(I am writing this in response to what I have read in the current "best manifold" topic circulating on the forum.)

My curiousity is relative to the hyper-pak intake:

I have been intrigued with the hyper-pak for a long time, but I keep hearing vastly different stories of people's experiences and opinions of this setup. From what I have gathered, the hyper-pak sounds like it is a bear to tune, is balky at low RPM's, and has a tendency to have fuel condense and pool inside its long, un-heated intake runners (further adding to inconsistent running). This is not to mention the stories of wildly different fuel delivery to each of the six cylinders, such that some are starved and burning themselves out lean, while others go sooty black rich almost immediately....

Has anyone made a well-behaved, nice-idling street car with this intake? With an automatic transmission? Or is it really best reserved for the drag strip and for oval racing, as it was originally designed?

I am also curious: has anybody devised a means of heating the hyper-pak intake in a fashion similar to the stock intake, with conducted exhaust-gas heat?

Surely almost everbody thinks the hyper-pak is a great-looking crown to a nicely-built slant six. Popping the hood on a car with a cleanly-built hyper-pak would make any of us just as proud as someone who owns a V8, without a doubt. But is there the happy ownership and driving experience to back up that pretty (unique) face?

this just seems like a very gray area...hope that there is some clarity out there on this sweet-looking (and certainly capable, under the right circumstances) intake system.

thanks again guys -

Mike T.

It'd really suck if you were torquing down a new out of the box Hyper Pak manifold onto a cylinder head and it cracked at the flanges. I think I'd just about lose it. What are the advantages of a Hyper Pak (besides looking cool) over an Offenhauser manifold?

If you look I did a long thread on installing one on my current daily driver, this mill uses a set of dutra duals and the Comp Cam 252.

Here's the skinny:
The intake has "cool factor"...(but won't get you any chicks at the drive-in).
The intake is unheated and does tend to make things "fun" with fuel pooling, rich fuel charges and hard starts in the winter time for those of us in the north.
The long rams really do help make a lot of low-end grunt off the line (a lot better than the super six ever did), sadly the intake doesn't "come on" for ram effect until about 3000-4500 rpm (so for my car with 3.55's it'll never see it on the highway at 65mph...would be nice at the drags).
I use a manual tranny.
I currently, use a 'heater' box that uses exhaust gas piped from the exhaust to help heat the plenum better to fix the fuel distribution problem(water heat is not immediate heat, and you'll have real fun on a snowy day when the choke pulls off, waiting for your car to pump 190 degree over there). The intake is so massive, that if you warm the car up the first, then let it hot soak, the first 8" of manifold will be up to temperature, and I've had the plenum area not so warm.
Timing and tuning is kind of a 'hit or miss', a big cam would be the key for this intake, the short cam I use makes lots of 'grunt' and gets good gas mileage, but I've had to play test and tune swapping jets, cams, drill throttle plates to get a couple of carbs to work right. (my mill would probably like a 450 cfm carb max...500-600 is a bit too big, and the 390 is still slightly small).

Another thing to note, since I split the plenum in my intake, I have noticed since the front of the engine gets direct benefit of the fan, the back 3 cylinders tend to warm up and be 'operable' sooner, while the front three being a bit colder have to either use a richer fuel delivery, or have a 'lean out' while the fuel puddles out in the colder runners compared to the back 3. (I noticed this has happened also on 66 Dart's Dual Weber setup with the fuel boiling out of the rear weber's bowl...)

Next month, I should have a Hyperpak machined and ready for EFI, this should take care of a few of the "ills" of the setup, but the drawback being the $$$ for setting it up and the time to tune it.

You also have to "massage" the casting with a die grinder to even get the triangular washers to fit. (See my post on 'fat pack' runners.)

Currently with a new 390 cfm 8007 Holley setup the best it can get, I am getting about 15 in town (last tank of gas all in town driving...more tests to come), and about 20-21 highway (previous tank of gas, jetting seems to be spot on, and using a plain secondary spring and 6.5 PV instead of a purple one and a 10PV...)

Recently a few members have recieved castings with some nasty flaws in them, the one I use on the Duster is an old casting and was beautiful, the EFI one is newer and has a few minor 'spots' to touch up.

Don't have an offy yet, but it would be on my "easy installation" list.

It's neat to pop the hood, I've had a couple people ask about my 360 under the hood...I've TO'ed a couple of Chevy owners who are frustrated by the fact my mill is much more 'fun' than their V-8.


-D.Idiot

thanks for the detailed responses....

D.Idiot, can you go into greater detail about your heater box for the plenum? Curious if you fabbed something up or if that is a retro-fit stock piece that you're using to pre-heat the intake. That seems vitally important with the hyper-pak, is it not?

Last week I did 100% in town driving, lots of stop and go, and due to the freezing temperatures I had to let the car idle up for 10 minutes to be 'effective'. Today I did a 99% highway haul....

13.2 mpg city (10 minutes at 1500-2000 is probably not 'good'...and neither is the 3.55's in 1st gear during rush hour in 30 foot runs)...

22.99 mpg highway (1 minute cold start...use the fast idle to dog it to the highway a few blocks away, and keep a consistent 60-65 mph, with passing at 70-75 mph)....


My A/F meters indicate a perfect jetting ratio for the mains and secondaries for 'street' use...for idle it's bit rich, and the 'transition' has a bog spot in it at 1500-1700...which occurs in the 'cold front runners' when the throttle plates open and the vaccuum drops a few inches...(re adjust throttle plate orientation, or bigger shooter and pump shot).


you wanted to know,

-D.Idiot

p.s. in this configuration I don't think I'll be getting a 16 sec. 1/4 time...