Seems I let a monster out of the closet! ^_^
Jon:
Turbo pressure is not additive, 2 5psi turbos produce a whopping total of
5psi to the engine, but a higher volume of air so the psi is more constant. A
single turbo vary's it boost more wildly than a twin setup.
Jack:
My Shadow had over 79,000K on it before it's untimely demise. ZERO oil
leaks.
The Single turbo groupees:
Twin turbos don't eliminate lag, they slightly reduce it. The concept is
that 4 cylinders can generate pressure X out of the exhaust. 8 can generate
more pressure but a single large turbocharger is harder to spin up than a
small one, even with the added pressure of the additional 4 cylinders. Gale
Banks had an article (this was years ago) with full statistics on Quad, Twin
and Single turbo setups for cars. The Twin seems to have the most preformance
increases. The Quad didn't do well with any engine less than 12 cylinders,
and the Single didn't preform any better with 8 cylinders than it did with 6.
Two smallish Turbos produced incredible effects with a V8. With a single
turbo there are interesting pressure differences from cylinder to cylinder (on
the exhaust side of things), and unless the turbo is in the exact middle of
the header to header arrangement it becomes less efficient. The nice thing
about the Twin setup is that the turbos are symmetrical off of the headers and
the boost is very stable and consistent when correctly setup.
The Twin turbo groupees:
Two turbos are twice the headache. You have to run vastly longer oil and
water lines. The heat into the pressurized air is much higher and an
intercooler is mandatory, water injection or extremely high octane gas is
recommended on boost setups over 15 psi. While preformance is higher, it's
not exceptionally so. Single turbos are easier to maintain and adjust. If
you don't have the twins setup right, you get imbalances (on the intake side
of things) that can cause some wierd effects at different RPM's. Race teams
tend to use single turbos under the "Keep it Simple Stupid" rule. Hot car
makers tend to use twin setups: Ferrari, Vector, Maserati, etc.. have all used
multi-turbo setups for production street monsters, but these cars love their
mechanics and see them often... ^_^
Yes, to truely use over 7psi of boost, you do need high preformance
pistons, heads and shafts. The block doesn't need any real mods though... but
I wouldn't try it on a "bored" block. However, keep in mind that the person
who is looking at these mods has thousands of dollars to toss about. Changing
things like pistons, cams and cranks shouldn't bother them too much. I would
also want a programmable engine controller to handle the motor. I don't think
a factory or even preformance controller can use the added boost to it's best
purpose...
That's about the limit of my turbo memory. I'll let the turbo guru's argue
it out from here, I'm a turbo novice.
Shaun H.
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:12:10 EDT