[footjoy]

YEAR Or did they I don"t know.

Just curious and what did they use for correction factor for driveline efficiency?

Thanks

Greg

[johnta1]

1972 I believe.

[RocktimusPryme]

Didn't the entire American auto industry change ratings at the same time?

[goatless]

NOT flywheel hp to wheel hp. They went from gross hp to SAE net hp. And yes, it was 1972 and the entire American auto industry made the change.

Gross is the bare engine and net is with air cleaner, accessories and exhaust hooked up as it would be in the car.

[footjoy]

OK thanks for the clarification. So what does BHP mean?

It looks like emissions changed in 71 or 72 .

I am trying figure out what factors drastically changed the horse power ratings.

Compression changed.

It looks like the HP ratings changed in some case 75 hp maybe even more.

Thanks

[RocktimusPryme]

Originally Posted by footjoy

OK thanks for the clarification. So what does BHP mean?

It looks like emissions changed in 71 or 72 .

I am trying figure out what factors drastically changed the horse power ratings.

Compression changed.

It looks like the HP ratings changed in some case 75 hp maybe even more.

Thanks

I think its brake horsepower but I could be wrong there.

And in those years its a combination of factors. Because of emissions changes, power did actually drop. But the rating method also changed as mentioned above which lowered reported power.

So combining an actual power drop with a more conservative rating method, you get a huge drop-off in the early to mid 70s.

[footjoy]

Originally Posted by RocktimusPryme

I think its brake horsepower but I could be wrong there.

And in those years its a combination of factors. Because of emissions changes, power did actually drop. But the rating method also changed as mentioned above which lowered reported power.

So combining an actual power drop with a more conservative rating method, you get a huge drop-off in the early to mid 70s.

I think thats where part of my misunderstanding is trying to achieve HP at the rear wheel with components used pre 72.

If that makes sense

Thanks

[RocktimusPryme]

Originally Posted by footjoy

I think thats where part of my misunderstanding is trying to achieve HP at the rear wheel with components used pre 72.

If that makes sense

Thanks

Again, I could be wrong, but in this case the word brake doesn't mean it is power at the wheel area. I think they are using a brake as a measuring device.

[footjoy]

Originally Posted by RocktimusPryme

Again, I could be wrong, but in this case the word brake doesn't mean it is power at the wheel area. I think they are using a brake as a measuring device.

I appreciate your help I have some research to do on my winter project to find more HP

Thanks
Greg


Sent from my iPhone using Tapatalk

[goatless]

Just a to help understand the difference- the 1971 YS 400 and it's 1972 counterpart are essentially the same engine. Same compression, cam etc. The 1971 400 is rated at 300 hp (gross) and the 1972 was rated at 250 hp (SAE net).

The 1970 YS 400 was rated at 350 hp (gross). The rated 50 hp drop from '70 to the '71 model year was due to reduced compression and other real factors that reduced power. The rated 50 hp drop from '71 to '72 model years was due to a different rating methodology but no actual loss of power.

["QUICK-SILVER"]

Made this post in one of your other threads. Just so you could get an idea about the difference in gross/flywheel HP and rear wheel HP.

Originally Posted by "QUICK-SILVER"

Greg,

Check this thread out. First page has "engine dyno" numbers. And the owner posted professionally tuned "chassis dyno" numbers today. Nearly 150 HP difference.
https://forums.maxperformanceinc.com...=808474&page=5

Your engine could have A LOT more than you think.

Clay

Clay

[unruhjonny]

Originally Posted by goatless

Just a to help understand the difference- the 1971 YS 400 and it's 1972 counterpart are essentially the same engine. Same compression, cam etc. The 1971 400 is rated at 300 hp (gross) and the 1972 was rated at 250 hp (SAE net).
...

also it's worth pointing out that for 1971 Pontiac gave both rating - to more or less ease customers into the forthcoming 1972 rating system.

[Chris-Austria]

I think from factory they never use "rear wheel HP". If you got the factory SAE HP you will have about 15% less at the rear wheels with a manual and 20-25% less with an automatic.

['ol Pinion head]

Originally Posted by RocktimusPryme

I think its brake horsepower but I could be wrong there.

And in those years its a combination of factors. Because of emissions changes, power did actually drop. But the rating method also changed as mentioned above which lowered reported power.

So combining an actual power drop with a more conservative rating method, you get a huge drop-off in the early to mid 70s.

Jeremy basically treed me on the jist of this, but just completed.

There was no considerable emission strangling changes done between the '71 & 72 model Pontiacs, the emission system pieces on each year were very minimal. the effect of calibrations for an EGR valve did not make its debut til '73 models. Loaded with emission pieces, 7.6-1 CR, a restrictive pellet style cat & other emission pieces, '75 & '76 models were the low water point.

Since there are published road tests of both, we can compare 400 L78 performance equipped '71 & 72 Pontiac models. The best published 1/4 mile roadtest time a '71 Pontiac 400 4spd A-body ran was a 14.32. the car, a modestly equipped GT-37 with 400 4bbl, M20, & 3.55 Safe-T-Track. Nearly a year later, a very similar '72 LeMans GT (with standard frontend not the heavy endura frontend) was tested with near the exact same equipment; 400 L78, M20, 3.55 STT... best 1/4 mile time recorded was a 14.40. Tested performance was basically the same, the '72 LeMans GT was slightly heavier. In the same lightweight 233 body style as the '71 roadtest, or in a lightly equipped bench seat 235 series, the factory built '71 455 HO cars were even quicker. 13.60's to 14 flat in the 1/4 mile, bone stock. Today, as well as over the last 25 years, within a well scienced out PureStock build, all within the PureStock rules, its not uncommon to knock off another second to 1 1/2 seconds off what were those best bone stock times from back when new.

Read as much as I could stomach of the responses to the Street Forum topic of footjoy's T/A's recorded rwhp topic. It's not that hard in a factory non AC 400 4spd '77 -'79 T/A to up factory performance from low 15 sec 1/4 mile times into the mid 13's. Thats a considerable improvement, & many times all an enthusiast wants to do with what often amounts to a relatively unmolested collector car. If that's the kind of performance you're after, there are several of us that have done it, or paid to have an engine built with milled 6x-4 heads on simply a "trw/sealed power" 406 or 412 shortblock, no headers, no RA manifolds. We're also willing to offer help. That type of build fills into what I've referred to as one one type of "Purpose Built" car. There are many types of Purpose Built "street driven" cars, & parts needs are often different between the types of purpose builds, but that's not something that everyone who "contributes" on topics in the "Street Forum" understands.

[Schurkey]

Originally Posted by goatless

NOT flywheel hp to wheel hp. They went from gross hp to SAE net hp. And yes, it was 1972 and the entire American auto industry made the change.

Gross is the bare engine and net is with air cleaner, accessories and exhaust hooked up as it would be in the car.

Originally Posted by Chris-Austria

I think from factory they never use "rear wheel HP". If you got the factory SAE HP you will have about 15% less at the rear wheels with a manual and 20-25% less with an automatic.

Somewhat correct.

ALL horsepower ratings are done on an engine dyno, not a chassis dyno.

Gross horsepower allowed the dyno team to set ignition timing for best power, and allowed colder intake air. There are other "tuning" allowances.

Net horsepower increased the intake air temperature, and required "factory stock" ignition timing, among other restrictions. There were multiple purposes: To reduce the horsepower numbers so the Insurance Industry didn't have a cow; to de-emphasize performance because, of course, performance is evil and racing is even more evil. And it was explained to the public by people who should have known better as "it represents the power of the engine "as installed" in the vehicle".

This is one of two main reasons that aftermarket dynos are "optimistic"; they DON'T follow the full SAE Net HP protocol--they take some of the same short-cuts and performance-enhancers that were allowed under the "Gross" rating method. The other is that the factory under-rates the engines so they don't get sued by people for false advertising. A GM crate engine ALWAYS makes more power on a magazine dyno test than what they advertise.

The "SAE Net" HP protocol was updated again in...perhaps 2007? There was lots of pissing and moaning because "American" engines tended to gain a couple of HP, while Asian engines tended to lose a couple of HP.

As far as listing a single percentage of loss through a manual transmission, and a single percentage of loss through an automatic trans, I'm sure it's not as simple as that. The actual transmission will have an effect; and I bet the transmission has more of a given horsepower loss than a percentage--but I am prepared to learn something. (i.e., a certain automatic takes 20 hp to run, whether it's behind a 200 hp engine or a 500 hp engine. So the percentage would vary greatly. For that matter, it probably makes a difference which gear it's in, with lower gears taking more power, and direct-drive taking the least.)

[ponyakr]

"...It's not that hard in a factory non AC 400 4spd '77 -'79 T/A to up factory performance from low 15 sec 1/4 mile times into the mid 13's..."


Would a build like that look something like this ?

http://lenwilliamsautomachine.com/400_Long_Block.html

Or do you have some speed secrets you'd be willing to share here ?

[RocktimusPryme]

Originally Posted by Schurkey

As far as listing a single percentage of loss through a manual transmission, and a single percentage of loss through an automatic trans, I'm sure it's not as simple as that. The actual transmission will have an effect; and I bet the transmission has more of a given horsepower loss than a percentage--but I am prepared to learn something. (i.e., a certain automatic takes 20 hp to run, whether it's behind a 200 hp engine or a 500 hp engine. So the percentage would vary greatly. For that matter, it probably makes a difference which gear it's in, with lower gears taking more power, and direct-drive taking the least.)

Yeah I have always questioned that "An automatic is a 25% loss" concept as well. I think it was probably more accepted in decades past, when 400hp was a damned stout motor. Point being there was a greater percentage of the hobby who had motors within probably 50hp of each other making blanket statements more acceptable.

Fast forward to now where 1000 hp is more attainable that ever, and its common for people to have 500+ hp street motors. How a TH400 would rob the same percentage of power from my motor vs a factory 400 is hard to figure.

[Stan Weiss]

They went from dyno with no accessories to having accessories on the engine and working and changed from SAE J607 to SAE J1349 to calculate the dyno correction factor.

Almost all engine dyno sheets you see today still use SAE J607.

Stan

[Tom Vaught]

Originally Posted by Stan Weiss

They went from dyno with no accessories to having accessories on the engine and working and changed from SAE J607 to SAE J1349 to calculate the dyno correction factor.

Almost all engine dyno sheets you see today still use SAE J607.

Stan

Very True. But most people care little about the "DETAILS", Stan.

We used to do a "Three Bag" Emissions and F.E. Test, now we do a "Five Bag" test that includes a WOT Cycle.

The 500 HP to 800 HP Blown Muscle Cars today are a lot faster (for the same dyno numbers) vs the old 1970 "Dyno" Numbers.

BUT as your said, there is a difference between a 600+ OEM rating 2019 vehicle vs a 1972 L-88 427 550 HP Chevy Corvette rating.

Tom V.

Aftermarket Dynos, with a properly prepped 331 cid engine, turbocharged, have made well over a 1000 chassis HP.

[Tom Vaught]

I do not believe I have ever seen more really fast "Production" Cars being offered for sale in 2019 vs my entire lifetime.

Sure there were the Dodge Hemis, the 427 Ford "Cammers", the 427 Corvettes, The 465 HP 454 Chevelles, but none of them will touch the Crate offerings from the OEMs today.

Tom V.