Here's a clip from the GVR4list that Martin posted about his tubular header.
"That setup is for T4 tangential divided housing. Spool up you ask, how does 25+psi of boost by 4500rpm on a T61/P trim .58 A/R sound?
We grouped the runners in firing order to decrease the boost
threshold (spool up), and the new header/T61 turbo setup spools quicker then the old stock manifold/T3-T4 setup we had. It would be a very tight fit to put in a GVR4 (we're making them for the 1g's and 2g's right now), but eventually we might make a few and run one on Adam's Galant. We used one tial 35 from each grouped runner section, but one 40 would work vented from one side of the collector also.
The price of the S.S. header is around $950, the first 10 are being made right now and about half of them are already spoken for.
BTW we are working with a fabricator/welder who works for a
CART team, the welds and quality of the header are the kind you
would find on an indy/CART car.
> > >
> > > Martin
> > > AMS"