Why not bring in a guest builder or builders?
Why build it at all, unless you want to prove once and for all, that you CANNOT make decent power out of a naturally-aspirated slant six... and, maybe that's what they want to do if the guy engineering this test hates Mopars as much as I am reading on here.
It has been proven over the years, time and again, that the only slant six cylinder head we have to work with, will defeat the best efforts of the best engine builders, without exception.
You just cannot put enough air through a cast iron OEM head to make much more than 275-300 horsepower out of a 225. The miniscule bore size has effectively dictated valves and ports that work very well on the 170 motor it was originally designed for, but will strangle a 225 to death, regardless of a nice porting job and big valves. Radical cams can only take you so far...
The best heads out there only can be made to flow about 220 cfm on the intake side, and they need to be more like 300 to effectively feed those 39 cubic-inch cylinders. Ain’t gonna happen... No way, no how ...
The only way to make a slant six run scary fast is through the magic of forced induction, or NOS. I don’t know anything at all about nitrous, so I will limit my comments to turbos and supercharging.
Two FABO guys, Ryan Peterson and Tom Wolfe, have successfully installed turbos on their 225 motors, with results that point to their achieving outputs over 500 horsepower. That’s 2.2 horsepower per cubic inch.!!!
Tom’s 3,400-pound ‘70 Dart runs 120+ in the quarter in 11 seconds flat, (into a 15mph headwind) whole Ryan’s 2,800-pound ‘66 Valiant, making about the same amount of power, has run 10.74 at 127 mph. That’s quicker and faster than a new Hellcat Challenger will run on stock tires, (!) and Ryan’s car did it on some narrow, 8” drag radials.
I am only quoting these times to verify that a slant six CAN be made to run, and run HARD, but it absolutely HAS to have some help in the breathing department to do it.
Neither of those two engines have any kind of exotic, sophisticated, equipment on them, both running one 4bbl Holley carb on a slant six 4bbl manifold, a run-of the mill ported head with larger valves like most people run, a short-duration, flat tappet cam, stock rocker arms and some 340-style valve springs, with a 5,500 rpm red line. MSD igniton with Mopar distributors take care the ignition because nothing esoteric is needed, as they never see, even, 6,000 rpm.
They both have forged pistons and rods, a stock, forged, steel crank and run about 28 (!) pounds of boost to do this. The amazing thing about slant sixes is, they are UNUSUALLY ROBUST in their design and infrastructure, being built more like a Diesel than a gas engine, with no thin-wall casting parameters, anywhere. They apparently, can withstand boost levels that would blow most other engines into a basket of scrap iron.
A slant six racer whose screen name on FABO is “Guzzi Mark” built a naturally aspirated slant six in an early (Gen. I) A body that ran some really impressive times, seeming to disprove my contention, but he’d put the car on a serious diet and reduced its weight to about 2,300 pounds... Most A body cars we race weigh more like 3,000 pounds, so it was kind of an apples/oranges thing. But, it did haul ***!!!
If these people writing the slant six buildup are serious about making power, they’d BETTER get a turbo on that motor, or it will be an exercise in futility... mark my words.
[ame="https://www.youtube.com/watch?v=7QzUfV8iTpQ"]Turbo Slant Six 10.74 @ 127 mph 7-19-10 - YouTube[/ame]
and
[ame="https://www.youtube.com/watch?v=EAxRmoDgsdY"]Turbo charged Slant 6 11.02 @ 120.56 - YouTube[/ame]
Just MY 2-cents...:violent1: