Ram Air IV versus 455 HO

[StealthBird]

Supergonzo, I think your quote "I regularly beat my LS6 70 Chevelle" would stir up a few people here.



Not sure about the weights. I've seen the weights on several early Birds and GTO's on NHRA digital scales (this was at Route 66 Raceway, the state of the art NHRA track). I have yet to see a 69 Firebird 400 under 3500 lbs. I weighed mine on the scales several times, and it weighed 3520 lbs without me. It's a 69 Firebird 400, TH400, P/S, PDB, no a/c, and on lightweight side, I had aluminum heads (66 lbs. lighter than #62 steel heads), aluminum water pump (4 lbs lighter than stock), aluminum intake (24 lbs. lighter than a cast iron), headers (6 lbs. lighter than standard manifolds), and a Reactor battery (21 lbs. lighter thand a Delco 1000 amp). In original form, it was 3641 lbs. Only thing that may get this under 3500 lbs. would be a 4-speed, manual brakes, and manual steering but even that would be close I think.

My friend weighed his 69 Firebird 400 ragtop, TH400, P/S, PDB, no a/c. It weighed a staggering 3950 lbs (without driver) on the NHRA scales. I simply could not believe it.


My brother's 68 GTO, TH400, P/S, PDB, hideaway headlights, 455 HO heads, 455HO exhaust manifolds, aluminum intake, weighed 3710 lbs. without driver.

The 67/68 Firebird were about 3450 lbs for the hardtops. My friend had his to 3350 lbs. with an aluminum intake and headers, manual steering and brakes, and a transplanted TH350.

Those dern Camaros always seemed to be lighter.

[supergonzo]

"Those dern Camaros always seemed to be lighter" Actually my own 69' Yenko clone weighs 3600 lbs, weighed it 4X times.
But I think its a little heavy for some reason.

I have to admit my 69' firebird has a fiberglass hood, 4spd, aluminum radiator,manual brakes. I would say 3520lbs would be more accurate for a typical model. Your right the earlier years are lighter.

I am certain the 68-69 goats all weigh close to 3700 lbs, I have 4 of them now, and have owned about 20 others. The 64-67 goats all weigh close to 3600lbs, depending upon options.
I was actually surprised the Firebird / Camaro's weighed that much.
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If Pontiac would have made a high compression 455HO in 1970 instead of a low compression motor in 1971.They would rank right up there with LS6's and Buick 455 Stage 1's as one of the baddest of all times. As it is in todays world , where most people build for near 10 to 1 compression for pump gas, they are very tough street machines to beat,as now the field has been equalized.
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[supergonzo]

As far as the LS6 goes... Chevy has the best heads for breathing period.
Problem 1 is the 70' LS6 weighs 3850 lbs, that doesn't help
Problem 2 is the intake manifold and the exhaust manifolds are choking the engine's breathing capabilities.
In other words they s*ck.

Chevy knew people were going to take their cars racing, and throw away the intakes for better ones and throw away the exhaust for headers. Once you do that to a BBC, you got a whole different animal. A car that most brands would have a very difficult time beating.

Pontiac GTO on the other hand, was a super cool image street machine. Pontiac was selling boatloads of GTO's while others were selling 1/3 as much most of the time. Chevrolet had 3X the dealer network and 4X the advertising budget as Pontiac and still couldn't out sell them!

Pontiac built good heads, excellent intakes, good exhaust manifolds, topped with great responsive Q-jets. And very little work was required to turn a showroom car into a "street cleaner". On the street they were tough to beat, but were never meant to be all out drag strip racing engines.

Ok, thats enough of a rant.

[SuperCars]

Okay, leave the 70 455HO with it's smaller D-port heads out of the question of this thread. Compare the 70 400RAIV with round port heads, and 71 455HO with round port heads. I notice the factory rating on each as: 70 400RAIV 370HP/5500RPM versus 71 455HO 335HP/4400RPM. Would it be true that the 71 HP is peaked out at 4400RPM. That's at 1100RPM under the RAIV rating, which seems to be very low RPM to rate its maximum HP. That is how the L88's were rated less than L71's in the Vettes.

[supergonzo]

These engines all used the same intakes and exhaust, the 70-71 were in heavier cars.
However:
The best breathing heads were 70 400 RAIV's
Followed by 69 400 RAIV's
Next would be 71 455 HO heads, slightly less flow on intake
Finally would be 72 455 HO heads, even slightly less flow in exhaust area. Pontiac engineers knew at this time, compression ratios were falling, and were trying to get as much torque as they could out of the heads, and not worry about upper RPM air flow, as the 400 RAIV's were built. The 455 HO's also did NOT use a RAIV cam although the heads were similar they used the earlier MUCH milder 068 (tripower) cam. Again due to emissions and better low rpm cylinder fill with low compression on those heads.

A 455HO does have a lower rpm peak than a 400.However
The 400 RAIV's were underated, as several magazine dyno test have been done (even recently) and showed in stock form they produced 400-420HP.
The 455 HO with its emission friendly cam has had dyno test in the neighbor hood of 360-370HP, if I remember correctly. The 4400 peak HP rating is definitely too low, and probably rated that way on purpose, to satisfy then very restrictive insurance rules.

[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.

[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 ?

[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]

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)

[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!
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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.