The 460 pistons after 1971 went from 11 cc's to 22 cc dish.

In an early block those pistons will offer about 9.6 to 1 sitting .010 in the hole at TDC with a 75 cc early chamber.






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The 460 pistons after 1971 went from 11 cc's to 22 cc dish.

In an early block those pistons will offer about 9.6 to 1 sitting .010 in the hole at TDC with a 75 cc early chamber.




Perfect, thank you!

Scotty J. "AKA" The "Mad Porter"
"EMC 2006" 3rd place finisher
Ported BBF iron head specialist & Aluminum heads from all sources.
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Need to know what block and heads you are using. Block deck height grew from 10.300 to 10.310 in 1971, and again to 10.322 in '72-'97. Heads varied in chamber volume from 76cc in '68-'71, to 96cc for '74- later non-EFI heads. From what I can tell, factory pistons for 460s were all the same, dished.

IF you are using your early 10.300 block and 76cc heads (C8VE thru D1VE) you should be around 10.5:1. Any combination of later block and/or later heads will yield a lower CR. But remember one thing, the cylinder heads with thermactor bumps in the exhaust ports will not flow as well. Another thing to remember is that 74-later heads were built with Unleaded fuel in mind, so they use hardened valve seats. That said, your early heads on a later 10.322 block with stock 460 pistons looks to be around 9.3:1


.

 

I have early heads and and early block. I’m using the crank from a later engine. So I should assume 10.5:1?

 

That 460 WILL run a 11.5 (mine run 11.7) STATIC# with flattops and 72 75 cc chambers. Remember that you, me, and nobody else will reach that static number . Remember exh valve overlap bleeds comp. At the high load low rpm band. When the cam comes in and you start into that 12.5 .. and your past that detention point. (93 pump gas) if you've built a few 460's building torque early but not so early as to melt a piston. 34- 36* all in

 

At any point in a well sorted hot street engine where the VE meets or exceeds 100% the actual operational compression ratio will become the mechanical static c/r.
We have many street combos ranging from 90% VE to near 107% depending on cylinder head design and intake manifolding.

The VE on a 460 EFI engine with OEM exhaust etc etc is about 70%

Calculated DCR as done via the UEM calculator using the @.050" + 15* is a decent mechanism to establish how a heavily loaded engine will act. 8 to 8.2 to 1 DCR is about right for 87 octane. 8.7 to 1 for premium though this is not ideal for a working vehicle. It has little relevance in a light weight street performance vehicle UNLESS the IAT's and ambient temps are high as well as cooling system temps.

Intake closing point determines Cranking PSI, DCR and where the HP peak will occur within a given set of build parameters.

Overlap when combined with an efficient exhaust system (headers with proper collector length) will actually YANK the intake tract into motion BEFORE the piston begins it's decent.
Vizard refers to this as the 5th cycle.
Link is here:

https://www.motortrend.com/how-to/0505phr-exh/

You can literally hear this on a dyno when the intake and exhaust harmonic dance with one another in sync at peak torque and max HP.

With a garbage exhaust system too much overlap simply contaminates the charge if operational exhaust pressure gets above about 1.5 psi.

There is less time for abnormal combustion with long duration cams that need higher static c/r AND when the Torque peak is moved up higher into the rpm band.




Scotty J. "AKA" The "Mad Porter"
"EMC 2006" 3rd place finisher
Ported BBF iron head specialist & Aluminum heads from all sources.
Custom ground cams
See our products in the Vendor for sale section
Customized crate engines
ParklandAutoMachine.com
R-H-P.biz
"Parkland Performance Auto Machine" Formerly RHP
(253)-988-6648
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Thanks for taking the time to help us to understand how to make what seems to be an impossible comp. To actually work. I half to add. Slowly building a timing curve that works doesn't mean you need to run a detuned motor with that 11.5 you can also use your converter to get your motor into that sweet spot that makes torque without detonation. Me. I even spray a .75 gal per hour at 70% water meth. BIG help when it 90% humidity and 95*