SAE v BHP on 318LA Stock Engine

M Body General Discussion

  1. 77 LeBaron

    77 LeBaron Well-Known Member

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    I know the basics on the SAE Net Horsepower v SAE Gross Horsepower but could someone tell me what the Gross HP would be for my SAE Net Horsepower rated 1977 Chrysler LeBaron ? It is rated at 145 Net HP on the 318LA engine , I know before the change in 1971 or 72 The 1970 Dodge Dart with basically the same 318LA engine minus emissions was rated at 230 HP So is it still basically the same just a different methodology used ? I know the emission components added lowered Horsepower but by how much ? I am just trying to figure out what my cars power would be in 1970 pre SAE but with the smog/emissions I have on my 1977 LeBaron. Thanks hope I did not confuse.
     
  2. Aspen500

    Aspen500 Well-Known Member

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    It's hard to say what the gross hp would be. Depends on the engine and other factors but net is usually 15-25% less than gross hp. A rough GUESS would be an advertised 145 net would be 175-185 gross hp.

    Remember that factory advertised hp may or may not be accurate. The 426 Hemi, for example, was rated at 425 gross hp but in reality was more like 500 hp. What I mean is, who knows if the 145 rated hp of your 318 is true or not. Could be more, could be less.
     
  3. Oldiron440

    Oldiron440 Well-Known Member

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    I believe the 77 motor had only 8 to 1 compression and the 71 was higher and the catalytic converters of the time where horsepower killers, so it's hard to compare the two Motors.
     
  4. 77 LeBaron

    77 LeBaron Well-Known Member

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    I am just looking for a ballpark guess here . 230 to 145 is a big drop. And the way the Horsepower is rated is by two different measures of the engine. I cannot find any NET to GROSS Horsepower conversion tables on the web. Some forums have the same estimates that Aspen500 posted. It is really surprising that someone did not come up with a conversion table taking into consideration and factoring in the emission and compression ratios .
     
    Last edited: Sep 24, 2017
  5. Aspen500

    Aspen500 Well-Known Member

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    There is no good way to do a conversion and be accurate. All you can do is get a rough idea. Depends on the engine, how many accessories they considered for net hp (alt, p.s., etc), the cam, heads, compression, carb, which emission standards is it built to meet, rpm the hp rating is referring to .............Too many variables. I'd still guess around 180 hp would be in the ballpark.

    About the test rpm, I remember Pontiac advertising the '73 455 SD at 290 net hp. It did have 290 at something like 4,000 rpm but at 5,500 it had closer to 400 net (I don't recall the exact hp and rpm's but you get the idea). So they weren't lying about the advertised hp, they just never said that was the total (kind of a wink,wink for the Government and insurance companies). I'm sure Mopar and all the others did the exact same thing. In fact I know they did;)
     
  6. BudW

    BudW Well-Known Member

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    I’ve owed a few 318’s in my life time (all 2-bbl). My ’68 Charger and ’71 Barracuda ran neck to neck – which is about what my ’77 wagon runs.
    Other than option wise (like A/C or even emissions) – I hadn’t noticed much of a difference in power in any of them - except for my '86 5th Ave.

    I suspect differential gears – is where the difference might lie.

    I would “guess” your ’77 Lebaron puts out about 190-200 Gross HP – but that is only my guess.

    On a side note: Back in June, I put my stock ’77 wagon on a dyno, with 42k original miles, 2.94 gear ratio. The car put out 135.17 HP at 3.99k RPM. Max Torque was 211.01 at 2.96k RPM. https://www.forfmjbodiesonly.com/classicmopar/threads/second-time-entering-into-a-car-show.6497/#post-72416

    My ’86 5th Ave is held down by its gear ratio, which is 2.21. I will be changing those gears out with a 2.94 ratio soon and I expect both cars to run about the same, then. My 5th Ave – the car “feels” like you can put a brick on the accelerator petal, get out of car, check tire air pressures, check engine oil level and car feels like it might have traveled 5 foot in that time frame - because of the “boat anchor” 2.2 gears it has.

    2.94, or even better 3.21 gears should wake my 5th Ave up.

    I’m going to guess your Lebaron has 2.4 or 2.7 gears in it (both much better than 2.2’s but still a lot of room for improvement).
    BudW
     
  7. GregG48213

    GregG48213 Member

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    Another factor to consider is what was happening around the time frame when these cars were produced: CAFE (Corporate Average Fuel Economy). One approach to improve fuel economy is to get the car in top gear as soon as possible. If I was in a hurry, I would manually wind out second gear in my '88 Police Diplomat; otherwise it seemed to upshift too early. This did necessitate installing a tachometer.
     
  8. MoparKidD-4

    MoparKidD-4 Well-Known Member

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    The main reason for switching to SAE net HP was to standardize the industry ratings so car companies couldn't just list whatever HP they felt like which had been done previously with gross ratings. Like Aspen500 said there is no conversion factor because A) different accessories/fans drew different amounts of power and B) gross HP ratings are not standardized to anything. These days you can still get a "gross" HP figure from an engine dyno with no power accessories on the engine, that only tells the partial story as once you add the power accessories and try to push that power through a transmission and rear differential you get even less power at the wheels.

    The best "dyno" is a drag strip IMO. Weigh the car, make a pass, plug in trap speed and weight into formula, and BAM you get exact HP at the wheels.
     
  9. 77 LeBaron

    77 LeBaron Well-Known Member

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  10. 77 LeBaron

    77 LeBaron Well-Known Member

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    Bud I think the final gear ratio is 2.76 for my 318 2BL Lebaron . Thanks for all the technical information .
     
  11. BudW

    BudW Well-Known Member

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    There is only one good way to know for sure, and that is to pull the inspection cover and read the numbers stamped on the ring gear. On different note, your differential fluid is probably way way way past due for replacement, anyway.

    A close second is to jack rear of car up, chock one rear (and a front) tire, mark the free tire and propeller shaft (chalk works good), have someone rotate a tire while someone under car counts propeller shaft revolutions. Rotating tire 20 times gives a great estimate to your gear ratio (divide propeller shaft rotations by 10).

    Early to Mid ’70’s, Chrysler quit placing tags on differential cover to state its ratio – so I doubt your ’77 will have a tag. What they did was paint a couple of paint stripes on the housing, somewhere – which in most cases, the paint falls/wears off in a couple of years.
    Not even the fender tag will tell you your gear ratio you have (but it should).

    2.71/2.76 ratio gear is not the best gear ratio to have – unless you do 90% highway driving.
    My guess (which is only a guess) is you have a 70% chance of 2.4:1 and a 30% chance of 2.7:1 ratio.


    In my opinion – just remove the inspection cover and give the ring gear a look over. Trust me, your existing differential will love to have its old nasty fluid (what little it has) changed out.

    The 7¼” differential only holds 2.4 pints of fluid, compared to 4.4 pints in an 8¼” differential (GL-5 90wt lube). Even a minor fluid leak can run 2.4 pints down to a critical level.

    Tip, if inspecting (or changing) rear differential lube, do yourself a favor and replace of the 30 (or 40) year old rubber plug, and replace with a new one. The rubber hardens and shrinks over time making it a bear to remove and it will leak in that area as well.
    Dorman 090062 – which is currently selling for $1.96 (US) at RockAuto.com
    BudW
     
  12. AJ/FormS

    AJ/FormS Well-Known Member

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    And there can never be a direct comparison. You would need to build two original engines and have two original cars. And two dynos; one engine and one chassis. And then you would need to compare those results to results of your engine; in and out, to see if it even makes the numbers.
     
  13. 77 LeBaron

    77 LeBaron Well-Known Member

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    Thankyou Bud I ordered that Dorman 090062 last night. I will accept the 180-200 BHP range estimate . I still cannot believe no one devised a formula for this. I have recently started to fall in love with the 1981-83 Imperials w/ the same 318 engine many great immaculate examples to be had at low prices. Got to stay of E-Bay !
     
  14. BudW

    BudW Well-Known Member

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    Too many things to factor in also factories were not very truthful to begin with – which is part of reason you won’t find a formula.

    Do you mean “Got to stay off of eBay”?
     
    Last edited: Oct 5, 2017
  15. AJ/FormS

    AJ/FormS Well-Known Member

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