Did the 340 really make 275hp?

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beans=exhaust-leak

beans=exhaust-leak

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[ame="http://youtu.be/aG7lSWCeTH8"]302 Found[/ame]



It is sooooo freakin hard to resist using all the great after market hi-po goodies to make the mighty 340 even mighty-er. The only real reason this engine was built close to stock is dad wanted a nice street cruiser type build. I considered sneaking in parts here and there to make it a monster, but I will save them for my own build I guess.

Here are a few specifics:
73 block and main caps, 3418915 J heads, cast iron stock intake 2531915, factory 273 forged crank, windage tray, 273 rods w/ floating pins, hyd comp cam XE268H-10, and a 750 holley.
On the Dyno it made 367hp at 5800 rpms and 375ft lbs of torque at 4100 rpms!!!
 
Yeah they under rated a lot of engine specs in that era to keep the insurance companies out of consumers pockets. However, I've read many articles that have found the stock 340 (`68-'71) to produce right around 275-290 hp. In this case it sounds like Chrysler was not trying to dupe the insurance companies. You have to read those hp ratings carefully though because (for example) they will rate a 426 HEMI at 425 hp but measure it at a lower than average rpm to keep that hp rating low and avoid outrageous insurance premiums.
 
The 340's were always under rated by the factory, part of the game that was played back in the day for insurance reasons, and also NHRA factoring reasons to fit in a class.
Win win situation for Chrysler and the buyers in the know.
 
Longgone said:
Yeah they under rated a lot of engine specs in that era to keep the insurance companies out of consumers pockets. However, I've read many articles that have found the stock 340 (`68-'71) to produce right around 275-290 hp. In this case it sounds like Chrysler was not trying to dupe the insurance companies. You have to read those hp ratings carefully though because (for example) they will rate a 426 HEMI at 425 hp but measure it at a lower than average rpm to keep that hp rating low and avoid outrageous insurance premiums.
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Yeah, what you said!
 
I watched a show on the Speed channel a few yrs. ago where they rebuilt several perf. engines by all companies to stock configurations and dyno'ed them. Almost everything was higher than rated. Some much, much higher. If I remember right the 340 was a 69 model and dyno'ed right at 330 hp.
 
Small chnages can mean alot. Mopar Muscle did a series of builds, a 340, a 383, and a 440. They used stock replacement parts, stock cams and rocker gear, stock exhaust, and NO blueprinting, as regular production engines surely weren't. In all 3 cases, factory rated HP was very close. Small changes made to them after made some big power increases. All were well under carbed from the factory. The bigger carb, cam, and headers really seem to have woken up your dads 340.
 
in their day (early 70's)...as I remember (can't believe I'm say'n that)....those small block "pure stockers" in a A body was a great combo. It was only when my buddies tried to "pump it up"....raise compression, massage porting, bigger cams...that they had issues. Primarily.... the 10 bolt heads were the weak point and would give em fits.
 
My last 340 car was a 73 Challenger 4 speed car, and I can say that bone stock engine had to have well over 300 hp, it did not have anything dun to it, factory exhaust and intake manifolds and breather with 82.000 miles on it, a 1968 383 roadrunner stock could not out run it, but it was at my 1/4 panel on an 1/8 mile track. I agree that it depended on a fresh clean cast like abodyjoe said, and what carb was used from the factory line.
 
When the '275' horse 340 came out in '68 the NHRA IMMEDIATELY refactored it to 310 horsepower. The '70 sixpac engine was refactored to 325 horsepower and the '71 340 was factored to 330 horsepower. Every factory stock rebuild I have seen made at least 315 horse and most were above that figure. Several years ago Dick Landy built a '68 340 to stock factory specs. even used the AFB carb and it made 315 . The '71 was IMHO the strongest of the 340 offerings. It had the wonderful TQ and the well designed TQ intake manifold.

Terry
 
drtybttr,
It has the 2.02 intake and 1.60 exhaust. I guess I should have mentioned that as well. However, that is what was in the heads when I bought them. Not 100% sure if the heads were born that way. I wanted to use some eddys, but that would deviate from the plan. Also, Dad is on this "dis-similar metal" kick. It cracks me up. He has mentioned time and time again that he would never use aluminum heads with a cast iron block and intake, as it would be "DIS-SIMILAR METALS".

hahahahahahahahahahahahaha! oh, dad.
 
I still say that the 275hp rating was conservative at best. The average had to be at least 300hp. 10:5:1 compression, 2.02/1.60 valves('68-71), huge 4.04 bore and short 3.31 stroke is a sure recipe for power.

The 290hp rating on a T/A Challenger and AAR Cuda was even more of a joke. One guy I was talking to explained that his stock one was closer to 350 hp.
 
There was a book out in the late 70s about how chrysler did there engine dyno program.If I remember right chrysler was doing rear wheel horsepower and saying it was crankshaft horsepower.The 340 was really over 300hp amd the hemi was over 500hp.The 440-6 was close hehind the hemi. insurance reasons was a factor for low Hp. remember these cars was ment to be driven by are grandmoms. Mark
 
there was a lot of un-truths about horsepower back in those days (for instance, Ford claiming 385 from the Boss 429- maybe with 2 or 3 plug wires unhooked lol).
 
..i too have seen stock rebuilds dyno 280.
..small changes wake this engine up but the stock rating was probably typical and the stock 10.5 :1 comp ratio was really only 9.5 :1 or so...they rated it at 10.5:1 so you could build and race to that spec for NHRA.
 
My recollection is that the 68 340 with 4 speed had the the highest output of the 4bbl engines. Automatic had a slightly milder cam as did all 69's and up. Does that ring true with anyone else? I had a 69 Cuda FB with 340, 4 spd, manual everything and 4:10 rear and it was pretty quick. Maybe the Wednesday cars were closer to 325 and the Monday/Friday cars were closer to 275?
 
340 wasnt the only engine underrated. I mean cmon,ya really think the 426 hemi made only 425 h.p? Chrysler was bad for underrating motors,just like the other's. Sure it makes that much h.p,but at 4000 rpm's,lol. Nevermind the fact you can wind em up to 5500 rpm,lol..
 
dartcuda1 said:
There was a book out in the late 70s about how chrysler did there engine dyno program.If I remember right chrysler was doing rear wheel horsepower and saying it was crankshaft horsepower.The 340 was really over 300hp amd the hemi was over 500hp.The 440-6 was close hehind the hemi. insurance reasons was a factor for low Hp. remember these cars was ment to be driven by are grandmoms. Mark
Click to expand...

I could see this, 275HP at the rear wheels is a realistic number.
 
needsaresto said:
340 wasnt the only engine underrated. I mean cmon,ya really think the 426 hemi made only 425 h.p? Chrysler was bad for underrating motors,just like the other's. Sure it makes that much h.p,but at 4000 rpm's,lol. Nevermind the fact you can wind em up to 5500 rpm,lol..
Click to expand...

Detroit horsepower ratings were changed for the 1972 model year from gross rating numbers to net ratings.

Net ratings were supposed to be more realistic real-world numbers, because the new testing methods utilized different methodology more in keeping with "as installed" conditions (accessory drives hooked up and operating, and exhaust running through a stock exhaust system, including mufflers.)

But, along with this new rating system (about 30-percent lower numbers, usually,) the 340 went through a "de-tuning" that year that included smaller intake valves, and lower campression. So, an "apples-to-apples" comparison with the '71 engine wasn't possible.

My 318 2bbl 1972 L-A engine went from 230 HP down to 150 HP with no mechanical changes from '71 (gross) to 1972 (net) rating.

Tht is a change of 35 percent! (.35 X 230 = 85.)

They were wildly inconsistent with this; if they had used that figure (35-percent) on the 275 HP 340, even with NO changes, it would have resulted in a drop of 96 HP, down to a net rating of 179 (ridiculous!) instead of the 240 they claimed.

I remember the '72 motors as exhibiting noticably less "grunt" on the drag strip (about half a second) but the NHRA experience has shown these 1972 motors to be only VERY SLIGHTLY less powerful than the 10.3 compression '71 340s. Racers somehow, have found a way around at least some of the power-robbing changes the factory introduced in '72. The NHRA HP factor for the '71 340 is 314 HP. the '72, 298... 16 HP for the lower compression and smaller intake valves... not much of a change (on the order of 5-percent.)

The exhaust manifolding (particularly, on the drivers' side) was just awful on these 340 cars; a decent set of headers made a huge improvement, and of course, they were jetted really lean from the factory, so a set of headers and some richer jets would really wake this engine up!

It's too bad that Ma Mopar didn't see to it that a set of W-2 heads were on every 340 that left the factory; Brand X would not have stood a chance! :cheers:
 
275hp RWHP is enough to push a 3300# car to about 105 MPH in the 1/4. I doubt ANY production line stock 340 car is gonna do that.

Most of the 340 cars ran high 90's in the 1/4. Like 96-98 or so. Even the tweaked cars for the mag test didn't tun 100 mph from what I recall.
 
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