Posted by Fred Coldwell on Thursday, June 28, 2001 at 10:25AM :
In Reply to: Re: 318 LA outperforms 318A poly... posted by MoparNorm on Wednesday, June 27, 2001 at 5:39PM :
Hi Norm:
Engine specs for 1968, 1969 & 1970 model years continue to rate the LA-318-1 standard engine at a maximum 210 hp (gross) but do not list the applicable rpm, which I imagine stayed the same at 4000 rpm. The 1968 model year sales catalog 81-305-8101 lists the LA 318-1 hp as 177 net at 4000 rpm, so for pre-smog years the ratio of gross hp to net hp is about 84.3% (177/210). In 1968, maximum torque was 318 ft-lbs at 2800 rpm, or one ft-lb. per cubic inch, which is pretty good by my book for a standard factory engine.
I compared a late 1966 A-318 poly to an early 1968 LA-318-1 wedge to get comparable pre-smog data and compare the engines mano-a-mano on a design basis. Increasing government smog regulations and the restatement of hp ratings in net instead of gross numbers (under pressure from the government to end the "horsepower race" that was boiling teen age testosterone) reduced the subsequent years performance numbers for the LA-318.
Comparing a late smogged LA-318 to a pre-smog 318 poly is not a fair comparison of basic performance or engine design because the reduction in LA-318 performance over the years came in part from a third-party outside source, government mandated smog rules. The 318 poly likewise would have experienced reduced performance numbers during the very late '60s and early '70s if it had remained in production when the government smog regulations took increasing effect. And a LA-318 that has been upgraded with a four barrel carburetor likely would show an increase in it's performance numbers too, as did the poly 318 with that modification. I'm a mono-fruit man when it comes to comparisons, so the performance apples I'd like to see would come from a 2 bbl 318 poly that has been smogged to meet the 1973 smog regulations in every particulate :).
As an aside, I recall (without looking it up) that the performance numbers for the late 1970's 360 were near the same as the presmog LA-318, so the smog rules may have been neutralized by an offsetting increase in cubic inches.
The higher rpm at which maximum torque was achieved in the LA-318 (2800 in the LA-318 vs. 2400 in the 318A) might have been a design feature based on the generally higher average road speeds in 1967 vs 1957 due to the Interstate highway system. Trucks generally would have kept the same axle ratios in each decade to obtain their gvw ratings. This is just pure speculation on my part, but a reasonable theory nonetheless.
I love discussing facts, but Mopar engine performance numbers for 1969-1975 are not easy to find. The hp numbers are not fully specified in Dodge truck sales literature I have for those years, so it takes time and effort to track them down.
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