[leroycash]

Don't know where to start with all this so I'll just start. I've got a 1950 Streamliner in desperate need of some more cubes. I'm looking for a solid Pontiac block to get started and am realizing the 455 I thought I'd use is becoming hard to find. They're out there, just pricey. I'm not in a huge hurry so I can spend a little time to find the right block but was wondering why so few 389's are used for mild performance builds. There seem to be a lot of them. There are a lot of 400's as well and that might be where I go. Still I'm wondering, is a good 389 a bad place to start?

 

[leroycash]

Hey thanks for the cube to hp rule. That's super encouraging considering the flathead 6 I'm replacing. 389 hp would be a great place to end up. One thing I'm starting to realize is the older Pontiac V8s had higher compression ratios and ran on higher octane leaded fuel. I wonder what limitations I would have with the head selection? Seems like a 9.5:1 is where I want to be from what I'm reading. Do you know if the heads are interchangeable up through the late 70s?

 

[leroycash]

I'm beginning to develop an interest in the Pontiac......
14 degree valve angle compared to the SBC 23 degree angle....
A 389 is bigger than a 383.....:thumbup:

Seems like I read about this somewhere. I have to admit the physics goes over my head pretty quickly. How is this an advantage? I recall the angle of the exhaust valve effects the quality, or pattern of the detonation in the cylinder chamber but I don't remember exactly how. You've made me curious to go back and find it. Thanks. I wonder if the valve angle feature goes back to the early 389 heads.

 

[leroycash]

Thanks, any block codes I should look for? Did you run with a 4-speed or automatic? BTW those tri-powered Pontiacs sound and look incredible.

 

[leroycash]

You will be fabricating motor and trans mounts to get the later model V8 in the car so I would suggest picking up a "mock-up" block. 326 to 455 Pontiac blocks are all the same size so, no matter what you end up building (400 block with a turned down 455 crank would be good), you will be able to bolt it in.
The more cubes you use the milder the build can be to get the same amount of power. Torque gets the car moving off the line and that is what Pontiacs make.
Mark

Yeah, I'm more at home fabricating mounts and brackets and setting up chassis than cobbling together an engine, but I'm ready to take the next step. Thanks for the reminder about the mounts, which are a little bit block-dependent, right? A 50 pontiac has plenty of room up front but the usual problems with interference between mounts, steering components and exhaust will be a challenge. Getting a dummy block makes a lot of sense. I checked around today but haven't come up with anything yet. I'll keep looking. BTW, it sounds like you're advocating for more cubes to keep the build simple, no?

 

[leroycash]

. The next part is the heads, of course some are better than others but you're often stuck with what you have, especially with a relatively rare engine like a Pontaic. The good news is that for a modest 1hp/ci goal almost any of the heads will work- but you need to have a valve job done and I would get them ported too.

Now this is where it gets interesting. I've been looking at various blocks available to me right now. There are two 421's. Man, that would be a rare build. A bunch of 389's, and I even have a guy here in H-town with a 428. These are the exotic choices. Given I'm still learning a few things (okay a lot of things) about building a motor from scratch the thought of getting hung up trying to find a rare part to finish the build scares me. I'm not sure any head will do. So I started putting together some more conventional block and head configurations using available 400 blocks and calculating what would get me my 9.5:1 compression. Most every block needs an over bore of .020 to .040. Adding deck height changes and various head gasket thicknesses I'm getting 8.1:1 and 8.15:1 with 70's era blocks and 10.02:1 and 10.1:1 with 60's era blocks all due to different head chamber displacements. So, my question now is how much flexibility do you have mixing and matching Pontiac heads and blocks from different era's? Getting to 9.5:1 might take some creative combinations.

 

[leroycash]

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.]

Q: 458 cu.in. Is this what you get with an over bore on a 389 and dropping in a 455 crank with machined journals? I'm gonna have to get my calculator back out.

[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).]

Super helpful information. Now I need the actual block.

[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.]

Oh man, it really would.

[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.]

That helps, I think this helps me narrow my search for the block to head combination as this angle is not common to all years. Thanks.

[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.]

I'm still trying to get a handle on the manual vs automatic to block thing. The block I choose will dictate the type of transmission - to a point. Some blocks are for manual transmissions and others are for automatic, right? At any rate its good to know what to look out for should I go with an automatic.

[You should consider getting Jim Hand's "How to Build Max-performance Pontiac V8s" published by SA Designs.]
Jim

Will do. Thanks again.

 

[leroycash]

Sorry Jim, I should have hit the multi-quote button. I've inserted my comments inside your original quote.

 

[leroycash]

Option #2. Step down to a 389/400 engine if a good 455 cannot be located but be advised, it is difficult to use production Pontiac heads on 389/400 engines. The 1967-1979 Pontiac heads that are available will either have too high compression for pump gas or too low compression ratio for good power. The best option with a 389/400 engine is to use 1967-1979 heads with factory screw-in rocker studs with hypereutectic dished pistons.

I have not given up on a 455 yet, but I'm less optimistic. Option #2 lays it out pretty well. Thanks. So you can use later year heads (67-79) on a 389 to keep the compression down. Are there any fitment issues with mixing and matching like this? Can I mix the years for cranks too? This could make parts sourcing easier.

 

[leroycash]

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".
FWIW
Jim

Thanks for you useful comments. I looked up the Eagle forged cranks today after reading your post. Then I ran a few numbers to see if changing the stroke would get me to my desired compression numbers comparing a 389 to a 400 block. Here's what I learned, I think. Sorry if I'm getting too far into the weeds here:
With a 389 block and a 0.030" over bore, if I increase the stroke by 0.060" using an Eagle 4.35" crank and 6.800" rods, and if I bolt on 6X heads (1977) I found with 93.74cc chambers on top of Mr. Gasket head gaskets at 0.038", I get a total engine displacement of 457.84 or 458 and a compression ratio of 9.3:1. Pretty close to my goal
With a 400 block and a 0.030" over bore, if I increase the stroke by 0.050" using an Eagle 4.25: crank and 6.700" rods, and if I bolt on the same 6X heads and everything else, I get a total engine displacement of 460 and a similar compression ratio of 9.32:1. Also pretty close to my goal.
So there are options out there but I had never considered altering the stroke. What problems am I wandering into? This seems too easy.

 

[leroycash]

? A 389 has a stroke of 3.75". A 455 is 4.21".

Did you mean a 4.25" stroke crank? Plugging a 4.35" crank into a 389 bored to 4.12 will give you a 464 cid. The SCR using your numbers is about 9.8:1

A 400 stroke is 3.75" like the 389. Adding 0.050" to that nets you a stroke of 3.8". The 3.8 stroke and a +0.030 over 400 will be a 411 cid. A 4.25" crank is 0.040" more stroke than a 455.

Using a 4.25" crank in the 0.030" 400 nets you 460 cid. SCR is about 9.73:1.

NOTE: CR is calculated w/a quench of 0.040" and a flat top piston having a 'generic' valve relief volume of 5cc.

I'm ignoring piston compression height/rod lengths for the time being.

Okay I'm really flubbing these numbers somehow. Thanks for the corrections. I'm using the compression calculator on Classical Pontiac. Maybe there's a better guide somewhere else? I guess I'm having a hard time getting my two block choices to 9 or 9.5:1. I was looking at changing the stroke to get there. The better heads with the improved valve angles have pretty large chambers and drop the compression way low - I think. BTW on my 400 block calc I entered a typo. The stroke increase was supposed to be 0.500" not 0.050". Still it seems I'm doing something wrong. I'm pretty sure I will have to bore either block 0.030 +/- given what's out there. My plan currently is to find a 389 or 400 block, bore it 0.030" (or whatever's necessary), bolt on some 6X, 6S or similar chamber size heads, check the valve clearance and select a good piston and rod combo, then think about the top end of the heads next. I think you said the flat top pistons have a recess for the valves adding 5cc's? So if I go back to the 400 block, bore 0.030" over to 4.15", use stock crank stroke at 3.75", bolt on a 6X heads at 93.74cc, assume a 5cc piston dish and a 0.038" gasket thickness I'm getting a 406 ci displacement at 8.45:1. Admittedly, I'm not entirely clear on the "quench" factor. Maybe that's where it's going wrong. That being said if I change the stroke on the above numbers to a 4.25" crank I'm getting 9.44:1 using the Classical Pontiac formula. I like that number but you're saying it's flawed, and I believe you. How can I fix this? Maybe I need to go back and look at the deck height, then figure out this quench thing. Can you splain that one more time?
You're comments have been super helpful, thanks.

 

[leroycash]

The 400 w/o stroking still makes a fine engine, as does a stock stroke 455, especially for a heavy street vehicle. Nothing wrong w/a 389, especially considering you'd be making custom motor mounts anyway.

If I stuck with a stock configuration for either of these blocks what SCR would you recommend?

 

[leroycash]

Whatever block you decide on, just be sure it has the provision for a block mounted starter. About '63 back had bellhousing mounted starters, this can make things a lot more complicated.

Good to know, thanks.

 

[leroycash]

9:1 is uber safe. No more than 9.5:1 w/an iron Pontiac head regardless of the year or casting number, when used w/a streetable camshaft. Higher SCRs requires more and more cam to offset, and the engine becomes less streetable and/or more dependent on octane.

When you get a chance read the Quench article from the Crankshaft Coalition wiki- it explains things better than I can here.

SCR:
• Static compression ratio calculator, this is the one I use, there are others. Get used to using just one- for example some calculators use a negative number for a piston dish, others use a positive number (catalog info for pistons also use both ways of expressing dish/dome volumes, so be sure you're understanding what they're trying to say).

Thanks a lot. Now I'm understanding it a little better. 9:1 is my min and 9.5:1 is my max. I read about "quench" factor on your wiki. Got it, thanks. I'm cross referencing my calculations now on three different websites and getting consistent numbers even though some want the piston volume in negative numbers - go figure. Assuming a 400 block (now leaning that way) there are several ways to get to my SCR. I'm guessing the paths are not all easy. The biggest variables are head selection, stroke and piston dome volume. On the last one I've been looking at flat top and d-cup's with 6cc and 17cc respectively. The 455 crank (0.500" added to 3.75" stock stroke to a 4.25" stroke) seems to get me to the sweet spot none of the stock iron heads
offer given chamber sizes jump from 72cc's (#670, #62, #12's for example) to 93.74cc's or higher (6X-4 and 6S). Without stroking the crank the highest I get is 8.8-ish:1 using the 72cc heads and a 17cc d-cup piston. This all assumes a 0.038" gasket, 0.040" quench and 0.030" cylinder over bore. Stroking the crank to 4.25", using a 93.74cc head and a 6cc piston dome volume gets me 9.04:1 SCR. I don't know how to get higher to 9.5:1 without milling the heads which seems like a lot for me to master at this point. Maybe I'm wrong. So if my only choices are to increase the stroke to 4.25" or mill the heads which way do you recommend? Seems like I'm getting close!

 

[leroycash]

I used a pair of 7H1 heads from a 350 f bird motor.Had them milled .045 . I eneded up at 80 CC s. I ported them mildly, removed the eyebrow in the exhaust side of the chamber to enhance cylinder blow down. Seems to have worked. My heads are 80 CC. I ended up at 9.39 to 1 static.
The only issue was when I went to bolt the valley pan on , the real estate was kinda thin between the port bottoms and the valley tin edge.

Hey, thanks for the insight. I was looking at the stroker kits too. Pricey huh? Cheaper than aluminum heads I guess. The stroked crank is still on the table but $ is always an issue.
I also went back and looked at smaller chamber heads again like 72cc heads from 68-70 years. I think the #62 in 1968, if I'm remembering right, had a chamber in the low 70's. It also has the bigger valves at the preferred angle. Using a Sealed Power piston at 6.7cc's and a thicker SCE copper gasket at 0.050" the SCR gets right at 9.44:1 where I'm trying to be. Of course the fitment issues with the intake and the valley pan would be like yours but in the other direction since I'm lifting the heads by 0.050" to compensate for the smaller chamber. Anyone out there had luck using thicker gaskets to get a desired SCR?

 

[leroycash]

Never mind. Thicker gaskets just expand the quench space beyond the desired 0.035" - 0.045" dimension. Would have been too easy.

 

[leroycash]

Good catch!

There are a few heads w/"ideal" specs for chamber volume, valve size, screw in studs, valve angle, etc. but expect to pay a premium for them when and if you find a set in good condition.

Personally I'd rather have a set of aftermarket heads than a stroker bottom end. Aluminum heads w/a set of aftermarket forged rods and a stock crank trumps iron D-ports and a stroker bottom end, IMHO.

Thanks, got ahead of myself there.

What is it about aftermarket heads that makes you say this? The prices I'm seeing are pretty high. I like the assurance of a new un-used unit for sure. The chamber sizes are nice and the machining seems super precise. Is it the improved airflow? I know we've come a long way over the last 35 years! Wondering if it makes sense for my street application.

Thanks again for your comments.

 

[leroycash]

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

Thanks for the comparison. Am I getting you right, you're comparison is between two 400 builds. One with a smaller displacement (stock stroke) where the power is at a higher RPM, and the other is a 400 stroked to a higher displacement (say 4.25") where the power resides at lower RPMs? Is the lower RPM scenario more reliable due to lower revs? I guess that makes sense. And the 421/428 reference as being ideal is due to the fact that it has a "mildly" stroked displacement at 4.00" even. BTW I have access to a 428 short block for a good price. The problem is its been bored 0.060 over. That seems risky to me. How much bore is too much I wonder? Also, when you mention your blown 475 are you saying the bore is 4.35" and the stroke is 4"? If so, what block are you working with? Sounds like a 421/428 configuration. If so maybe a 0.060 over bore isn't so risky. Man, a 428 would be outside the box.
Thanks again for your comments.

 

[leroycash]

Whether the added airflow (and yes- airflow is the root of why aftermarket heads are good) that can allow more power while using 'less' cam than might be otherwise needed if using iron D-ports would benefit you more than added displacement (displacement favors torque production all else being equal), is something we all have to weigh one against the other.

Good stuff. I think I'm following you with respect to the argument you get plenty of displacement (more than I will probably need on the street) with a stock 400 without stroking to a higher displacement. And that dollar for dollar a good set of aftermarket heads - producing greater airflow - along with the correct cam translates to more (read, efficient) HP. Is this regardless of displacement? Or would you cam the larger (stroked) displacement differently regardless of whether you use aftermarket heads or cast D-ports? And, just so I know, where can I go to get the basics on cam selection. I don't know how to evaluate/talk about cams yet.

Thanks again.

 

[leroycash]

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

Okay, that was crystal-clear. Thanks. I understand the 461 pretty well and see several places that help with parts for this setup. The 428 crank option is interesting too. Seems like a good compromise, as you mentioned from an earlier post. Good displacement and revs. I spoke with the guy who has the 428 short block and he'll sell the crank for $125. I'm planning to look at it next week. I'm hunting down the Icon piston right now and will run some numbers to see what SCR it affords. I'm getting 9.15:1 with a 6cc KB piston and a 6X-4 head. None of the aftermarket heads hit the chamber displacement I need for this scenario. Still looking there too. So milling the 428 mains to 3" is no big deal given the quality of those original castings. I remember reading those castings were superior. This setup gets me to 433 cu.in.. I'm guessing this is known as a 440?!? One final question, if I can get my hands on a good 428 block is there some other concern you would have going with this vintage, and very cool setup? In the end performance and reliability trump cool.
Great reading your stuff.