Subject: Re: Air compressor

From: [email-masked] (Barry Workman)
Date: Thu, 13 Jul 1995 03:52:32 GMT

[email-masked] (Alan Muller) writes:

>>
>>In article <[email-masked]>,
>>Jim Naylor <[email-masked]> wrote:
>>>Greetings-
>>>
>>>Would anyone know if it is practical to convert a running (fairly low
>>>mileage) '71 Ford v-8 engine (350 cid) into a four cylinder engine with
>>>the other four acting as an air compressor? Would the heads need to be
>>>modified, or could one side be used as the compressor. Would the manifolds
>>>need modification (to keep the gas out of the compressor, at least)? Would
>>>it need a different carburetor? Would the ignition changes be extensive?
>>>Or am I barking up the wrong tree entirely?
>>>
>>>Any help (or even a recipe, maybe?) would be greatly appreciated.
>>>
>>>-- 
>>>Jim  Naylor                      ______ aging sentimentally--        
>>>[email-masked]                     it's bound to be fatal. ______
>>>Wichita, Kansas                             
>>
>>Yes--

>I have seen commercially made compressors of this sort using Ford V8s,
> Ford V4s, and Wisconsin air cooled V4s.  All those I've seen used a
>special cylinder head on one bank for the compressor and a special one-
>bank intake mainfold on the engine side.  The engine, of course, needs 
>a governor.

>Good luck.

>am
The reason this works, of course, is because a V-8 is two 4's
wedged together.  Firing order is 1-4-3-3-2 as I recall.  Seems to
me that plugs in the intake side is all you'd need to do, assuming
that there is a one-way check valve on the compressor side.
-- 
    - Barry Workman

---

From: [email-masked] (Mark Kinsler )
Date: Wed, 12 Jul 1995 19:55:43 GMT

I'd try it.  What the hell.  Only you'll need to modify the head on the
compressor side.  First things first, though:  See if the engine runs okay
with the plugs taken out of one bank.  If it does, then proceed.  I
imagine that you could make one-way valves out of the existing intake
valves by replacing their springs with something much lighter.  You'll
have to get creative about the exhaust valves.  I wouldn't try to make a
multi-stage compressor out of the engine on the first try because this
would be one heck of a project.  It's worth considering for the future,
though.  The nice thing about leaving the head relatively intact is that
you'll have cooling water through it to keep your air cool. 
  I don't think that the carb is a big deal.  The commercial compressor I 
saw had what looked like a stock carb on it and the unused plug wires 
grounded.  
   Other thoughts about valving:  remove the rocker arms from the exhaust 
valves on the air side so they'll stay closed.  Change the springs on the 
intake valves to real light ones.  Plug the intake and exhaust manifolds 
on the air side and drill the intake manifold for an air filter for each 
air cylinder.  For air exhaust valves, connect a check valve to each 
spark plug hole.  Join all of these together into an air manifold (just a 
piece of pipe) and you'll have the mother of all compressors.  I haven't 
tried this, but I'd certainly like to.  Now all I need is an engine...

                                 Mark Kinsler
                                  Looking lustfully at the 
                                   Buick's V6.

---

From: [email-masked] (gary preckshot)
Date: 13 Jul 1995 19:57:11 GMT

In article <[email-masked]>, [email-masked]
(Mark Kinsler ) wrote:

[question about modifying an auto engine to be a compressor]

> I'd try it.  What the hell. 

[Followed by two paragraphs of enthusiasm..]

Everything that's been mentioned in this thread, except one thing (swapping
heads), ignores the most important modification, and the one that takes the
most machine work.  That is, compressors are purposely built so that they
have a residual volume of as close to zero as possible.  This is so the
cylinder exhausts the air it compresses, rather than just heating it in
place.

In terms familiar to auto mechanics, this means you need heads and pistons
so that your compression ratio is 100:1 or better.  So the primary
selection criterion when choosing an engine is that the piston top should
be flat and should come flush with the top of the block at TDC.  Or, like a
VW engine, individual cylinder pots should be removable so you can easily
achieve zero residual volume by machining.

The reason for flat topped pistons is then you can bolt a flat topped head
to the bank you're using for the compressor part.  You don't need elaborate
valve gear, or even the valve gear original to the engine.  Most small
industrial compressors use leaf valves, for the minimal dead air space such
a valve has.  In short, you want the valve as close to the piston top as
you can get it, and as small a volume between the piston top and the valve
surface as possible.  IC engine valves do not have these characteristics.

G.

---

From: [email-masked]
Date: Thu, 13 Jul 1995 15:51:37 -0400

>Good luck.

I'm making a complete WAG here, but if I were designing a commercial
version I'd use a special camshaft that opens the nominal exhaust
valve on the intake stroke, with symmetric lobes that opened the
valve twice per rev (compressors don't need to be 4 stroke).  The
check valves on the outlet side would screw into the sparkplug holes
feeding an outlet manifold of some sort.  This would mean cobbling
together a single exhaust system with no Y-pipe that attached to the
one real exhaust manifold, and using the exhaust manifold on the
compressor bank as an intake - you'd also want to rig an air filter on
the "inlet" of that manifold.

The advantage to this approach is that you don't need a special
intake manifold or cylinder head (although you might want to cut
the compressor head a few thou to bump up the CR). All you need is the
camshaft, the spark-plug sized check valves, and a sheet metal gasket
to cover the nominal "intake ports"  on the compressor head - the special
camshaft wouldn't even need lobes for the unused intake valves, but
blocking off the ports would keep fuel/air mix from sneaking into the
compressor side through the intake manifold.  I would think having
a custom camshaft cut would be cheaper than casting a special head and
intake manifold.

Don