Supercharge Or Turbo?
As a newbie to forced induction, this has been great, answered a lot of questions. I have been researching non stop for weeks reading everything I can find to help me out. I like the conversation.
From another newbie...
Originally posted in a different forum... the wrong one.
A year ago, I couldn't even spell "slant six"... but I got on the Slant six.org website and this one, and began reading, and learned a few things. That's pretty amazing in itself, 'cause I'm what they charitably call a "slow learner.":read2: Sometimes, a lot worse,,,:angry7:
Be aware that my personal "hobby" car is a 1972 Valiant with a 360 Magnum V8 equipped with a Vortech V-1, S-Trim, serpentine belt-driven centrifugal supercharger that makes about 525 flywheel horsepower. Not that
THAT is any great shakes ('cause it's not, I realize) but it does give you a clue that I have not been a "slant six guy" from day one.
As I immersed myself in the postings about /6 performance, and videos on You Tube of various /6-powered cars, I began to realize some things about these slanted little devils that had escaped me for years. Here's are some things I had missed.
In a general way of looking at the /6 archetecture, it says one thing in a big way: This cylinder head may be a perfect head for a 170 cubic inch engine, but trying to make a normally-aspirated 225 breathe through those same 170-sized ports is a job for Superman.
What I mean by that is, the ports and valves, as manufactured, are just too small for the amount of cylinder displacement they are asked to feed, in a high-performance 225 environment.
The /6 has 225 cubic inches, If it were a /8 it would be 300 cubic inches with 8 of the 225's (37.5 cid) cylinders instead of 6.
Just for comparison purposes to show what size these ports and valves are, the 1967 Chevy Z28 came with 302 cubic inches (virtually the same size cylinders as a 225 /6 engine,) and their intake valves were 2.02" in diameter (slant six "oversize racing valves" are 1.75, or fifteen percent smaller than the "stock" Chevy valves, and the 1.6" Chevy stock exhaust valves are still 6-percent larger than the "oversize racing" /6, 1.5" exhaust valves.
The Z-28 Chevy ports in the head are commensurately larger, so that the flow numbers are a pretty good match for the valves, in their stock configuration.
The bottom line is, a mildly ported (302) Chevy intake port will flow close to 300cfm to feed the same size cylinder that the /6 is trying to fill with that 1.75" valve that is in a head, that after porting, will flow 220cfm, absolute max...
A big, heavy crankshaft doesn't help matters, especially when winding up 1st gear.
So, here's what I have learned:
I watched videos of the chopped, 2,350-pound MadMax 1st generation Valiant with a normally-aspirated /6 running 11.50s with NO power adder of any kind.
That car is incredibly fast and quick (watch how it hooks!!!)
I've never seen anything like it!
I didn't REALIZE that a normally-aspirated Valiant or Dart could run like that!
I happened onto two more videos on You Tube that opened my eyes even further.
There were two videos of turbocharged 225's that blew my mind. Tom Wolfe has a 3,300-pound '70 Dart that has run 11.02 with a new motor (at 122 mph), into a 15-mph headwind, while another forced induction racer (turbo66Valiant) posted videos that showed his pristine '66 Valiant running some 10.50's, which is about a full second quicker than the already fast, but unblown, Mad Max car.
Not to belittle the Mad Max car, because it's stupid fast for its combination, but that '66 Valiant is I believe, 500 pounds heaver and a full second quicker. And, its running a 727... probably about .2 slower than a 904.
So, what did I learn from all this???
Not so fast; I said I was a slow learner, and I surely am...
I did a lot of research about the /6 motor, and one thing stood out:
It's built like a brick pagoda. Its aluminum ancestry seems to have left it with an infrastructure that has no equal in the modern automotive world, when it comes to strength and ridigidity.
Remember that big, heavy, crankshaft I was carping about awhile back?
Well, I found that the early models are forged, have internal balance, and bearings the size of the 426 Hemi.
As close to an
unbreakable stock crank as you can probably find.
The cylinder walls can be bored over .100", the head can be milled that much if need be, and the top of the block is pretty thick, but I have no reliable numbers for that.
What all this means is, unlike the Buick GN turbo motors which (the stock stuff) don't seem to want to stay together if the boost goes much over 25-pounds, it's an open question as to just how much boost one of these /6 motors could stand, if someone greally got serious, because K-1 is making some great-looking forged rods for a 225, and forged pistons are available from Wiseco in a .065"-overbore, creating a 234 cubic inch motor.
Shaker223 and turbo66valiant are probably generating over 500 flywheel hp as we speak, but can 600 hp be far behind?
It's not necesssary to build a 500hp motor to have fun with a turbocharged /6.
One of Tom's early engines was pretty much stock with a Buick turbo stuck on the bottom of a stock exhaust manifold, and it went high 12's...
The possibilities are endless!:cheers:
I'd think twice before pulling that /6 out of ANY A-Body....
Might be shooting yourself in the foot...
