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Old combustion chamber design which is new to me. What are the tradeoffs?

Old combustion chamber design which is new to me. What are the tradeoffs?

Old combustion chamber design which is new to me. What are the tradeoffs?

(OP)


Quote:

The Lycoming "BB" V-12 was designed in 1932 by Auburn's Chief Engineer, George Kublin. Lycoming invested over $1-million in the new engine: $400,000.00 in designing, engineering, and development; and $600,000.00 in new machinery, tools, dies, buildings, and all other manufacturing-related requirements. The Great Depression killed off luxury sales, so the V12 was sold to American LaFrance for use in fire engines. There, it lived on another thirty years.

I've been building engines for fifty years, but when this one came in the door, it was new to me. What were the pros/cons to a pocket combustion chamber such as this?

FWIW, when ALF took over the production, they added a second plug per cylinder. The additional distributor was driven off the rear of the gear-driven generator.

Jack Vines

RE: Old combustion chamber design which is new to me. What are the tradeoffs?

Looks to me like a ton of surface area for heat loss, and a bizarre assembly sequence with a lot of extra parts. Looks like the valves have to go in through the extra bolt-on piece that goes on the side of the combustion chamber.

If you're going to have rocker arms, you might as well put them on top of the head and point the valves down into the cylinder.

I suppose it's not subject to dropped valves or catastrophic failures of the cam timing system.

Looks like intake and exhaust both have to do a 180 degree turn between the port and the manifold.

RE: Old combustion chamber design which is new to me. What are the tradeoffs?

(OP)
Yes, to all the above, but it's hell for squish.

jack vines

RE: Old combustion chamber design which is new to me. What are the tradeoffs?

Wow.

Mike Halloran
Pembroke Pines, FL, USA

RE: Old combustion chamber design which is new to me. What are the tradeoffs?

I see almost no advantage to this configuration. It has very high volume-to-surface-area before expansion, and flame paths are all extremely long.

This reads to me as a product of an era where things like combustion chamber design were based heavily on guesswork- not a design you'd want to crib from.

RE: Old combustion chamber design which is new to me. What are the tradeoffs?

Looks like an early version of pre-chamber combustion, just a bit more complex.

RE: Old combustion chamber design which is new to me. What are the tradeoffs?

(OP)

Quote:

I see almost no advantage to this configuration. It has very high volume-to-surface-area before expansion, and flame paths are all extremely long.

Agree, mostly. The flame path is reasonably compact compared to flatheads of the same era.

I found a spec sheet and the compression is only 7.5:1.

jack vines
Obsolete Engineering Division
Mager Engine

RE: Old combustion chamber design which is new to me. What are the tradeoffs?

A flat head with over head valves. Like many designs of those times, someone thought they had a great idea, maybe it would have done okay on the low octane gas in those days, they should have bumped up the Cr a bit, maybe it wasn't so knock sensitive. Sure looks like nice induction and exhaust restrictions though. So Packard you got to play with one of those? It would or will be interesting to hear how it runs, please keep us posted.

RE: Old combustion chamber design which is new to me. What are the tradeoffs?

(OP)
We have two of these and are confident we can get one running. The 1954 block checks out OK, but there were three cylinders not getting what they needed. Two center cylinders on the right bank were running way hot. Our current thinking is somehow the firing order got off or two wires were crossfiring. With twenty-four spark plugs, two analog distributors and old, hard wiring, either is possible.

One cylinder on the left bank wasn't firing enough to keep it clean, but again, who knows what?

One bit of trivia; when designed, the Lycoming BB may have had poured babbit main bearings. A later redesign by ALF didn't close up the main bores, just went with thick bronze backed babbit inserts. These appear usable. We spent two hours old school hand fitting and checking the clearances down to .002".

With current engine R&Rs, it's all about getting the electrical connections back and functioning. With this monster, it's bolts, nuts, pipes. There's enough iron to build a half-dozen 200hp 4-bangers.

I've built some long rod engines, but this one is the tallest ever, with a rod/stroke ratio of 2.2.

jack vines
Obsolete Engineering Division
Mager Engine

RE: Old combustion chamber design which is new to me. What are the tradeoffs?

It's dying for a stroker crank

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: Old combustion chamber design which is new to me. What are the tradeoffs?

(OP)

Quote:

It's dying for a stroker crank
At 3.625" X 4.25", it's already a bit undersquare and long stroke. Personally, I think it needs to be twin-turbocharged.

jack vines

RE: Old combustion chamber design which is new to me. What are the tradeoffs?

you asked what were the trade-offs they are an inefficient squish long flame path and a problem with flame speed not to mention the clear and unrestrictive intake exhaust paths the whole design is way off, there are types of diesel's and petrol engines that run pre-combustion chambers but their design run what is called charge air stratification where the cylinder is comprised mainly of just air and around the spark plug (petrol) of glow plug (diesel) and are run rich around the initiator to initiate the burn event then the rest of the free oxygen is consumed giving low combustion temps and so forth low Nox and low HC/CO as the exhaust is comprised mainly of free oxygen the engine that is showen would be good to put on a 5 gas analizer and see what the emmisions are very bad I can see just from the design of it a good book for everyone who wants know about engines is The High-Speed Internal Combustion Engine by Sir Harry Ricardo (1930s) the other one we have found is lotus engine software called (LESoft) you can only through the freeware model a single cylinder but then all engine devlopment starts with a single cylinder saves devlopment costs and machining costs check the books and program out they are free from your libary or the internet

RE: Old combustion chamber design which is new to me. What are the tradeoffs?

(OP)
Thanks for the information. Question:

Quote:

an inefficient squish

When we reassemble the short block, we'll measure the deck height, but the cross-section drawing looks like it would have squish from hell to breakfast (an obsolete engineering term) because all of the piston area is forced up into the tall narrow combustion chamber.

jack vines
Obsolete Engineering Division
of Mager Engine

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