72 340 actual hp?

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65CudaFish said:
I read a comparison article of a 1957 Poly 318A engine dual quad set up and it said that it had as much HP as the 375HP 340 6 Pack. So that says allot for the 340. It was a creditable article.
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Most engines you can get 1 Horsepower per a cubic inch displacement.
 
I think the only thing in stock on my car is the windows, ha ha ha ha
 
Seriously though, it is a good idea to keep the two 340's separate, they are very different as stated in the article in the earlier post, allot can go wrong, like everything in a hurry. When building a 340 for racing from a 73 engine the only thing that is 1973 on mine is the block, everything else is different. I am going to put the 1973 heads on it though with stock porting but 2.02 intakes installed. Right now it has hot running ported J heads on it that are known for cracking in the runners!
 
dmoore said:
Castcrankdebut.jpg
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If I read this right, 340's built prior to April 11, 1972 used forged cranks. It wouldn't surprise me if the majority of 340's built for 72 model yr. cars were built by then. Just my thoughts.
 
Keep in mind on the steel crank thing.....there ware LOTS of 72 models made with steel cranks. Most, in fact. THe new model year began back then in September. So that means from September to April (six months) the 72 340 had a steel crank.
 
jerry6 said:
Factory ratings were bs back then , that or they took the last motor built on Friday before labour day week end
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If I remeber correctly,NHRA re-rated the 275 horse 340's to 325 for drag racing purposes. And,yes the way horse power was rated,changed in '72.
 
65CudaFish said:
Yeah it did, the compression ratio that is, the cast crank was in the 1973, I don't think it was in the 72 maybe late ones. But the cast crank was actually better then the steel one back then. It was said to be the nicest balancing on the circuit at the time. But today, I would go with a steel eagle from Mancini Racing and H beam rods. Some of the old MoPar steel cranks were badly forged and balancing holes were drilled everywhere some would not seal without rope seals and in some cases more balancing. But strong yeah! Lighter no! And much harder on rod end play wear. Today's technology is great, it just cost a fortune. :burnout:The 340 I had along time ago was factory except for the headman headers and it had to be timed at 1 degree ATDC in Southern Cal. because of the compression ratio and would top at 135 MPH with that timing, but man did it get there quick, it was a 1970 model.
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"But the cast crank was actually better then the steel one back then"

This is the very first time I have ever heard this from anyone....and I've been play'n with these cars since 77.....................
 
73 up were shot peend to help strength . f the forgings were not so hot , why would the casting be any better ? Personally had 2 360's late 70's , 1 440 72 and a 318 70 go bad , bearing noise , seized , and bad cam . After that most of them went 100,000+ miles with no trouble , except plastic timing gear wearing on 360 and 318 .
 
StrokerScamp said:
Keep in mind on the steel crank thing.....there ware LOTS of 72 models made with steel cranks. Most, in fact. THe new model year began back then in September. So that means from September to April (six months) the 72 340 had a steel crank.
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That is how it is now but back then I believe it was different.

My 1979 Dodge was built in Oct 79, yet is a 1979 model.
 
dodge freak said:
That is how it is now but back then I believe it was different.

My 1979 Dodge was built in Oct 79, yet is a 1979 model.
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They may not have been built as early back then as they are now but I remember my Dad saying he bought his new 69 Charger in late Nov. of 68 so they were built earlier than the model year.
 
so the 72 340 probably had around 250 hp like it was rated at..

well my dart is supposed to arrive today or tomorrow so i will post pictures once i get it , then i will have to find some time to get the motor up to about 340 hp over the winter or in the spring, then i will be ready to cruse and hit the drag strip..
 
it all depends HP was "rated" lower due to insurance changes and cafe standards being lowered..... it was not at all uncommon for your 250/275 hp 340 to be sluggin out up to 350 easily...have seen it with my own eyes way more than once!

also someone said earlier that the 72 340 could ALMOST be made to earlier specs...what does ALMOST mean??? I worked at Chrysler, I had the engineering specs printed for me and I built dozens of 72 & 73 340's to 68 specs....most were so close very little need to be done..but once they were done the performance was noticeably improved....ALSO the myth about X heads is sickening....they had X J & U and they were the exact same head!!! a few had smaller valves but all that was needed to bring those back into performance range was a lil grinding and WHOOP 2.02 & 1.60 ready to rock!!
IT just kills me when guys think that X heads are worth 3x what a big J or U head is worth...bull droppings.... U heads are even MORE RARE......I think some guys just LIKE the X stamping...because that is THE ONLY difference!

NOW if you consider slight modifications....you could easily get 410 hp out of them back in the day and not spend $400 bucks to do it..... quite a few books out there STILL on how to mod any year 340 to seriously kick some ***
 
Sgt Mopar said:
check this link out. I got a '72 as well. wish it was earlier. maybe someday i'll get one. hope this link will help. has some 340 specs over the years.

http://www.allpar.com/mopar/mopar340.html
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ya thats actually were i found most of my info

66cuda said:
NOW if you consider slight modifications....you could easily get 410 hp out of them back in the day and not spend $400 bucks to do it..... quite a few books out there STILL on how to mod any year 340 to seriously kick some ***
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ya i would like to find some of these books, i would like to get it up to around350 - 400 hp , it would be nice if it would still only cost $400 but more like a couple grand nowadays.
 
The cast crank would not affect the horse power, that's just bench racing b.s.
Reliability wouldn't be affected either unless you buzz the engine to 7000 rpm continuously.
They were cheaper to manufacture, that's why they went to them.
JMHO.
 
tarrin8 said:
so the 72 340 probably had around 250 hp like it was rated at..

well my dart is supposed to arrive today or tomorrow so i will post pictures once i get it , then i will have to find some time to get the motor up to about 340 hp over the winter or in the spring, then i will be ready to cruse and hit the drag strip..
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Nice, good luck with it. Like I said keep it in it's proper category of the three kinds of 340's there were. Also it is best to keep it simple, configure a cam, induction & headers package and you will have a nice engine. Maybe rear end gears later. Be careful because allot of the aftermarket stuff is junk. The MoPar Performance distributor is a good streetable system but is curved for a quicker mechanical advance, which stock springs can be put into it to slow it down. It is adjustable though and comes with full instructions. Simple is good though, the engines were made to produce power. I read an article on a 1969 Roadrunner once and they bought the car new, bumped up the cam added headers and 489 Spicer's in the rear end and took it to the track and it did a 1 1/2 foot wheel stand out the box and th ET was 10.90 and that was with a 4 speed:burnout:
 
66cuda said:
it all depends HP was "rated" lower due to insurance changes and cafe standards being lowered..... it was not at all uncommon for your 250/275 hp 340 to be sluggin out up to 350 easily...have seen it with my own eyes way more than once!

also someone said earlier that the 72 340 could ALMOST be made to earlier specs...what does ALMOST mean??? I worked at Chrysler, I had the engineering specs printed for me and I built dozens of 72 & 73 340's to 68 specs....most were so close very little need to be done..but once they were done the performance was noticeably improved....ALSO the myth about X heads is sickening....they had X J & U and they were the exact same head!!! a few had smaller valves but all that was needed to bring those back into performance range was a lil grinding and WHOOP 2.02 & 1.60 ready to rock!!
IT just kills me when guys think that X heads are worth 3x what a big J or U head is worth...bull droppings.... U heads are even MORE RARE......I think some guys just LIKE the X stamping...because that is THE ONLY difference!

NOW if you consider slight modifications....you could easily get 410 hp out of them back in the day and not spend $400 bucks to do it..... quite a few books out there STILL on how to mod any year 340 to seriously kick some ***
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It's just damn near impossible:banghead: these days to run a old 340 at a standard bore. I was sure the later heads had thicker castings than the earlier ones. That is what I've been told over the years, because they are the same heads as the early 360. The J heads I hear are the hottest running ones!
 
dmoore said:
"But the cast crank was actually better then the steel one back then"

This is the very first time I have ever heard this from anyone....and I've been play'n with these cars since 77.....................
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Yep better balanced meant better longevity. But the strength was taken away for sure. I'm not exactly sure where I read that, it may have been Carol Shelby's Speed Secretes, the old Direct Connection book. It's very informative of what was going on back then but also very expensive to buy now!
 
Dartnut said:
The cast crank would not affect the horse power, that's just bench racing b.s.
Reliability wouldn't be affected either unless you buzz the engine to 7000 rpm continuously.
They were cheaper to manufacture, that's why they went to them.
JMHO.
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If anything it may help it if it is in fact lighter, most are, but it wont be as strong!
 
65CudaFish said:
If anything it may help it if it is in fact lighter, most are, but it wont be as strong!
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318 is the same stroke. A Poly 318A crank will fit in a 340 or a 318LA crank will fit. The early 273 wont work though because the hole in the back of the crank was smaller and the later torque converters alignment nipple wont fit into it. The Poly was a steel crank, just not as strong as the later steel ones. And many 318LA cranks were steel. I have a 318LA crank in my 340.:D
 
I think that was the real rating for all 340s...about 250 crank hp for a 4bbl and 275 crank hp for the 6pack. no matter the year. Compare how fast todays cars are with 300hp then compare it to credible times the 340 did back in the day. If a 340 had 325-350 hp from the factory id think it would run much faster times than high 13's for the six pack, and low 14's for the 4bbl in the 1/4 mile...Just my 2 cents.

Before you disagree..a 04 4.6L GT mustang is rated at 260hp and runs a 5.8 second 0-60 and a 14.1 in the 1/4 mile..It leaves me to believe the 340 has around the same horsepower.
 
tires in the old days were a HUGE limiting factor , + gears in the transmissions are lot shorter and more plentiful today , so 260 hp today will do much better lots more than just hp in play
 
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