122s B18 Judson Positive Displacement Supercharger

That's a cool unit. I like seeing the old blowers on VW bugs too.

vintagewrench said:

16-valve 300 ci four actuated by rocker arms. 3 3/4 inch bore by a 6 3/4 inch stroke. - low rpm engine but it will push the car to 130 mph.

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Just a little under square. What is the idle speed on something like that? I am assuming it is slow and has a rather hefty flywheel.

carbonmike said:

Just a little under square. What is the idle speed on something like that? I am assuming it is slow and has a rather hefty flywheel.

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It actually for the time, has a light weight flywheel.

It does not have a tach, but since it is a racing car it has a high idle of maybe 800 rpm.

It has three sets of rear end gears and with the 2.2 to 1 gears on a 2.5 mile track it's top speed is about 125-30 mph, but it takes a couple of laps to get up to it.

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 is high compression, F is low compression. I have no idea how to tell one from the other. From what I've understood, the F head is more desirable for port casting. My take on the whole deal is to go with the F head, deshroud the valves, then cc, and shave to whatever static CR you are looking for. I was lucky enough to have mine come out at 9.5:1 after decking the block for a .030 piston to head clearance.

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/articles/volvo_b20_head_identification.html

That part of the head is nice and visible even on a fully assembled engine.

vintagewrench said:

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?

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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...

Looks like a Nazi supercharger.

Nvm

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.

Looks like you're starting at 8.7:1 on a B20 bottom end.

http://www.k-jet.org/files/greenboo...nual/TP10867-1_1974_140_section_0_general.pdf

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.

vintagewrench said:

This F head with the smaller B18 bore will lower the compression ratio below 1968 specs which will be good for the supercharger.

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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.

Redwood Chair said:

The E head only came on the 70 1800 and some 71 142's so it's not likely you'll bump into one.

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E heads were also used on the '71 1800.

Cameron
Portland

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?

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.

Redwood Chair said:

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.

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Thanks again!! What could I use to program the timing with this system?

.

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.

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.