I assume you are talking about a 617?

I have a few takes on this...kind of all over the place but here goes.

IF you only want 150 hp, I believe some have achieved close to this (like 145) with maxing out the stock pump and swapping a newer turbo, exhaust and intercooler in.

Since you have a G, you probably are more focused on low end, so this set up may serve you best. A newer, faster but not necessarily bigger turbo will give you some more power by spooling sooner without sacrificing mpg too much. For example, a Holset He221 is small but flows a lot of air on both ends and since it is a newer design should spool sooner as well.

Now, as a 6mm owner in my 603, I wish I had gone to 7. I am limited to about 90cc of fuel, which in theory could make 260 hp. No idea what I have but I estimate maybe 240. My end goal is around 300 now though so being able to turn it up to 110cc would have been nice. Instead I will need a new pump. Overall though, I am satisfied with my current performance so I may stay with what I have.

If you are going to go through the expense of building a pump it would be best to get the bigger elements and have it set for low power. If you get 6mm elements out of a pump for dirt cheap then maybe that would work too. The 6mm would definitely be good for more that 150hp with mods.

I have had no decrease in mpg. In fact my best to date (which was 31 on a full tank) was with new pump and exhaust, manifold, turbo, etc. Whether that can be attributed to any one of these in particular is up in the air. I still got 29.5 with the pump and stock exhaust and stock manifold though.

Lastly, I drive the car as I would normally without mods so if I was constantly flooring it, etc I would expect much worse mpg. But, it's nice to be able to open it up here and there when needed

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Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k