I need to build an engine for my 71 Camaro weekend HPDE car. What am I losing by building the smaller cubes vs larger besides 9 cubic inches? If the engine is built to 1.5 hp/in then it is very expensive for those last 15 hp. I was planning to use the small bore LSx 7 heads on the 418. Is there a durability difference between the 2 that should sway me?

 

Strokes longer than 4.0 are prone to having skirt wear issues, generally not worth the small gain.

 

Ididn't even think about the 4.125 stroke. I was comparing the LS3 based combo to a scratch built LS7. The bulk of the price difference being the block.

 

ahh well now you know. the ls7 is such a nice starting point with the big bore though and factory 4.0 stroke. not to say plenty of people have done very very well with ls3's either, but if it were me and it was my choice id def go ls7 block and aftermarket callies rotating assembly.

 

Would the reason be for more durability? I don't think it should make much more power since it is only slightly bigger.

 

Stock LS7 rotating assembly is fine.. you don't need some heavy *** Callies internals to go fast and be reliable.

 

Which one is more cost effective for you? ie.. Whatcha got laying around? The 418 will make great power, so will the 7. Id go with the lesser expensive, but Im married with children, so cost effective is key for me. Both will make more power than you can put down on the street!

 

I have no parts to start with, just need to choose and get started. This engine will, by far, be the most expensive part of this car which is why I may alter my original plan for an LS7. I just hear things about piston and blowby problems with a 4 inch stroke in an engine that was not designed for it.