is there any difference between a pontiac 455 sd and a 455?

Asked by themaninc Nov 14, 2013 at 09:41 PM about the 1973 Pontiac Firebird

Question type: General

what's the difference between engines? 455 sd verses 455

15 Answers

163,205

http://en.wikipedia.org/wiki/Pontiac_V8_engine -- check out the 455 portion of this link it should give you some insite into the differences.

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163,205

In 1973, a further refined and even stronger version, the Super Duty (SD) engine was introduced with "only" 310 hp (231 kW)/231 kW (SAE Net) using a similar camshaft specifications to the Ram Air IV 400. The 455 SD used round-port cylinder-heads similar to those used on the 1971 and 1972 455 HO, with specific "LS2" intake and cast-iron exhaust header-manifolds. Still, it was the strongest American engine offered that year. Its power was achieved through bending of EPA emissions-testing procedures, which led engineers to de-tune the engine to 290 hp (220 kW) via a camshaft change to the same profile used in the early RA III 400 engines for mid-1973 and 1974, after which point it was discontinued. While an evolution of the RA IV and H.O. engine designs, the 455 SD was a much improved engine. In addition to the more refined cylinder heads, block casting reinforcements in the lifter galley and main bearing oil pan rail area along with the addition of forged connecting rods with larger 7⁄16-inch-diameter (11 mm) bolts, the SD was made with a provision for dry sump oiling from the factory. This truly was a racing engine, detuned for use in passenger cars.

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20

Super Duty 455's used Pontiac's legendary round port cylinder heads while the non Super Duty used standard D-port heads. The SD blocks utilized 4 bolt mains, forged connecting rods and pistons, and the blocks were cast with a provision for dry sump oiling. The lifter galley was reinforced with additional bracing to prevent cracking as well. Pontiac used a revision of it's standard 455 emissions rather than classify it as a brand-new engine. Since the standard 455's were already emissions certified, it allowed Pontiac to skip the certification process required of all new engine's. Without that it's highly unlikely that the SD-455 would have been approved for production. The SD-455 was the last of the true muscle cars. They were genuine 13 second cars when other so called '73 and '74 cars were struggling to manage 15 seconds in the 1/4 mile. It's a miracle that the SD-455 was even considered much less produced considering the market for high performance cars was definitely on it's last leg.

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50

The only "13 second" SD455 cars were the prototypes that were issued to the magazines of the period for testing. They significantly different from actual production cars, as documented here: https://www.hotrod.com/articles/pon-0505-inside-455-super-duty/ MOTOR TREND tested a later regular production SD455 and couldn't get out of the low 15s with it. These cars weighed nearly 3,800 pounds. Combined with 290 SAE Net HP (Actual product engine specs), they just weren't fast.

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50

I had a 1974 SD 455 Formula Firebird, no air,Turbo 400, 3.42 rear, ran consistent Mid-13's over 105 mph. Also would run over 150 mph. SD Firebirds were the real deal in 73 and 74 I added a shift kit , rejetted carb, and recurved distributer, ran Low 13's . Awesome car.

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20

GuruVDYBF is right on the money, the SD455 has become over hyped folklore. The camshaft was a pollution cam, the manifold had EGR, and the carburettor ran ultra lean, put that all together and it struggled to get under 15's unmodified!

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50

GuruC2TVH - Thanks for your thoughtful reply. I can only laugh at the other comments such as this one: "I had a 1974 SD 455 Formula Firebird, no air,Turbo 400, 3.42 rear, ran consistent Mid-13's over 105 mph. Also would run over 150 mph." As it rolled off the showroom floor, a 14.5 @ 98 MPH from that 3,800 smogger would have represented the absolute best case. As we know, the SD455's block was strong and featured nice provisions for subsequent lubrication mods. Other than that, the engine made some 25 HP less than the uncelebrated 1971 455 HO, which was actually capable of running very high 13s in the 102 MP range (Firebird and low content T-37 Tempest) straight off the showroom floor. The 455 SD really suffered in terms of its low compression ratio and compromised cam, carburetor, and ignition specs. The magazine test cars got the RA IV cam, milled heads, thinner head gaskets, functional hood scoops, optimal ignition specs and perfected carbs fitted with larger secondary jets and optimized metering rods. :-)

40

These two guys are above me I'll total dumb fuck bench racers. Even detuned without headers high- compression the bigger can bigger gears the car still in clock 13:5. Now the other 455's that year and later we're just passenger car engines that will only run 15. They didn't pick the SD 455 to be the top 5 muscle car engines ever for nothing. Don't listen to these two smucks above. https://oldcarmemories.com/5-best- high-performance-v8s-muscle-car-era/

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Again: The only "13 second" SD455 cars were the prototypes that were issued to the magazines of the period for testing. They significantly different from actual production cars, as documented here: https://www.hotrod.com/articles/pon-0505-inside-455-super-duty/ MOTOR TREND tested a later regular production SD455 and couldn't get out of the low 15s with it. These cars weighed nearly 3,800 pounds. Combined with 290 SAE Net HP (Actual product engine specs), they just weren't fast. Put a 100% PRODUCTION LINE STOCK (please read that at least 4 more times) on a modern inertia chassis dyno and you'll see something on the order of 230 HP at the wheels. Combined with a 3,800 pound car (plus driver), that's an upper 14 seconds/98 MPH car. The only "stock" SD455s that turned mid 13s @ 105 were the specially prepared prototypes that were tested by a few of the period magazines back in the day (CAR AND DRIVER and HOT ROD being two of them).

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50

Attention GuruSSY6N So you're saying that a relatively recent article that's primary based on nostalgia is more significantly than actual empirical evidence from known production line stock SD455s? Here's a vintage MOTOR TREND road test of production line stock (not to be confused with the specially prepared 1973 magazine prototype). 0 - 60 MPH: 7.3 seconds 1/4 mile: 15.0 seconds @ 96 MPH Top Speed: 124.3 MPH Link to the actual article's test results page: https://www.flickr.com/photos/141864703@N03/47966612963/in/album- 72157689935719041/ People writing modern articles about old cars are typically doing little more than regurgitating old myths than can easily be disproved my more reliable and original information. HIGH PERFORMANCE PONTIAC drag tested a known 100% production line stock 1973 SD455 back in the 2007-2008 timeframe. That car ran upper 14s @ 98 MPH, though it id have a recurved distributor, K&N air filter element and was fitted with wider than stock modern rubber at the back. 100% production line stock vs. same, something as innocuous as a 2013 Honda Accord V6 automatic sedan would out accelerate a PRODUCTION LINE STOCK (not to be confused with the prototype magazine ringers I've recently detailed with a link that included interviews with the SD455's original engineers) SD455 with room to spare. https://www.caranddriver.com/reviews/a15116988/2013-honda-accord-sedan-v-6-test- review/ That's because the Accord's horsepower to weight ratio is superior.

30

guruVDYBF- I would have to respectfully disagree. My uncle had one back in the day. We would talk Pontiac all the time. He has since passed...but he was a wealth of information as I am too young to remember, (man...I miss those conversations) . Are you talking about the standard Trans Am issue 455? That was 250HP from factory. It rans numbers better than those I see above. My uncles was no AC, automatic with 3.42 gears. It was definitely a high 13s car. With simple mods it was obviously faster. There was nothing that Ford, Chrysler or the rest of GM had in 73-74 that was comparable. It was a great muscle car of the day, whatever the quarter miles times are. Now a SD455 with AC had a 3.08 sounds like what you are talking about. All AC SD's had 3.08. Thx

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40

Guru as much misinformed about the SD. Now a regular 455 was slow and ran 15's but the SD was a much different animal, I will call bullshit on this one. DD

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40

I guess I guess this fool didn't realize the little SD Cam they used there's the same Cam that went in a ram air lll 400 and it was rated 366 hp. I'll also add that a stock SD is probably 400 horse with open headers. And would stomp a muddy hole in a ram air lll. In fact it would easily beat a Ram Air IV. That's why the SD 455 is picked to be one of the top 5 muscle car engines of all time. You can really get some horsepower out of this with some compression in a bigger cam.

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40

No test car with ram air IV ever left the factory. Once they realized it wouldnt pass the emissions with enough cushion they destroyed the Ram Air IV cars and no one got to test one outside of the factory. The no it all is blowing smoke up your asses.

40

I'll say it again as stock SD that's running properly can run a 13.50. This guy above me is an idiot and it's never owned one. Nunzi Romano took a completely stock SD and put headers and gears on it and his tune and it ran 12 70s and made the front page of 1984 Pontiac magazine. People are so full of shit. This car from the factory it was 400 horse with shitloads of torque. Imagine what you can do to it. But the 74 455 probably ran 15 but it was just a passenger car engine and not a SD

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