Stroker Combo's
Combo 1: 258 (4.2L) crankshaft and rods pressed on 242 (4.0L) pistons and
assemble engine using cam of choice, etc. The down side of this is that the
258 crank and rods on the 242 pistons make the piston to deck clearance out
of factory spec. The piston sits about .020" to low in the cylinder making
the optimum "quench" ratio to large. This combo will work and a few engines
have been built like this; the possible problem of bad emissions,
spark-knock (possibly needing higher-octane fuel to reduce), and carbon
build up, could occur. The good side to this type of build up is that it is
the least expensive of all options.
Combo 2: Same set-up as combo 1, but "decking the block" shaving the
block-to-head contact patch down to get the "quench" within factory specs.
The down side to this is that the closer you get the piston to the head, the
higher your compression ratio goes and your already increasing the stroke
which is also increasing your compression. This is a popular combo that has
also been built in to a few stroker motors. The possible side effects are
high compression, spark-knock (possibly needing higher oct. fuel), could
also occur. The good side is a lower cost build up that should run a
little cleaner than combo 1.
Combo 3: 258 crankshaft and rods pressed on to custom pistons that have
been "dished" out to keep the compression ratio down to a range that will
allow low octane gas. The down side to this is mostly the cost to have
custom pistons made and figuring out what piston top (unproven) design will
suit the engine best. The good side is that the pistons can be made to any
dimension needed keeping the compression ratio down and block decking could
be eliminated.
Combo 4: 258 crankshaft and longer 242 rods pressed onto custom pistons
that have been "dished" out to keep the compression ratio down and have the
wrist pin relocated to allow for the longer rod. This combo allows for a
better "rod ratio" keeping the piston at TDC longer to allow optimum
combustion. The down side of this is again the price of custom pistons and
having to choose an unproven piston top design to use. The upside is
compression ratio of choice, better rod ratio (possibly making for a cleaner
running engine), and block decking optional.
Combo 5: This one is not for the timid. 258 crankshaft that has an off set
grind making the stroke even longer, custom rods and custom pistons.
Assembled in a 242 block. I don't have any true details on this set-up so
I can't give you any more information at this time.
The displacement is as follows.
4.0L is a stock newer straight 6 jeep engine
4.2L is a stock older straight 6 AMC/JEEP engine
4.5L is combo's 1-4 with a stock bore 4.0L block.
4.6L is combo's 1-4 with a .030" over bore 4.0L block.
4.7L is combo's 1-4 with a .060" over bore 4.0L block.
4.9L is combo 5 with a .090" over bore 4.0L block.
