space between the head and the block? that would cause the engine to overheat instantly. here is the difference between open and closed deck..

This is an open deck, our vq. as you can see there is an area around the sleeves where coolant goes. this is common on most non forced induction cars and importantly aluminum blocks to help aid in cooling. aluminum if i remember correctly doesnt deal with heat as well as iron. it is also not as strong as iron.


This is a closed deck motor. as you can see this area around the cylinder is not present. however the block is made of iron which is much stronger and can deal with heat much better. most factory turbo charged cars have closed deck configurations such as the RB26, 2JZ, 4G63, etc


you have to evaluate what the use of your car is going to be. if you want a daily driver you might want to stay open deck to help keep coolant temps down. sleeving is pretty much exclusively for drag racing where you make one pass then the car can sit and cool off. and as other people said no one has really tested the limits of the stock vq sleeves. louies car made 7xx whp if i remember the car was tracked and no issues at all. powerlab made 9xx whp on stock sleeves. so i dont really think sleeving is necessary if you plan on staying with stock displacement.

 

a couple years back sleeving the VQ for 550 and above was pretty common only because this was considered a slight gray area that only a few vq tuners had experience w/ as far as these power levels were concerned. And it was automatically assumed this was the way to go as a extra insurance policy. Now it is a different story.