How much power do engine mods yield?
First up, I would like to see which OE chevy heads flowed 280CFM,even modified.Like none.Even admitted by their most avid supporters,an "all out" unit from the day is lucky to post 250CFM,backed up by Smokey Yunick himself.I again take issue of the notion that the slanty head sucks,simply because it doesn't.Yes, the bore is a
definite restriction,and if ma mopar had cast a little more meat on the long side of
the pocket,things could be better.But valve size isn't the only factor,and the shape
and orientation of the slanty port has a superior discharge coefficient compared to
other ports w/larger valves, and swirl properties as well. The small bore/chamber is an excellent deterrent to detonation, as is the spark plug location,even w/o a
"squish" to speed up combustion.Is the 225 ever going to be a high rev monster?No.
But name how many 400HP 302 fords&chevies are running around w/o bigass cams,
steep gears,and loooooose converters,like none.Of course excluding anything with
modern variable intakes&cams etc.,which is kind of like cheating,but we'd all take a
retrofit system in a second if an affordable/viable one ever appeared!
Secondly,I'm done to death w/the "torque vs. HP" canard, there is no such thing.
More torque IS more HP, and so is the same torque at a higher RPM,they can't be
exclusive.The question is not improving torque, but efficiency at the desired RPM
range you wish to operate your engine in.You either want more efficiency at low
RPM,or higher RPM.Some improvements benefit BOTH,which are the ones you
really want.Such as compression,larger valves,and any fuel/ignition optimization,
along with exh. improvements.High RPM's go faster,but generally require sacrifice
in a whole bunch of areas,and there is a limit to whats tolerable for everybody.
Whats yours? Sounds like You know where you're headed,so best of luck to you,
:coffee2:
Killer6,
I am in no position to argue the subtile shapings of intake ports of which you speak, because I have never even used a flow bench; all I see are results... but, I see a lot of those. You may remember a FABO member (805 Mopar Kid) who had an interest in naturally-aspirated, slant sixes. He worked at an automotive modification facility, and his daily-driver was a 1968 Dart with a modified 225 slant six. He wrote on this forum, at length, about the many modifications he made to that Dart, which included better intake plumbing (carbureted,) a freer-flowing header-based exhaust system, a fully-ported cylinder head with bigger valves, higher compression, stronger valve springs, a deeper rear-end gear, drag slicks, a higher-stall torque converter, a shift-kit for the 904, and a whole bevy of performance mods I have obviously forgotten.
It was pretty much an all-out effort to go fast,in a mid-sixties A-body.
After he had spent lots and lots of hours, modifying this car for drag racing, it was a whole lot faster than a stock slant six 225 1968 Dart..... at 14-flat and 98mph.
I took my 1964 Valiant out for the first time a few weeks ago, and with "only" ten pounds of boost, ran 13.50. And, that was with a very poor 2.1-second, 60-foot time.
I was not very proud of that time, but my engine is (hopefully) going to run a whole lot faster/quicker, once I raise the boost level to something more productive, like 15 or 20 pounds, assuming I don't blow it sky-high, between now and then.
It just seems to me, that, going fast is a whole lot harder with a naturally-aspirated slant six than is should be.... and, I am pretty-sure that the small ports and valves we're stuck with, is the problem...
That is the crux of my argument. The engine in 805 Mpar Kid's Dart made about 300 hp. It was at the modification-level that the next significant gain in horsepower was going to cost a big chunk of change.
Three hundred horsepower from a turbocharged slant six is just over half what they can produce, with the right parts, and with a 5,500rpm redline and a smooth idle.
It's not easy and it's not cheap, but like I said, it's arguably, the best way to outrageous performance with one of these beasts...:cheers: