down on power?
- Thread starter 200cifox
- Start date
mysavioreigns
Famous Member
I'd guess a couple things:
Increased emissions stuff is going to make it less powerful
The 60s numbers probably weren't actually accurate.
Increased emissions stuff is going to make it less powerful
The 60s numbers probably weren't actually accurate.
There were two different standards.
60s used "Estimated Gross HP" which was just a calculation based on engine size, and did not account for parasitic losses.
80s had more emissions, derated engines from the gas crisis, and they started using "Net Brake HP" which was the HP rating at the flywheel after all parasitic losses in the engine took effect, and was actually bench tested if I recall correctly.
In reality, a stock 200 in a 65 mustang put about 60 RWHP to the road, which is about the same as yours.
60s used "Estimated Gross HP" which was just a calculation based on engine size, and did not account for parasitic losses.
80s had more emissions, derated engines from the gas crisis, and they started using "Net Brake HP" which was the HP rating at the flywheel after all parasitic losses in the engine took effect, and was actually bench tested if I recall correctly.
In reality, a stock 200 in a 65 mustang put about 60 RWHP to the road, which is about the same as yours.
The 1960's motors were rated at brake horsepower, 1980's motors are rated at net hp.
The 60's motors didnt have that craptacular emmisions gear tacked on.
The 1960's motors IIRC were rated at 9.0:1CR, about 1980-1981 the 200 was running about 8.5:1 compression ratio.
Starting in mid 70's all Ford gasoline engines also had the timing retarded to reduce emmisions which also killed power.
The 60's motors didnt have that craptacular emmisions gear tacked on.
The 1960's motors IIRC were rated at 9.0:1CR, about 1980-1981 the 200 was running about 8.5:1 compression ratio.
Starting in mid 70's all Ford gasoline engines also had the timing retarded to reduce emmisions which also killed power.
The SAE Gross figure of 120 hp for a 1967 Ford was really no more than 65 rear wheel hp.
From a study I did in the late 70's as a kid, I found that with compression ratio drops, and EGR emissions area Federal Motor Vehicle standard gear, most cars lost about 13% power.
With Ford,it was all gained back with much better heads, bigger valves, custom cam grinds, and different carburation. This means that an 85 SAE Net hp 1984 Fairmont 3.3 is still making about 67 rear wheel hp.
So an apparent 41% power drop is not a power drop, its a rating drop.
My study of Fords European Pinto 1600 and 2000 engine showed that the SAE Gross (pre 1972) figures, verses the later SAE Net or DIN Net was only about 16% lower on US and Australian Fords. The differences in rating standard was the huge drop in compression that US 1972 compliant cars had to cope with.... the test fuel had gone from 93 octane to 83 octane, and that is a 13% drop in power when EGR is also needed. So 16+13% (about 29%), is the standard 1971 to 1972 drop, unless the car maker had been fudging the power curve.
A prime example is the 11:1 compression 1971 351 Boss, with 330 SAE Gross hp at 5400 rpm, which really had 350 hp SAE net at 5800 rpm. The next years (as the rare Super Cobra Jet engine for Smog Panteras and Australian Falcon GT's), it ended up with only 266 hp at 5400 pm on 9:1 compression and 83 octane gas. That was only a 24% drop, but it really should have been rated at 380 SAE Gross Hp, a huge 43% drop, just like the Ford 200 from 1967 to 1984.
For your info. The Rear wheel hp is less 33% for a C4 auto, and less 26% for a manual trans.
Sources are from Wheels Magazine and Australian Street Machine, plus Popular Hot Rodding and Car Craft articles from 1977 to 1995.
From a study I did in the late 70's as a kid, I found that with compression ratio drops, and EGR emissions area Federal Motor Vehicle standard gear, most cars lost about 13% power.
With Ford,it was all gained back with much better heads, bigger valves, custom cam grinds, and different carburation. This means that an 85 SAE Net hp 1984 Fairmont 3.3 is still making about 67 rear wheel hp.
So an apparent 41% power drop is not a power drop, its a rating drop.
My study of Fords European Pinto 1600 and 2000 engine showed that the SAE Gross (pre 1972) figures, verses the later SAE Net or DIN Net was only about 16% lower on US and Australian Fords. The differences in rating standard was the huge drop in compression that US 1972 compliant cars had to cope with.... the test fuel had gone from 93 octane to 83 octane, and that is a 13% drop in power when EGR is also needed. So 16+13% (about 29%), is the standard 1971 to 1972 drop, unless the car maker had been fudging the power curve.
A prime example is the 11:1 compression 1971 351 Boss, with 330 SAE Gross hp at 5400 rpm, which really had 350 hp SAE net at 5800 rpm. The next years (as the rare Super Cobra Jet engine for Smog Panteras and Australian Falcon GT's), it ended up with only 266 hp at 5400 pm on 9:1 compression and 83 octane gas. That was only a 24% drop, but it really should have been rated at 380 SAE Gross Hp, a huge 43% drop, just like the Ford 200 from 1967 to 1984.
For your info. The Rear wheel hp is less 33% for a C4 auto, and less 26% for a manual trans.
Sources are from Wheels Magazine and Australian Street Machine, plus Popular Hot Rodding and Car Craft articles from 1977 to 1995.
I dont mean to sound stupid but some of that doesn't make sense to me.
It was my understanding that brake horsepower was the rating of the engine on a stand attached to a dyno brake with no parasitic drag to run belts for any accessories like alternator, water pump or fuel pump and almost a open header system.
The net horsepower rating is for the engine with all accessories on it like water pump, alternator, power steering belts, etc. and a regular exhaust manifold.
On the Fox body Mustangs we have this "coffee can" light off catalytic converter attached to the exhaust manifold that is roughly 4in in diameter at the top and at the bottom has a 90 deg turn into a roughly 1.75in to 2in diameter exhaust pipe.
Then we had EGR valves that use a delay valve so the addition of exhaust gases doesn't occur til higher in rpm range so it doesn't cause the car to bog down on acceleration.
On power loss for a manual trans 26% may be true on the older trans but most tests I have seen with the newer T5's and such only show about a 16% to 17% parasitic loss, I assume this is partly from running auto tranny fluid instead of heavy gear lube. In 1981 we were running the Borg Warner SROD which my manual refers to as a T4. It was basically a 4 speed T-5 and 4th gear was slightly overdrive at .98 to 1.
I have also seen some people show as much as 42% loss for automatics, again I assume this is partly due to different converters and valve bodies.
As you said the Boss 351 used 11.3:1CR and the 1971 Cobra Jet used 9.0:1
Isnt the rule of the thumb about 5hp per compression point? That should mean 20hp less just from the compression drop.
The Boss 351 used a aggressive high performance solid lifter cam, the Cobra Jet used a less aggressive hydraulic cam with emissions in mind.
The heads IIRC are not that different port and valve wise but the Cobra Jet uses larger chambers to help drop compression.
So then why should the Cobra Jet be rated at a higher horsepower level than the Boss 351?
It looks like Ford also dialed in 4 deg retard into the stock cam in 1973 351HO and compression dropped to 8.0:1. This motor was also rated at 266hp.
You also state a drop in octane from 93 to 87 caused a power loss.
Isn't this more a reflection of the drop in power from lowering the compression to be able to run low octane gas? Not from the gasoline itself?
It was my understanding that brake horsepower was the rating of the engine on a stand attached to a dyno brake with no parasitic drag to run belts for any accessories like alternator, water pump or fuel pump and almost a open header system.
The net horsepower rating is for the engine with all accessories on it like water pump, alternator, power steering belts, etc. and a regular exhaust manifold.
On the Fox body Mustangs we have this "coffee can" light off catalytic converter attached to the exhaust manifold that is roughly 4in in diameter at the top and at the bottom has a 90 deg turn into a roughly 1.75in to 2in diameter exhaust pipe.
Then we had EGR valves that use a delay valve so the addition of exhaust gases doesn't occur til higher in rpm range so it doesn't cause the car to bog down on acceleration.
On power loss for a manual trans 26% may be true on the older trans but most tests I have seen with the newer T5's and such only show about a 16% to 17% parasitic loss, I assume this is partly from running auto tranny fluid instead of heavy gear lube. In 1981 we were running the Borg Warner SROD which my manual refers to as a T4. It was basically a 4 speed T-5 and 4th gear was slightly overdrive at .98 to 1.
I have also seen some people show as much as 42% loss for automatics, again I assume this is partly due to different converters and valve bodies.
As you said the Boss 351 used 11.3:1CR and the 1971 Cobra Jet used 9.0:1
Isnt the rule of the thumb about 5hp per compression point? That should mean 20hp less just from the compression drop.
The Boss 351 used a aggressive high performance solid lifter cam, the Cobra Jet used a less aggressive hydraulic cam with emissions in mind.
The heads IIRC are not that different port and valve wise but the Cobra Jet uses larger chambers to help drop compression.
So then why should the Cobra Jet be rated at a higher horsepower level than the Boss 351?
It looks like Ford also dialed in 4 deg retard into the stock cam in 1973 351HO and compression dropped to 8.0:1. This motor was also rated at 266hp.
You also state a drop in octane from 93 to 87 caused a power loss.
Isn't this more a reflection of the drop in power from lowering the compression to be able to run low octane gas? Not from the gasoline itself?
Anlushac11":14jtozt0 said:
Correct. And while connected to this dyno brake we can derive either Gross "brake horsepower" or Net "brake horsepower", exactly as you described above. Both terms are still properly referred to as "brake horsepower"; one is gross and the other is net.
"Brake horsepower" was first used in the early times dating back to the steam engine days when the so-called "Prony Brake" was developed as a means of measuring torque output. "Horsepower" was then calculated from the torque indications (just like most dyno brakes do today).
Joe
Anlushac11":3y75e49c said:
A Rodger Huntington article from Hot 302s and 351s was researched by me in 1988, and I can't quite remember if it was 1973 351 HO or Cobra Jet.
It was a dumb choice, and not an apples verses apples comparison.
Perhaps 351 Boss verses the Cobra Jet or so-called 351 HO wasn't a wise choice, especially since there were five homologated compression ratios (from 10.7 to 11.3), many revised head types even in the same casting number, something like three different 290, 300 or 310 degree mechanical cams, and then the later 351 4V's got a special 280 degree hydraulic cam. It's a shame an emissions compliant 1970 Boss 302 wasn't around in 1972 to show that the 290 hp gross would be more like 290 hp SAE net at 5800rpm. To be sure, compression ratio was on a massive nose dive, and that was most of it. The 351HO 1973 engine (which didn't pass US 74 emissions but was allowed to be used in many low volume production Panteras and some pre 1974 year October 1973 Fords) had a softer hydraulic cam and other alterations to be sure, but fact remains, most of the power loss from lower compression and retarded ignition was needed to meet smog requirements, and Ford didn't tell the whole truth about gross hp ratings, often taking the power rating lower down on the curve. Adding a full exhast verses tube headers to some dump pipes, and revising the heat and altitide corrections from SAE Gross to SAE Net would often result in variances in where the power peak was.
Anlushac11":3y75e49c said:
The differential and transmission as a unit take off 26% for a rear drive T5 with a modern low friction lubricant, and 7.875" diff on a 1992 5.0 HO EFI V8 Ford Falcon XR8 with 225 section tires. It had 221.6 hp Din Net and just 175 rear wheel hp on a Chevy Offroad and Marine dyno.
A front drive Honda CRX or transaxle race car Formula Ford has as little as 17% loss. It varies due to thermal loads and oil type.
Tire width and tread aggression increase parasitic loss. Automatics and race tires can result in 42% power loss easily, and this is highly related to what gear the car is in when dynoed, as intermediate gears loose much more power than the so called direct drive. The method to work out the power loss is to use the counterwieght coastdown test, and define the amount of driven power needed. EPA Dyno results have imputed road loads, and SAE papers allow you to determine the actual power loss in top gear very accuratley if vehicle drag is known.
There are many issues which cause the power loss to vary, and 17 to 42% variance sounds about right, depending on what gear the power run is done, what tire size and type, and how hot the power train is.
IIRC, 80Stang had a 31% power loss on his 3.3 engined Mustang with a SROD with 7.5" diff, 83 rwhp verses 109 DIN Net (62 rear wheel killer watts and 81.5 flywheel net Killer watts imputed to the DIN standard. Finish-ing skool Metrics!
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www.ponikorjaamo.com/ti80/80_dynograph.jpg
