Jeep 4.0 in 69 Barracuda

John's First Comment
"I am not one to follow the crowd. While my buddies were building v8’s (350’s, 360’s & 351’s), I built my race slant six which was good for an easy 13.9 second quarter mile. At some point I will build a stroker slant six. When I do that build, I don’t see the point of going .100 over, but going .060 is worth it and should only be a 3 or 4 cid loss at roughly a 207CID (using the 170 block)."

John,

Nobody would accuse you of "following the crowd" if you had built a turbocharged slant six for the Barracuda, as there are probably fewer than ten of those engines in existence in this whole country (my opinion, only) and virtually, no "CROWD"... I built one and was hard-pressed to find information from people who had them, who could give me advice.... LOTS of modified, naturally-aspirated slant sixes out there, but that blown engine is a totally different animal.

Second Comment
"That’s kind of the point. There are no surprises with the Slant Six."

Which brings me to the question: How many turbocharged slant sixes have you worked on? How much information, in your experience, do you have about what these forced-induction engines "like?" Are you aware that they only need 18 degrees of total spark advance to run the best, as far as power-output is concerned? And, that tests have shown that the rear axle ratios that yield the best quarter-mile times and speeds, are in the 2.76:1 range? No need for a 4.56 at the drags... And, that these 500 horsepower engines have a low redline... only 5,500 rpm.... and, they are done. How many people know that? Not many, I'd say, so the turbo slant has a few surprises up its sleeve...

Third Comment
"Unlike the Slant Six, there are several aftermarket performance options including stroking to over a 5.0L. Let’s not forget the fact that factory fuel injection with 1 of the easiest and budget minded fuel management designs out there. And with the 4.0L, I can turbo or supercharge it with aftermarket support."

The idea that you would need more than 231 cubic inches (a slant with a stock stroke and .045"-over pistons,) is not a subject that you'd expect to come up, because the 500+ horsepower available from a boosted slant would be sufficient to power A bodies of even the most demanding drivers, you would think. But, maybe not.... The AMC engine could easily be made to out-perform the 225 with forced induction. That is, IF it were strong enough to withstand the same (elevated) boost pressures that make the slant six the stellar performer it is. And, the 4.0 or 258, probably is that strong...

Speaking of the boosted slant motor, John said: "But it was not in the works for this project" and, I was curious as to why. The "hairdryer" 225 has plenty of power, bolts right in, and is pretty-much bulletproof in the long-run. The engines I have seen make 500+ horsepower (400 would be a cakewalk,) have Holley 4bbl carbs with no need for the time-consuming research that is part and parcel of adapting efi to these turbo motors.... so, they can be up-and-running pretty quickly. The OEM fuel injection that comes from the factory with the AMC engine would have to be modified, big-time, to work well with forced induction, especially, if it were going to make power in the neighborhood of the forced slants'.

Your "easy" 13.90s are good for a naturally-aspirated slant six, but, consider this: My '64 Valiant runs high 11s in the quarter (a long way from a 13.9-second e.t.,) with a turbo 225, 1 4bbl carb and an automatic (904) transmission, using only 15 pounds of boost. It has a ported (shade-tree,) head with 1.75"/1.5" valves and a 9:1 compression ratio. According to the online Wallace calculator, it makes 370 horsepower. And, it's a docile engine with a smooth idle. A naturally-aspirated slant can only make about 320 horsepower, absolute max, and has to be a "full race" version with a ragged idle and really high compression, to do that.. and has terrible driveability problems. No contest.

So, I am convinced that a boosted slant six has so much going for it that it makes NO SENSE to build anything else, if a slant six is what you are working on.
But, I fully agree that a slant six is NO MATCH for a 265 Hemi. Blown or unblown! In the meantime, have fun with your AMC six; those are great engines, too!!!