Hello Rick,
Well since you seem to be using this in a truck with a 2500 stall, you are
probably not biulding a 7000+ rpm racing motor. My humble opinion is that
spending $1500+ on a custom rotating assembly that will never see the light
of day above 6500 or so is a waste of a good pocket book. If someone will
sell you an offset ground crank, proper rods and pistons for a stroker
motor like that for less than $1500, I would be hesitant, but I have been
wrong before. If you want the increased cubic inches, I would suggest
finding a 360 motor for the biuldup. With the low rpm ranges the best
street piston is the Keith Black series of hypereutectics, price, power,
and durability wise. A hypereutectic is a very (very) strong cast piston
with a high silicon content, it does not need any internal metal supports
to hold its strength as regular cast do. The KB pistons use alot of custom
racing tricks that you would pay a lot for on a forged. The valve pockets
are done for the exact chamber location (there are no 4 "eyebrows", just
2), the valve pockets are cut way deeper so that high lift cams do not
cause any havoc, the top is machined beautifully, the rings are located
higher up, they need larger ring clearances which works perfectly for
buying standard cheap moly type rings which are purposely made with a gap
that is way too big, and most importantly the oil ring groove is a set of
drilled holes instead of a open hole casting, this makes the piston super
strong. They also include locks for full floating rods if you choose that
route. The best part is that the price is right, I found the 360 ones in
Summit for under $200 for the set. I do not know if they make them for the
318 though.
Now an issue of engines that I feel very strongly about is the quench
hieght. This is the minimum distance between the piston and the head.
Most people do not check this but using too large a clearance is horrible
for both power and economy. With the standard steel rods you want about a
0.038~0.042" clearance. Any more you will lose some power and the engine
will ping more, any less and when the rod stretchs you might lose the
clearance to the head. With the typical FelPro head gasket compressed
thickness of 0.039" this means that the top of the piston and the top of
the block should be flush. Chevys are the worst for this, Fords are very
good, Mopar I am learning as quickly as I can since my memory is bad about
the few that I did work on.
Now the heads, my opinion is that the best money is spent here. First all
"proper" valve jobs are 3 angle, you can do more angles though sometimes.
A "good" head person can do some serious work with a valve job that an
untrained eye cannot see. I would say that as much as 10% more horsepower
can come from having a "real" valve job done vs a $50~$100 el cheapo. You
can move the valve face margin up and down the pocket/valve face, make it
skinny or thick, back cut the usual thick stock valves, lower the exhaust
seat relative to the intake, all of these (and other) steps can increase
the power and/or durability. I would reccomend having bronze liners
installed on the guides, and positive seals installed on the intake valves
also. I am really kinda new to the mopar scene so I do not what heads are
the best and so forth, but if it is like the Chevys and Fords, aftermarket
or factory performance cast iron upgrades are usually worth the money. A
"proper" valve job like what I would do to my own heads would take the
better part of a day so with figuring the average shop hourly wage this can
get expensive.
Please forgive for the long letter, trust me it would take a book to put it
all down. One word of caution, I have not followed any of the Mopar
publications, but the Ford and Chevy ones are horrible with their engine
biuldups, and many state grossly inflated dyno power numbers. The best
that I knew of was Circle Track but I have not picked up one of these for a
bit either, I hope they have not changed.
Regards
Nicholas
At 10:32 AM 3/5/98 -0500, you wrote:
>Basically I'm doing a complete drivetrain rebuild on a 5.2 (from a dakota)
and it is a daily driver. What I'm looking for are some good performance
parts for the rebuild. Stock compression with a 30 or 40 over bore. Because
I may have to have a set of pistons made anyway it would be relatively easy
to get the crank reground and stoke the motor slightly using some longer
rods. It would be fun to have the first and maybe only 340 Magnum (5.4l).
The heads will be stock with the usual port/bowl cleaning and a 3 angle
with little change to the combustion chamber. Other mods are MP cam/lifter
set, MP springs, Extrude hone manifold, Grand Canyon Throttle Body,
Complete Jacobs ignition setup, Underdrive pulleys, Headers.... so on. The
trans is also getting a complete rebuild with a 2500 stall converter.
Should be fun. I'm looking for good performance with civility.
>-------------------------------------
>Rick Lewis
>U.S. Technical Support Manager
>SolCom Systems Inc.
>"Ultimate RMON Network Management"
>http: www.solcomsystems.com
>Tel: 703-758-6722
>Fax: 703-758-3568
>-----------------------------------
>
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