What's the REAL Compression Ratio for Stock 69 440 HP??

[wyrmrider]

The factory warranty program may have paid for the r&d but the problem is the same for any open chamber mopar
remember I'm talking street not race only builds with a narrow high rpm power band
need a wider power band then still works to add some lower end of the power band torque

 

[Dusty997]

Do you want to be able to use 87 octane or ok with using 93?

Sorry for the Necromancy....but if one wanted to be able to use 87 what pistons would be the go to?

 

[V_TastyTacos_V]

What oem flat top piston was ever that far in the hole for a 383?
I've had a couple 383's that have those low CH flat top replacements.

The 383 in my Charger has pistons .140" down. Something like 7.3:1 compression.
Think I found why my car's a gutless turd.

 

[TorRed]

Deeply interesting information here! So who sells these pistons that enhance quench with open (906) heads? For a 383?

 

[dvw]

I built a 440 for a friend. He wanted it near stock with a very smooth idle. Used quench dome pistons. Equalized the depths of all the open area of the chamber. set it at .040" quench. Did the bowls and put 30 degree intake seats in them. Used a small 214@ .050" cam. Stock intake, carb, air cleaner and exhaust manifolds. True 9.7-1. it rattles a bit on 93 octane in the summer at full 36 degree timing setting. Other than that it runs really nice. Should have made it 9.5-1
Doug

 

[BSB67]

I built a 440 for a friend. He wanted it near stock with a very smooth idle. Used quench dome pistons. Equalized the depths of all the open area of the chamber. set it at .040" quench. Did the bowls and put 30 degree intake seats in them. Used a small 214@ .050" cam. Stock intake, carb, air cleaner and exhaust manifolds. True 9.7-1. it rattles a bit on 93 octane in the summer at full 36 degree timing setting. Other than that it runs really nice. Should have made it 9.5-1
Doug

That’s good info Doug. Do you recall what the cranking cylinder pressure was.

The one engine that I am familiar with is very similar to the one you described in the same mid-west type elevation, but with a 220-ish cam. On the edge at 9.5:1, and blew about 160 psi, IIRC.

 

[lewtot184]

The 440 in my r/t would blow close to 180psi with kb184 pistons and the 272/.455 cam; 9.4:1 compression. Of course different test gauges may give different results.

 

[33 IMP]

Sorry for the Necromancy....but if one wanted to be able to use 87 what pistons would be the go to?

Imo, the ideal piston for a stock iron head big block would be one with a reverse dome to get quench with the open chamber head, and a D-shaped dish on the other side, to get compression where you want it. Some clever calculating will be required, and I have no idea if such a piston is shelf stock anywhere. (I kinda doubt it)
A custom piston might be required to achieve the above.
Or, you simply put a flattop piston way down the hole, give up a bunch of power and torque..... and still maybe detonate on 87. (Especially the 10-15% corn garbage) .

 

[Dusty997]

kinda what i was thinking. I think im going to run the Stealth aluminum heads on mine.

 

[Kern Dog]

Detonate on 87. (Especially the 10-15% corn garbage) .

There are many that think the ethanol actually tests higher in octane than pure gasoline with the same rating.

 

[lewtot184]

Imo, the ideal piston for a stock iron head big block would be one with a reverse dome to get quench with the open chamber head, and a D-shaped dish on the other side, to get compression where you want it. Some clever calculating will be required, and I have no idea if such a piston is shelf stock anywhere. (I kinda doubt it)
A custom piston might be required to achieve the above.
Or, you simply put a flattop piston way down the hole, give up a bunch of power and torque..... and still maybe detonate on 87. (Especially the 10-15% corn garbage) .

Kb 184 piston is the perfect match for an iron open chamber head and pump gas.

 

[lewtot184]

There are many that think the ethanol actually tests higher in octane than pure gasoline with the same rating.

Ethanol doesn't have octane rating. It is a colder slower burning fuel that mimics higher octane gasolines. Anyhow, that's my take on it.

 

[dvw]

That’s good info Doug. Do you recall what the cranking cylinder pressure was.

The one engine that I am familiar with is very similar to the one you described in the same mid-west type elevation, but with a 220-ish cam. On the edge at 9.5:1, and blew about 160 psi, IIRC.

Never checked the cranking compression. I was originally shooting for 9.5-1. But my machinest cut the heads a touch to much.
Doug