[goatwgn]

Originally Posted by b-man

Over square - bore dimension bigger than stroke, all Pontiac V8 engines fit this description with the exception of the 326 and 455.

Under square - stroke dimension bigger than bore

Square - both the bore and stroke dimensions are equal

The 455 only needs to be bored approximately +.060” to become ‘square’ (4.210” x 4.210”).

Same thing goes for the 326 with the factory 3.72” bore and 3.75” stroke but only needs to go +.030 over bore to be square. Funny that in 1963 which was the very first year of 326 production the bore was actually 3.76” for some reason and was then reduced to 3.72” for 1964 through the end of production in 1967. Great little V8 which might be the one with the highest reliability and longevity of all Pontiac V8s.

Both of these slightly under square Pontiac engine offerings are excellent street engines for their intended purposes, neither one should be overlooked when either big torque in the case of the 455 or excellent economy in the case of the 326 is desired.

Some here might be surprised to learn that many if not most of the big-cube Pontiac race and street engines are under square. With bore sizes under 4.40” for most and strokes 4.50” and larger Pontiac engines don’t necessarily need to be over square to be great racing or street engines.

I agree on the longevity of the 326. My '66 326 2 bbl went pretty trouble free for 292000 miles, when I pulled it (still running well, but a bit weak) in the late 1980s for a 455, which in itself went 100000 miles, of hard use, and the only reason I pulled it to redo it in 2011 was to reduce the compression to be able to run it trouble free on low octane gas. I was running the old 10.5 to 1 engine with a mild cam with dialed back timing, and octane boosters.

[steve25]

The problem with original Hemi heads heads in relation to timing needs is the total lack of squish.

And if you do get the piston dome near enough to the chamber walls to generate some turbulence then the flame travel goes to Hell in the Hemi head faster then the added timing can make up for!

Just go look at the power improvements in the aftermarket Harley heads designed for squish.

[mgarblik]

Originally Posted by steve25

The problem with original Hemi heads heads in relation to timing needs is the total lack of squish.

And if you do get the piston dome near enough to the chamber walls to generate some turbulence then the flame travel goes to Hell in the Hemi head faster then the added timing can make up for!

Just go look at the power improvements in the aftermarket Harley heads designed for squish.

Dead on target and the reason the hemi heads work so well in racing and not so great in low RPM, street engines with emission requirements. Racing engines: High RPM, high flow, low turbulence, hemi is perfect. Especially true on nitro where squish and quench=explosion and severe detonation. Usually, when I say this, a Mopar nut will say, "then explain the modern hemi" The modern hemi is a "Hemi" in name only. It is really a 2 valve pent roof chamber. It has both a quish and quench pad. Small, but they are there, unlike the original Chrysler Hemi design. They are needed for mixture motion, turbulence, low speed driveability, emission control, primarily, HC emissions from the dead space created by the hemi shape.

[Formulajones]

Originally Posted by mgarblik

Dead on target and the reason the hemi heads work so well in racing and not so great in low RPM, street engines with emission requirements. Racing engines: High RPM, high flow, low turbulence, hemi is perfect. Especially true on nitro where squish and quench=explosion and severe detonation. Usually, when I say this, a Mopar nut will say, "then explain the modern hemi" The modern hemi is a "Hemi" in name only. It is really a 2 valve pent roof chamber. It has both a quish and quench pad. Small, but they are there, unlike the original Chrysler Hemi design. They are needed for mixture motion, turbulence, low speed driveability, emission control, primarily, HC emissions from the dead space created by the hemi shape.

Who's worried about low rpm street manors in the street section?

[dataway]

Tight squeeze.

[Formulajones]

Originally Posted by dataway

Tight squeeze.

Yeah....I think they work pretty well They've been in the record books since the 50's and still continue to be the mainstay in top fuel and funny car. Just look how competitive they are in Pure Stock and FAST classes.

[Region Warrior]

Blew the doors off a 70-455 GTO with a 69-428 in my brothers 68FB back in the 70's.

[dataway]

They need to add a "Freakin Stock Pontiacs" section

[steve25]

Sub title that "The reality street section"!

[Formulajones]

Originally Posted by steve25

Sub title that "The reality street section"!

Sub title that " the old farts reality street section"

[MarkS57]

Originally Posted by Formulajones

Sub title that " the old farts reality street section"

Can't deny that one...followed by "Decrepit old farts reality street"

[RocktimusPryme]

Originally Posted by Formulajones

Sub title that " the old farts reality street section"

"400 HP is enough dag nabbit!"

Joking aside, while its certainly an older crowd (Im 36, this might be the only place left where I get called young) there are plenty of very progressive minds on this board in the name of making horsepower. Especially if you hang around long enough to pick out the names you should be listening to, you will generally get steered in the correct direction here.

Im part of other hot rod groups that are waaaaay worse on the old guy mis-information speak. Which people can think what they want, but I hate when someone who genuinely doesn't know gets influenced by that "3/4 race cam!" mentality.

Back to the topic, Considering pretty much everyone who can afford to adds that stroker crank in their 400, I would think the reason to go bigger than the 428 is obvious.

[Formulajones]

Originally Posted by RocktimusPryme

"400 HP is enough dag nabbit!"


Back to the topic, Considering pretty much everyone who can afford to adds that stroker crank in their 400, I would think the reason to go bigger than the 428 is obvious.

Exactly!! The only reason I build a 428 more than 20 years ago is because we simply had the parts laying around, and back then aftermarket stroker cranks weren't readily available like they are today.

Doing engines today I generally look at 455 and larger. Prefer cubic inches. Especially considering the costs involved are nearly the same.

[Skip Fix]

I have a 4" stroke 400 block plan using my RAIV heads for my 65 GTO project.

[MarkS57]

Originally Posted by Skip Fix

I have a 4" stroke 400 block plan using my RAIV heads for my 65 GTO project.

I figured I would put these on my 65 after the 428 build, not a 421 but it will be 4" stroke engine. From the Full Size Ames catalog 65 model year

[Nicks67GTO]

My 4" stroke 400 block, 312cfm e heads, T2, sft cam combo absolutely rips. There is TQ everywhere, it likes to rev and I beat the **** out of it autoXing. Glad I went 4" stroke.

[FrankieT/A]

I have always wanted a really big cubic inch motor that was just over sized. Meaning normal idle, normal driving characteristics but like 500 cubes. That wasn't really realistic back in the day. Other old guys(like me) can tell you that you couldn't just go in a catalog or online and buy a stroker crank like you can today. Things were not made in China like today. You want a stroker crank? You have to go to Moldex or Hank The Crank for a seriously expensive crank (about $3000.00). Oh, did you want rods for that? Another $1500..00 in 1970's dollars for that. Oh wait we're gonna need pistons, custom Venolia? Cha Ching!!! And this is Chevy stuff. Pontiac, Olds, Buick you need a loan application. To get a stroker kit today, what? 17-1800.00 bucks? Crank, rods, pistons, bearings, rings...at your door in a week. You get the point. Large cube engines are almost commonplace these days.

Like others have said in this thread "I like an over square engine" My retirement engine might be a 455 .030 block with 428 4" crank and some serious flowing E heads.

[Rocky Rotella]

As many had previous stated or eluded, the 455 was the natural progression of Pontiac’s largest full-size engine—which started at 421 and had already moved to 428—to maintain good acceleration as vehicle size and/or weight increased. And as mgarblik had so well explained, everyone else was doing it, too.

Pontiac’s official explanation can be found in the “engine changes” section of the 1970 Pontiac Engineering Manual. It states:

“This year a new 455 cubic inch displacement V-8 replaces the 428 in all applications. Its larger displacement gives it improved performance. The basic block design is the same as the 428, with the bore centers and water jackets remaining essentially the same. The additional displacement comes from a 0.031-inch bore increase and a 0.210-inch stroke increase. The crankshaft is new for the increased stroke while the heads and camshaft are modified from those on the 428.”

Additionally, I once asked Mac McKellar this very question. Why the jump to 455? His answer then was twofold and I’ll summarize.

1. Pontiac had been increasing engine displacement to improve performance ever since its V-8 was introduced in 1955. During the 1960s, its small-car 326 went to 350, its intermediate-car 389 went to 400, and its full-size-car 421 went to 428 and then to 455 (at least developmentally). Its OHC-6 increased from 230 to 250 as well. Mac said the 455’s longer stroke was an effective way at ensuring that plenty of torque was available to satisfy the average customer’s acceleration expectations, particularly at take-off and in low rpm passing conditions.

2. Pontiac’s closest competitors—Chevrolet, Buick, and Oldsmobile—had each stepped up the displacement of their largest engines at that time, and Pontiac—who celebrated most of the 60s as the nation’s third largest automaker—wasn’t prepared to be left behind, especially when GM opened the 455 to the intermediates (A-body). So Pontiac’s Sales department was also pushing Engineering for a 455.

Ironically, the continuous displacement increases at Pontiac (and really with all GM brands) ended around 1970 when emissions and fuel economy became significant issues, and ultimately led to the stark displacement reductions of the later 1970s.

While the explanations above mirror what many had already stated, it gives insight into Pontiac rationale as a company and from an key insider.

[Douglas Willinger]

During the time of Pontiac's engine development from the aborted LS-1 SD400 (Ram Air IV headed Ram Air V short block) engine development,what was the rationale for the piston valve relief design of the SD455? Was told by a gentleman who sold me an SD455 piston that such was for high compression, yet the SD455 was ow compression. Was it for superior resistance to engine knock, say with an SD400/428 or 455 with high compression, and perhaps some superior octane fuel?

Originally Posted by Rocky Rotella

As many had previous stated or eluded, the 455 was the natural progression of Pontiac’s largest full-size engine—which started at 421 and had already moved to 428—to maintain good acceleration as vehicle size and/or weight increased. And as mgarblik had so well explained, everyone else was doing it, too.

Pontiac’s official explanation can be found in the “engine changes” section of the 1970 Pontiac Engineering Manual. It states:

“This year a new 455 cubic inch displacement V-8 replaces the 428 in all applications. Its larger displacement gives it improved performance. The basic block design is the same as the 428, with the bore centers and water jackets remaining essentially the same. The additional displacement comes from a 0.031-inch bore increase and a 0.210-inch stroke increase. The crankshaft is new for the increased stroke while the heads and camshaft are modified from those on the 428.”

Additionally, I once asked Mac McKellar this very question. Why the jump to 455? His answer then was twofold and I’ll summarize.

1. Pontiac had been increasing engine displacement to improve performance ever since its V-8 was introduced in 1955. During the 1960s, its small-car 326 went to 350, its intermediate-car 389 went to 400, and its full-size-car 421 went to 428 and then to 455 (at least developmentally). Its OHC-6 increased from 230 to 250 as well. Mac said the 455’s longer stroke was an effective way at ensuring that plenty of torque was available to satisfy the average customer’s acceleration expectations, particularly at take-off and in low rpm passing conditions.

2. Pontiac’s closest competitors—Chevrolet, Buick, and Oldsmobile—had each stepped up the displacement of their largest engines at that time, and Pontiac—who celebrated most of the 60s as the nation’s third largest automaker—wasn’t prepared to be left behind, especially when GM opened the 455 to the intermediates (A-body). So Pontiac’s Sales department was also pushing Engineering for a 455.

Ironically, the continuous displacement increases at Pontiac (and really with all GM brands) ended around 1970 when emissions and fuel economy became significant issues, and ultimately led to the stark displacement reductions of the later 1970s.

While the explanations above mirror what many had already stated, it gives insight into Pontiac rationale as a company and from an key insider.

[FrankieT/A]

I had my first Pontiac when I was 16. It was a 1970 Catalina Convertible with a 400 2BBL. I wasn't into "Pontiac" per se, I was happy to drive anything. My first foray was when I bought my current 1978 T/A which I bought new. Point of the story is, I met an old guy ready to retire that was a mechanic in the service dept. If he is still with us he's got to be a 105 by now. Yes, "mechanic" not "technician". Anyway, he said something to me that always stuck.

"Pontiacs are designed for torque, build for it..."

Thanks Jesse where ever you are...