On a .030 over 440 with iron 906 heads,,how high can I go with the compression and drive daily on 93 octane??

10.5:1 should be doable. My 408 stroker is very livable at that comp. Just keep the timing down to a reasonable level.

Stumpy ..thanks for the quick response... thats about what I was thinking,,,timing 34 Degrees....anyone else got other ideas??

LOTS of other factors to consider. Gear ratio, cam specs, car weight, type of exhaust system even the AERO of the car itself !

The other most important factor is probably cam specs. 10.5:1 is doable, for myself though with a 440 I dont think id try over 10:1 unless I was running a pretty agressive cam just because Id be annoyed if I put an engine together and then had to keep the timing retarded more than I wanted to run on the pump salad oil we get nowadays. Quench is important too, with 915s youd have a better shot than open chambered 906s.

10.5:1 is pretty impressive, youre running iron heads on that? How much did you have to retard your timing? If its working more power to you!

Id say most guys build for around 9.5:1 with a pump gas 440 though if they have iron heads. Once you get up that high the difference between 9.5 and 10.5 wont be much ponies or torque unless youve got a cam that needs the extra compression. You just have to ask yourself, is something like 8 hp worth the aggrivation and/or the expense of octane booster or blending gas? You might even loose power from having to retard the timing with 10.5:1 vs the timing you should have with 9.5:1.

906's wont give you quench because of the open chambers & that's going to limit you the most.

The biggest problem is going to be detonation. I'd try 10 to 1 or less. The open chamber heads will detonate if you don't put a good plan together. That is planned compression, cam, head flow and carb. You can do alot more with closed chamber heads.....but thats not the question here. Plan your compression then contact some of the cam guru's here on the board. Biggest thing is NOT to go overboard.

I run 10.0 on the 906 headed 440 in my 63. But I have good quench so I run 36 to 38 total with no ping and it runs fine on 92 pump. I use the KB quench dome pistons but I will tell you its alot of work getting a good even quench on all of the open chambers with the 906 heads. All chambers are not the exact same so you have to check and measure all the chamber depth's and the quench dome hieght and I had to work them to get them all between .040 to .045 quench. I use the MP .557 cam also and I run 4.30 gears with 29" tires and a Dynamic 9.5 converter. It all works great on my combo but without quench I would not go to 10.5 with an iron headed 440. I would shoot for about 9.5 without good quench unless you plan to run a very agressive cam and alot of gear. Good luck , Ron

Dynamite,
This is actually a very good question that too many people don't ask before buying parts. The quick answer is this.
You need to keep in mind that you really do not care what the compression ratio is as long as you end up with the appropriate amount of cylinder pressure to run the octane of fuel you want to run and not get detonation (or preignition). Assuming you want to run 93 octane fuel we suggest 165psi with iron heads and 185psi with aluminum heads. The trick to this is figuring out what compression ratio will give you that certain cylinder pressure. This is something we do for our customers. The things that determine your cranking cylinder pressure are the compression ratio, the head material, the cam, and the altitude. Bottom line is this. The bigger the cam and the higher the altitude the more compression you can run. Don't get sucked in to that Car Craft, Hot Rod (Non-Mopar) mentallity that 10:1 works for everybody. Cylinder pressure is what makes power and it is what cam cause detonation. It is critical to get it right. Give us a call and we will be glad to help you pick out a combination of parts that will get you the results you want.
Good Luck,
Kevin

Kevin's right. Except I run a bit higher numbers than Hughes with success. (at sea level...) With care, 185psi using open iron heads will not detonate on 93octane with 10%ethanol. But your tuning must be spot on.

Cam is the big variable for sure.
So is weight, gear and so on....

My 440 doesn't ping at 10.6:1 with a 242@50 racer brown cam 3400 stall, 373 gears etc

In contrast My old 68 newport would ping on 2-3 shift with a stocker cam, and around 8.5:1 comp.

If its' built mild, the compression will make it ping.

Another factor to consider if you are building from scratch,is why build in a potential problem with too much compression? Most engine builders agree, one full point of compression will only gain you 3-4% max horse power in a given combo

I built a 440 / 906 headed engine for a friends street driven Charger. It has approximatly 9.5:1 compression and a fairly mild Hughes cam HEH1928BL. We could have went with more cam and compression, but he did not want to have to start changing gears / converter as he just wanted a nice street car and did not plan to race the car.

You can go 11 t0 1's, just back the timing down. Good gas of course.

Thanks for posting the
165 psi iron
185 psi aluminum
cranking compression rules of thumb.

Is this a dry compression test with the engine warm and the throttle body propped wide open
or
is it a 'wet' compression test
with a shot of motor oil in the cylinder beforehand ?

Do you take the measurement on the
3rd stroke of the cylinder,
4th stroke,
highest reading of an 'tell tale' needle on the gauge, etc ?

Just curious as to the little details.

Thanks again.

Many new cars have aluminum heads and run up to and more than 11-1 C/R on pump... Fuel injected and computer controlled of course and these cars have mild cams so they must have lots of cranking compression.... Lots of the smaller 4 cylinder engines have been running high compression combos for years.... TBF

I agree

the specs on the 2009 Ford Escape hybrid engine
for example
claim that it can run on 87 octane
with a 12.3 to 1 static compression ratio
by using an Atkinson Cycle style camshaft

http://autos.yahoo.com/ford_escape_hybrid_fwd-specs/?p=all

another way to think of this is that
the "dynamic expansion ratio" is 11 to 1
while the "dynamic compression ratio" is 8.5 to 1
due to late intake valve closure

poor low rpm throttle response (bogging)
is compensated for
with the torque available from the electric traction motor