compression ratio question on a stock 400

[troy.70R/T]

I have a stock 400 out of a 75 wagon. I think it is rated at 180 Hp with the two Barrel that is on it. I want to put a 4 barrel on it, headers, K&N air filter and change the cam. I have a purple shaft cam that is supposed to be almost stock for a 70 440 Hp motor. (sorry I don't have any specs on the cam) My question is this. I want to mill the heads to raise the compression ratio. From the Factory service manual It says that it is 8:1 right now.   How much compression can I run with cast pistons and not hurt the engine. Thanks.

[Challenger340]

Assuming Pump Fuel stay around 9-9.5:1 should be fine.

Getting there by milling the Heads may prove more difficult and expensive ?
2 Issues

#1.)You lose Around 2.3 cc's per .010" milled off the Bottom Deck of the Head, so for example if you wanted to bring the head Chamber Volume down around 10cc's, you would be taking about .040" off the Head decks, (4 X 2.3 = 9.2 actual)
then,
To maintain "Intake Manifold Fit", you would need to Mill the Intake Faces of the Heads.
The published spec is .012" off the Intake Face of the Head, for every .010" Milled off the Head Deck.( I personally stay closer to .010" per .010")

This can, depending upon how much you remove, make Valve Cover sealing an Issue, because the top of the intake face is the V/Cover sealing rail where the V/cover gasket sits.
It will seal, just mentioning so you pay attention.

#2.) When you start Milling the Heads lots, to dump cc Chamber Volume and Bump Compression, invariably, depending upon how much you actually take off, you may run out of Lifter Preload "Range" in the Lifter.
This may result in your having to "Ditch" the stock non-adjustable Rocker Arms, in favour of some "Adjustable" Rocker Arms and Pushrods to compensate for the Milling, and allow you to be able to provide correct Lifter preload again.

Some Math
8.0:1 400 engine
roughly assumes a swept volume of 820 CC's, into a current Clearance Volume of approx 116 CC
To get the same Engine "up" to around 9.0:1, will require the Clearance Volume to "shrink" to about 102 CC's, by removing 14 CC's. (All things being equal of cource, gskt type, etc.)

It can be done, I've done it many times with the "Open Chamber" 400 Heads, however, usually when faced with this amnount of Milling and costs for Adjustable Rockers, this is why Guys generally opt for Installing "Closed" Chamber type Heads on 400's, that are 7-8 CC's smaller to begin with, and can use the Stock Rockers, with a "Steel Shim" type Head gasket to drop another 5 CC from a Composition Head gasket(if thats whats there now ?)

Most "Closed" Chamber type Heads are supplied Factory with the smaller 1.60 Exh Valves, the exception being the "HP" '67 440 version Casting # 2780915, which came with the Larger 1.74" Valve used on all "Open" Chamber Heads.

So, it boils down to 'choices' ?
Incur the Time and expense to MILL your existing open Chamber Heads(if in good shape), about .050" on the Decks and .055" on the intake Faces, retain the 1.74 Exh Valve,then ADD a set of Adjustable Rockers/Pushrods
or,
Buy some "Closed" Chamber heads,(preferably in good shape), and hopefully ones that have been rebuilt with the addition of the Larger 1.74 Exh Valves, and Install them with Steel Shim Head gaskets, and stock Rockers.

Hope this helps
Bob out.

[troy.70R/T]

Thanks for all the information and time you spent replying to my post. I think I should just put the 400 in the way it is except with some headers and a 4 barrel and spend my time and money on building a 440. Thanks again Bob

[femtnmax]

In the book "how to build max performance mopar big blocks" by Andy Finkbeiner, on page 14 concerning block selection...the 400 block was considered a smog engine...but the factory engineers designed the block with extra beef around the main caps....The B1 performance cylinder heads offered by Koffel's Place were developed with the 400 block in mind because it was the only production block that could handle the high power output of their cylinder heads before aftermarket blocks were available.  The book goes on to say you can add a stroker crank to the 400 and make a very strong running engine.
Sounds like it is worth considering.
As challenger340 said, the quench type cylinder heads with smaller cc combustion chambers are a very worth while investment.   As quoted on speedtalk forum:  Quench is more important than everyone realizes.

[troy.70R/T]

I defenantly realize that quench is very important especially with higher compression motors. I have been looking at alot of the engine builds in the engine build section to figure out what I want for the 440 I build (or I may build a stroker) I just kind of wanted to have some fun experaminting with the 75 400 that I have, but if there is to much mony in volved in that then I will just have to wait till i can build an engine basied on everyone elses experiances and advice. thanks for the advice and ideas.    Troy