What is Factory Torque Rating for M code?

detritusmaximus said:

I had watched a few of his videos before. I was a little disappointed that he used the 11.0-1 pistons for both runs. At that point, with the 750 Holley and long tube headers, it's really no longer an M-code.

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He said they put those pistons to get to factory spec of 11:1 compression. He must not know that compression as advertised was not true. Also he was in route to make it boss spec ... and he did later on ( he tested all high ho small blocks at factory soec - 351c won, boss spec)

detritusmaximus said:

I had watched a few of his videos before. I was a little disappointed that he used the 11.0-1 pistons for both runs. At that point, with the 750 Holley and long tube headers, it's really no longer an M-code.

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This guy dynoed 70 M spec 351c, claming just a refreshed engine - but who knows about cam. But peak power is at 5,100rpm, which ineicates milder cam then CJ. 650 carb.

Hemikiller said:

71/72 Q-code used flat tops, same as the 70-71M and 70-72 H code engines. Dished pistons came in '73.

The only apples to apple comparison I'm aware of is by Chevrolet, who published gross and SAE Net figures in some of their 1971 brochures. The 454 in the Corvette showed a difference of 100hp, the Camaro engines differed by 50~60 hp and similar amounts of torque.

In comparison, the 351CJ showed a measly 14hp difference between 71 & 72 - which tells me it was under rated to begin with. There are also HP variations depending upon the chassis. The intermediates had a lower HP rating at 248/299.



He also stated he used an M-code camshaft from Elgin - which they do not and never have made. Dollars to donuts it's a CJ cam in that engine.


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You might be right on him having CJ cam. Acording to Autolite publication from 70s, CJ cam (Or ford performance can as it was named before CJ existed)
gain 65 hp on M code.

YellowHorse said:

He said they put those pistons to get to factory spec of 11:1 compression. He must not know that compression as advertised was not true. Also he was in route to make it boss spec ... and he did later on ( he tested all high ho small blocks at factory soec - 351c won, boss spec)

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Yep. He saved time and money by jumping straight to the pistons for the Boss spec. So it's not really an M test. I'd really like to see the results of dyno tests for all factory spec Clevelands (including the Boss 302, Australian 302C and the Australian 351 GTHO and Phase 3). As built by the factory, stock carbs/ignition/exhaust.

Do any of you know what a reasonable loss factor is for our cars running a C6 vs C4 vs toploader? I see 15% used as a rule of thumb....I've never searched for comparisons of engine dyno vs chassis dyno vs 1/4mi MPH or ET.

This is from an old Car Craft article

detritusmaximus said:

As I recall, the 70 closed chamber heads had a slightly smaller chamber than the 71 closed chamber heads. Just a couple cc's and a little extra compression ratio, but maybe enough to account for 15 hp/10 ft-lbs, along with any carb changes.

I do suspect that many people get excited about the Q code because it's a Cobra Jet (which sounds cool) and the M is just a 4V (not as cool sounding).

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I tried finding info to corroborate the smaller 70 chamber, but can't find anything. Maybe it's just internet hearsay.

detritusmaximus said:

I tried finding info to corroborate the smaller 70 chamber, but can't find anything. Maybe it's just internet hearsay.

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1970 D0AE-N 4V heads are 61.3cc-64.3cc

1971 D1AE-GA 4V / Boss 351 heads are 64.6cc - 67.6cc

1971-72 D1ZE-DA 351CJ heads are 73.9cc-73.9cc

1973-74 D3ZE-AA 351-4V heads are 76.9cc-79.9cc, same as all 2V heads.

detritusmaximus said:

I tried finding info to corroborate the smaller 70 chamber, but can't find anything. Maybe it's just internet hearsay.

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Everything I have shows the '70 and '71 4V heads with the same volume, 62.8cc. However, I have always questioned this, because the same resources show the 351C Boss head having 66.1cc, which doesn't make sense that the Boss head, with a lower dynamic compression ratio due to the more aggressive camshaft, would need a larger volume head. I have also seen some reference that the '70-'71 also have 66.1cc. I have a set of D0AE-N closed chamber heads in the workshop, guess I'll have to get a burette and measure them (just ordered one from Amazon). When I get my Q code heads (D1ZE-DA) back from the machine shop I'll measure them also.

Don C said:

Everything I have shows the '70 and '71 4V heads with the same volume, 62.8cc. However, I have always questioned this, because the same resources show the 351C Boss head having 66.1cc, which doesn't make sense that the Boss head, with a lower dynamic compression ratio due to the more aggressive camshaft, would need a larger volume head. I have also seen some reference that the '70-'71 also have 66.1cc. I have a set of D0AE-N closed chamber heads in the workshop, guess I'll have to get a burette and measure them (just ordered one from Amazon). When I get my Q code heads (D1ZE-DA) back from the machine shop I'll measure them also.

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I found this on the Boss 302 forum:

https://www.boss302.com/smf/index.php?topic=35017.0


BOSS351 head casting #'s

djjsc​

April 02, 2018, 12:45:52 PM

"The 1972 OHO manual lists both the '71 M & '71 R heads having 66.1cc chambers & are the only heads spec'd @ 66.1cc. That would account for the M-code compression difference 'tween '70 (62.8cc, 11:1) & '71 (10.7:1). Using same head w/ pop-up pistons gave 11.3:1 on the '71 BOSS. "


and this:

Re: head casting #'s

1971rcode​

January 22, 2008, 02:53:28 PM

"I would say if there was any other casting number for the boss 351 heads i would say it would be the D0AE N . but you must remember that Ford listed the combustion chamber space for the Boss 351 as 67cc, which is what the D1AE GA heads had , and the D0AE N heads as 63 cc , just food for thought."

Hemikiller said:

This is from an old Car Craft article

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Man, the C6 is a piggy. I wonder if rollerizing brings it back down. Guess I better get busy on my C4.

Hemikiller said:

This is from an old Car Craft article

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Any data on manuals?
The C4 is looking better good.

70cobrascj said:

Any data on manuals?
The C4 is looking better good.

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Nothing in my files on manuals, but I've seen 4%-8% tossed around. It would take a lot of dyno time to get concrete numbers. Lots of variables too.

I remember that print article from back in the day, saw it posted on a forum a while back and screenshotted it. I don't look at those power numbers as absolute, just a means of comparison. My assumption is they'll vary by RPM and load.

Don C said:

Everything I have shows the '70 and '71 4V heads with the same volume, 62.8cc. However, I have always questioned this, because the same resources show the 351C Boss head having 66.1cc, which doesn't make sense that the Boss head, with a lower dynamic compression ratio due to the more aggressive camshaft, would need a larger volume head. I have also seen some reference that the '70-'71 also have 66.1cc. I have a set of D0AE-N closed chamber heads in the workshop, guess I'll have to get a burette and measure them (just ordered one from Amazon). When I get my Q code heads (D1ZE-DA) back from the machine shop I'll measure them also.

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Here's a screenshot from the 335 Series Off Highway manual that Ford put out for racing modifications. I've attached the PDF. There are some errors and contradictions, such as the intake duration on the 70-71 M-code cam, but it's mostly all there.

The interesting part is they show advertised compression ratios, then the piston, gasket and head data below. If you use the data they supply, you can never get to the advertised numbers.




If you look at the specs in the Boss 351 owner's supplement, seems Ford isn't too sure what they were building.

Maybe your highlighted variation is based on the presumed variation in chamber volume: 64.6 to 67.6. Could also explain why some get detonation and some don't.

detritusmaximus said:

Maybe your highlighted variation is based on the presumed variation in chamber volume: 64.6 to 67.6. Could also explain why some get detonation and some don't.

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Some report pinning, which usually due to low octane or incorrect timing/ advence.

. A 351 cubic inch motor with flat top pistons will achieve 10:1 compression ratio with quench chamber heads having 63cc combustion chambers and standard 0.035" deck clearance. However 10:1 compression ratio can also be achieved with open chamber heads having 70cc combustion chambers (milled) and zero deck clearance. Cleveland heads can be milled up to 0.060"; the combustion chamber volume of quench chamber heads is reduced 1cc for every 0.006" milled, and the combustion chamber volume of open chamber heads is reduced the same amount for every 0.005" milled.

basstrix said:

Man, the C6 is a piggy. I wonder if rollerizing brings it back down. Guess I better get busy on my C4.

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One of mine has a C4 in it with a shift kit. Motor is a 351w, stock with all the bolt-on upgrades. The C4 is holding up fine, and I'm anything but gentle on it.

detritusmaximus said:

I had watched a few of his videos before. I was a little disappointed that he used the 11.0-1 pistons for both runs. At that point, with the 750 Holley and long tube headers, it's really no longer an M-code.

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Believe I read in an old hotrod magz. The 351C likes a big Holley like 4781 for a gain of 25hp over a 1850...

basstrix said:

Man, the C6 is a piggy. I wonder if rollerizing brings it back down. Guess I better get busy on my C4.

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Yes it does. How much, I don't know.