440 compression

[ks114]

Quick question. I thought someone here may be able to answer this. I have a stock 1972 440 HP with 213 heads. I have a set of 915 HP's to install.
From what I can find, the 72 motor originally had 8.2:1 compression. What will the compression be with these heads? I've read that the 915's will increase compression anywhere from a half to a full point. Thoughts?

 

[BeepBeepRR]

I built an old RV engine. Closed chamber heads will help you out thats for sure. The problem with the low compression engines is that the piston sits too far down in the hole. Hughes has a cam and the 915 heads will help it alot. Also You might want to ask people about different head gasket thickness helping out too. I was told to use steel shim gaskets. But that was before i went and bought new pistons.

 

[PurpleBeeper]

I've always "ballparked" using 915 heads, along with an original style steel shim head gasket, to be worth about 1/2 point static compression....but there are a lot of variables. If you resurface the heads, I think you could "ballpark" your compression ratio around 9:1'ish.

 

[Lefty71]

This helped me a lot....
http://cochise.uia.net/pkelley2/DynamicCR.html
I downloaded the calculator program (super simple). I just cc'ed my 906's at 86cc (similar to your 213's), and my 915's at 79cc, The end result was one full point, but the information learned about the dynamic was exactly what I was looking to know about my build. HTH, Lefty71

 

[Lefty71]

I was told to use steel shim gaskets.

You have a lot of options now with the Cometic MLS gaskets, but they sure cost more than the old steel shim method....

 

[wyrmrider]

what is this going in? gears etc
no matter what you do you do not get any quench without changing pistons
I run 915's on several engines I think you are looking at 8.5 or less put 1.74 or 1.81 exhaust and 2.14 intakes if budget allows

Think of this voodoo for street gears -- with that compression you have to get the intake closed early on a non race car motor
or
454/454 253/258 208/213 112/108 EFI OK Lunati Voodoo idle 5000 112 would give better idle and power brakes use small dia (for a 440) headers
and some street port work would be nice
or
479/494 255/261 208/214 110/106 LA 1400-4800 Howard Torque winner : 711381-10 but 110 ok if you want hot rod idle and less mileage
about as big as you want with stock converter. little more exhaust would work with less port/ exhaust/ headers/
or
Custom exhaust lobe from Mike Jones depending on your exhaust
.461 .307 lobe 254 202 120 Jones special
@.275 lobe lift Jones is 64 when DC 260 is 42 This cam is really big at .200 to .300 lobe lift


“Unlike some of the other company's chrysler cams, this profile is designed to take advantage of the chrysler's .904" lifter. .307 lobe lift Part# HD64307-112
if your deck is square and smooth you can run a steel shim gasket else stick with .028
run a stock intake or aluminum look alike if you do not spring for the performer TQ works as well as anything and better and most for this combo
do not run a Mopar HP/ Magnum cam in a low compression big block unless you are running a stock class drag only
the late closing intake and exhaust kill you

 

[Garys1969RR]

Quick question. I thought someone here may be able to answer this. I have a stock 1972 440 HP with 213 heads. I have a set of 915 HP's to install.
From what I can find, the 72 motor originally had 8.2:1 compression. What will the compression be with these heads? I've read that the 915's will increase compression anywhere from a half to a full point. Thoughts?

You need to know the size of the combustion chamber on each head. Then you can go to a calculator and put in the numbers for the actual change in C Ratio to expect. You also need to know the distance below deck your piston is, when at TDC. I would guess its .050 to .075. Use a gasket thickness of .020. Your 915 heads are prob about 79cc, and the 213 are prob about 92 cc, but that's a guess. You can use those figures to get a rough estimate, then put in the real numbers when you find out what they are.

 

[PRHeads]

On a roughly 10:1 440, 1cc is worth about .1 in the CR.

It takes about 10cc to change the CR 1 point.

As you go above 10:1, each cc is worth progressively more(slightly), and as you go below 10:1 each cc is worth progressively less.

At about 8.25:1 each cc is worth .06.
At about 13.25:1 each cc is worth .16.

 

[Garys1969RR]

That's a good rule of thumb, PR. So if he has a 90 cc chamber, and goes to an 80 cc chamber, he has gained 1 point. So has gone from 8.2 to 9.2. Only problem here is that the factory C Ratio claims were usually quite optimistic. Lol. It's probably more like a real world 7.5, so he will be going to an 8.5. So he'll end up with about what he thinks he already has.

 

[Garys1969RR]

So it would be best if he can get some actual numbers, to see where he's at to begin with.

 

[PRHeads]

Not exactly.......

At 8.2:1, 10cc doesn’t get you a full point.

 

[Garys1969RR]

Not exactly.......

At 8.2:1, 10cc doesn’t get you a full point.

Oh that's right! Your only gaining about
.06 point per cc. So 10 cc is going to only increase it by .6, or from 7.4 to about 8.

 

[wyrmrider]

what Gary said several times
without pistons close the intake early
and use a cam designed to close the intake early not a bigger cam advanced too many degrees as that fouls up the overlap and power stroke

 

[Garys1969RR]

So true. I once had a 77 440 in a 69 RR. Very similar to your 78 440 I'm sure. Low compression, mild cam. The thing actually ran pretty good. Being new to the game, and finding a good used 509 cam for $75, I decided to try it. .509 lift, and 292 duration. Well it ran noticeably worse after putting the 509 cam in there. So I next built a high compression 451, put the 509 in it, and that motor screamed! So low compression = mild cam, close the intake valve early to build cylinder pressure. High compression = longer duration cam , close the intake valve later which will keep cyl pressures down at lower RPMS. This helps to prevent pinging. Then at higher RPMs the cylinders fill better, and as pressures go up, pinging is less likely due to higher RPMs, Since the piston has less residence time near TDC. I was able to run street and strip @13 to 1 C Ratio, with that cam and 98 octane fuel. 38 degrees total advance. It ran great! No pinging issues.

 

[wyrmrider]

absolutely correct gary
only place that 509 would work in a low compression motor is in a race only vehicle with really low gears
it's a bracket level cam even with high compression

 

[ks114]

Just got the heads off of the motor. The pistons, at TDC, are below the deck approx. .75. I will be using .020 head gaskets with the 915 heads. Can someone figure the compression? Thanks in advance!

 

[BeepBeepRR]

What size pistons? .30 over?

 

[BSB67]

Quick question. I thought someone here may be able to answer this. I have a stock 1972 440 HP with 213 heads. I have a set of 915 HP's to install.
From what I can find, the 72 motor originally had 8.2:1 compression. What will the compression be with these heads? I've read that the 915's will increase compression anywhere from a half to a full point. Thoughts?

You don't need to measure a bunch of stuff here to make the fundamental decision, which is, should I change the heads, right? Here is my opinion - yes, you should do it if the budget allows and you are replacing them with a set freshly/properly rebuilt 915s. Depending on the head gaskets, 8 cc to 15 cc change. Use what PRH said above.

The important part that is missing from the discussion is head condition. If you are installing fresh 915 with new guides and a competition valve grind/back cut valves, shim head gasket you could add 60 hp. If they are used 915's with small exhaust valve, you might loose 10 hp even with the bump in compression.

I have a set of good 915s that I let friends borrow. They add about 50 hp on any 440 we put them on. Partly because of the compression bump, but mostly from the good head, imo.

 

[Garys1969RR]

I can figure your C Ratio using a C R calculator. I think your pistons are prob at .075 below deck. You missed a zero in there. LOL . You will have to wait until I can get on my laptop later on. And let's assume you have 79 cc chambers. Factory says 73, but they are always bigger. At first guess, I'm thinking between 9 and 10 to 1

 

[Garys1969RR]

Ok given the figures you have, and using a flat top piston with no dish or valve reliefs, and 75 thousandths down below deck, we're coming up with 9.8 to 1. And if you go from a 79cc combustion chamber to a 73 CC chamber, you will be at 10 point 3 to one.