Why is the 73-74 455 Super Duty engine (LS2) generally held in higher regard than the 71-72 455 H.O. (LS5)? On paper, the H.O. seems better.

1972 455 H.O.- 300 HP@4000 RPM, 415 lb-ft@ 3200 RPM, 8.4:1 compression
1973 455 SD- 290 HP@4000 RPM, 390 lb-ft @ 3600 RPM, 8.0:1 compression
both numbers are net rated HP.

Is it because the SD was around when all other cars weren't making any power? Or is the SD underrated/ H.O. overrated?

 

The horsepower war was over and the SD was the ONLY car packing big(ger) guns in '73 & '74. It had more power than the same year Corvette.

From what I've heard people that have driven both back in the day say the SD actually pulled harder even though on paper the numbers didn't add up. Who knows the exact details?

The SD had better rods (forged), intake, and heads, although the compression was down a bit from previous years.

I'd LOVE to have a 1973 SD... or ANY '70 to 73 455 ci Trans Am.

 

Correct me if I'm wrong,but the difference in horsepower may be down to changing the way the HP was quoted.From Gross to Net rating.
I'm sure that '72 - '73 was the change over.

 

^^^ That's a very good point.

Forgot about that. The gross hp ratings were based on electric waterpump with no accessories attached and are the most optimistic possible, were the "net" rating are real-world numbers with all smog, ac, alternator, waterpump, etc running on the motor too.

That's why the LT1 of today (300hp 'vette) has a higher net rating than the old LT1 ( 1970 'vette 370 gross hp).

If you did the math the 370 hp gross rating would be more like 290 net.

 

SD had round port heads "96" the along with ram air 3 or 4 manifolds and a factory 800 quadrajet, aluminum dual plane intake, ram air 3 or 4 valvetrain...nice rods and nodular crank

 

1972 was the first year of net ratings, so the numbers in the 1st post are net for both years. the gross figures for the 1971 model were 335@4800/480@3600, compared to the 1972 net figures of 300@4000/415@3200.

 

Back in the early 70's as was mentioned HP ratings were hard to compare due different methods of measuring.
The sd heads ar number 16 btw not 96. Also note that pontiac used the head numbers on other year heads.
I think the sd 455 engines were the last true powerful engines out of pontiac.
True that pontiac carried the torch into the late 70's with the w72 400 engines, but they were mere 15 sec machines.
While the sd could run high 13's off the showroom floor with tires of the day.
With decent rubber they rivaled the ls-1 of today.
I suggest you check out

www.classicalpontiac.com

for more info.

 

If memory serves me correctly ( I was 13 or 14 ), the SD was a little under-rated due to the insurance regs at the time. The first big oil embargo hit in '73 also, so GM was trying to appear like they cared about things like pollution and gas economy.

 

Actually it was 1971 , both net and gross hp was given by Pontiac.
335 gross hp /305 net hp for the HO.
Ho had also the ramair 4 aly intake and round port , but rew was limited to 5200rpm as for many big inc poncos.The SD rew to 6000 with no problem .

HO is a sweet engine but SD is a improvment and LS-1 rules

 

The SDs are held in such high regard for both points, that during 73-74, they were hands down the fastest cars you could buy, ANYWHERE, on the road, and the fact that they are still, to this day, one of the fastest Trans Ams ever made, including today's LS1s. The 455HO is also a great motor. My friend has a 72 TA, 455 HO with the M22. Fast, but not a super duty. The SD was in design for years, with specific attention to performance with smog and emissions restrictions. The HO motors were basically regular V8s with smog equip. thrown on them. The hp ratings, as is the General's trademark, were underated, just like our 02 LS1s make alot more then 325 ponies. Also the change from gross to net affect numbers. GM was and still is known for simply changing the sticker to sandbag the horsepower and lower insurance.

 

Interesting information

 

Another small tidbit of info is that Pontiac outsourced the head design on the SD. It was a little known company called Airflow Research (AFR).
Summer of `72 Preproduction SD's with 3.90's and supertunes were running 12 sec Quarter miles, these cars all featured R/A IV (041) cams vs the production cars R/A III (744) cams. HO's used the smaller tried and true (068) Ram Air HO cam.

 

Be careful...a lot of mis-information in this thread. SD motors had:
#16 round port heads (96 round port were 68 RAII heads)
- heads came with tuliped valves--HO didn't (at least my 191 heads didn't)
round port exhaust manifolds (RAIII was D port)
cast iron intake with removable heat crossover - HO had aluminum intake of same design
dry sump oiling provisions cast into block-seems like increased lifter gallery webbing, but can't remember for sure.
while it did come with a 800 cfm Quadrajet, so did the HO 455 (different design)
Forged rods (HO were cast)

That is all I can remember right now. Enjoy!

Galen

Forgot to mention...#16 D port were '68 400 heads...have seen some that came off 350s with pressed in studs and small valves?!?

 

This post is awesome, I'm so glad I'm not the only classic Pontiac F-car lover on here.

 

Galen definitely has the information correct. Here's some more information that hasn't been mentioned: The #96 head casting number was also used on the '71 400 motor. In fact, I have those heads on my 455. They provide a perfect 9.2:1 compression ratio. The SD #16 heads were based on the RAIV/HO head design, but had many improvements over the previous generation heads. SD heads were probably the best factory Pontiac cylinder head as far as flow is considered (not including RAV). Also, the SD block was unique compared to the standard 455 and even 455 HO. It had reinforced crosswebbing in the lifter valley, provisions for a dry-sump oiling system, larger distributor diameter, 4-bolt main caps, and had the aforementioned forged connecting rods. This last bit is directly tied to why there were so few made: the company hired to produce the rods couldn't handle the output required. The reason a stock 455SD can outperform a stock 455HO is mainly due to it's ability to rev higher, had better flowing heads, a new intake manifold, and I think a hotter cam. I'm not sure off the top of my head regarding the cam. I know initially Pontiac wanted to use the RAIV cam and even tested it. It made great power, but couldn't pass the '73 emissions. So, Pontiac tossed the RAIII cam in. In 1973, it ran a 13.54@107 MPH. Damn fast for '73!!!! Gotta love them!! My car has a '73 block, #96 heads, and a Wolverine cam that's slightly more aggressive than the RAIV. It's a great car, pulls like crazy!! Love the torque of a 455!!!!

 

http://highperformancepontiac.com/te...973_emissions/

The link above discussed the emissions problems with the SD455 and why it was only offered in the F-body.

http://highperformancepontiac.com/tech/pon_0505_sd/

This link explains why the SD455 was so much different than the standard 455 or the 455HO.


There are two VERY good reads on the SD455s. And you can take just about everything in those articals to heart because a very large amount of the info is streight from the mouths of the engineers who designed the SD455s. Also the 73/74 SD455 had an 830CFM quadrajet. They had the largest CFM rating of any quad ever made. The 455HO and 500ci caddys in 69/70 had the 800CFM quads.

 

im no SD expert but i owned a 72 455 H/O auto car - one of 1286 trans ams made in 72 due to a GM strike , mine was lucerne blue which was about 25% of those produced - so pretty rare . 72 was the last year for the lighter bumpers-(73 and 74 added the 5mph bumper law), 72 was last year for a functional shaker hood with the solenoids that open the rear flap(remember they would open up on WOT? and 72 was the last year for a factory aluminum intake manifold (SD used iron manifold) SD also had the famed SD rods which were forged with 7/16" bolts , SD was basically a race motor - add intake,headers hi-comp pistons and go racing!

 

The SD also had provisions for a Dry Sump oil system from the factory.