Lars, the dynamic compression ratio stuff might be too confusing.
Oh yes, but I do believe I understand ( more or less....er....less ) what it's all about.
This one explains it quite well:
Dynamic compression ratioBTW: that site has a link to this:
Cam Timing vs. Compression Analysis written by none other than 'panic' / Jeff
On the salt I watched the little Scout. It was really moving along. As I remember, it averaged just under 90 mph through the mile with a blown head gasket slowing it down near the exit. This is much, much faster than a standard Scout would go at that altitude and on that surface. Most of the bike's build is fairly conventional and it is running on gasoline. Lots of boost must be giving the bike the speed.
Yep...and maybe too much. I do think I am on the limit as to how much power I can squeeze out of the poor thing
without doing some serious damage to it.
Remember this used to be a little 500cc thingy that went maybe 45-50mph and now it goes
close to 90 mph ( with two farting head gaskets at a density altitude of 6290 feet ).
The failures I see on the close up views of the gaskets make me very concerned about excessive combustion chamber pressures. These are not old gaskets that have been eroding after long use and many heat cycles, and they finally let go. They are new gaskets with very few miles on them. No heat erosion or fatigue issues here. Pressure may be the culprit.
Yep; these are new gaskets and yesterday I finally had the time to take off the front cylinder-head to check
the gasket. That one had VERY few miles on it as it was installed prior to the last run I made.
....but even so, it was slightly leaking as seen here
( so I was in fact running
two leaking gaskets on the timed run )
Yes pressure is the problem ....BUT I'm tempted to disagree with you on the "heat-erosion" issue.
Again one can see how the edge of the gasket has melted
so I do believe there's a "heat-erosion" problem that makes the gaskets unable to cope with the pressure
As you know one want to avoid any sharp edges in the combustion chamber
(and I did go through a lot of work on the head to polish them to erase all sharp edges)
as these will act as 'hot-spots' where pre-ignition can take place
My theory is that that's exactly what the edges of the gaskets are doing
....heating up the edges, and eventually melt them.
It's a LOT 'easier' to suffer pre-ignition on a supercharged engine than on a N/A.
BTW: I took a look at the spark plug, and to me it looks good.
I did read somewhere in the forum how you can't 'read' the plugs in the usual way
when running on racing-gas ( I was running the 108 octane racing gas )
as it will never give the blown(ish) color we're usually looking for.
This one should give an good indication as I 'killed' the engine right after leaving the timed mile
If you have the room above the engine, a single piece of heavy steel plate above all bolts can be jacked into place by levering against a frame tube.
...mmmmm: that may be an idea.
We'll see after I tested how things go with the copper gaskets
I agree that based on the video the power is there, so the cams can't be too bad. Unless you have some alternate parts that can be simply swapped in (cams, rockers) I'd leave that stuff alone to avoid introducing a variable.
I will.
As I said ; I do believe too that the power is there and
the exact amount of valve overlap isn't that interesting to me.
All I know is that it's VERY small and everything I've read on supercharging tell
that small overlap is a good thing in a supercharged engine...which is quite logical come to think of it
How much spring are you running?
I take it you mean
valve-spring pressure ?!
200 psi ( valves fully opened ) / 110 psi ( valves closed )
as 'simulated' here in this set up I did
BTW ; I realized I had a couple of small video-files that Tom took out there
and I put them together to make a little video.
Now I wished I had more, as this will be a great souvenir for when I get
old and fart'y, and sit there and dwell on memories
.-)
Click image
OK. so I cheated on the narrative, as the last shot is from the first ( un-timed ) run
but heeey; that's called 'artistic freedom' ...ha ha.
Topic: INDIAN 741 Supercharged...See you in 2011 (Read 788772 times)