>Hello listers ...I'm looking for information on just what difference the
>Higher compression head makes to my jeep flathead. ???
>I have one of these heads that I might put onto my nicely running, new
>motor.
I didn't know there was such a thing. All I can imagine is that it has been
milled. This will reduce the size of the combustion chamber, and also the
clearance between the valve and the metal in the combustion chamber. The
result of a smaller combustion chamber is higher compression (a more
forceful bang of combustion). This will stress the rods a bit more, and you
should use a higher octane fuel. You can also increase compression by boring
the cylinders oversize. If I were you, I would compare the volume of the
combustion chambers between the old and new head. I did this by pouring
mineral oil in measured amounts into the combustion chamber while the head
was upside down and flat on a bench. When the oil was level with the
surface, I noted how many cc's of oil it required. You want to make sure
that when the valves are at their highest point (most open) that they do not
make contact with the head.
>Having driven this brand new engine now for several hundred miles, I have
>inherited "some problems" that a previous owner or two have created !!! To
>add insult... I went ahead and put in an Warn overdrive.
That shouldn't hurt, it should help.
>I know these sidevalve engines are not designed to operate at 2001 highway
>speeds ...however, the slightly larger tires definitely give me "more"
>speed (unfortunately, only up to a point)
That's right, it isn't road speed, but engine RPM, that you should worry
about.
> But, the Lil' flathead is really at the end of its rope to actually
sustain
>that performance up and down the backroad hills, forget the dual highways.
Don't expect too much from any 4 cylinder.
>(By the way I got 15+ miles per gallon on a recent 120 mile run with the
new
>engine)
That is good mileage.
>Now the previous owner (or two) has changed the rear ends from what I
>"think" they said was a 5.6:1 ratio ...to a 4.1:1 ratio
>This would give me even more, more, top speed except that the Lil'
>flatheads are out of steam by the time you get to 50mph !!!
Did you change the speedometer gear? If not, you are indicating 50mph but
are actually going faster. Larger diameter tires have the same effect.
>Oh, I know some will write and tell me they easily get 60mph out of theirs
>...true, and so do I ...BUT on the slightest grade your out of power.
>Why ?
Gearing and engine design.
>Because you're already at the top of this engines power abilities.
>Anyway, who wants to run their engine at totally full power while running
>down the highway everyday ?
>
>That said, I do have my standard MB (nice running) ...so I DO have a
>complete comparison here.
>
>I would like to get a few more horses and a few more foot pounds of Torque
>Therefore, the Higher Compression head question.
>
>Basically the two changes to this jeep - larger diameter tires and the
>faster differential - both combined, actually by together, have created an
>awkward situation where I have to slip the clutch too much to get the jeep
>rolling in first gear, then there's not enough power left at high speed to
>make too much use of it This is probably at the point where the Overhead
>valve engine shines - big time with it extra 12+ horse power ...eh ?
I think you currently have the T90 transmission. You could hunt for a T98, a
four speed with a low first gear. I believe these also have a backup light
switch. I am in the hunt for one of these myself...
>
>I have, what I am told is this.
>One of my engines has the ribbed high compression flathead. So, just how
BIG
>a difference would this make?
You need to improve the intake and exhaust systems to realize the most
benefit. I have heard the Solex carburetor (JC Whitney sells them) gives
more power due to better design, and with the exception of the choke cable,
is a perfect fit. I will try this someday, along with a larger diameter
exhaust and less restrictive muffler. I am working on finding a way to put a
K&N air filter in the stock canister. Don't forget the importance of the
ignition system. Going to a multi spark system & hotter coil might help, but
beware of detonation. Someone could probably grind a better cam also, if
someone already hasn't. Someday I will figure out how to degree a cam, that
is supposed to make a difference also.
>
>1]
>So, Is there anyone out there that has run their jeep with the standard
>head and then switched over to the high compression head ...there must be
>someone who has felt the difference???
>
>2]
>Anyone know the compression ratio of the standard head compared to the high
>compression head.
There used to be a program, I swear it was called Camquest, where you could
enter your bore, stroke, combustion chamber cc's, carb size, # of cylinders,
rear end ratio, tire size or whatever, and it would tell you how much cfm
you needed for a carb, your horsepower, compression ratio, and would
recommend a camshaft. I can't find it now, but will continue to look.
Lisa
>Sorry for the length of this post.
>Regards
>Rob Pearson upstate, NY
>42MB and a handful of Cj2As and a DJ bitza !
>
>
>
>
>
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This archive was generated by hypermail 2b29 : Sun Sep 02 2001 - 11:15:37 PDT