Dyno Day! HP, bHP, rwHP? SAE Gross vs Net?

A local shop, Nextgen, ran a Dyno Day for Mustangs in Northern California this past Sunday. Cost was $50 for 3 runs (reg. $100-$180).

Since my 351C 4V finally got on the road again in June after breaking down in April before heading out to the 50th Bday party in Vegas, I wanted to know if I built (repaired) my motor correctly.

You hear about 400 and 500 HP engines all the time. My flat tappet cam was supposed to get me about 475 HP, per the cam maker. Dyno Day was the day of truth and happiness or truth and disappointment. Actually, I was scared the motor would blow up. So be it.

The 1972 351 HO R Code was factory rated at 275 bhp and 286 tq. I tempered my expectations and hoped for these numbers. The Dyno Shop Boss said if 275 hp was factory, he told me to expect 200-220 hp. WHAT!!?? Only 200? What was the difference between factory spec and his numbers?

3rd Dyno Run:



After 3 runs, "Christine" pulled a best of 280 rwHP @ 5900 and 286 tq @ 4000-ish. That matched the FACTORY specs. And for some reason, the Dyno Boss was shocked and said "WOW! ...got respect for these Clevelands!" So, I was happy too. But frankly, I didn't know why. I was hoping for 300 or 400 HP.

After returning home, I had to research the DIFFERENCE in horsepower ratings. Here's what I came up with.

3 TYPES OF HORSEPOWER AND TORQUE METHODOLOGIES

1) SAE GROSS (bHP - Gross) was the system for Pre-1972 Cars. Engines were dyno'd on an engine dyno, as opposed to a chassis dyno, with minimal or NO accessories and NO muffled exhaust. This is what Engine Builders show on their engine chassis, often eliminating the factory air cleaner, belt driven accessories like the alternator, power steering pump, water pump, fuel pump, and fan, and mufflers, thus eliminating almost all parasitic losses from accessories. The RATING is at the FLYWHEEL with minimal or NO ACCESSORIES.

2) SAE NET (bHP - Net) This was the system of measurement used from 1972 to date. Engine's are dyno'd on an engine dyno, as opposed to a chassis dyno. All factory equipment, like the air cleaner, power steering pump, a/c compressor, fan, etc and full factory exhaust system with mufllers, is KEPT on the motor to get as close as possible to REAL WORLD conditions. The RATING is at the FLYWHEEL with ACCESSORIES.

3) WHEEL POWER is often shown as RWHP or WHP for rear wheel or wheel horsepower. This measures Horsepower or Torque at the wheels on a Chassis Dyno, as opposed to an Engine Dyno.

* bHP or Break Horse Power is the measure of power at the Engine's CRANK.

PERCENTAGE DIFFERENCES BETWEEN THE 3 TYPES OF POWER MEASUREMENTS

Why are the Horsepower numbers so different? Why do people scratch their heads or get so depressed when they found their 450HP LS6 Chevelle made only 288HP at the rear wheels? The ANSWERS seems to be in 2 areas: METHODOLOGY OF MEASUREMENT and PARASITIC LOSSES due to friction or breathing. There is a 3rd area, i.e. manufacturer under-rating or over-rating for insurance or per company policy, but I won't cover that here.

1) SAE Gross VS Rear Wheels HP/TQ: A general estimate for the difference between SAE GROSS HP (bHP-gross) and RWHP is 30% to 40%. This depends on many factors, such as manual vs. automatic transmission, manual or power steering, mechanical or electric fan, etc. New school cars will have more ELECTRIC run accessories, like electric fans, electric power steering, etc. Thus, their parasitic losses from friction will be lower, probably less than 30%. Old school cars with air cleaners sucking air through a straw-like snorkel and less efficient power steering pumps will have large parasitic losses.

2) SAE Net VS Rear Wheel HP/TQ: A general estimate for the difference between SAE NET HP (bHP-net) and RWHP is 15-17% for manual transmissions and 20% for automatic transmissions. The frictional losses come from the Power Train, ie transmission, drive shaft, differential and axle.

3) SAE Gross (bHP-gross) VS SAE Net (bHP-net) HP/TQ: A general estimate for the difference between SAE GROSS HP (bHP-gross) and SAE NET HP (bHP-net) is 15-20%. Closed Element Air cleaners and belt driven accessories (fan, alternator, power steering pump, water pump, etc), and a full exhaust system with mufflers are responsible for most of the power differences.

MY RESULTS:

My relatively "STOCK" OPEN CHAMBER 4V CLEVELAND made 280 rwHP and 286 rwTQ. That is equivalent to an estimated 400-466 HP on the pre-1972 SAE GROSS system and an estimated 330-350 bHP on the current Real World SAE NET system. 400-466 HP is not too bad, in my opinion. The power is very streetable, very cruis-able with good vacuum for my power brakes, etc. These numbers are very similar to late model all-motor Mustang 4.6 GTs, Mach 1s, and near Boss 302 at the REAR WHEELS.

MY "BASIC" NEAR-STOCK "351HO" CLEVELAND BUILD SHEET:

- Original Factory 351C 4 Bolt Mains, 0.030 overbore (357 CI)

- Original Factory 4MA crank

- Original-style TRW forged alum flat top pistons

- Original Factory 4V Open Chamber Iron Heads [approx 9.5:1 compression]

- Original-style Single Groove Stainless Steel Valves (MULTI-GROOVE VALVES ARE ONE OF THE WEAKEST LINKS)

- New Hardened Push Rods, Studs and Guide Plates, ARP Head Studs

- New Hydraulic Flat Tappet Cam (mild/street 226/235 dur & 540/560 lift on a 1.73 rocker) - despec'ed from factory Solid Cam

[NOTE: Ford's Cam Lift was based on 1.6 Windsor rockers, but Clevelands had a 1.73 rocker ratio, so the actual lift is higher on factory #s.)

- New hyd lifters, valve springs, locks, hardened valve seats

- New Scorpion 1.73F Alum Roller Rockers

- Original Factory Boss 351 D1ZZ Spread Bore Aluminum Intake, made by Buddy Bar for Ford

- New Fel-Pro Gaskets everywhere, but 1/4" RTV bead between Block & Intake Manifold

- Aftermarket Edelbrock 750 cfm Carb (15 years old) with 1/2" alum spacer, port matched by me...

- Original Factory 18" Air cleaner with Snorkel (straw) and Trap Door, but adapted with dual ram air tubes to each side of the radiator for Cold Air Induction

- Petronix Ignitor III billet distributor w/Rev Limiter

- Ford Racing 9MM wires

- Autolite Spark Plugs

- Moroso 6qt Oil Pan

- Melling Oil Pump

- MPG Oil Redirect Line

- Speedmaster Alum Water Pump

- 100 Alternator - 1 Wire

- Rebuilt Power Steering Pump

- Factory Belt-driven Fan

- Sanderson shorty headers

- 2 1/2-inch Pypes exhaust with X-pipe

- Dynomax VT dual mufflers

- Pacesetter Resonated Tips (modified)

CONCLUSION:

And there you have it. Nothing fancy. That's how I got 280 rwHP and an estimated 400-466 HP at the flywheel (SAE Gross). And I'm OK with that.

NO TUNING YET

There has been NO tuning. I think I set up the Rev Limiter wrong at 6000 RPM instead of 6700 RPM, so the dyno tech let off at 5900 RPM each time. He felt it wanted to keep going as it quickly and smoothly hit 5900 RPM. Anyway, some tinkering will tell me if the issue is rev limiter, carb, valve springs, etc. And she ran LEAN so I will be increasing the JET SIZES on the Secondaries to get to 12.5 AFR at WOT. Should be more power there.

MORE POWER?

Can I get more power? Yes, easily. Play with timing, advance/retard the cam, lose the restrictive factory air cleaner, go to manual steering, install an electric fan, convert to an electric water pump, etc... That could be another 20-40+ HP. Might even have a 500 HP motor (SAE GROSS) at the end of the day. But it's not a DRAG STRIP car (yet) so I wanted to keep some of its vintage history intact. Mild restomod as opposed to wild...

DONATE YOUR JUNK TO ME

Don't throw away your OPEN CHAMBER 4V HEADS. But if you don't want them because of people, like HorsePowerTV who say they are no good and suggest you buy Edelbrock heads instead, OK, just donate your iron 4V heads to me. NO SHAME for the Open Chambers 4Vs in my book.

CLEVELANDS ROCK!

Semper fi!

Clevelands DO ROCK!

Nice numbers and beautiful car bro congrats!

Clevelands DO ROCK!

Nice numbers and beautiful car bro congrats!

Click to expand...

Thanks my brother!

DONATE YOUR JUNK TO ME

Don't throw away your OPEN CHAMBER 4V HEADS. But if you don't want them because of people, like HorsePowerTV who say they are no good and suggest you buy Edelbrock heads instead, OK, just donate your iron 4V heads to me. NO SHAME for the Open Chambers 4Vs in my book.

CLEVELANDS ROCK!

Semper fi!

Click to expand...

Awsome I just built a new 351c using the open chamber heads & have been saying the same thing Just as good if not better than closed chamber it's all in the setup & matched components ! your setup is similar to mine & more than adequate for street use Check out my vids here

http://www.7173mustangs.com/thread-take-a-ride-in-the-72-video

http://www.7173mustangs.com/thread-got-the-new-faux-351cj-running

DONATE YOUR JUNK TO ME

Don't throw away your OPEN CHAMBER 4V HEADS. But if you don't want them because of people, like HorsePowerTV who say they are no good and suggest you buy Edelbrock heads instead, OK, just donate your iron 4V heads to me. NO SHAME for the Open Chambers 4Vs in my book.

CLEVELANDS ROCK!

Semper fi!

Click to expand...

Awsome I just built a new 351c using the open chamber heads & have been saying the same thing Just as good if not better than closed chamber it's all in the setup & matched components ! your setup is similar to mine & more than adequate for street use Check out my vids here

http://www.7173mustangs.com/thread-take-a-ride-in-the-72-video

http://www.7173mustangs.com/thread-got-the-new-faux-351cj-running

Click to expand...

Thanks my brother! Nice work! Here's a copy of the Dyno Sheet.

It just goes to show that the 4V head is where it's at!! Congrats ,nice rite up.

Thanks my brother!

We can stand a little taller and hold our heads up a little higher. You know, I had 2 guys talk down about my Cleveland last April, and it was getting to me for months. One guy used to own a Boss 351, then started saying that I got the "wrong" heads, that I needed to switch out my Open Chamber 4V for the Closed Chamber 4V. Then, another guy, who has a Pantera, said the same thing, going further that to suggest the Open Chamber 4V heads were "no good for the street".

Then, I went into researching every kind of head out there, not just the 4V, but the Edelbrocks, the CHI, AFD, ProComp, Trick Flow, etc... But that was way out of the budget. So, I focused on just using and appreciating what I already had, then dial how I will use my Mustang... which was CRUISIN' TO CAR SHOWS and a couple 1/4 Mile runs each year. Glad I kept the Open Chamber 4V iron heads and saved $3000+++. Glad I did the dyno run.

In the end, all Clevelands from the humble 2V to the Closed Chamber 4V are good. Each has its purpose. The 2V makes great torque down low, offering faster 60 foot times. The Open 4V keeps compression manageable on all-around high performance street car. The Closed 4V can give soaring compression over 11 or 12 to 1, turning any Mustang into a Drag Strip beast.

I enjoyed the videos and I think 280 is a great BHP number. I would gladly take that. I think the sound of the Dynomax is mild compared to my Flowmasters. Might be time for a switch because I am not a fan of really loud cars like mine.

Thanks for the report and nice write-up, Dave. Sounds like you've got a nice beast there in Christine.

::beer::

thanks my brothers!

by the way, the 280 was rwHP (@ rear wheels), so it's actually closer to 330-350 bHP (sae net w/accessories @ flywheel) and 400-450 HP (sae gross pre-1972, engine maker #s)...

thanks my brothers!

by the way, the 280 was rwHP (@ rear wheels), so it's actually closer to 330-350 bHP (sae net w/accessories @ flywheel) and 400-450 HP (sae gross pre-1972, engine maker #s)...

Click to expand...

Yep, that sounds right. And thanks for the shout out for the humble Cleveland 2V heads. As can be found in other threads on this site and YouTube

I rebuilt my 2V Cleveland pretty mildly and am very happy with the results.

I enjoyed the videos and I think 280 is a great BHP number. I would gladly take that. I think the sound of the Dynomax is mild compared to my Flowmasters. Might be time for a switch because I am not a fan of really loud cars like mine.

Click to expand...

The Dynomax VTs are mild... relatively quiet, but there is this reversion sound that is pretty fat and low subwoofer-like FEEL-able, at certain frequencies as the valve fights between open and closed.

She used to have rusty long tube Hooker headers and 2-chamber Delta 44s. EXTREMELY LOUD, leaky, and hot. My wife was too embarrassed to cruise with me. It sounded like a race car, everywhere I went. Sometimes, I miss that In Your Face sound.

But with the Dynomax, I can sneak up on people, then REV to 6000, shock 'em as the valves fully open to some pretty big cheers. I added resonated tips, so the sound is mellowed at tailpipes too...

Great write up, thanks for posting it. As you said, if your not looking for a SCR greater than about 9.3:1 with a stock stroke, the open 4V works fine, including the smaller valved 73 and 74 heads. It all depends on what you are trying to do as to which parts are used. Chuck

Dave,

Thanks for sharing the results...looking forward to the day when my 73 CJ is ready to roar. Interesting on all the ways to view HP and makes it clear why the confusion.

Wow... thanks for posting your results and that great write up. Its always nice to get a little loving for our clevelands. I'm the proud owner of a 73 Q code, 4 speed Grande (T5).

thanks Chuck, Jeff, 73StangCoupe... Semper Fi

Glad to see you went with what you had (o/c 4V's) than listen to know it alls about changing them to c/c's. While the c/c heads are awesome for all out power and racing applications, their o/c counterparts are by no means crap heads. It really p's me off with know it alls (that actually know F all) about c/c heads being the greatest thing ever made and o/c heads just being junk. To me it shows how ignorant they really are, and about ten years ago we went about proving how wrong these know it alls really are. A guy who wanted an engine built had a set of o/c 4V's and was told by "experts" to change them for a set of c/c's. Anyway we spoke with him to see exactly what he wanted. He was after 500 hp+ engine he could run on the street with no problems. Ok but why do you want to get rid of your heads. Everyone reckons o/c don't work properly, blah, blah, blah. We convinced this guy that what he wanted to achieve could be done with his heads and no dramas with compression or any detonation issues. Anyway the basics were as follows (trying to remember over 10 years ago now) 2 bolt block fully tested, then machined and prepped correctly, ARP studs, girdle, grout filled to bottom of welsh plugs, oil returns polished, etc. 351 crank offset ground, Eagle 6" rods, CP (I think) pistons, custom ground hyd roller (can't remember specs, but it was not a wild grind) spun by a Rollmaster timing set and the heads were the smaller valve ones (the first set I'd ever seen) they were polished chambers, 2.10 intake, 1.71 ex ferrea 6000 series valves, intake port tongues added, exhaust port plates (these are the 2 greatest things you can do to 4V heads) intake bowles reworked and extensive work on the exhaust side of the heads, all machine work for springs, adj rockers, etc, Yella Terra shaft rockers, a locally made redline torker single plane intake, a reworked 750 D/P Holley, a full MSD ignition set up ( using a 6AL) When this engine was finally assembled and taken to the dyno for running in and testing, well the results even surprised us. It made around the 560 hp mark and torque was around 470 ft/lbs. all on pump fuel. This engine pushed an XA hardtop into the low 11's and it had terrific street manners and an idle that sounded very mild. But as usual the know it alls said "no way can you do that with o/c heads, and with an idle like that must be running gas to get those times, blah, blah, F'n blah.

It really is no wonder I got out of that game, listening and having to deal with d###heads all the time. Anyway enough of that for now as just starting to think about w**kers is giving me the s**ts. So if anyone tells you that o/c heads are no good just ask them to give them to you as you like collecting and using junk parts.

Glad to see you went with what you had (o/c 4V's) than listen to know it alls about changing them to c/c's. While the c/c heads are awesome for all out power and racing applications, their o/c counterparts are by no means crap heads.

... grout filled to bottom of welsh plugs

... intake port tongues added, exhaust port plates (these are the 2 greatest things you can do to 4V heads)

... It made around the 560 hp mark and torque was around 470 ft/lbs. all on pump fuel. This engine pushed an XA hardtop into the low 11's...

Click to expand...

wow. 11s!!

i would love to hit 11s or even 12s. but i'm just hoping for low 13s in a couple weeks after some more tuning. fty spec was 15s back in 1972. but how much more do i need before i have to think about brakes, suspension, tires, transmission, u-joints, axle, etc? lol

what is "grout filled to bottom of welsh plugs"?

i had the MPG Port Plates on the intake and exhaust. but i couldn't get them to seal very well on the exhaust side. when i had the blow by problem last April, I suspected the problem were the intake tongues so I removed them both, but it turned out to be the Timing Chain Cover. the Sanderson headers have a raised flange, thus they are gasketsless and gaskets actually create a leak. they were installed with gaskets between the block and plate, but no gasket betw plate and header. Thus, i have to rethink how to install the Port Plates with or without gaskets on the block side IF i want to try them again. Wondering if I can be leak-free just using RTV ONLY on both sides of the port plates?

Welsh plugs are what you guys call freeze plugs. So you fill the blocks water jackets with a material like Hard Blok to the plugs as a way of strengthening the block.