400 or 455 or in-between?

[eodprice]

So i have been milling over this problem for months now. Heres my situation, I have a running 400 of unknown condition in my goat as of now. i have a butler built 455 block and rotating assembly with new Probe forged pistons .30 over, butler built heads, and other odds and ends parts. My problem is, my 455 block is already .30 over and i need to go bigger. The machine shop (best in san diego area) says the wall thickness may be to thin at that point. I know what your thinking, Get a new block. Well a virgin block owned by someone who will ship is hard to find. so heres my question. Can i pull my 400 bore it to the pistons i have, turn my crank to 3.00 and basically make a stroked 400? Or someone one here with a lot more experience then me have any ideas?

[Ron Sutton]

It's been awhile, but I was a Pontiac lover as a young guy. Your 455 +.030" pistons are for a 4.180" bore. The 400 is a 4.120" bore standard, so we're looking at going .060" over. The later 70's 400 blocks are too thin wall to go .060" over & not have problems. The older 400 blocks were thicker wall and many would handle the .060" overbore ok if they didn't have too much core shift. You need to sonic test them.

I would suggest you have your 400 block sonic tested and you'll have your answer if it will work or not. Otherwise you're back to looking for a block.

If you do make this transition, after you have the crank main journals turned down to 3.0" from 3.25", I also suggest that you have the crank heat treated and/or the journals chrome plated to regain the bearing journal surface hardness.

[eodprice]

Ron,

Thats probably what ill end up doing... buying a new 455 block. I just need to find someone who will work with me and ship it. Im on deployment so its hard to track one down. Really want to get home and take leave and take some leave and Finnish this in time for summer/ fall.

[Ron Sutton]

Here is a used 428 block. This has the same 3.25" main journals, but a 4.120" bore. These were usually very thick wall & capable of going to 4.180" with no problems. Of course without checking it for cracks, you don't know what you're getting.

http://www.racingjunk.com/Blocks/182083420/Pontiac-428-Block.html

[astroracer]

Sell the 455 and build the 400 into a 455+. Look here:
http://www.krepower.com/Pontiac%20Street%20Engines.htm

[moparcolt]

I have a 1972 400 that is .070 over with no problems at all. I dont think a 455 is going to be a problem at .060 over but you could go .040 over maybe. They sell .040 455 pistons, depends on the condition of the bores.

My 400 has 455 pistons that are either .030 or .040 cant rememberbut it had to be bored .070 over.

I have a friend that has a .090 over pontiac but cant remember which block he is using.

The 400 has smaller main journals which in turn causes them to have fewer oiling issues. The 455 has such large journals on the mains that they have high rpm oiling issues.

That is the better combination, 400 block with 455 crank.

[eodprice]

Sorry for my reply being so late guys, Im currently in afganistain and the internet is hit or miss. Reading all this and weighting the pros and cons of both i think i will press on trying to find a 455 STD block that i can use the balanced rotating assembly that i have at this time. If that does not pan out, my next course of action will be to sonic the 455 core i have now and see if i can go larger, sell the new .30 over pistons and go with ross pistons from Butler. Now, if that block truly is a "boat anchor", I guess ill put my time into the 400 block. You all have great points about this option. The main being the reduction of oil starvation to the mains at higher RPMs. Second being the bore and stroke will be very close. the only cons that i can see to this, making it choice three, is the cost and not knowing what condition the 400 block is in. I have done a compression check and leak down about 8 months ago and as i recall all where within 10 percent with no loss of pressure over a 5 min time period. This makes me feel a bit more comfortable about "Option three". In all, thanks for giving me some options and i guess ill just buy all the interchangeable "pretty" parts while I'm here away from my baby.

[Tom Welch]

I have a 428 short block that needs a rebuild, I had it in a 78 T/A several years ago, I will sell it cheap since I know it needs a rebuild, the block is solid. I f you think this will help send me a pm and I will give you all the details.

[72blackbird]

Not all 455 blocks are created equal- if you have a 75 -76 no. 500813 455 it may no doubt be too thin to take to .040" over. These were lightweight thinwall castings so it may be done- as Ron suggested have the 455 sonic tested to see if can be bored out further. Probe also makes 455 .020" over pistons- I used these in my 455 since I started with a Standard block. I know that doesn't really help you with the parts you have, but if you find a .040" over 400 it gives you another option.

As to the oiling issues the larger journal Pontiacs may have, I've found that having the block align honed, along with careful blueprinting of the oil clearances and chamfering the oil passages on the crank will assure consistent oiling and a happy engine, whether it has 3.00" or 3.25" mains. You should also consider buying a 400/455 stroker crank (Ohio crankshaft has these, $665/ forged)- this will drop into a 400 block with no machine work, and will let you use the forged rods you have (assuming they are 6.625" Pontiac length).

Geno

[MonzaRacer]

First of all, with a Pontiac you dont need high RPM to make power if properly built. As for building the 455, yes UNLESS its one of the thin wall blocks as stated it will go 040 or 060.
honestly to reduce rotating friction, why not turn down the crank to a 400 main spec of 3in, bore the block to fit the 455 pistons, typical "stroked" 400 and if you get "teched" the block says 400!
Just looking for a 428/455 block to reuse all your parts might be feasible, but heck use a 400 block, spend about $150-$250 to turn down mains and enjoy.
But as far as thin wall blocks, I have not seen too many of the last 455 blocks that came up thinner.
And if you have a street Pontiac that has to turn more than 6k rpm, its not built for street duty.
Biggest strength of Pontiacs is their ability to hammer out brutal torque a low rpms. Edelbrock even made them better!

[digger1978]

400 blocks are more plentiful than 455 blocks. That is why they came out with a 400 crank stroked so you would get a 455ci engine. You can get them in either cast or forged and will allow you to make a 462 or 468ci engine. You also have the option to order 2.200" journals and run BB Chevy rods.

[Skip Fix]

The 455 crank will need some welding or a shim for the thrust in a 400 block. Better to get a new crank, and forged while you are at it, made for the 400 block, 4.21 stroke and Pontiac rod journals. And yes you can use the some pistons in a 400 block if you decide to. Some later 557 casting 400 blocks have thinner mains and are weaker especially if going near 400 HP or more.

I've leaned hard on a .040 455 block , a current build right now is 0.060 over. Bet your block would be OK, sonic test it , fill it to the bottom of the water pump holes and go for it.

[Nicks67GTO]

If you want a wealth of Pontiac knowledge and a truckload of Pontiac parts for sale, head over here... http://forums.performanceyears.com/forums/ and scroll past all the modern Pontiac bs that no one posts to. The classic parts of PY are a treasure trove and some of the builders on there that post a lot, are pretty big names in the Poncho world.

[keith4909]

Just get it sonic tested. Jim butler pontiac goes .060 over all the time. I have a 455 in the shop now going .060 over. Good luck.

[eodprice]

Sorry for not getting back sooner. It's been pretty busy over here. I'm still deployed right now and won't be leaving the dump for another month yet. But I have decided and already bought 40 overs for the 455. My roommate had it sonic tested and it's all good. If my calculations are right it's gonna turn out a 462. I was able to call butler and they hooked me up. All total from them I got KB icon pistons, edelbrock head with their port/polish/valve job done, Doug's headers, and there poly engine mounts.