GM big blocks

[David]

Was there a corporate limit on displacement in GM outside of Cadillac? How did Olds, Pontiac, Buick, and Chevrolet all wind up at 455 or 454 cubes?

[FMP]

I think when ci increase from the 400-425-455 , they tired to keep things in a certain under - over square range? Cadi just needed more big cube torque from the 425-472-500 I'm guessing to keep things civil and smooth with low rpm grunt.

[nitro_rat]

i think there was a 10 lbs per cubic inch rule in the 60's. all the big cars probably came in around the same weight - 4500 lbs.

[FMP]

Nova's excluded. They had Corp rule about cubes and vehicles, intermediates likes the Cutlass stayed at 400ci until the special order Hurst received the 455. From then going forward into 70 the 400 was dropped. The big cars, Delta etc had the 455 first. Could be ordered with the 390HP/500torque. The Toro was available with a 400HP rated 455. The Cadi being the flagship sounded better with a 500 ci. Although some of the big wagons could have used more ci.

[Forkin' Crazy]

It was the big engine cube race. The BBC started as a 396. Big bore was 427. Throw a longer stroke crank 454. Evolution. ;)

[CDave]

Don't know but I imagine racing sanctioning bodies rules played a part.

Not to mention with bigger cubic inch engines you get higher piston to cyl. friction with lower rod ratios. So to overcome larger bore/longer stroke friction you have to run longer connecting rods and that means taller blocks. You get into the law of diminishing returns.
You get to a point on a production vehicle where it doesn't make sense to keep making larger and larger passenger vehicle engines.

https://www.enginebuildermag.com/2016/08/understanding-rod-ratios/

"Rod ratio is the mathematical relationship between the overall length of the connecting rods and the stroke of the crankshaft. Divide rod length by the crank stroke and you get the rod ratio.
The lower the rod ratio, the greater the side forces exerted by the pistons against the cylinder walls. This increases wear on the piston skirts and cylinder walls, and creates a higher level of vibration inside the engine. The increase in friction can also elevate coolant and oil temperatures."

[FMP]

5" bore spacing, the goal was for even more displacement than 500
https://www.hemmings.com/blog/article/cadillac-472-500-v-8/

[XstreamVking]

My mom drove a 69 Rivera. 455ci and close to 400hp/ 500tq that car would burn both tires as far as you wanted it to. The old big blocks were torque monsters.

[David]

NASCAR limit then was 427. No NHRA reason for 455 cubes. Bore stroke ratios were different. How did 4 divisions arrive at 455 - yes I know Chev was 454

[Tin Man 2]

A bit to do with marketing, the advertised cubic inch figure was simply rounded to the best sounding number for marketing. Just one example, the hot 375 HP 396 was actually a 402 but 396 sounded better. All the company’s did this Ford had 3 different 351 engines were they all actually the same cubic inch? Very doubtful. I’m to lazy to do the math but most engines are rounded to the most marketable number.

[FMP]

Besides all the above, most cars between division shared hood lines, frame rails, engine bay spacing. Not that a lack of space was an issue. How long or tall did they need to build a block to maintain the under/over square range. Let's take a look at the bunch, each 455 , V°, bore and stroke, deck height.

[FMP]

The 402 didn't happen until 71or 72

[rochelle howell]

'70.

[David]

Buick 455 4.31X3.9 with 4.75 spacing
Pontiac 455 4.15X4.21 with 4.62 bore spacing
Olds 455 4.125X4.25 with 4.625 bore spacing
Chev 454 4.25X4 with 4.84 bore spacing

All different engines.
My guess is an internal GM policy lead to the same displacement. Too big of a coincidence otherwise.

[Markus]

There were policies for engine size at the time. 400 ci for mid-size cars, and probably a similar policy for large cars.

https://books.google.se/books?id=mE8_DwAAQBAJ&pg=PA128&lpg=PA128&dq=gm+policy+engine+displacement+455&source=bl&ots=66T7JCS-pe&sig=ACfU3U0bA3hc0NaMiW-pFYkabeAw9eIsAw&hl=en&sa=X&ved=2ahUKEwjVzuuJl_jiAhWlUt8KHRE2Bc8Q6AEwFHoECAgQAQ#v=onepage&q=gm%20policy%20engine%20displacement%20455&f=false

[David]

The 400 limit for internediates was well known. But I don't remember a 455 limit. Another puzzler is tha all the divisions made 350s

[FMP]

As mentioned above the Hurst started the ball rolling,
https://www.hemmings.com/blog/article/1968-hurst-olds-2/

We had a 69 Delta Custom hardtop 455 with the big valve D heads, it was a heck of a fast car. The HD THM400 was optioned, top end was amazing. Off light not too much would get around it for long, then up top it would eat the road. That engine in the intermediate was fun.
https://m.youtube.com/watch?v=NpmxaamNwhw

I'll add for the day before a Honda owner starts fart canning off.

What's puzzling, the 350 was the standard engine for lots of models. The 350 olds had a couple stages of power. The W 350 are very strong.

When you bought a Buick you received a Buick engine etc. Very few had cross branding division engines. That became more through the 70s them 80s.

[FMP]

When Chev brought out the first big blocks to replace the 409 etc, Cark K received one of the first hand full.

[rochelle howell]

Pontiac Trans Am worst offender for other brand engines. Late 70's, early eighties you could get Pontiac 400, olds 403, Chevy 305, or bastard Pontiac 301(turbo or non). 78 I believe was a olds 403 unless you got a 4 speed, then you got a Pontiac 400( last year for it)

[CDave]

Never knew there were different GM 455's. Thought they were all the same.

[FMP]

And 400s , 350s, 307s

[FMP]

Pontiac Trans Am worst offender for other brand engines. Late 70's, early eighties you could get Pontiac 400, olds 403, Chevy 305, or bastard Pontiac 301(turbo or non). 78 I believe was a olds 403 unless you got a 4 speed, then you got a Pontiac 400( last year for it)

And if you ordered the TA, bird with a trailer tow package you received the non web 403, as the 88 ,98 and wagons from Olds. Very rare block. 403 are big bore motors and are small blocks like the 350, 307, and the smallest 260, but have larger bores than the 455. If built with the right parts can be a great engine. As can the Diesel 350 Olds to gas.

[Forkin' Crazy]

Yea, a friend had a TA with a 403. With a little work it was very impressive at the drag strip for the money he had invested. I had a chance to buy it on the cheep (hail damage) and I regret not getting it!!!

[FMP]

Dick Miller build
https://www.hotrod.com/articles/0504em-oldsmobile-engine/

[rochelle howell]

And if you ordered the TA, bird with a trailer tow package you received the non web 403, as the 88 ,98 and wagons from Olds. Very rare block. 403 are big bore motors and are small blocks like the 350, 307, and the smallest 260, but have larger bores than the
455. If built with the right parts can be a great engine. As can the Diesel 350 Olds to gas.
Looked for a pic of non window 403. Seems like no one can come up with one?!?!?!?!

[FMP]

Not many around. I read it first in the 80s, it wasn't folklore.

[FMP]

Not many around. I read it first in the 80s, it wasn't folklore;

As far as 403's go, some people doubt that a solid web engine was ever made. According to Mondello, 2500 solid web 403's were produced in 1977 and they were used in big Buick and Olds wagons. You can determine if you have a solid web by looking at the serial number.
Quantity Produced 2500
Block Casting Numbers 557265-4A, 553990-4A, 554990-4A
Blocks with these casting numbers were used in certain 1977 Buick Station Wagons built in 1976, the Pontiac Bonneville with tow package, the 1979 Pontiac Trans Am with tow package (w/block casting #554990-4A), and in 1977 Olds 98's. Block casting number is found behind the timing cover between the oil fill tube and the oil sending unit. Might also be found in 1977 Toronados.
All "4A" blocks don't necessary have solid main webs. #554990 has been found to have open webs. 1977 models built early in the model year, fall of 1976, are likely to have solid main webs.
Source: Mondello Olds V-8 Engine Technical Reference Manual

[FMP]

Probably in the 3.23:1 HD wagons , also the Toro 403 front drive equipped GM motorhome of those years.
Motors made 330 torque at 2300

[XstreamVking]

The bad boy of the 455's might have been the HD 455 in the Trans-Ams. Way underrated by the factory, (285 haha) they were later given a 435hp estimate. They were a 73 and 74 option only. Lot of unique parts in them.

[FMP]

1971 Pontiac
L75-code 455 that touted 25 extra ponies, but there was still another available step to the LS5: a 455 H.O. (High Output) that gave drivers 335 hp and 480 lb-ft of torque to play with.

Then SD 455 , low compression in those years but still ran with the best of them.
The best 455 street from Buick stage 2 455, very strong. Would out gun a LS6 Chevelle.
The best from Olds was rated 400hp W34 Toro GT front drive. It was the same motor as the W33 Delta rated 390hp. The non AC car had a different grind than the AC, also I think the manual trans was more duration. But the 365hp version had the highest torque rating.

Then came the W43 four valve semi Hemi 455, absolutely beautiful. Then if that wasn't enough the OW43 Cammer 455 7000rpm 700 hp just the beginning.
https://www.streetmusclemag.com/news/the-w43-oldsmobiles-dohc-455-v8-that-never-was/

[CDave]

And 400s , 350s, 307s

Knew about those.

[FMP]

Knew about those.

Big and small blocks. ,307chev and small Olds

[rochelle howell]

Probably in the 3.23:1 HD wagons , also the Toro 403 front drive equipped GM motorhome of those years.
Motors made 330 torque at 2300As a kid in late 80's that HD wagon was on the list of cars to look for in the junkyard. Factory rear sway bar and nodular iron 8.5 posi rear. Never found one, or the Lincoln Versailles ( fancy ford Granada ) with 52 inch leaf spring ford 9 inch disc brake posi. Junkyard gold!

[FMP]

That's the stuff. Didn't the little Cadi Seville have the rear disk setup?