[Mr. P-Body]

455s are more expensive cores due to the misconception that "bigger is better". Not so. ALL the 3.25" main blocks (including 421 and 455 "HO", but not SD) are "weaker" than 389 and 400 blocks (3" main). Yes, that means the cranks aren't quite as strong. To put that "in perspective", remember, BBC and Hemi have a 2 3/4" main. The 3" main Pontiac is not only "bigger" in the mains, but also about 4" shorter. In short, Pontiac CAST cranks are nearly as strong and tough as Chevy and Dodge FORGED cranks. Vinny Meyeda goes 6.80s over 200 with a nodular Pontiac crank and "stock block" 406. That's about 1,800 HP from CAST parts. He shifts around 8,500, too, so get the idea that a Pontiac CAN'T rev out of your mind. Feed it and oil it, and it will rev as well as ANY American V8.

The 389 is the "forgotten *****". The short block is very nearly identical to 400 except the final bore size (4.062" vs. 4.120"). Same crankshaft, etc. Using an Eagle "stroker" crank with "custom" pistons makes a VERY strong 458 CID engine.

There are three basic motor mount "systems" from '59-'79. The "two-bolt" mount (pre-'70) is the most common. All the blocks from '70-mid '75 have five mounting holes, supporting both the two-bolt mount AND the three. Later blocks only support the three-bolt mount, and probably should be avoided. The 557 casting (last 3 digits) is the "weak" one. The 988 is much better ('75-up).

As heavy a car as the '50 is, the larger cubes would be desired. If you "lucked upon" a 421, THAT would have "cool factor" beyond any of the others. They're tough to find, though. A 389 block with the 4.25" stroke, the '67-later heads (have the "good" valve angle, where the earlier stuff is 19 degrees) and a '66 TriPower unit on top (all available "new" now), would be the ultimate Pontiac "street rod" arrangement.

NOTE: The "advantage" of a shallower valve angle is a better "approach" to the cylinder through the intake path, providing a straighter "shot" at the center of the cyinder (intake) and "rolls" the exhaust valve over to make a straighter "shot" at the exhaust port. The practice of "angle milling" small block heads stems from the desire to improve both of these issues. It's not as significant for the small block's exhaust, as that port is excellent. The Pontiac needs all the help it can get on the exhaust side.

TH400 is the minimum level of transmission that will "live" behind a high-torque Pontiac. TH200-4R has been known to "take it" if the internals are upgraded. We've seen a lot of trouble with both TH350 and TH700-R4, simply not up to the task.

You should consider getting Jim Hand's "How to Build Max-performance Pontiac V8s" published by SA Designs. The original work was done in '04. There's a "rewrite" available (not by Jim, himself) but none of the principles were contacted for that. More "tractor motor" crowd stuff, rather than embracing the present (stuck in 1979...). Though a bit dated today, it still has many good pieces of information and history of the Pontiac. The old HO Racing and Pete McCarthy books are okay, but WAY obsolete.

Feel free to add questions here, or if you have trouble finding things, PM me. I'll point you to the right people. Pontiacs show more "cool factor" than most other American cars, and a Pontiac-powered Pontiac street rod is among the COOLEST!

Jim

 

[Mr. P-Body]

I was typing when AP72 posted. A couple things he says need addressing.

Due to the length of the intake track, the shape of the port (a true "venturi") and the "long" connecting rod, the Pontiac makes more torque at a lower RPM than most American V8s. What makes the Pontiac "different" than the Olds and Buick (the only ones that make that level of torque) is the ability of the Pontiac to accept modifications. Not unlike a Chevy, when you add perfornace parts to the Pontiac, it responds well. Think of it sorta like a small block on steriods. But rest assured, ALL engines are different when it comes to the approach to making power. This concept "one is the same as another" is what got Pontiacs the negative reputation in the '60s, when small block guys left in droves as GTO stomped everything on the street. They would try to make power at a high rev and ignore the torque. This led to the feelings that Pontiacs don't "run" and blow up. And it's true. If you approach it like a small block, this IS what happens. Approach it from the correct angle, and you get the engine that powered GTO. And never forget, GTO didn't get a reputation for LOSING... No other muscle car has a mystique around it like GTO. In '64, add slicks and run 12s all day... Smokey said regarding the Pontiac, "Don't rev it up, GEAR it up..." Today, we do both...

The Pontiac oiling system is excellent, just misunderstood. The only change we make is to restrict the oil (at the lifter bore) when using a solid lifter. Like the Chevys, this prevents "filling" the valve covers and starving the mains. The 60 lb. oil pump is the true "high volume" pump, regardless of what is said in various catelogs. The 80 lb. pump is the "high pressure" version. I PROMISE you, Melling knows more about oil pumps than Summit.

Demon carbs should be avoided. The company no longer exists. It was never anything more than a genuine immitation Holley anyway. Rochester Q-Jet is among the better carbs for the Pontiac (single 4-bbl), and of course, 2GCs on the TriPower. Once the "need" for more than 800 CFM arrises, we use AED Holleys.

Don't mean to step on everything he said, but he's propegating erroneous mythology. Having built literally hundreds of Pontiacs AND Chevys (including record holders and track champs), I am in a good position to know of which I speak.

PAX

Jim

 

[Mr. P-Body]

I have addressed ap72's "issue" with me on a personal basis. Perhaps someone here (with more local "credibility", as I guess being a professional engine builder isn't enough) can explain the dynamics of runner length, cross section and velocity to him, so he understands they are NOT "all the same". And, at least for a street engine, torque is hardly meaningless. In fact, it's EVERYTHING. Torque is "the ability to do work", involving the "twisting force". Horsepower is a measure of power spread over a given distance and in a certain time frame. Torque is what "moves" cars.

Barry Grant ("designer" of Demon) died last year and his company went under. I was unaware there was another using the name and marketing the carb. Doesn't matter, still a genuine immitation...

I apologize for any "ruffled" feathers, but the man came here looking for accurate information. Attempting to discredit that because it doesn't "match" one's personal opinion (based on myth and ancient information) serves only to confuse the OP. I "shipped" three Pontiacs last month, including one 700 HP pump gas streeter. A couple small blocks and an Olds snuck out at the same time... -

If something is merely my opinion, it WILL be stated as such. If it's not "qualified" as an opinion, you can take it to the bank.

Jim

 

[Mr. P-Body]

We can put the crank "strength" issue behind us, as we all appear to concur.

The block is not the issue regarding compressioin ratios. All Pontiac heads "fit" all Pontiac blocks, at least in the eras we're discussing. The chamber volume of the head, coupled with the "dish" volume in the piston, are what control compression based on displacement. By using a combination of chamber volume and dish volume, it's plenty easy to get exactly the static ratio you're after.

The "best" d-port heads (shape of the middle exhaust ports) are the late '60s and '70 400 heads. No need for "exotic" parts. Forged rods are readily available at a reasonable price. Eagle cast cranks are right at $300, certainly not a "budget breaker". IMO, the idea of the 421 is absolutely the coolest, though the blocks are a bit problematic, depending on the year of production. '65 and '66 blocks present zero "fitment" issues. There is no difference between an "auto trans" and manual trans block. Every Pontiac I've ever seen has the provision for the clutch "ball". A VERY few cranks "got out" without the relief for the pilot BEARING (Pontiacs don't use a bushing, use BCA #7109). All the aftermarket cranks have the relief. Earlier blocks ('64-back) use 7/16" bolts to hold the bellhousing (ala Ford, except '64 GTO), but the bolt pattern is the same. Starters attach to the block on '64 GTO and '65-later blocks. Starter mounts to the bellhousing on the others, but FabCraft has the necessary adapter to install the TH400 (or other later trans) and still use the starter.

The ONLY engines I know of that offer a greater range of interchangeability across eras are SBC and SBF. And it's very little at that.

FWIW

Jim

 

[Mr. P-Body]

The 72 CC iron heads (d-port) are readily available and make good power (62s are a '69 casting along with 48, 16s are the common '68, 12s and 13s for '70. 12 seems to have a superior exhaust port, but aside from that, once porting begins, they're "all the same". We've done a number of both 400s and 461s ("strokers") using them with excellent results. The "key" is to "dish" the piston correctly. The quench in the Pontiac is really significant IF you're "pressing the edge" of compression. Otherwise, it's not as big a "deal" as in some others. That is, a "simple dish" (a circle) is completely acceptable at 9.2:1, but not at 9.5:1. Pontiacs "enjoy" a unique chamber. It's more "efficient" than most other "wedge" types, mostly by virtue of being 100% machined. While "efficient" SOUNDS good, it makes them prone to detonation if all factors aren't exactly right. This is why we recommend avoiding the "edge". The difference in power is less than 1%, so why subject the engine to potential damage and make it an "adventure" to tune? In racing classes where engine modifications are strictly monitored, it's a different issue, where squeezing every last inch-ounce is necessary to remain competitive.

The 400 has an advantage over 461 if higher revs and high-end HP are the goals. For a general rule for a street engine, "no replacement for displacement". The low-end power generated by the strokers is among the best of any engine family "out there". Base your decision on which 'type' of engine you want. The 400 will have a higher "fun factor", but a shorter life. The stroker will ROAST the tires "on command" and will live longer. A 4" stroke (ala 421, 428) offers "the best of both worlds", where it can safely rev, AND it generates significantly more low-end torque than 400. A 6.8" rod and a 4" stroke yields a "perfect" 1.7:1 rod/stroke ratio (same as Chevy 327). Our blown/alcohol 475 (4.350 x 4) shifted at 9,200. Yes, a real Pontiac... -

Jim

 

[Mr. P-Body]

Let's "level-set" here. A 400 means it has the 3 3/4" stroke. The 3" main block is more desired because it's physically stronger. Though the aftermarket cranks are a little longer stroke than a "standard" 455, they're functionally the same thing. A "stroked" 400 (refered to as "461" in the Pontiac community) will act just like a 455 only tougher. Considering the price of a 455 core, and grinding the crank, you're better off (money-wise) to get a 400 block and a $300 Eagle cast crank (equal or better than the Pontiac nodular crank). The quality is excellent.

The crankshaft in the 428 is what you want. The 4" stroke, it's either a good nodular casting or "ArmaSteel", also a good casting. The mains get ground to 3" and the rods to 2.2", so if it's been ground before, it's no big deal. Ken's Speed and Machine in Brooksville, FL sells the correct thrust bearing "kit" that shims the large journal crank into the small journal block (100% reliable). Icon has the correct piston listed as "440 Pontiac", using the 6.8" rod. EXCELLENT combination. The 428 block is a paper weight if .060" over. Don't want it anyway, as it has the 3. 1/4" main.

Jim

 

[Mr. P-Body]

Put that WT block on the auction block. GTO guys will PAY for them. Use a portion of the proceeds to get a 400 (017 or 988 casting) block. These are the strongest production blocks after '59. The pistons available for the 4.250 stroke "key" on the standard 400 bore (4.120). A 389 block is "used up"
by then.

Your 16s, if properly done, are very good. A "dished" piston is required to add chamber volume. We've learned, a dish and a small chamber can make more power than a deep chamber and a flat-top. I suspect it's due to the "longer" short-turn in the shallow heads. I KNOW the 72 CC E-heads flow a little better due to that.

Icon now offers a stepped-dish piston that provides 9.5:1 with 72 CCs. It uses the Eagle 6.635" "BBC" rod. They (Icon) also have one for the 6.8" rod, but the dish must be enlarged (it's for the aluminum heads).

FWIW

Jim