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It was a different rating system that went into effect. I think '71 and earlier motors were rated with no accessories or parasitic loads like water pump and so forth. In '72, they rated them with all pump and compressors running. I may be a little off on this explanation, but that was the general idea.

That and pump gas was limited in its octane rating, so low compression ratios were the order of the day due to the Arab Oil Embargo and increased awareness that we had to do something to help clean up the air. It was junk gas and you had to wait in long lines to get it.
 

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Yeah most the time on horse power rateings, when you have a difference it is that one came with a 2 barrel carb and the other with a 4 barrell .
But application of motor or type of car also matters generally too type head and or camm used, CCR etc .

For instance 350 in a 71 Pont is Gonna kick more horses than say an Industrial 350 used in a old 1 ton pick up .

Im lookin at my book .
But im lazy short on patience and more Ford orientated in Muscle car's .
But can tell you this .
On 72 Ford 429 2 Different heads, 2 different cam's were used .
One motor is shown as 429 other is shown as 429 PI
PI stands for Police Interceptor .
The police Interceptor motor came with different head's and a Holley 4163 Motor craft Carb .

The PI motors were easily Identified by the Head's by lookin at spark plugs .
13/16ths Big Plug was 429 stocker and the 5/8's smaller plug was the Hi Perf . Police Interceptor head .
The smaller 5/8's Spark plug generally indication of bigger valves , bigger camm etc.

These Changes in different variation's of same sized motor's are indicated in Chilton's manual's and blue book manual's with small print and or small circled numbers .

You merely look at a Number next too Horse power rateing's .
Then at Bottom of the Book it will have small print next too same number , indicateing if motors a Boss 429 or if came with Air Conditioning Etc.

In the Old Day's this is how Hott Rodders did it .
Mix and match Hi performance factory part's that we got off other car's .
That and Port and Polishin head's <<< requireing hour's of Grinding with Dremel tool's , and CCing Volumes too see if they were eqaul etc .

We didnt have all the aftermarket raceing company's that you have today ?
Mass Produceing any part you can perceieve or develope like they have now .

This Era is definately a Wonderfull time for Car's
If combustion motor raceing technology isnt at it's Apex ?
Then I cant imagine what could be next ?

Exactly what are you trying too figure out on a 350 ?
4 Bolt Main, CCR ?
Head's ? Camm ? Bore ? Stroke ?
68 Buick's were actually 348 CC motors, for example .

Im lookin in my Book I See 4 Different compression Ratio's .
2 different carb's a 2 barrel and 4 barrel .
If I was too look again at Cam Duration I would most likely see the same Motor's have different camm grind's, etc .

A Lott of Variation's come intoo play with Horse Power Rateing's ?
Even the way Horse Power is determined as Tech Inspector pointed out .
I use too be able too remember exactly what way Horse power was determined , along with what it was they started doing differently .

But Im Old !
Inventing the Wheel has takin a lott out of me .
Cant remember exactly what it was ?
But no matter anyhow ?
Im really too busy , trying too figure out how too make my own horse power numbers up .

A Good show on a Dyno is Nice ?
But has too put a Good show on when it's on Treadmill ?
Actuall horse power too Wheel's with good Torque Horse power rateing is what winn's Races .

Ive really Got away from Putting much store or thought intoo horse power rateings .
Just dont mean much .
About the only real purpose of them is a basic guide line on Dyno .
That and Indicateing in motor's manual's that there's a difference and or Variation in different application's of Motor's as a result of a performance modification , offerd by the factory, or a guide line off a Dyno as too what should be expected from a particular combination and modification of a motor .

Be aware that the Car MFG 's are not totally truth full on there rateing's .
Qaulity control had a lott too do with it .
As Bigg horse power numbers = better sale's ?
Most horse power rateing's were developed under Ideal Circumstances and Controled Condition's .
Something that was hard too keep up with under mass Production Enviroment condition's .

As a result Horse power is at best a crude guide line as too what is possible, or expected, with certain condition's and or modification's of a motor ?
Keeping this in Mind Ive been long winded enough .
Some one else explain the Science Of Torque Horse , and Actual Horse power , as I truly pullin a Blank here .
18 hour's on road im exhausted .
Most likely on this Subject I could go on for another 350 page's , start 3 dozen argument's etc.
But think I explained general Gist of horse power rateing's that are found in Big Book manual's and usual reason's for there variances .

Suggest that you get hold of a Big book chilton's and studdy on it some .
Read all the Lil Foot note's and small print .
Compare cam grind's , Bore and stroke, along with type plugs , valve specs , CCR, carbaeuration and compare them from Old's, Buick's GMC, Chevy's etc .
This is how we figured thing's out in Olden Day's .

Im So Old One day I Invented the Wheel .
Mr. Scatty Boo came along seen my wheel , and bored a whole in center of my wheel !
I was so madd that he ruined, my wheel, I chased him with a huge stick !
Then the rest is History ! :D

Sean
 

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Discussion Starter · #4 ·
The reason I want to know is that I am working on a 72 in my Chevy Pickup and I want a baseline were to start to figure my horsepower increases due to adding:

Edelbrock intake and carb
K&N top air filter
1.52 roller tip rockers
1" carb spacer
Ceramic headers with flow thru exhaust
MSD ignition and wires

If I start with a base number of 175 I figure the adders get me to about 235 which seems low to me.
 

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250 hp with headers intake and carb seem about right.

You need better heads, a little more cr, and a little more cam and 350hp with 400 ftlbs can be had.

You need torque to get that truck moving. If you have a 3.08 gear and autotrans, like most 72's, then use a cam with less than 210 degrees duration on the intake. A compcam 252H would be a pretty good choice (206/206 degrees) used with edlebrock alum performer heads. These heads have 170cc intake ports and come in 64, 70, and 72 cc chambers, if I remember correctly. Get the size that will make around 9.5:1 cr with your current pistons.

Go to chevyhiperformance.com and check out the old tech pages. They did a nice 350 goodwrench motor build with 8 parts. They went from 190hp to over 500 with bolt ons. If you want power then you need good heads and a little more cam. A 383 stroker kit would be nice too.
 

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Mertz said:
The reason I want to know is that I am working on a 72 in my Chevy Pickup and I want a baseline were to start to figure my horsepower increases due to adding:

Edelbrock intake and carb
K&N top air filter
1.52 roller tip rockers
1" carb spacer
Ceramic headers with flow thru exhaust
MSD ignition and wires

If I start with a base number of 175 I figure the adders get me to about 235 which seems low to me.
Techinspector and F-Bird got it right, they changed the way they rated them, there is only a very slight difference between a '71 and a '72 350. The '72 figures are much closer to the "real world". Some of the "sacred cows" of the Musclecar Era wouldn't look so good on paper if they were rated using the SAE method but numbers on a page don't slow 'em down any. ;)
 

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The reason the 235 figure "sounds low" is that most dynos don't use SAE NET, but use something closer to GROSS HP (Techinspector and F-bird pointed out the difference). There's no real difference between most 71 and 72 engines (with some exceptions, as Sean was pointing out), just the rating method changed.

Most dyno operators don't run an alternator or a complete exhaust system like SAE NET requires (must use stock air filter and housing, simulated stock exhaust -- same size pipe and same components, length, etc.). If in a clean room no air filter is used, some run straight headers with a large diameter flex pipe connected (sometimes with an exhaust fan), some run the water pump on the engine, some use a water hose stuck in or an electric pump. That's why dyno runs can vary a lot -- the only true comparison is when two setups are run on the same dyno. Dynos are usually used to fine tune an engine, so it really doesn't matter about the end numbers. As long as the setup is the same after each change or during the tuning run, you can still see what makes the most power. Put the same engine on a different dyno setup and you'll get totally different readings, but the same changes should still net the same peak power setup.
 

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Mertz said:
The reason I want to know is that I am working on a 72 in my Chevy Pickup and I want a baseline were to start to figure my horsepower increases due to adding:

Edelbrock intake and carb
K&N top air filter
1.52 roller tip rockers
1" carb spacer
Ceramic headers with flow thru exhaust
MSD ignition and wires

If I start with a base number of 175 I figure the adders get me to about 235 which seems low to me.
from my sources, a '72 4bbl truck 350 was rated @ 260 HP
 

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Discussion Starter · #9 ·
My service manual and Motors manual say 175 but I believe what was said here with regard to how it is rated. There are to many variables to know exactly what the rating is. I figure with my modifications I am probably around 270 to 300. More important than HP is torque. I am getting great off the line performance and don't have any problems towing my 5000 lb trailer.

Thanks to everyone for clearing up the rating differences.
 

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Your engine is basically the same as the standard Goodwrench 350, which GM rates at 260hp (gross) with headers & 4-bbl carb.

The same 4-bbl engine in a '71 Nova was rated 270hp (gross, with headers & no mufflers), and in a '72 Nova w/iron manifolds and the somewhat restrictive transverse dual muffler was rated 200hp (net).
 

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Discussion Starter · #12 ·
I read the articles and found the comment on the spacer very interesting. I got some seat of the pants performance out of mine. It must have to do with the vortec heads that already have good flow that caused the power drop. I was not aware that these heads were so reasonably priced. I will look into them again if I ever need a valve job.

Some good reading at both parts of the site.
 

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Not wanting to hi-jack this thread but the hp rating for my 1979 sbc 350 is 155 hp. That was used in a van (i think) would it be safe to safe putting a 4bbl carb and headers on this engine and shoving it in an s-10 it would make more hp than 155??
 

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Headers help a lot. But not as much on stock engines (stock compression, stock cam, stock intake, stock heads ect.)

Headers and free flowing exhaust can add 20 to 30hp on a completely stock 350. So, yes, it would be over 155hp.

But add mild cam, do a little home bowl work, maybe use a thinner head gasket to raise, install a performer intake with a Q-jet and the engine can make close to 300hp without any driveability or mpg penalties.
 

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454c10, here's what i've got now- 600 cfm edelbrock carb, airgap intake, electric fan, going to add the headers ( for the s-10's). if i have 75cc chamber heads ( 8.5-1 cr??) how thin of a head gasket would i need?? and do you know what the cr would be??
 

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Assuming you have 8:1cr now.

Going to a 0.020" head gasket would make it around 8.4:1 cr.

Swapping to 64 cc heads using a standard 0.040" head gasket would get it up to 8.8:1.

A good set of aftermarket, small port (less than 180cc intake port), 64cc heads and thinner gasket would get it up to 9.3:1 cr, then install a cam around 210 degrees duration and you could make over 300hp and still use the stock gearing and converter.
 
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