So I recently picked up a hot rod car mag from 1961, was flipping through it and spotted a pic of the HyperPak exhaust manifolds. The article was jut talking in general about what modifications to do to get more power. Under the pic of the HP manifolds, it said Chrysler claims 10% gain from just the exhaust manifolds!

10% relative to what?

Let's say you already have done head work, larger valves, porting, appropriate cam, carburetion/intake flow good, etc. and have Dutra Duals and good exhaust flow from the Dutra duals. Let's say you are at close to 200 hp. Then would the hyper pack give 10% more? I doubt it, but that is pure speculation on my part.

Let's say it means 10% from stock. A stock '67 slant has 145 hp, so 10% more would make it 169.5 hp, not too shabby...

Any other takes on this?

brian

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we can all try the new castings if this goes through and have actual data on our builds, before and after hyper packs...

exciting prospect...

brian

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LOL....If only a 1967 225 got 145hp at the crank once you added the alternator, fan belt, power steering, and A/C back into the equation...
love those gross HP numbers....110 HP at the rear axle/maybe...and use the hyperpak exhaust manifolds with the stock engine (assume adjustments to carburation because of better flow)...120-121HP...no problem....and since it's an adder...the bigger the build the better...up to a point...
After putting that much time and effort into a 225...it would get Headers from the get go if hyperpak exhausts were not available...because you want everything you can get for race time...

Just sayin'...

OK, so the factory numbers are not correct for hp at the crank? I assume lots of loss by time you get to rear wheels.

How are those numbers generated, with no alternator or fan?

I read that in the old days, GM overstated HP numbers, Ford was about right and Mopar generally understated their numbers. Any truth to that?

brian

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To Quote Dan from a previous engine post who hits it right on the nose about Pre-1972 Gross HP testing vs. 1972+ Net HP Testing:
Manufacturers manipulated data so they either could boast their engines were better than the competition, or understate them so the insurance companies didn't scalp the driver if he was under a certain age and loose potential sales...in a fair amount of car magazine articles the media got slipped a prepped car, or in some cases they modded to car to get the most power out of it (a common trick was to unbolt the exhaust manifolds from the heads so the exhaust was free flowing...in one particular Ford Mustang Test they picked up .5 seconds in the 1/4 with that trick)...

A real good stock early Slant will put 95ish at the wheels.

IMHO, the HP exhaust manifolds do a better job of being user friendly than the intake does. They are better than a stock manifold, but as DI said, they are not as good as headers. They do have the cool looking factor going for them too.

The thing you have to remember, the HP parts have a lot of legend and lore attached to them that is nothing more than legend and lore.

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Official Cookie and Mater Tormentor.

Thanks for posting Dan's previous information on how they reported HP, very interesting.

For the 426 hemi dual quads in the Dart, I've read that it was purposefully detuned at the factory to tame it down a bit. One needed only to tweak it after they bought it to get gobs more power out of it.

brian

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https://tinyurl.com/yynpj4v2

Question: the Hyperpak exhaust bolt bosses are to bolt the exhaust manifolds to the Hyperpak intake. Is that needed to support the exhaust manifolds? That is, if one uses a different intake manifold, does one need to fabricate something analogous on their intake to bolt to the exhaust bosses?

If the answer is "no" then why did they bolt together in the first place?

brian

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I suspect to support the Hyperpac intake would be my guess.

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65 Dart station wagon slant 6 - now under construction
47 Dodge Custom 4 Door sedan
87 D100 Short Bed slant 6

Retired USAF 1966-1986
Retired US Postal Service 2004-2014

No. The intake is what would need the support in my opinion. I am running them with a clifford 4 barrel and no support brackets.

Rick

I will try and get some video of the noise this make.

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

awesome...that's noise I want to hear!!! lol

Yes, videos are always great to see/hear...

OK, good to know on the bosses.

brian

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It may not be vertical support at all, but rather so that the manifolds move in unison. Can't have the intake floating in one direction and the exhaust in the other...might cause too much tension/crack maybe?

After all, the regular factory manifolds are bolted together too. Maybe that's not just for the heat box...

brian

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This past week I removed the Hyperpak exhaust manifolds and re-installed my Clifford long tubes. Before I pulled them off I did a test fit of the manifolds that Lou brought me.

The Offy 4 barrel and the Offy 2 X 1 barrel will both work with very minimal problems. The 2X1 may need a very small clearance "grind" put on one of the rear exhaust manifold bolt bosses, and the 4 barrel may need a very small amount of grinding at number 1 intake runner. Both of these bolted up as is but I would probably clearance them just a bit. I will post some picture later after I upload them to Photobucket.

I also test fit the same manifolds with Dan's Argentine manifold and they worked also.

My plan is to hand off the exhaust manifolds to Lou in 2 weeks so he can check fit them on a engine with P/S and A/C brackets.

Rick

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6