The V8 Owners Forum -

Hi all,

Years since I posted on here. Looking for advice on my current build.

I have an interim 3.9 block that has the full width caps. I have had the cross bolt holes drilled and taped. I intend to have the block top hat linered by V8 dev and bored to 96mm.

I have a pair of Wildcat heads, together with pistons with valve cutouts for the Wildcats and light weight chevy rods.

A few years ago I bought a raw crankshaft casting on Ebay. I believe the crank came from a batch made by a chap on here, BoostedLS1. I think I got the last one. I am still to have this machined. Emailed a couple of companies last week, but no luck so far.

My question is, should I stick with the small journal 3.9 block, or cut my losses and ditch it in favour of a large journal block.

From my research of previous posts on this and other forums, opinions seem to be mixed on the value of the large journal crank, with some arguing that it is overkill and only weakens the block, increases friction and weight etc... On the other hand, it seems sensible to want to increase crank strength with the expected power output from the Wildcats.

I intend to use a Kent M238 cam. I would expect to be producing around 380/400hp, with the occasional blast of 7000+ rpm?

Any advice greatly appreciated. Obviously crank machining is expensive and I want to be certain I am going down the correct route before tinning up.

For what's worth, I favour the larger journal crank. I'm building a 4.6 block with a stroked 4.8 crank for a supercharged engine..aiming too at around 400hp. Every bit of strength in the block/crank will be desired.

For what its worth I would go with the larger journal crank.
Everything I read about performance engines is they are using larger diameter bearings - so infect they are spreading the same force over a larger area so would give lower pressure the bearing oil film has to manage.
Also a stiffer crank for higher rpms is a benefit.

I believe the large journal crank also has more/better counter balancing to enable better engine balance.

In performance engines at the highest level, at least for a normally aspirated engine, the trend is towards smaller journals not larger. if boost is involved then strength becomes an issue but otherwise it is not significant. A smaller journal has a much lower bearing surface speed, this results in less friction, It is also more forgiving of oil system capacity. On a Rover V8 of either type the oil pump is marginal for anything more than a stock rebuild. Nascar engines are highly developed, all the engines in every car on the grid run at a maximum a Honda BE bearing size. The main bearing is 350 Chevy or Small block Ford size or smaller. i would keep the small journal stuff personally. As you are running a cast crank from a raw casting you can basically have anything made. Look at what output you eventually want. Running a supercharged methanol 3.9 Rover at around 480 BHP we have had zero bearing issues. a friend who runs a 4.6 in a similar supercharged set up but much less power has always had bearing issues.