Ram Air IV versus 455 HO

[supergonzo]

However the 73 455 SD was the best of all of these. Even though rated at 310(290) net HP.

The 73 455 Sd intake was cast iron, by emission necessity. So it was fair in performance.
The 73 455SD heads out flow any other Pontiac heads made, other than RAV Tunnel ports. I have 2 sets of these and one going on a 73'T/A I'm building. At the time were said to out flow even HEMI heads! Although this is not true. What is true is that the heads were meticuously cast. Meaning most factory heads (any brand)have large casting differences among them, even within years. Depending upon the casting machine you could get a good LS6 head or a fair LS6 head. One that is clean and one that has casting imperfections in the passages, or even half closed passages alltogether. This is true of all brands.

The 73 455SD heads were all made very well. I have never seen a crappy one. They used slightly bigger Ram Air type exhaust manifolds than even the RAIV /455HO's.
As mike said: Today a 455SD with the original planned RAIV cam in it, and uncorked exhaust, 10 to 1 compression.. is a bad ass. One that is capable of staying with anything ever built in the muscle car era. Even in 1973 HotRod magazine tested one with 3.42 gears at [email protected] you read the article they mentioned that they had the air conditioning on while track testing it!! Other tests by other mamagzines were similar.

As a side bonus if you have ever driven a 70-74 Trans AM, they make any 60's muscle car feel like you are driving a school bus. They handle virtually like today's cars.

[StealthBird]

The SD455 head is truly the best head from a performance standpoint, but the huge chamber on the head, required to maintain low compression, was a killer.

On the topic of port comparisons and port flow, the SD455 stands alone. The Pontiac Engineers hogged the SD455 head intake runner out so much that they broke through the pushrod bulge (the main airflow obstruction on a Pontiac head) within the runners. They remedied this by inserting special pushrod tubes in those runners. They also raised the port roof so high that they broke through the valve cover bolt holes. Tuners soon found out about this, as many Pontiac people replaced the factory rocker arm lock nuts with adjustable versions for a few more rpms on the SD455. With the engine idling, setting the adjustable polylocks proved to be difficult. The engine is idling, the valve cover is off, and you're wondering why the engine is dying? On the SD455 cars, removing the valve cover bolts over those runners caused a massive vacuum leak. You had to replace the necessary bolts if you idled the car with the valve covers off.

Seems a little extreme for 1973, but the SD455 was the Pontiac bad boy that made it to the party too late.

Pete McCarthy did some serious flow work tests a while ago, and ran all the Pontiac heads through a Superflow. There was always some debate on what was truly the best street head.

Best performance head : 1970 Ram Air IV
Best intake port : 1969-70 Ram Air V
Best exhaust port : 1968 1/2 Ram Air II
Best D-port head : No.16, No.48, No.12 (tie)
Best low-compression D-port head : No.96(1971)
Best low-compression post-1972 head : No. 6X
Best balanced head (exhaust to intake) : 1963 421 SD
Best low-lift (under .400) head : 1967 No.670
Worst exhaust-to-intake port ratio : 1969-70 Ram Air V
Worst intake-to exhaust ratio : 1968 1/2 Ram Air II
Biggest surprise : Intake port, No.17 350 head
Biggest disappointment : 1969-70 RA V, 1973-74 455 SD (tie)
Biggest "sleeper" : 1975 No. 5C
Most undercammed : 1963 SD, 1971 455 HO, 1973-74 455 SD (tie)
Most underexhausted : 1964 GTO (No.9770716)
Most potential for porting : 1973-74 455 SD, 1968 1/2 RA II (tie)

[Charley Lillard]

I am rebuilding a 73 SD engine right now. Do you recommend 10-1 and a RAIV cam ? Solid or hyd ? Will it idle with AC ?

[supergonzo]

I agree with Mike 1000% A well prepped 455SD is one hauling mean machine. The block even had Dry Sump racing provisions built in!
----------------------------
Charley it depends on your budget, but I would recommend a Hyd roller possibly a Comp XR276HR or a XR288HR depending upon what you want to do with the car. A HYD roller with 230-240 degrees duration would make you very happy and it will idle just fine. 10 to 1 for pump gas would be fine. You need ROSS Pistons, they are the best and they are off the shelf most times. Throw in a set of aluminum rods if you have money to burn and that 455SD will rev like a small block.

[StealthBird]

The SD455 heads are so rare and valuable today that it's a shame to port or shave them in any way. The original SD455 was designed with the RAIV cam. The prototypes used the RAIV cam, but couldn't pass emissions (there's a whole story about that that's pretty cool)

The skies the limit if you want to build it with "secret" parts. Aluminum rods, lightweight pistons, hydraulic roller, it really depends what you want to do with it, and if sounding totally stock is a priority.

[Charley Lillard]

I don't need anything exotic as it will still not see much driving. If I wanna go fast I have other stuff. I know I need to bore it and put new pistons so I might as well go 10-1. The cam looks fine but if there is a good hyd cam that would compliment the 10-1 and still idle well I should go for it. I am told intake gaskets are hard to find and the repo ones fall apart, any suggestions ?

[Chevy454]

[ QUOTE ]
Even in 1973 HotRod magazine tested one with 3.42 gears at [email protected] you read the article they mentioned that they had the air conditioning on while track testing it!!

[/ QUOTE ]

Unfortunately, that wasn't with the production cam. Darn Feds...

[StealthBird]

Rob, that was true, but what was so impressive was that that SD455 ran that time with 8.4 compression, weighing 3800 lbs, a ridiculously 3.42 rear gear, emission equipment, and an EGR on a steel intake. Simply amazing in any era, not to mention 1973!

[Steve_Hoog]

Charely

There are 10 and half dozen ways to build a Pontiac, but to think you won't go fast in it... that is a huge mistake. The majority of stock components adjust the compression with head cc and gasket crush. I believe you have a SD, if memory serves me correct. You will probably want to stick with the factory heads. TRW (Seal Power or whoever they are now) did make a shelf piston for those rods, it only had two valve reliefs. If you find some nice .015 crush gaskets, run a zero deck, and mill the heads accordingly to achieve your final compression ratio.... I think you will be happy. Running low 12's with a 9.5 455, is a piece of cake and you get to use pump gas. Then again maybe you will want a highway cruiser. Some of the old cross country racers use to order these SD's with the highway gears, and achieve some serious cruising speeds.

Steve

[supergonzo]

For those non Pontiac people, basically any round port exhaust head Pontiac motor has real good potential. RAII/RAIV/RAV/455HO/455SD

"Running low 12's with a 9.5 455, is a piece of cake and you get to use pump gas." I agree no problem.

Don't cut the heads though, get the right pistons instead. Any HYD cam with 240 degrees duration and under .520 lift and you'll have a fast and reliable street cleaner, while enjoying 60 degree air temps inside the car in summer!