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Subject: San Jose visit / TR6 cam saga continues
Author: paisley@boulder.nist.gov (Scott W. Paisley 303-497-7691)
Date: 12/2/94 4:52 PM
>I then tried this little wacko test. Removed the pushrods from the
>exhaust valves, and tried a compression test. Compression was the
>same, but I was hearing a POPing sound from the engine. What was
>happening was the intake was opening while the piston was coming up on
>the exhaust stroke and blowing air out the intake! Pretty fun eh?
>This actually could be normal, due to the overlap of the cam.
>However, I was surprised at the intensity of the popping sound. After
I guess I don't get this. Let's take a look at what happens while you're
doing the compression test:
Intake stroke - Intake valve opens, piston sucks in air/fuel mixture. Intake
valve is open.
Compression stroke - Air/fuel mixture is compressed. Both valves closed.
Power stoke - None here, no spark. Mixture expands back out. Both valves closed.
Exhaust stroke - Since your exhaust pushrods are gone, this is yet
another compression stroke. Exhaust valve should be open, but isn't, so
both valves are closed.
Intake stroke - Intake valve opens near TDC so piston can suck in more
fuel/air, right? But remember, the exaust stroke was actually a
compression stroke, because the exhaust valves never open. So as
soon as the intake valve opens - *POP* through the intake, since
the fuel/air mixture is still highly compressed.
Am I missing something???
>thinking about this, I know that if I move the cam timing, I'll want
>to set the intake valves opening later. e.g. retard the cam. If
>anything, I'm getting an education!
>Cheers,
>
>-Scotty
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