Jake, IMHO you might consider looking to adapt a manifold from a non-cross-flow 2.0 gasser. It also has long runners (albeit no where as long as the SDI ones... much easier to find and likely much, much cheaper.
Let's see... you mean like from an Audi 2.0l reverse-flow block? Like the other gasser reverse-flow blocks, my turbo sits too high and would interfere with it's layout. Now I would definitely try that if I were to change my exhaust manifold to relocate the turbo lower and out of the way, but that's a bigger project... re-doing the turbine outlet exhaust system, relocating the turbo, changing the oil return line, re-doing the air inlet tract going to the compressor inlet, not to mention boost tubing coming off the compressor outlet...
The SDI manifold will not stay in my car for long... I have visions of grandeur to build a complete motor incorporating this manifold and a VNT-20 turbo I just bought. This, and a RedRotors-modified pump, big honking injectors and custom programming will make this a Monster TDI! 
Since intercooling and fuel injection mods are unlimited, exploit this to the fullest possible extent! Plumb a dual-IC setup ora massive unit that covers the entire front-end or something! 
What are the rules about changing turbos? IIRC is must be from a unit that was incorporated in the OEM engine, although you are able to go through the parts bin in case there were different, better units from different years?
With my current setup, intercooler efficiency of the single audi5k intercooler at stock peak boost pressure are very efficient, so little would be gained by adding another intercooler, and there would be the negative of added weight and volume in the intake tract that could actually decrease overall performance. Also, although intercooler are unrestricted, you can't just go cutting holes, etc and do unauthorized modification to get them to fit. You've got to carefully place them. Anyway based on test results of the intercooler outlet air temp as well as pressure loss through the intercooler, I think I am already near-optimal on the intercooling situation.
FYI: Here is the section of the rulebook that has most of the items that cover street prepared class:
http://mouton.best.vwh.net/sccasolo/Rules/sp.htmlI can only update/backdate '75-'84 Rabbits and Jettas. That leaves as the only turbo diesel engine option, the '83-'84 engine code "CY" turbo-diesel 1.6l solid-lifter, for which there were 2 turbos available: a KKK and a Garrett, both of which came with the same peak boost pressure specs (9-10psi).
There are a few other interesting options I've considered, but they are not what most folks do to their street cars. Water injection is permitted (but no alcohol.) Also, CNG-fumigation is permitted. Like I said before, my car is pretty fast as is... I'm not in need of a huge power gain. Of course, if there is something big I've left on the table, I'd like to find what that is, but trust me I've given this a lot of thought and you can rule out upping the boost pressure (beyond maybe blueprinting the stock turbo to the upper limit of the specification, probably not more than 10psi).
Oh yeah, I do think there is a lot of potential to be had in the fuel injection. And this is an area I have been and will continue to focus a lot of research time on. I have seen HUGE power increases in this area already. (One of the main power boosters that allows me to kick out around approx 120hp on stock boost pressure out of a motor that originally had 68hp! Not to mention how much higher the power curve extends that the stock motor (whereas the stock governor petered out starting at around 4500rpm, I've gotten mine to pull with full power up to about 5500+rpm!)
Believe me, it's very good that I stay in this class. Were I to mod my turbo, I'd go into prepared class, where lightened cars trailered-only need apply, with lexan windows, stripped interiors, double a-arm conversions, fully-internally built motors, etc. Or street mod class, not much better. Street prepared is where I can hang with the 1.8l "JH" sciroccos, Rabbits and GTIs, etc. It's a good competitive class where VW drivers have taken national championships. Frankly I feel in current state of tune, my 1.6lTD was at least as competitive as a prepped to the limit 1.8l"JH" motor, so anything I can do to make it even better will only further the advantage! On the disadvantages of my setup, a 2-dr version would be approx 55lbs lighter than my 4-dr version. And a scirocco although not lighter than a Rabbit (actually a little heavier) may be more competitive yet, likely due to a lower center of gravity. There is a rule change proposal in the works by that way that would combine 8v sciroccos with the Rabbits/Jettas onto the same line... which would mean that an '83-'84 1.6lTD swapped into a scirocco would be legal!
The old T3 turbos are relatively unresponsive, inefficient units. A GT-15 or KKK K03 would give a nice improvement in spool-up time and will have greater efficiencies. Both were used in later 1.9 IDIs.
I'm not really going to argue with you there, except that I do think they are quite efficient matched to a 1.6lTD, but only at high engine RPMs. And I'm sure with modern ball-bearing and/or variable vane technology, one could come up with one that's even more efficient. I just can't on my car, because there's no way that would survive a protest at nationals. And I would likely be protested for such a modification, were I to win at nationals in my diesel. I'm the only one who's raced a diesel at all at SCCA nationals! There are over 1000 racers competing in nationals each year. If I were to win my class in a diesel, you better believe I'd have people crawling all over it looking for protest-fodder. It's also going to make some major waves in the racing community, which I would love to see happen.
Just to get back at everyone who told me that it was impossible for a diesel to be nationally competitive.
