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post #1 of 7 (permalink) Old 12-03-2018, 07:03 PM Thread Starter
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Help with components for 461

Reaching out to Bear and others. Bear I read old post when you installed -30 cc to get compression then went to Alum after. I want to do this once. I have a good running 400 that now has blow-by. It has flat tops with 72 cc heads (68 #16 ’s) crower 60243 1.5 rockers, manual trans and 3.55 posi. 3450 lb 64 lemans. Just going to start tear down but believe heads are good ( recent rebuild with new valves and harden seats) Is there any combo out there that works with new stroker rotating Assemby and iron heads? Want to get to under 9.5:1
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post #2 of 7 (permalink) Old 12-04-2018, 10:39 AM
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With some of the Butler rotating assemblies, you can get the pistons made for ANY CR you want. If some of their standard pistons won't work, they'll order custom Ross brand pistons, to make your rotating assembly meet the specs you want. I'm sure that if you tell them the exact combustion chamber of the iron heads you have, they can calculate exactly what pistons you need, in order to achieve the CR you want. And, since they'll be making a profit off the deal, I'm sure they'll be glad to discuss it with you. Just assuming that the Butlers have sold more Pontiac stroker rotating assemblies than anybody else.

I personally like the idea of using Auto Tec pistons, which are made of the 4032 material, which expands less, requiring less piston to cyl wall clearance. The Ross pistons, and most high end forged pistons are made of the 2618 material, which is used for racing pistons. But, if you go with Auto Tec pistons, you'll most likely have to order 'em yourself, along with all the other rotating assembly parts. Butler has a deal with Ross. So, I would assume that they would not consider ordering Auto Tec pistons for you. But, I certainly don't know that for sure.

I think Paul Knippen has mentioned that he can order Auto Tec pistons. So, he might make up a rotating assembly for you. Not sure if any of the other big name Pontiac engine builders will do this, or not. Most shops seem to make deals with certain companies & try to deal with those companies exclusively.

If you live close to a good Pontiac engine builder, who doesn't own a big time shop, he might be able to order the correct parts for a good assembly. They will know of a machine shop that can balance the assembly. If you live in the NY area, Richie Hoffman is a well respected Pontiac engine builder & racer. I'm assuming that most of the smaller, more independent builders, will have the freedom to order whatever brand parts a customer might want.

Paul Carter has mentioned, on the PY site, that he is not taking on any more engine builds right now. But, he can probably make up a balanced rotating assembly for you, with the parts you want. He works at Koerner Racing Engines, in AZ.

Last edited by bigD; 12-04-2018 at 11:28 AM.
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post #3 of 7 (permalink) Old 12-04-2018, 04:26 PM
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Ok, first things first. If you're going to run those #16 heads, then please do either cc them yourself or have it done. Pontiac heads have been known to vary some from the factory specs, and unless you're the original owner of the engine and are in a position to be positive about their history, they may have been cut some in the past, reducing their chamber volumes somewhat. Even 3-5 cc's can make a significant difference in your resultant compression ratio. You've got to know where you are now in order to know how to get where you want to go.

The usual way of getting to 461 inches is to have a 400 block bored +0.035 over (4.155) and run a 4.250" stroke crank. You'll want to know what your actual bore size is right now and what it's going to take to get there. If it's already been bored +0.040 or more in the past for example, you'll want to know that before you start ordering parts.

Another decision to make: Are you going to zero deck the block? Pontiacs "usually" have the pistons about 0.015 down in the bores when they're at TDC. Here's where things can get tricky. The most accurate way to measure is to use the rods and pistons you'll be running in the build, but if you can't order pistons until you know how much dish volume you need, that kinda puts you into a Catch22. If you're really walking the fine line on compression, zero decking the block and "losing" that tiny bit of volume can be enough to put it over the edge and into detonation land. However there are some real advantages to zero decking. It promotes turbulence in the chambers and that promotes even combustion and helps avoid hot spots - both of which are good for avoiding detonation and making power. FWIW, I didn't zero deck mine "either time", although on this build I could have and been would have been ok.

Once you know what your chamber volumes, deck clearance, and your finished bore size will be, then you can figure out how much piston dish volume you're going to need to put compression wherever you want it. Make sure that you get D-shaped dishes and don't run 'thick' head gaskets unless you have no other options. Round dishes and/or fat gaskets both do the opposite of what zero decking does. They decrease turbulence and promote hot spots - neither of which you want.

You'll also want to decide what you want to run for rod length: the standard Pontiac 6.625 or the longer 6.800 "BBC" style. There are advantages to both. In 'the old days' the popular train of thought was to run the longer rods because that gets you a more favorable rod length to stroke ratio that was thought to put less stress on parts. Recently I've heard that idea called into question though, and I haven't decided what my personal opinion is yet. (I'm running the longer 6.800 rods in mine). Depending on which pistons you get, the possible disadvantage of the longer rods is that they can require the pin location to be such that the bottom oil ring encroaches on the pin bore, requiring an additional spacer in the bottom ring groove to deal with that. That was the case with the first set of pistons I ran, but my most recent build that's using Ross pistons from Butler doesn't have that issue.

Now, just playing around and assuming that your heads really do measure out at 72 cc's, your deck clearance is the "Pontiac usual" 0.015, and your finished bore size will be 4.155 (head gasket bore size 4.300 and compressed thickness of .045), 25cc's of piston dish will put it at 9.511:1 with a quench distance of .060 (0.045 gasket + 0.015 deck). That should be safe for 93 octane as long as your fuel mixtures are right and it doesn't go lean, and your cooling system is good.

"Safe" compression if you've done any reading at all is one of those topics that tends to polarize people into having very strong opinions. Some believe that you can get away with "more" by running a late intake closing event cam to reduce dynamic cylinder pressure, some disagree. My personal opinion is that it doesn't matter unless you're building a race engine and trying to milk every last ounce of power out of it. I've run quite a few 461 engine simulations using my copy of Engine Analyzer Plus from Performance Trends, and the net difference all other things being equal between 9.5:1 and 10.0:1 on a Pontiac 461 is about 8 peak HP and 9 lb ft of peak torque - on a build simulations that are already close to 550 HP. My opinion is that's not much to write home about, so there's not really a reason to push the envelope on compression. That much difference will only show on a time slip on an otherwise perfect run - you'll never feel that difference in the "pants-o-meter".

Hopefully this will be enough to get you thinking?


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post #4 of 7 (permalink) Old 12-04-2018, 05:48 PM
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Besides getting the dish you need, another advantage of buying custom pistons is that you can get enuff extra pin height(compression distance) to achieve zero deck height, or very near it, WITHOUT cutting extra material off the block decks.

But, as Bear mentioned, you'll have to know all the exact measurements needed. And, just as the heads may have been cut down at some point, so too the block may have been cut down, in a previous build.

I assume you'd need to know the exact distance from the center of the main journals, to the deck, after final deck square-up machining has been done. Then you would subtract your rod length & 1/2 your stroke from that distance, to arrive at the pin height needed to achieve zero deck height. If I'm wrong, somebody please correct it.

If you can get it to even .005 deck height, and use the .039 thick 1016 Fel-Pro head gaskets, that would be a .044 quench distance, which would be great.

Last edited by bigD; 12-04-2018 at 08:39 PM.
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post #5 of 7 (permalink) Old 12-04-2018, 08:53 PM
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Originally Posted by 64Lemans1 View Post
Is there any combo out there that works with new stroker rotating Assemby and iron heads? Want to get to under 9.5:1
Yep. Use the 461 kit for the 400

Get some 4X heads from a 73-74 455. (114 CC chambers and hard seats for unleaded)

CC them to be sure of chamber size. Check them before you buy.

Mill them down to around 108 CC ( .030 if they are 114 CCs)

Zero deck the block (.005 is Ideal)

Flat top pistons with 6 cc reliefs

5140 rods

Forged slugs

M54D oil pump standard volume/pressure

Cam should be in the 218 I /226 E maybe even 224 I / 232 E with an LSA in the 112-114 range for decent idle and wide power band. Use good valve springs that match the cam. Better figure on installing screw in rocker studs (BBC) to
ensure the studs dont pull out of the heads (as bottleneck studs probably will at .480 lift and heavy valve springs)

Dont go nuts with cam duration or lift. Keep the lift under .480 Poncho heads wont allow for much more after about .480 without cutting guides/getting longer valves . Pontiac heads dont improve flow wise after around .450 lift anyhow.At least according to Stan Weiss flow charts , and what a few reputable pontiac builders have told me.

This combo should get you a 9.4 to one stump puller that you can run a stock converter
Naturally you will need to curve the distributor a bit different than stock
Tweeking a carb will no doubt be needed as well

I am sure there will be a few who have a different opinion on my "recipie' biut thats to be expected

I just answered the question you asked based on my own experience
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post #6 of 7 (permalink) Old 12-04-2018, 09:06 PM
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Oh, I really like what Bear Posted btw. He went into great detail and all he posted absolutley needs to be considered in your build to get it to come out right .

My guess is he has built a few Poncho motors .
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post #7 of 7 (permalink) Old 12-04-2018, 10:52 PM
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Here is my opinion.

You are most likely going to find that the #16 heads have around a 75cc chamber if not milled.

Pistons are generally .015-.020" down in the bore.

Felpro head gaskets are 4.3" in diameter and come in .041" or .039" thickness when compressed.

Using these numbers in the Wallace Compression Calculator Compression Ratio Calculator - Wallace Racing you can get an idea of what the cc's will be needed for your valve reliefs so that you can get a compression ratio around 9.0. Going 9.5 could be a little on the high side for iron heads (but doable with the right cam/timing) but most likely need 93 octane. If you shoot for 9.0, better chance of getting 91 octane at most gas stations wherever you go. So you could go 9.0 and probably up to 9.3. You can also go under 9.0 and still be good with the right cam choice.

Now compression is assuming you are not at any great altitude like Denver. If you are at higher altitude, then you want to raise compression. So assume you are at a "normal" altitude like the rest of us.

Plugging in the numbers into the Calculator, I used 400 .030" over, 4.25" stroke, 75cc heads, deck height .020", gasket dia 4.3" w/.039" crush.

With a 30CC dish, compression is 8.94 Pretty close to what you want. Get your head chamber down to 72 cc's, and your compression is 9.14 - Perfect.

With a piston down in the hole .020" PLUS a head gasket crush of .039", you get a quench/squish clearance of .059". Not ideal, but OK as this is factory. A better number would be closer to .045" with forged piston.

So option #2 . Heads are 75cc's and you go with .027" Cometic head gaskets. Your compression becomes 9.13 BUT your quench/squish area is now .047". Now you have both numbers pretty much ideal.

With this, you DO NOT have to deck the block unless it was needed to square the block up or if the deck surface showed any signs of warping. If the deck surface is cut, this would then change all figures above and you would then have to recalculate for compression.

Some do like to "zero deck" the block which means milling the block down so the piston top is even with the block surface and not below the surface the .015-.020" it is from the factory. If this operation is done, you want to consider the quench/squish distance. Zero deck and a .039" head gasket might have the top of the piston much to close to the head, especially when things expand when hot. The .041" might also be to close for piston/head, but could work if all things were perfect. The .045" is a better clearance between the piston/head. So to use either of these Felpro gaskets, you would not want to "zero deck" the block, but rather, have the piston set below the deck .005", so the Felpro .041" gasket plus .005" deck height = .046" of quench/squish clearance.

Bottom line? You will need to know and calculate your head chamber cc's, piston bore, how far down in the hole your piston will be, head gasket thickness, and then select the closet cc dished piston to get you to the compression you are looking for.
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