CR Question

[bigal614]

hey guys, I was told today that the 03's had a CR of 9.85, could that be right/ I always thought it was 10.1?

[Raudermaster]

That's what I thought too.

[B.C. Bake]

If I remember correct, you can look at the stats in the little manual in the glove box, if you have one that is? It's on the few to the last pages in the back, that will tell you your cr. ;)

I looked at my 04 and it's page 211 ..........10.1:1 CR

[bigal614]

Ok, cool, I wasn't aware of that. The car is locked up at the shop so I was trying to find out without having to get over there.

[1of327]

What is a CR?

[rayjay]

IIRC, the CR on the 04 was upped from the 03 spec.

[1of327]

I'm Diggin' seeing all the Flags...

[Bluerauder]

What is a CR?
Compression Ratio --

[juno]

IIRC, the CR on the 04 was upped from the 03 spec.

Not likely as it would involve changing the heads or pistons.

I have seen the 9.85 numbers and the 10:1 numbers, not sure which is correct.

Very simplisticly, CR is the change in volume of the gas or the area (same thing under ideal gas laws) when the piston is at the top of the compression stroke.

Higher CR's require more octane but result in better fuel econonmy and responsiveveness/hp.

[rayjay]

I have seen the 9.85 numbers and the 10:1 numbers, not sure which is correct.

IIRC, 9.85 was for 03, 10.1 for 04. There are posts on this somewhere here. As for me, I've have to go cut the lawn. Not sure what the CR is on my John Deere.

[bigal614]

Very cool, Thanx guys!! I had heard that the 04 were a hair higher but wanted to make sure!

[bigal614]

Hey Ray Jay, would the 04 long block work ok in an 03 with the xtra CR?

[Bluerauder]

hey guys, I was told today that the 03's had a CR of 9.85, could that be right/ I always thought it was 10.1?
Compression Ratio is listed as 10.1 to 1 in the '03 Marauder Owner's Manual, page 214.

[Loco1234]

the o4 has (2) O2 sensors... hence it can run with more advance safely...
hence more effective horsepower etc....

thats difference in power....

[rayjay]

Hey Ray Jay, would the 04 long block work ok in an 03 with the xtra CR?

I don't see why there would be any difference, or if the minor CR difference would be worth the change. The 04 heads were alleged to have been upgraded to avoid the problems encountered with the early 03 heads. What exactly was changed has been discussed here too long ago for my memory. The 04 also has dual knock sensors. Someone upgraded their 03 and it made no more horse power or torque.

[MENINBLK]

Higher CR's require more octane but result in better fuel econonmy and responsiveveness/hp.

Not true.
There are lots of engines with 10.1:1 compression that run on 87 octane.
It is the design of the combustion chamber that determines the octane requirement.

[Dragcity]

Not true.
There are lots of engines with 10.1:1 compression that run on 87 octane.
It is the design of the combustion chamber that determines the octane requirement.

And the point of timing.....

[sicilianmarquis]

when i went to the ford guy, he told me the Mach1\Marauder(2003 and 2004) engine is the 4.6l32v DOHC 10.1 CR, with hypertonic pistons.

the 03' and o4' Cobra 4.6l is the one with the lower compresion, b\c it was make for the supercharger ( and steel pistons for strength)

and also the 4.6l 2v (mustang GT, and grand marquis\crown vics) have 9.1 compression

thats what ive been told, and read

[Loco1234]

In general the CR makes the bifference difference in octane rating but their are other factors.... such as mentioned above...

and yes if an 03 were outfitted with dual O2 sensors it wouldn't make any more horsepower... however if you outfit the 03 with the MAV4 computer and custom reprogram it you can run with more adavance longer (without worry) due to better monitoring of the motor. Thus you will have more power gains with an 04 than an 03. "But u have to utilize this upgraded feature...
It also's for a much higher torque # and band throughout the RPM range.
My HP=425hp
My Tq=427Ft/Lbs

[juno]

Don't you mean knock sensors?


In general the CR makes the bifference difference in octane rating but their are other factors.... such as mentioned above...

and yes if an 03 were outfitted with dual O2 sensors it wouldn't make any more horsepower... however if you outfit the 03 with the MAV4 computer and custom reprogram it you can run with more adavance longer (without worry) due to better monitoring of the motor. Thus you will have more power gains with an 04 than an 03. "But u have to utilize this upgraded feature...
It also's for a much higher torque # and band throughout the RPM range.
My HP=425hp
My Tq=427Ft/Lbs

[Marauderjack]

the o4 has (2) O2 sensors... hence it can run with more advance safely...
hence more effective horsepower etc....

thats difference in power....

Uh.....Do ya mean KNOCK sensors??:confused::confused:

[Marauderjack]

The difference between 9.85:1 and 10.1:1 CR is not significant and I think the increase in '04 was due to larger spark plug bosses and more threads so dem plugs will stay put!!;)

A small amount of carbon will increase the CR 0.5 or more not to mention hot spots and more detonation potential!!:cool:

Marauderjack:burnout: