Moparts

Differences between 71 and 72 engines?

Posted By: feets

Differences between 71 and 72 engines? - 10/29/14 12:58 AM

I know that the change from net to SAE rating systems knocked the numbers way down.

The compression was dropped significantly but I don't know how much of an impact that had on the engine output.

Did the cams change?

I've got an old Motor repair manual that shows a slight change in timing.

Anything else change?

Looking at the old road tests it seems the 1971 and 1972 Imperials ran about the same times (slow as molasses) with the 90 hp rating change and a swap from a 2.94 gear to the 3.23s.
Posted By: RodStRace

Re: Differences between 71 and 72 engines? - 10/29/14 03:36 AM

Don't forget the cam timing and (in some engines) Floor Jet EGR.
Posted By: Dan Halen

Re: Differences between 71 and 72 engines? - 10/29/14 03:50 AM

IIRC, they retarded the cam timing a few degrees.
Posted By: poorboy

Re: Differences between 71 and 72 engines? - 10/29/14 03:50 AM

Feets,
The changes between 71 and 72 were 2 fold.
1) lower the numbers to make insurance companies happy
2) more restricting emission standards. Though the auto companies knew tightening standards were at the door, they largely ignored it was coming. I suspect they thought the general population and their lawyers would be able to make the new standards go away. When that didn't happen, they hung a lot of stuff on the motors to meet the new tougher standards. They d-tuned the motors (lowered compression, retarded ignition and cam timing, leaned out the carbs, just to name a few) and the add on stuff( egr valve, air pumps) choked the motors even more. Some of the stuff they did could be easily reversed (ignition timing, removing the air pump, enriching the carb), while other stuff was more difficult to reverse (cam timing, compression) They got a break in 73 when the government allowed the use of cat converters, but hung more junk (or rehung the junk they were able to remove because of the cats) on after 73 until they finally started designing the motors to meet the standards. Gene
Posted By: DaytonaTurbo

Re: Differences between 71 and 72 engines? - 10/29/14 03:51 AM

With the 440 losing two full points of compression, yeah that will affect engine output. Ask anyone who's driven one!
Posted By: Kern Dog

Re: Differences between 71 and 72 engines? - 10/29/14 07:25 AM

Quote:

They got a break in 73 when the government allowed the use of cat converters, but hung more junk (or rehung the junk they were able to remove because of the cats) on after 73 until they finally started designing the motors to meet the standards. Gene



Your points are valid but it was 1976 when the catalytic converters were first installed. There never was a 1973, 1974 or 1975 Mopar with a catalytic converter. I've owned Chevies and the same holds true there.
Posted By: moparmarks

Re: Differences between 71 and 72 engines? - 10/29/14 03:15 PM

Quote:

Quote:

They got a break in 73 when the government allowed the use of cat converters, but hung more junk (or rehung the junk they were able to remove because of the cats) on after 73 until they finally started designing the motors to meet the standards. Gene



Your points are valid but it was 1976 when the catalytic converters were first installed. There never was a 1973, 1974 or 1975 Mopar with a catalytic converter. I've owned Chevies and the same holds true there.



True. Also I've owned a butt load of 72's and none had an EGR valve or air pump.
Posted By: feets

Re: Differences between 71 and 72 engines? - 10/29/14 04:54 PM

Quote:

Feets,
The changes between 71 and 72 were 2 fold.




Yeah, I'm aware of the politics and other nonsense going on at that time. I did find slight timing changes to the distributor. The biggest thing on the Imperial was the inclusion of standard electronic ignition which was optional on other cars. I could not find cam timing changes or a different camshaft.

BTW, my 74 Road Runner had EGR but no smog pump or cat.

Obviously, dropping compression will kill some performance but I didn't know what else had been done.

Any idea what the cam specs for the 440-4v are for 71 and 72?
Posted By: 72roadrunnergtx

Re: Differences between 71 and 72 engines? - 10/29/14 05:01 PM

"True. Also I've owned a butt load of 72's and none had an EGR valve or air pump"

Some California big blocks were equipped with air pumps in ’72.
Posted By: GTX MATT

Re: Differences between 71 and 72 engines? - 10/29/14 05:29 PM

Quote:

Any idea what the cam specs for the 440-4v are for 71 and 72?



From what I've been told the cam specs didn't change from the mid 60s through the end of production, non HP engines still used the same cam 260/268 Duration, 0.425"/0.435" lift. HP cams were still 268/284 Duration, 0.450"/0.458" lift.

There is a lot of fuzzy and cloudy info on these engines, but this is what I've been told (here and other places) and it seems logical. The published specs even differ from source to source on the early engines regarding the lift on the HP cams (some say .458, some say .465 lift). I'm not sure if they ever moved the cam timing around, not that they degreed them anyway.

I believe the only significant difference on the later engines should be compression ratio. Head/intake part numbers changed, and they used TQs, but as we know all the heads and intakes flow basically the same in stock form. Also, I've never seen a later set of HP exhaust manifolds, anyone know what those look like? Were they even any different? Did the later HP engines use a windage tray?
Posted By: feets

Re: Differences between 71 and 72 engines? - 10/29/14 05:32 PM

Quote:

"True. Also I've owned a butt load of 72's and none had an EGR valve or air pump"

Some California big blocks were equipped with air pumps in ’72.



My Imperial is a Kalifornia car with a smog pump. Last time I had it out the fitting broke off the passenger side exhaust manifold. It now sounds and looks like a trailer park queen.

I plan on turning a slight taper on a piece of steel using the lathe and banging it into the hole on the manifold. That should make for a decent temporary fix.
Posted By: dogdays

Re: Differences between 71 and 72 engines? - 10/29/14 06:36 PM

Let's get things straight...49-state cars got EGR in 1973 and 1974. No EGR in 1972. They got catalytic converters in 1975, with some exceptions going later.
European cars started using O2 sensors (Lamda Sond) around 1978, and US cars around 1980 or 81.

There's a lot of BS around about that time, many of you were not even born yet. I had a new '72 chevy nova with 350/3-speed, and it had transmission controlled spark (TCS) Vacuum advance blocked out in the lower gears. It had evaporative emission control. My friend got a new '73 and it had EGR, EEC and I'm not sure about TCS. But it had lost 10hp from the year before.

R.
Posted By: moparmarks

Re: Differences between 71 and 72 engines? - 10/29/14 06:36 PM

Quote:

"True. Also I've owned a butt load of 72's and none had an EGR valve or air pump"

Some California big blocks were equipped with air pumps in ’72.



Yes but was not standard on all US cars. I've seen air pumps on GM cars as early as 69.
Posted By: moparmarks

Re: Differences between 71 and 72 engines? - 10/29/14 06:46 PM

Evaporative emission control started in 1970 on CA cars and then 71 on all cars.
I think the biggest change between 71 and 72 was the SAE rating myself.
Posted By: GTX MATT

Re: Differences between 71 and 72 engines? - 10/29/14 07:00 PM

Quote:

Quote:

"True. Also I've owned a butt load of 72's and none had an EGR valve or air pump"

Some California big blocks were equipped with air pumps in ’72.



Yes but was not standard on all US cars. I've seen air pumps on GM cars as early as 69.



GM started installing AIR pumps in '66 for Cali cars. Starting in '68 I believe ALL open element air cleaner/manual transmission cars came with them.
Posted By: Woody

Re: Differences between 71 and 72 engines? - 11/01/14 02:22 AM

Not sure about big blocks, but on top of the compression drop, the intake valves were downsized to 1.88 from 2.02 for the 1972 340's. Another 1972 340 mid year change was from a forged crankshaft to cast.
Posted By: 71birdJ68

Re: Differences between 71 and 72 engines? - 11/01/14 03:51 AM

I have a 75 /6 Dart with a cat on it.
Posted By: feets

Re: Differences between 71 and 72 engines? - 11/01/14 07:01 PM

Quote:

I think the biggest change between 71 and 72 was the SAE rating myself.



The biggest change was the rating system but they also took out two points of compression.
© 2024 Moparts Forums