Twin Turbos

[Frederic]

> I noticed in a reply about whippled hummers that Frederic Breitwieser
> has a 413 with twin turbos.  I am interested in the possibility of
> running twin turbos with the current Magnum 5.2L engine.

Actually, its a 383B mopar block that's been stroked to 431 cid, via a
turned down 440 crank and 440 YJ rods, and custom wiseco pistons for a
9.2:1 c/r.  the engine will go in the truck this weekend if the rain
lets up.  Anyway, I used moly rings for minimal wear under the
additional pressure (10lbs max - its a tow vehicle not a race vehicle).
This is one of the key things to remember to do.  Also, the intake
manifold is fairly intersting.  Following an article in one of the Mopar
ragazines I milled eight holes in the intake runners of an aluminum
Edelbrock "Streetmaster 383" intake, made injector bungs on a friend's
lathe, then TIG welded them into the holes.  Using a die grinder, I
ground out the "hang down" thats in the intake runner, so the only thing
exposed inside the runner would be about 1/16" of the injector tip.
 Took a bit of experimenting to get it right.  Then, I sealed off the
runners that clamp to the heads, sealed off each injector bung, and
pressurized the carb seat surface to find leaks.  Lots of leaks <grin>
Cleaned that all up, then too the modified intake to a machine shop
where they could "deck" the tops of the injector bungs to be the same
height.  They still haven't done this as of yet, and keep blowing me
off, but that's another story.  They will also make the fuel rails since
I made two sets that were absolutely terrible.

Anyway, with this intake configuration, I can slap a carb on the intake
until I figure out all the EFI stuff.  I waffled between EEC-IV Ford
stuff (have a low-performance ECM and harness from a 88 Crown Vic) as
well as the 93 GM TPI setup found on Camaros and Firebirds.  Turned out
my GM ECM is bad, so I'm seeking a 730 ECM and Andy Quaas and I will be
sharing notes since we are working on engines with about the same
displacement.  The choice to go GM was more due to the GM steering
column I have sitting here with cruise, tilt, etc, as well as a caddy
body harness, with all motors, switches, digital dash, and all that
happy stuff to embed into the truck.  See, a junkyard caddy harness was
$150, whereas a "replica" harness for the 75 Dodge truck will be 3 times
that, and have power nothing.  Unused connectors can always hang.

Anyway, with the above information, you can see where I'm going.  Now,
onto the turbos.  I have two smaller turbos because my top RPMs on this
engine would be in the 4000 range (I originally was going for 5000 RPM,
but no point in a tow vehicle), therefore I don't need vast, oversized
turbos since the "top end" is very low.  I have two turbos from Dodge
Daytonas, and will try them and see if they provide enough air for my
10lb goal.  If not, I can "step up" as necessary.  I prefer OEM parts
for easy, convienent replacement and junkyard availability.  Anyway, the
iron intake manifolds that came with the 383 have had the exhaust bolt
holes for the Y-pipe welded close (brazed actually), then redrilled and
threaded so the daytona turbos will "bolt right on".  Cracked two left
manifolds trying to tap the new holes.  Anyway, turbos are mounted.  The
remainder of the exhaust system post-turbo hasn't been fabricated as of
yet, and that will be the last thing to do.  Quite honestly, since
emmisions testing are no longer required for my 75 truck in Connecticut,
I might just run straight pipes down the frame and have them stick out
post wheel, without mufflers.  4000 RPM is not going to be *that* loud,
with two turbos absorbing a fair amount of noise.  Time will tell.

Connecting the turbo fresh-air outlets to the intake required a little
creativity.  I have an edelbrock carb opening on the top of the
streetmaster intake, thus a plenum had to be constructed out of sheet
aluminum.  The turbos are at the back of the engine, therefore two Ford
throttle bodies have been bolted to the back side of the intake,
immediately next to each other, one for each turbo.  They have been
"ganged" and the throttle cable will connect in between the two throttle
bodies.  More than likely, I will replace them with GM units so the
GM ECM gets the throttle position sensor it wants.  Have two FWD
3.8L Throttles that will fit with minimal drilling into the plenum I've
made.  On the back side of the plenum, there is aan ATR adjustable
sneeze valve, which will be set for 10psi so that additional pressure
over that setting will blast out into the open area.  I think its ATR.
It was a leftover from my twin-turbo Buick V6 project.  Anyway, inside
the plenum is a 2" thick transmission or oil cooler, that I sized the
inside dimensions of my plenum around, as once welded, I wanted an
air-tight fit.  All pressurized air from the turbos will blast into the
upper plenum, go through the intercooler, then into the lower plenum,
then through the carb bore, then into the runners following the OEM path
of a carb-based intake.  The injectors I selected are 56lb units,
however the more I play with the math, I am thinking they are gross
overkill.  Something in the 42-48lb range would probably be more
suitable.

What the intercooler will be attached to hasn't been decided yet.  I did
some preliminary experiments on a Buick V6 engine using radiator coolant
as the "intercooling fluid", and while I didn't document this even
remotely well, I will state that this actually works.  Kudo's to Bruce
"Grumpy" Plecan who drilled the idea into my head.  The idea is to tap
the radiator fluid pre-engine post-radiator since the coolant is about
100-110 degrees at this point, and the fresh air post-turbo is closer to
200 degrees.  While not the absolute best design, Bruce was right in
saying that the intercooler temperature would be more consistant,
therefore providing consistant performance, and is MUCH easier to plumb
than a Peterson coolant tank, a box of ice, a 12V marine sump pump, or
any other creative solution you come up with.

> 85 Shelby Intercooled Turbo Charger,2.2L,5-spd man.

One of the things you *should* do, and I've done this many, many times,
is to sit and stare at turbocharged cars.   You can learn a lot about
the mechanicals (mounting, brackets, etc) from the OEMs, so sit in front
of your car that I snipped out your tagline, and see what they've done.
 Wander the junkyards for other turbo'd cars, and see what different
companies do.  Also, here are two weblinks of others who have achieved
what you desire.  Dodge, Chevy, Ford, the concepts are pretty much the
same.

http://www.eecs.tufts.edu/~askulte/ttt/logbook.html
http://www.geocities.com/MotorCity/Downs/8668/tthowto.htm

Corky Bell has a book called "Maximum Boost", and if you can get through
his interesting sarcasm <grin>, you'll find it a great resource.  There
are some minor inaccuracies in there, and a lot of this is all
subjective, none-the-less its a good resource.  I'd also recommend you
go with a fuel injection system, either OEM parts or something like
Haltach or Electromotive or DFI etc.  The reason being (and this is just
my opinion) that lean conditions under boost will kill your engine
faster than running it without oil, therefore the more precise control
that EFI can give you, if configured correctly, will help your engine's
survivability.  And without boost, you can get acceptable mileage too.

If you are looking for low-end boost, another option is to skip the
turbochargers, and go with a Paxton or Vortech supercharger.  They are
much easier to install (an afternoon), and give the 5.2 engine a lot of
kick for the effort you will put into it.  Of course, they are in the
2600-3200 US dollar range, complete, from Summit Racing for example.
Many ways to skin this cat ya know :)

One last comment I will make before I bore everyone to tears... is that
you are right on the border of the single/twin turbo line.  Corky Bell's
rule of thumb is 350 cid.  Anything 350cid and larger, requires two
turbos, whereas below that line, requires one turbo.  Nothing wrong with
two undersized turbos on a 318, or one larger turbo.  In general,
smaller turbos will spool up faster due to the lighter rotational weight
of the blower pieces that spin to 80,000 RPM, and the orifaces entering
the turbo of course would be a smaller diameter, therefore higher
velocity of exhaust flow going in.  Well, you get the idea.  On my Buick
V6 block, which is a mere 252 cid (plus .030 overbore), one turbo seemed
just dandy.  However, converting to two turbos, we saw improved
performance by using two Daytona turbos (same ones I will be testing on
the truck motor actually), and it worked fine.  Then, as we built the
motor up enough to withstand the the punishment, we used two TE43's (I
think), which are very large turbos.  However, at lower RPMs turbos of
this size were completely useless, and it wasn't until the 6500 RPM
range that things started to really hum.  Unfortunately, the V6, with
all the girdles, valve train support, and other fabricated
"strengthening" things we added... the crank still kicked out at 8000
RPM after only 30 minutes.  But 849 HP at 38lbs of boost was a lot of
fun, using the same intake/intercooler design that I described above,
and will be installing into the truck.

Hope that helped somehow :)