• When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

HP and HP2 what is the difference

I understand, I wanted to point out that a person shouldn't consider that number as a true fact, it's an approximation & the HP pistons certainly do have a taller compression distance.
When I get a chance I’ll check the parts manual for the piston part numbers for the HP and non HP motors.
 
Now that I think of it, when I got my 69 non-HP 440 I noticed some sources listed HP 440s as 10:1 and non-HP's as 10.1:1

I thought that was odd and even commented about it on FBBO, but no one responded.
 
Doing a little looking through the hamtramck historical ...both 440hp and base 440s(not including 6 pack) of the same year ran the same compression until 1971. All 440's in 69 were 10.1:1. In 1970 it was lowered to 9.7:1 for both 440s. In 71 the 440hp is listed as 9.5:1 for the hp...and 8.8:1 for the other 440's. I would not be surprised if a 71 440hp and a 70 440hp had the same piston and was rated differently?? Part number would tell. The compression were usually over rated so I could see them getting by w that

I think the 383 4 barrels may have the same piston...on hp or non hp. 2 barrel 383s usually typically had a lower compression piston.

I was thinking the 71 440HP had a AVS where the lower horsepower had a holley?
 
When I get a chance I’ll check the parts manual for the piston part numbers for the HP and non HP motors.
I would think possibly hp would have forged and none hp cast pistons same comp. but hp being heavy duty. Just a thought.
 
I don't think anything ever got forged pistons, except hemis and max wedges..... but I could certainly be wrong !
 
I had a 70 6 pack motor that probably had 20,000 miles on it. It had the original cast pistons yet and they were developing small cracks around the wrist pins making them unusable. I wish they would have done forged pistons in the 6 pack. It was hard to throw away a piston in that low of mileage motor. It had 440 HP2 stamped on it.
 
.....when I got my 69 non-HP 440 I noticed some sources listed HP 440s as 10:1 and non-HP's as 10.1:1

Lol, And then you find something like this in the '69 parts book...…..

upload_2019-12-9_9-49-38.png


"It's the same thing only it's different"
 
:( I'm disappointed that the 6bbl didn't get forged pistons...
Mine have the flat tops and valve notches.
 
Ya, given that Mopar made so many special parts for the A12 cars, including different pistons, they could/should have gone to forged. Oh well.
 
HP= High Performance

HP2= HEMI. Used on 66 Belvederes.

From my friends Mopar Website www.ralphsrapidtransit.com, and I qoute "What's an HP2?"
Plymouth was not advertising their Hemi on the Fender like
Dodge did with Big Numbers underlined by the word HEMI.
They came up with the formula "HP2". The H represented
the great word HEMI the P was squared so the first P was
Power, the Second was Plymouth."

These are the only things I can think of off the top of my head.
 
HP= High Performance

HP2= HEMI. Used on 66 Belvederes.

From my friends Mopar Website www.ralphsrapidtransit.com, and I qoute "What's an HP2?"
Plymouth was not advertising their Hemi on the Fender like
Dodge did with Big Numbers underlined by the word HEMI.
They came up with the formula "HP2". The H represented
the great word HEMI the P was squared so the first P was
Power, the Second was Plymouth."

These are the only things I can think of off the top of my head.

I do recall the HP2 Ads. However the OP was asking about the stamping on pad of a 440. I had one of those HP2 blocks out of the many I had, but never thought much about the 2. I never was concerned if the block was a HP or non HP, 440 blocks are the same.
 
What about the HP3
shock.gif
 
On the HP2 emblem, my car is a mid January build and it has the 426 emblem on front fenders. I talked with a gent from St Louis who worked on the trim line starting in 63. According to him no Hemi cars were built until late October, something had to be sorted out with the engine fit issue Dodge and Plymouth models. We talked for hours and one thing stands out what he said. If a certain part was to go on and wasn’t in the cart, some other part went in it’s place, then maybe it got sorted out on the outside lot, maybe not. The line can’t be stopped to wait on the part needed. There were change orders from up top and they were a huge deal, a lot of paper work.
 
On the HP2 emblem, my car is a mid January build and it has the 426 emblem on front fenders. I talked with a gent from St Louis who worked on the trim line starting in 63. According to him no Hemi cars were built until late October, something had to be sorted out with the engine fit issue Dodge and Plymouth models. We talked for hours and one thing stands out what he said. If a certain part was to go on and wasn’t in the cart, some other part went in it’s place, then maybe it got sorted out on the outside lot, maybe not. The line can’t be stopped to wait on the part needed. There were change orders from up top and they were a huge deal, a lot of paper work.
I know this is getting off the subject of HP2 engine blocks, but I inspected/verified a 1966 Hemi Belvedere II a few years ago. It was built in early December 1965 and had the HP2 signs on the front fenders. I heard that stood for Hemi Plymouth, 2 carbs. I think the reason that the 426 signs were lifted from the Dodges, was that no one knew exactly what HP2 was supposed to mean.
 
In 62 Hoover sourced the industrial blocks for their high nickel content. I'm not sure if at some point all blocks were.
The high nickel blocks had an AAQA casting on the block. A buddy of mine has a 413 block with this.
 
If a certain part was to go on and wasn’t in the cart, some other part went in it’s place,
I've always said "When it comes to Ma Mopar, never say never".
 
Auto Transport Service
Back
Top