Judges

[DaJudge]

A 71 455 HO has an aluminum intake, round port heads, essentially a RA IV top end. A 70 455 has iron intake, d port heads, it was basically a big car engine in a GTO. A 71 455 HO is much more desireable than a 70 455.

[gtaa9]

Big difference between the two.Even with lower compression I would pick the 71 455HO over the 70.Why did Pontiac call the 70 455 a HO motor?Either you or steved said the 70 455 was out of a big pontiac.Was there any differences with the big car 455 and the 70 455 motor?When the factory put the 455 in the 70 GTO was there any mods done to it to made it differant from the big car 455?

[Steve_Hoog]

Jeff

455 in any 70 car was basically the same, the cam was 067 in M40 and 068 MT.

So why the less HP than the 69 428 HO that used the same cams?

The head CC’s had to be more than 400 to present a streetable compression ratio and we know the heads were of less quality than say a 48. So what if they had put a 48 or even RAIV head, guess boost the HP 30 to 50 points for the added compression and flow. Then add the biggest cam, RAIV and you would get an unbelievable motor. Guessing 425 to 450 HP?

As much static as Pontiac got from the Chevrolet division about trying knocking them off the top, you think this dream motor would have helped? And don’t forget, the RAV engine was ever so close to a reality.

I must also correct myself, I believe the 63 SD 421 rated 410 HP making it top chief.

[gtaa9]

I pick it because of the RAlV top end round port heads ect plus driveablity.Does the 428HO have round port heads?I know the 455HO has lower compression than the 428HO but the 455HO motor is more tammer with tons of torque.

[Steve_Hoog]

428 used high compression D 72cc like 16 and 48, the heads on the 455HO are 111cc and it seems maybe they used the 1.5 geometry in the rocker area instead of the RAIV 1.65. Many people have proven the D ports can be made to flow as well as the round ports, and you would probably tell little difference at the track. I will go performance over the stigma of some hard to find heads until such time my pocket book is endless.

In contrast a few lucky people have the rarest exotic Pontiac goodies, for example Tom (TJS). A very nice person who has some of the hardest to find factory stuff, and has the means to use it well. I admire that, but he is in different league than me at this time.

So I go for the quickest my buck can buy, I won't waste time chasing 111cc round ports. There is nothing wrong with it, if that's what a person needs.The may actually be a good head to use with a blower set up.

There is just too much horsepower loss by running 111cc on a flat top with 8.1 compression, compared to the same motor with some 72cc would make 11.0. I have heard it estimated that each compression point is worth about 50 HP.

[gtaa9]

D port heads are more common than round port heads.I agree with you its all about the pocket book.As far as round port heads go there rarer and more popular with the collectors.D port heads are more commnon with the population money wise and like you said they can breathe as good or better than round port heads with alittle work.

[gtaa9]

I'm not raging on the RAlV I think its an assume motor.I read some were that in stop and go traffic it tended to over heat because of the cam it had is this true?

[Steve_Hoog]

Dunno, never had a RAIV. I drove a 69 TA one time with a IV for about a block and the only thing I heated was the tires. At the owners request much to my surprise.

[yellowjudge]

This would be my thought all this saga: The round port heads were superior then, & now. That is why they were on more costly mtr. If you want better heads, I would go w/tech, & buy new alum. heads.