Author Topic: '78 Pontiac 400 stock horsepower  (Read 4413 times)

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Offline lethal_inject1on

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'78 Pontiac 400 stock horsepower
« on: April 08, 2013, 09:05:23 PM »
So, I'm reading that the stock horsepower from a '78 400 was either 180hp or 220hp.... is that fact ?

That just seems really, really low.. Even by 1970's standards.

Offline pancho400cid

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Re: '78 Pontiac 400 stock horsepower
« Reply #1 on: April 08, 2013, 09:18:54 PM »
Sad but true. 

Per Hitman's info L78 400 was 180 HP.  W72 400 was 220 HP.   L80 403 Olds was 185 HP.

http://www.78ta.com/specs1978.php

The good news is it is pretty easy to wake these engines up...

An engine that makes less than 1/2 HP per cubic inch of displacement is fine.... when it's pulling a John Deer.  The manufacturer's had no real ability to deal with the emissions standards of the day.  I'm glad that they got it figured out......
« Last Edit: April 08, 2013, 09:20:29 PM by pancho400cid »
1978 Trans Am - Brown - Current Project
1978 Trans Am - Silver - Future Uncertain

Offline lethal_inject1on

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Re: '78 Pontiac 400 stock horsepower
« Reply #2 on: April 08, 2013, 09:45:57 PM »
How can I tell if I have the W72 or L78 ?

Offline mikekop

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Re: '78 Pontiac 400 stock horsepower
« Reply #3 on: April 09, 2013, 01:20:46 AM »
As long as someone didn't swap them out, the W72 has chrome valve covers.

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Offline LilSki

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Re: '78 Pontiac 400 stock horsepower
« Reply #4 on: April 09, 2013, 09:10:20 AM »
It is pretty well documented that the W72 was underrated and was closer to 300HP.
Kevin
79 Trans Am: (77 nose), WS6, M-21, 461, Hotchkis TVS, PTFB Contol arms. 
85 Trans Am: Vortec 350 w/LT1 cam/T56, TPI conversion w/Megasquirt II.

Offline lethal_inject1on

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Re: '78 Pontiac 400 stock horsepower
« Reply #5 on: April 09, 2013, 10:09:40 AM »
Has anyone had their stock motor dyno'd to reflect that 300hp assumption ?

Offline 72blackbird

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Re: '78 Pontiac 400 stock horsepower
« Reply #6 on: April 09, 2013, 12:18:35 PM »
Time to fire up the bench dyno.  ::) ;D

Offline pancho400cid

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Re: '78 Pontiac 400 stock horsepower
« Reply #7 on: April 09, 2013, 01:07:12 PM »
It would not surprise me that a W72 would do better that 220HP on a Dyno.  I know mnfr's play games up and down with published numbers all the time to suit whatever angle they were working (marketing, insurability, class acceptance for racing, etc.)

As for Bench Dyno readings..... I'm "gonna" put chrome-plated rods and a space-shuttle cam in my next 400.  I expect bench dyno readings of at least 800 HP!   :o  ;)

« Last Edit: April 09, 2013, 01:09:02 PM by pancho400cid »
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Offline lethal_inject1on

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Re: '78 Pontiac 400 stock horsepower
« Reply #8 on: April 09, 2013, 02:09:38 PM »
Might as well install space shuttle thrusters while you're at it :)

Offline 72blackbird

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Re: '78 Pontiac 400 stock horsepower
« Reply #9 on: April 09, 2013, 05:49:43 PM »
How can I tell if I have the W72 or L78 ?

An L78 will always be a 500557 block - some 77 W72s did have 500557 blocks, so you'll have to check your cowl plate to see if it was a W72 or not. 78 W72s do have 481988 400 blocks. All W72s should have 6x-4 heads.

Offline Grand73Am

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Re: '78 Pontiac 400 stock horsepower
« Reply #10 on: April 09, 2013, 09:55:25 PM »
So, I'm reading that the stock horsepower from a '78 400 was either 180hp or 220hp.... is that fact ?

That just seems really, really low.. Even by 1970's standards.

I guess it depends on what you're comparing the hp numbers to. You may already know this, but engine hp ratings were higher before 1972, because the way horsepower was measured was different than the way horsepower was measured after 1971. Before 72, the ratings were gross hp. 72 and later, the ratings were net hp ratings, which is a lower number. So, for example, there was a year or two there where the exact same engines went from like 400 hp to 250 hp in advertised ratings, with no actual change in the engines. So, 60's to 1971 engines weren't always really as high horsepower as they were sometimes advertised, and the 70's engine weren't always as low as they were advertised. In other words, the differences in horsepower wasn't as great as it seemed by the numbers, because the numbers were arrived at using different ways of measuring.  Although with lower compression and emissions equipment in the 70's, the power did go down, not just in the way it was rated. But the difference in the rating method was a big part of the lower numbers. Of course, the lack of acceleration in the 70's was also related to the 2 series rearend ratios that were used in a lot of the cars from 75 and later to get better gas mileage, while eariler cars usually had lower rear gears(higher numerically) for better acceleration.
This is a link to a page that explains it much more thoroughly and better than I can:  http://ateupwithmotor.com/automotive-terms/47-gross-versus-net-horsepower.html
Steve F.