I am thinking about building a iron block nitrous motor. I know a lot of people bore the LQ9 block out to 4.030 and use a 4" crank to make the motor a 408, but can the LQ9 block be bored to 4.070 safely and use a 4.1" crank? I already have the heads that will be going on this motor so that is why I am not going straight to a LSX block. I am looking to spray around 500 to 700 between 2 different stages. Has anyone else every built a LQ9 block with that big of a bore and stroke? If this is possible are there any special things I should do to the block or anything to check in the block? Thank you.

 

The iron block can be bored to 4.07" but it require sonic testing. Some are boring to 4.0845" and some to 4.125" with the cooling ports filled with some kind of cement grout to add strength to the wall

 

Ok, I am gonna stick with a 4.070 as my heads would not really be any good for anything bigger. What about that larger stroke?

 

For myself, the iron block will accept the 4.0" stroke with no modification to the block, while the 4.1 & 4.125" will require trimming the block in some area. Eric did many professional build with 4.125" stroke with iron block.

Many will say that above 4.0" stroke is not advisable due to the oil consumption and some say it is no problem with the oil consumption.

 

Like was said, many iron blocks can be bored to 4.065" or 4.07", but you should sonic test it first as a few will not have enough cylinder wall thickness. That's a lot of nitrous and pressure, personally I'd stay with 4.03" for insurance and stability purposes. I would also stay with a 4" stroke, it's not recommended going longer with big shots of nitrous or a lot of boost due to piston pin placement and a weaker piston crown. I'd stay with the tried and true 408 and spray the heck out of it.