Is the aluminum block on the SR20DE stronger than the cast iron block on the QG18DE? I'm asking this because I might want to go turbo with my GXE later on and I want it to hold up as well as the SR20DE engines.
I would probably say the SR20DE also. The 1.8 isn't really meant for performance the way the 2.0 is, and it would seem like Nissan would engineer it a little less strong than the SR. However, the old GA engines are plenty strong for whatever you need (there's some turbos hanging around here), so I would guess that the 1.8 is plenty strong.
Aluminum is ok at lower power levels but I have to disagree with some of the praise for the aluminum SR block. I prefer cast iron over aluminum. It is stronger, sometimes heavier but look at all the external reinforcing ribs on the SR and understand that an iron block wouldn't need that. If Nissan Manufactured an iron version of the SR block it would display a great deal more strength than the aluminum one. Now if I was building a maximum effort NA engine the aluminum would be great. However, a balls to the wall turbo or highly juiced motor with those catastrophic cylinder pressures needs the strength of iron.
The GA was not designed for performance. If it had been designed from the outset for performance you would see them gulping down more boost pressure and leaving SRs in the back even with a 200cc deficit. The power is in the head not whether the block is aluminum or iron or kryptonite. The block and rotating assembly is going to set the power limit as far as durability and durability is iron.
Engineers design things to a specified level of stress. The SR20DE was way overdesigned to accomodate the turbo. Even though a cast Iron block will be stronger for a specific wall thickness and reinforcing, you can make a much stronger engine with aluminum if you design it that way. On the otherhand you could then design a cast block to be stronger than the aluminum one you just designed. All depends on the specs-which none of us really know.