Net and Gross HP

Horsepower ratings for the US made 351C 4V

1970: 300 SAE Gross BHP

1971: 285 SAE Gross BHP

1972: 280 SAE Net BHP

1973: 264 SAE Net BHP

1974: 264 SAE Net BHP

The change from gross to net horsepower occurred in 1972. These figures are from memory, so go easy on me if I've made an error. AK Miller, a Ford contractor, tested a production line 1970 351C 4V and found its max bhp was 287 not 300. Ford was being optimistic. the test results were published in Hot Rod Magazine. It is often said by enthusiasts that muscle car horsepower ratings were under-rated to avoid insurance penalties, but in the case of the 351C this is not true.

Having driven 1970 through 1973 Mustangs with every V8 power train option, my impression is that the 1972 cobra Jet was the most powerful of the 351C 4V motors (hydraulically cammed versions). It was stronger than the 1970 & 1971 versions, which were choking for air by 5500 rpm due to the small 600 cfm Autolite carburetor, small cam & single point ignition.

A common trick in the seventies was to stick the 1970 heads on the 1972 cobra jet, and install the OHO hydraulic cam (same timing specs as the Boss 351 cam, 0.505" lift). Equipped in this manner the motor was very strong over a very wide power band, it was a Boss 351 that didn't need its valves adjusted. Adding headers and a 750 Holley pushed its output to 370 to 380 bhp. The motor idled with a slight lope and had good drivability, and exploded into its powerband at 3000 rpm. The sbc & Mopar guys had nothing equivalent, yet the Cleveland could do this with just a few bolt-ons.

cowboy from hell

quote:

A common trick in the seventies was to stick the 1970 heads on the 1972 cobra jet, and install the OHO hydraulic cam (same timing specs as the Boss 351 cam, 0.505" lift). Equipped in this manner the motor was very strong over a very wide power band, it was a Boss 351 that didn't need its valves adjusted. Adding headers and a 750 Holley pushed its output to 370 to 380 bhp. The motor idled with a slight lope and had good drivability, and exploded into its powerband at 3000 rpm. The sbc & Mopar guys had nothing equivalent, yet the Cleveland could do this with just a few bolt-ons.

Yeah jack! That's what I'm a talking. Old school rules. That is what I am gonna do a couple of years from now. DeTom likes that build.

quote:

Adding headers and a 750 Holley pushed its output to 370 to 380 bhp. The motor idled with a slight lope and had good drivability, and exploded into its powerband at 3000 rpm.

Id bet thats the reason the automatic equipped BOSS 351s had a 10" torque convertor.
Jeff

Mustangs with "Boss" motors (solid lifter motors) all had 4 speed toploader (manual) trannies, without exception (Boss 302, Boss 429 & Boss 351). The small torque converters went behind the Cobra Jet motors.

quote:

Originally posted by Cowboy from Hell:
Mustangs with "Boss" motors (solid lifter motors) all had 4 speed toploader (manual) trannies, without exception (Boss 302, Boss 429 & Boss 351). The small torque converters went behind the Cobra Jet motors.

Yeah when I was first trying to get my rebuilt engine, the lady had told my mechanic that it would be a BOSS 351 and he told me. For about a week I was on cloud nine, thinking about my new BOSS 351 Pantera. Then I got to thinking about how rare it was and how I was depriving some mustang owner somewhere who might have a car without an engine. But then the lady called back and told him it was Cobra Jet spec and I was dissapointed and relieved at the same time.

There's an additional complicating factor. Ford's advertising department
had 3 engineering curves to pick from. Prior to the 428 Cobra Jet, Ford
would advertise the 'Engineering A-curve' power. That was the maximum
output you could get of an older engine with looser clearances than a new
one with dynamometer headers. That was the A-power curve. Then there
was the B-Curve, which was the engine with no accessories and the C-curve
which included exhaust system backpressure and all accessories. When Ford
introduced the 428 Cobra Jet, they advertised the B-Curve power rather than
the Engineering A-Curve. The 428CJ was capable of approximately 400 hp
(A-Curve), 325-335 hp (B-Curve), and 310-320 (C-Curve). NHRA and others
immediately factored the ratings for match racing.

Given the NHRA's factoring on the Boss 351, I'd guess that Ford also used
the B-curve rather than the A-curve.

Dan Jones

Ok I stand corrected...I remember a friend of mine buying one for his maverick new from the Ford dealership.
Jeff

Thanks George,

So, for a typical DeT Pantera 351C with Holley Carb, Edelbrock dual plane intake manifold and Stock DeT exhaust and headers - What HP gain are we realistically talking about?

Thanks

B.G.

quote:

Originally posted by andriyko:
...a typical DeT Pantera 351C with Holley Carb, Edelbrock dual plane intake manifold and Stock DeT exhaust and headers - What HP gain are we realistically talking about...

First realize that the stock Pantera exhaust must have had about the same back pressure as a Mustang or Torino exhaust, because the motors were not recalibrated for installation in the Pantera. That's going to be a tough pill to swallow for some folks, who have believed the advertising of that era that claimed the Pantera exhaust raised the output of the motor by 30 bhp. That's just not possible without having to recalibrate the carb, ignition and having the motor re-certified for smog.

Second, the Edelbrock Performer intake, to my knowlege, does not perform any more efficiently than Ford's oem dual plane manifold. So there's no gain there either.

That leaves the carburetor. The M code Cleveland motors were equipped with an Autolite carb of approximately 600 cfm rating. The Q code motors were equipped with a Motorcraft carburetor of approximately 750 cfm rating. Because the Q code motor is in a moderately higher state of tune than the M code motor, I expect a small carburetor to impact the output of the Q code motor more so than the M code motor.

These are my best guess figures (all figures in SAE gross BHP):

'71 M code motor + 600 Holley = No Gain = 285 BHP

'71 M code motor + 750 Holley = +10 BHP = 295 BHP

'72 Q code motor + 600 Holley = -20 BHP = 300 BHP

'72 Q code motor + 750 Holley = No Gain = 320 BHP

'73/'74 Q code motor + 600 Holley = -20 BHP = 284 BHP

'73/'74 Q code motor + 750 Holley = No Gain = 304 BHP


cowboy from hell

Thanks George.

Looks like you are confirming what I have been told. Except ...

For BHP SAE NET we are looking at 10 to 20 BHP less than the figures you gave?

B.G.

quote:

Originally posted by andriyko:
...For BHP SAE NET we are looking at 10 to 20 BHP less than the figures you gave...

Bohdan I believe the figures would be approximately 40 BHP less. Notice I bumped the '72 Cobra Jet from 280 Net to 320 Gross. The '71 351C 4V & '72 351 Cobra Jet do not make good motors to compare before & after ratings because their specifications are so different. In fact, its impossible to compare any Ford engine between the '71 and '72 ratings, because Ford motor compression ratios dropped across the board in '72.

Skimming through a Chilton manual for those years, looking at GM motors, Mopar motors, etc, there are few motors where all the specs remained the same between '71 and '72. Either the compression ratio dropped, the rpm for peak BHP dropped or the intake valve timing changed (indicating the camshaft timing was retarded). One instance where all those parameters remained the same were the Mopar slant sixes, the 198 cubic inch slant six was rated 25 BHP less (20%), the 225 cubic inch slat six was rated 35 BHP less (24%). Those specifications were also the same with the Olds 455 cubic inch V8 which was rated 50 BHP less between '71 and '72 (14%).

cowboy from hell

George/all

I will be rebuilding my original 351C this winter and want to keep it pretty stock. It has a Torker, MSD and a 600 Holley. I've been trying to decide what cam to get (lift/duration) and I think you just answered my question. I have (still in the box) a Crane stud conversion kit & roller rockers)Is that BOSS 351 cam still available from Ford? If not what were the specs on it? Second question: I only have about 100 mi's on a new clutch which works perfectly ans was wondering when I rebuild the engine can I put everything (disk/flywheel/pp) back in or should I have the flywheel resurfaced and replace the disk? I had the flywheel resurfaced when I replaced the clutch.

thanks

The camshaft I mentioned earlier is a hydraulic flat tappet camshaft, it was sold originally via Ford's Off Highway Parts program, I don't have the Ford part number in front of me, but that's not important anyway, because Ford no longer sells it.

The cam was sold by both Crane and Lunati at one time, but it has dropped out of both of their catalogs too. It is still offered by Melling however; I'm at the day job & away from my notes, but I believe the part number is 24224. Ford rated the duration as 290 degrees intake & exhaust, the same as the Boss 351 solid lifter cam. The duration at 0.050" lobe lift is 219/219 degrees intake & exhaust. The valve lift is 0.505"/0.505" intake & exhaust.

Since this is a hydraulic cam, it does not need adjustable valve train. Since the cam lobe profile and gross lift is old school (mild) the Boss 351 valve spring is plenty of spring, and the stock stamped steel rocker arms are sufficient too. I wrote sufficient, not ideal. Ford's bolt down roller rocker arms would be ideal. A word of caution regarding the Boss 351 springs, a camshaft with 0.505" lift is all the lift those springs can accomodate, they will coil bind around 0.535" (working from memory).

This was a good cam in its day, but its day is long past. The Comp Cams XE274H cam would be a better choice today in a hydraulic flat tappet camshaft, fairly equivalent in idle quality, wide power band and drivability, but look at the improvement in spec: duration at 0.050" = 230/236 degrees, valve lift is 0.562"/0.565". If there is a drawback to using this cam compared to the older design, it will definitely require better springs, roller rocker arms and heavy wall push rods.

Since either cam is of a flat tappet design, be sure to use Valvoline VR1 racing oil in your motor. It contains the ZDDP that is missing in almost all other oil these days.

Go ahead and re-use your clutch as is.

cowboy from hell

George, one more cam question. Can a dual plane manifold live with more duration than a single plane? If you didn't care if you had any vacuum at all, say you had no vacuum advance, and no vacuum assist breaks or anything, how much duration could you safely go with??????

quote:

Originally posted by DeTom:
...George, one more cam question...

No, you've asked two questions my dear friend.

quote:

...Can a dual plane manifold live with more duration than a single plane...

The more a motor's powerband extends beyond 5000 rpm (therefore more camshaft duration), the more a single plane intake manifold will complement the motor. It makes absolutely no sense to design a motor with a powerband of 4000 to 8000 rpm and equip it with a dual plane intake manifold in an attempt to make the motor idle at a certain low rpm. The dual plane intake manifold is robbing too much torque from such a motor. It is better to just raise the idle rpm of the motor and equip the motor with a single plane intake manifold.

A powerband of 3000 to 7000 rpm is a fence straddler, there is as much powerband below 5000 rpm as there is above 5000 rpm. This is the rpm which the cast iron Cleveland 4V heads naturally want to operate at, when set atop a 350 cubic inch motor. The Blue Thunder intake manifold was designed to straddle the fence as well as a two plane intake can, with an emphasis on lower rpm operation (street use). With a properly set-up carburetor, the Holley Strip Dominator and the Parker Funnel Web 4V intake manifolds straddle the fence just as well, with the emphasis shifted to performance at higher rpm.

Truth is, a 350 cubic inch motor will be significantly better off on the street with 2V heads and one of the 2V intake manifolds (Edelbrock Performer, Edelbrock RPM Air Gap, Parker Funnel Web 2V).

quote:

...If you didn't care if you had any vacuum at all, say you had no vacuum advance, and no vacuum assist breaks or anything, how much duration could you safely go with...

What is meant by "safely"? A cam can be ground to achieve a x type powerband, x type idle characteristics at x rpm, x type drivability characteristics, to work in conjunction with x gearing and with a car weighing x pounds, transmitting its power through a x type transmission, with a motor burning x type fuel, with x type cylinder heads, x compression ratio, x type intake system and x type exhaust. Fill in the "x's".

cowboy from hell

quote:

What is meant by "safely"?

No back fireing through thecarb is what I meant. BUt I think I see what you are getting at. You tell the cam company x and they grind you a cam you want. Thanks George.

Thanks George,

What valve springs do you recommend? I also have a new Holley 770 vacuum secondaries in a box, will that work with the cam? Finally what compression ratio do you recommend?

thanks again

The valve springs depend upon which cam you are considering. The "old school" cam works good with the Boss 302/Boss 351/429 SCJ springs. The XE274H should be used with the springs recommended by Comp Cams.

A Holley carb in the 750 CFM range is the right size for the Cleveland in most applications. It may need to be jetted to carburete smoothly from idle to WOT. You don't need a fancy intake manifold either. Acquire a 1970 - 1971 cast iron intake, have a machine shop open up the 4 holes to the same size as the Holley carb.

I would set the compression ratio between 9.5:1 and 10.0:1. To achieve this, when you rebuild the motor install a set of fordged flat top pistons, zero deck the block, and use the 1971 (D1AE) closed chamber heads (assuming you are ignoring my advice about small port heads and using 4V heads). While you're at it, install some good rod bolts on the connecting rods and have the reciprocating assembly dynamically balanced. Don't neglect to either have your harmonic balancer rebuilt by Damper Dudes or to purchase a Romac balancer. For a timing chain set purchase a Roll Master set.

I can't emphasize enough that a set of Aussie closed chamber heads, an Edelbrock Performer intake manifold (can be acquired dirt cheap on ebay) and the Comp Cams XE274H is perhaps the best low budget street combo. The Aussie heads have smaller combustion chambers than even the 1970 4V heads, so a set of dished pistons are needed to keep the compression ratio below 10.0:1. A piston with a dish that mimics the shape of the combustion chamber will maximize what little "squish area" there is in the Cleveland heads. I believe Keith Black offers these off the shelf.

I also want to emphasize that a custom ground camshaft, specified by someone knowlegable about the Cleveland will work better than any off the shelf cam. Mark McKeown is highly recommended. Mark can provide most of the parts I have mentioned, he can set up a set of Aussie heads for you, etc.

Bottom line, do business with somebody who really knows the Cleveland motor, most self-proclaimed Cleveland experts don't know diddly. Cutting corners on engine work is never cost effective, it always bites you in the butt one way or the other: in premature failures, poor performing engine, having to re-do work, leaving you stranded, long distance towing bills, embarrassment, nagging wife (you have to spend more money on that thing!), frustration, high blood pressure and forehead stitches (from banging your head against the wall).

cowboy from hell

George has some great advice. If I may add a couple of things to his list. While the engine is at the machine shop I would have the rods converted to full float piston pins, they just bush the small end of the rod with a brass bushing, and drill a small hole for oiling. Then make sure dual retainers are installed to lock the piston pin in the piston. Reduces the drag in the assembly and helps the piston and rod combo locate better in the cylinder. Second I would port match the intake runners to the intake port on the head. Takes little time with a grinder and the flow improvements are well worth the effort.

Jeff

Thanks George & Jeff,

I think I have the right way to go. I'll keep you informed.