3 valve block vs. 4 valve block

[jrs]

Can I use a 3 valve head from an S-13 on a 4 valve block? I have to use the 3 valve head due to the rules of my scantioning body.

[doainwpg]

with enough work it can be done but it would be much easier for you to just get a sohc block to go with the sohc head.

[jrs]

I had heard that the 4 valve block/crank was stronger than the 3 valve block/crank. I have already broken two cranks (3 valve) and of course the blocks ended up with holes in them. Nissan Motorsports sold me some "special" rod bearings for the 3 valve crank, but told me to change them out after every 3 races. If I can switch to the 4 valve crank/block and stop the breakage, it would save me $$$$$. I'm just trying to establish what is different between the two blocks.

[KADreams]

How the hell did you manage to break two cranks? Could you give more info on your setup?

[jrs]

Race car. Carillo rods, JE pistons, stock crank that had been nitrided. I found out that the 3 valver's have weak rod bearings, if one goes out the rod ends up outside the block. Nissan Motorsports now tells me I should have been changing the rod bearings after every 3rd race. (that was an expensive lesson). I believe the comment from them was that I should use the 4 valve crank/block with the 3 valve head. These engines have extremely long strokes, so you don't want to turn them at a very high rpm. Oh, and don't forget this little additional tid bit. Most 3 valve blocks were NOT made in Japan. To use one in motorsports, full machining is required and even then you might find casting flaws in the process. So it's best to grab two blocks at the salvage yard, and keep one as spare. ahhhh, the joys of racing.