[steve25]

Let's talk about how in the world Pontiac gave the 1969 428 HO motor a 390 hp rating when the 1969 366 hp 400 RAIII manual trans motors atleast for the first half of the production run had more Cam and with the small chamber casting number 48 heads far more compression !

Also note that the then new 1970 455 in the A body cars where only rated at 370 hp with everything being the same but for the hp Exh Manifolds.

[chiphead]

You already know the answer. The pre-72 HP ratings are very suspect. They would tweak up or down the settings on the dyno to suit the situation. Got a weak engine that needs the numbers padded for marketing? Remove accys, air filter and set tune on kill. Need to shave a few to pass HP/weight mandates? Detune and re-test. The 72-newer SAE test clarified a lot of the gamesmanship.

[MarkS57]

Did to 70 455's come with the 068 cam? I believe the 428 HO's did; at least the MT ones (WZ's?).

[steve25]

In the top of the B body line Grand Prix, yes it came with the 068 Cam as shown in this Pontiac literature.

Note the higher rpm Torque peak besides the 10 extra hp.

['ol Pinion head]

Originally Posted by MarkS57

Did to 70 455's come with the 068 cam? I believe the 428 HO's did; at least the MT ones (WZ's?).

Of the '70 Pontiac 455 big valve engines, only the stick coded engines had the S grind (068) cam. Have torn down too many originals, a WA, 2 YA's, a YC, & over a half dozen XF's with original cams. Have not removed the original cam from my '69 428 HO GP's XG engine, but am betting since its an auto code, it will also have the P cam.

[242177P]

Originally Posted by steve25

Let's talk about how in the world Pontiac gave the 1969 428 HO motor a 390 hp rating when the 1969 366 hp 400 RAIII ...

I've explained this before.

330 hp in Firebird --->3300 lbs
360 hp in GTO ---> 3600 lbs
390 hp in GP ---> 3900 lbs

['ol Pinion head]

Adverised HP ratings were to a degree, arbitrary, & were totally tied to GM's policy of the hp to weight ratio could not be less than 10.0-1 (other than Chevrolet's golden child, the corvette. Several before discussed examples include:

- the throttle limiting tab on the '67 & '68 Firebird 400 Qjet with resultant advertised HP ratings in the 325-340 range.

- the 330hp rating on '70 400 4bbl engines in a '70 Tempest or LeMans. In hindsight, the automatic engine offered could have easily been the base 400 4bbl YS instead of the small valve XV 400, as either engine was backed by a Turbo 400 transmission which adds weight over the HD 3spd manual. When so ordered, even a super strippo 70 Tempest Coupe with 400 WT engine & a HD Muncie 3sod, the resulting car will not weigh under 3500 lbs, wet.

Selecting the '69 GrandPrix, near the first month of production, power disc brakes were not standard. Very soon after, power disc brakes & their accompanying 7" wide wheels became standard, & as such added more weight to the vehicle. Ordering out a total strippo non AC, manual steering, drum brake Model J with the 428HO engine & a Muncie 4sod... I'd bet with fluids (wet) such a stripped '69 GP would not weigh under 3900 lbs. In effect, the 10.0-1 "rule" would be safe.

[MarkS57]

Originally Posted by 'ol Pinion head

Of the '70 Pontiac 455 big valve engines, only the stick coded engines had the S grind (068) cam. Have torn down too many originals, a WA, 2 YA's, a YC, & over a half dozen XF's with original cams. Have not removed the original cam from my '69 428 HO GP's XG engine, but am betting since its an auto code, it will also have the P cam.

According to the Wallace site, the 69 428 HO looks similar to the 70. The 390 MT's got the 068 cam and the AT's the 067. However, it also says the 390 HO MT got the 48 heads and the AT's 62's.

[steve25]

Since we are talking about the 428 are you saying 242177P that the 360 hp 428 came in the GTO, because they did not!

And the other kicker her since we are talking about 428 motors is the 1967 428 360 hp motor that was a 2bbl motor!

So if we are too believe the numbers here we have a 428 2bbl motor making 10 hp more then 4 bbl 400 350 hp base line motor in the A body line.

The only 360 hp rated non 389 motor in the GTO was the 1968 mid year 400 option RAII motor, or as I posted above the 1970 455.

I had 2 1969 mt trans 428 motors and they did not have casting number 48 heads.

[242177P]

Sigh. In 1967, the base 400 in the GTO was rated at 335 hp. Meanwhile, the top of the line Ram Air 400 in the 67 Firebird only had "325 hp". If I put you in a room that has an eight foot ceiling, and ask you to bounce a ball off the ground as hard as you can, you're never going to bounce it any higher than the ceiling.

Oh, and the 67 GTO had two motors rated at 360 hp. The 400HO, and the Ram Air.

[MarkS57]

Originally Posted by steve25

The only 360 hp rated non 389 motor in the GTO was the 1968 mid year 400 option RAII motor, or as I posted above the 1970 455.

I had 2 1969 mt trans 428 motors and they did not have casting number 48 heads.

1st, great thread!

For 1968 GTO's, there was some mis-information out there years ago regarding the 360 HP engines. When I got my first 68 GTO (1975), it was the base 400 4BBL engine w/ a 4 speed & 3.36 rear, I had a go around with my insurance company regarding the horsepower figure. The ins company was saying even the base engine was 360HP. It took a bit to get them to see that there was a difference between the various RA & HO engines & the base 400. Eventually, they determined I had a 350HP 400 and they didn't jack my rates.

Yeah, the 48 heads were a surprise to me. 62's & I think 216's (?) I've seen before.

[steve25]

The lower hp ratings in the F body's was due to limited throttle openings when you are comparing motors in the A body cars fitted with the same Cam, heads and stock Exh Manifolds or not.

[Half-Inch Stud]

my 69 YK 428 HO had long Branch manifolds, 48s, and a decent Q-JET. 390 HP seems to be an honest Rating.

GTO HO EXH manifolds and Cams vs Long Branch...hmmm seems the RPM for HP was set low.

[1968GTO421]

Interesting thread, moreso since my '68 GTO has a '69 Grand Prix 428. I know it needs work cuz it pulls like a worn 350 with its 6X-4 heads and any guess as to quality and actual mileage on the previous, previous owner's rebuild.

[242177P]

Originally Posted by steve25

The lower hp ratings in the F body's was due to limited throttle openings when you are comparing motors in the A body cars fitted with the same Cam, heads and stock Exh Manifolds or not.

The limited throttle openings were there because of the corporate edict. And, I hate to
be the one that has to break it to you, but the 69 Grand Prix isn't an A-body.

Honestly, I love the 428s. And I'd love it even more if my 69 428 possessed some kind of
extra-magical kick to it, but let's be realistic. Even though mine was factory rated at 370
horsepower, it was never in the same league as a RamAirIV. Weird.

I know you're smarter than this, what's the hang up??

[Dragncar]

What is sad is that "corporate" kept us from having 428s with RAIV heads and all the rest of the goodies in GTOs and Firebirds. The street wars would have been a whole lot different.
Ah, then you have the 1970 10-1 SD 455 street monster that Chevy was NEVER going to let us have. That project eventually became the 73-74 low compression SD 455. Which still was a great engine. But the original intent was far different and more powerful.
Chevrolet could not have that now.

[Stan Weiss]

Originally Posted by Dragncar

What is sad is that "corporate" kept us from having 428s with RAIV heads and all the rest of the goodies in GTOs and Firebirds. The street wars would have been a whole lot different.
Ah, then you have the 1970 10-1 SD 455 street monster that Chevy was NEVER going to let us have. That project eventually became the 73-74 low compression SD 455. Which still was a great engine. But the original intent was far different and more powerful.
Chevrolet could not have that now.

You are just dreaming. That would still not be enough head to produce the HP to hang with the Chevy's. Now a 428 (I like the shorter stroke) with good forged rods and pistons and a street / production version of the RAV head would be a different story..

Stan

[MarkS57]

Originally Posted by Dragncar

What is sad is that "corporate" kept us from having 428s with RAIV heads and all the rest of the goodies in GTOs and Firebirds. The street wars would have been a whole lot different.
Ah, then you have the 1970 10-1 SD 455 street monster that Chevy was NEVER going to let us have. That project eventually became the 73-74 low compression SD 455. Which still was a great engine. But the original intent was far different and more powerful.
Chevrolet could not have that now.

For want of a forged rod perhaps & not so much focus on the tunnel ports? But point taken, Bowtie management had a lot of pull. As in 63 when it was obvious PMD was a bonafide challenge to Chebby.

[Dragncar]

Originally Posted by Stan Weiss

You are just dreaming. That would still not be enough head to produce the HP to hang with the Chevy's. Now a 428 (I like the shorter stroke) with good forged rods and pistons and a street / production version of the RAV head would be a different story..

Stan

No, not dreaming anything Stan. There was actually 2 sets of 90cc SD455 heads made. Dan Whitmore had a PMD engineer bring a set by his shop back in the day. Casting # 96. They even had the pushrod tubes like the 73-74 SD 455 heads. Dan held the heads in his hands, its all true.

The engine was going to be a 455, 10-1, forged pistons and rods, the SD 455 block, N crank, RAIV aluminum intake with the SD 455 Q jet, RAIV cam and valve train, Ram Air ex.
A street monster. It would have made well over 450HP and more than a equal to the LS6 454 on the street.
Not "dreaming" at all Stan. This thing almost happened.
And there were 428s with forged cranks and 2x4 tunnel ram intakes for RAV heads in the works too. They made some intakes and some Kellogg cranks also but 3" main for the RAV block.
Chevy killed a LOT of PMDs plans that would have put them at the top on the street.
A person who knew what they were doing could keep up with a LS6 with a RAIV in stock form. This 10-1 455SD would have pummeled the LS6.

[Stan Weiss]

Originally Posted by Dragncar

No, not dreaming anything Stan. There was actually 2 sets of 90cc SD455 heads made. Dan Whitmore had a PMD engineer bring a set by his shop back in the day. Casting # 96. They even had the pushrod tubes like the 73-74 SD 455 heads. Dan held the heads in his hands, its all true.

The engine was going to be a 455, 10-1, forged pistons and rods, the SD 455 block, N crank, RAIV aluminum intake with the SD 455 Q jet, RAIV cam and valve train, Ram Air ex.
A street monster. It would have made well over 450HP and more than a equal to the LS6 454 on the street.
Not "dreaming" at all Stan. This thing almost happened.
And there were 428s with forged cranks and 2x4 tunnel ram intakes for RAV heads in the works too. They made some intakes and some Kellogg cranks also but 3" main for the RAV block.
Chevy killed a LOT of PMDs plans that would have put them at the top on the street.
A person who knew what they were doing could keep up with a LS6 with a RAIV in stock form. This 10-1 455SD would have pummeled the LS6.

Really?

Stan