78.4 Crank?, drop in? Options

[thomasotten]

I have been reading about the 78.4 crank. But I can't figure out from what vehicle they came out of. The 914 2.0 had the 71, right? Is this a "drop in"?

[SLITS]

The 2.0 crank is 71 mm stroke.

I was told that a 78 mm was a drop in - no case grinding at the parting line for rod bolt clearance, but that was sometime ago and I can't be sure.

I didn't think the 78 came out of anything - it is a stroker crank made by SCAT and others.

Sorry, I couldn't help on this one.

[NoName]

DPR makes good 78mm cranks and you can buy them (and con rods) here. If you can get the "All About Performance VW Engines, Part II" book from Hot VWs, they have a FAT Performance article on building a large displacement Type IV motor and they give some clearance numbers e.g., connecting rod to case clearance should be at least 0.040-inch and a minimum clearance of 0.060-inch between lobes and connecting rod caps. Use a reduced base circle cam. You also want a (Connecting Rod Length) / ( Crankshaft Stroke) ratio of around 1.75 or 1.8.

[cgnj]

Hi,

With a VW journal, Scat rods will need to be cleared. CB super race rods may require less work ( I have not used the CB rod). No experience with Chevy journal.


Carlos

[Jake Raby]

It does not "Drop in"

Ading the crank, without adding the rest of the combination is the biggest mistake we see.

One must approach the assembly of an engine of this caliber with a "Performance mindset". This means that when ONE part is added that adds performance, EVERY part that relates to that must be altered. In this situation you must attain the proper rod ratio, and proper compression height on the pistons, as well as choosing a cam that gives you the correct characteristics for you head flow, as well as the fact that it must "physically fit" inside the case, without colliding with the cam..

Do your homework before you buy the first part. Parts are available that will drop right in- but not off the shelf, unless its a shelf of mine.

BTW, we use standard 66mm stroke cranks to make our 78.4 with a Type I rod journal. The66 stroke crank had a 2.165 rod journal just like a TI, its just wider on the big end.... (IMG:style_emoticons/default/boldblue.gif)