- Apr 10, 2014
- Reaction score
- California, USA
- My Car
1972 Mustang Mach 1
351 HO R Code
3rd Owner since 1983
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 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)
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.
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.
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