Dumb Engine Questions

[bfegan]

Having followed the infamous MM/ebay car thread, the twin plug threads and the various engine rebuilding threads I have several questions:

1. If one replaces the pistons, rods and cylinders with appropriate dimensions to produce 3.6L (or any other size, for that matter) why is it necessary to change out or modify the crank and/or the case?

2. Does a Crankfire ignition system obviate the need for twin plugging for street/DE type use?

3. I recognize that increasing the weight of pistons and rods puts additional stress on the crankshaft. However if revs are kept below 6500, does that additional weight pose a serious problem?

These engines have been around for a long time. I would think that someone would have tested/validated just about every combination of mods available to increase engine displacement. Does anyone have first hand experiences in these areas?

[svandamme]

1 the cyllinders go into the crankcase, larger bore means the crank case needs to be bored so the bigger jugs fit

2 nope , if you go high compression, you need twin plugs
ignition with a crank signal just means you can use electronic ignition , distributor less. which is cheaper then an RSR twinplug distributor(mucho $$$)

3 get the engine rebuild book by Wayne... it contains loads of information on mods

[oldE]

"1. If one replaces the pistons, rods and cylinders with appropriate dimensions to produce 3.6L (or any other size, for that matter) why is it necessary to change out or modify the crank and/or the case?"

Displacement is determined by bore (diameter of pistons) and stroke, the throw of the crank or the distance between the centerline of the crank and the center of the crank journals. In order to get larger displacements, since expanding the bores can only go so far before you run our of cylinder wall, you need to replace the crank with one which will give a longer stroke.

"2. Does a Crankfire ignition system obviate the need for twin plugging for street/DE type use?"

Twin plugging fixes a problem with detonation in large cylinders and higher compression ratios. A hotter spark might not accomplish this for you.

"I recognize that increasing the weight of pistons and rods puts additional stress on the crankshaft. However if revs are kept below 6500, does that additional weight pose a serious problem?"

Force increases with the square of speed. It really depends upon how much extra weight you are adding. Other factors include the degree of balancing, upgrades to the crank and valvetrain. How fast do you need to turn the motor over and how much money do you want to spend?

There are a lot of guys around here with the first hand experience. (I ain't one of 'em)
Les