to the difference between say an A head and and F head, but I can say that my NA form b18/b20 hybrid compared to my NA b18 was a dog until wound to 6-7k

You say it worked "exceptionally well" but have you driven a properly built b20 running boost? Have you compared a b18/b20 hybrid to a b20 with the same boost, timing, fuel consumption?
No, I aways ran B18 or B18's I bored out to a B20 specs w/a B18 head and a thick head gasket.

The sedan I had the blower on was a .020 over B18 w/a carbureted B20 head, a new stock cam and it pulled strongly all the way from about 1500 rpm to 5000.

Here in Vermont there are hills and mountains everywhere and the supercharged engine would pull most all of them in 4th gear and accelerate if you wanted to. With a stock B18 or B20 3rd gear would be necessary.

This was also using much better gas (late-70s) compared to what is used today. Maybe what worked then does not work today because of the added ethanol?

Last edited by vintagewrench; 05-24-2016 at 02:33 PM..
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Old 05-24-2016, 02:29 PM   #48
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from my recent experiences, a b20 bored .030 with a piston to head clearance of .030 (rather tight squish), and a k-cam, and E head (9.5:1 static CR) running ~7# of boost out of a TD04HL-15g turbo, pulls harder on the same fuel and timing map than the B18, bored .040, piston to head at ~.050, and the same head, running 18# from the same turbo. the static CR was about 7.7 on the b18/b20 hybrid

Personally, I would rather have a thin head gasket and carve the crap out of the combustion chambers than a thick head gasket to lower the static CR.

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Old 05-24-2016, 02:57 PM   #49
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75 was the only year for a factory black box ignition on a B20.

Or fool with the advance counterweights in the dizzy, although that's an inexact science.
I have a '75 dizzy with the black box, if interested.

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Old 05-25-2016, 10:37 AM   #50
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B18

Here is a photo above of the B18 head that came off of this engine w/the larger part of the squish area on the left-hand side of the engine.

Based on what some of you have learned and experienced it seems like a good time to take look at the various combustion chambers.

I found a photo of a E head combustion chamber below. Is the F head chamber the same basic shape even though its CR is lower?

Have not seen a carbureted B20 head in a long time and I am wondering if it is patterned after the B18 head or is more like the E and F units?

E chamber
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