Did the 340 really make 275hp?

[K.O. SWINGER]

every dyno test of a factory built 340 68-70 that i have seen and I have been watching for for over 30 years puts them about 300 hp when tuned properly ,but the push is how well they breathed so they really respond to up grades.

 

[dartcuda1]

The computer don't account for wheel spin,shift points,suspension travel,and real world events so rwhp sounds more likely in real world situations. Mark

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.

 

[needsaresto]

I remember watching a show that had Mr Norm on it. He talked about how a customer was complaining about his 340 car being down on power,so Mr Normès dealership performed a supertune on it,and did a before and after dyno run with a rwhp dynometer. About 230 h.p before and well over 300 h.p after. Dont know what the hell they did,but as was said ealier,the 340 responds to mods and tuning very well.

 

[crackedback]

HP/Wt to MPH rarely lies, especially RWHP. Flywheel HP is subject to plenty of outside influences, like crappy converters, etc.

Wheel spin usually provides higher MPH than expected so that is the other direction. None of that other stuff really makes a difference in MPH at the track. Et, yep it all makes a bit of difference, MPH, nope!

Ever see a car run an 11.70 at 130 mph. Plenty of ponies... no leave!

 

[RustyRatRod]

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).

Naw, that was probably close cause Ford ain't ever been spit.

 

[moparlover]

i remember reading that the 426 hemi was 425hp stock. by doing one single thing, taking off the factory exhaust manifolds and putting on headers it jumped to 475hp.

i'm sure it was similar with the 340... the one in the dyno above has headers

 

[BBBCUDA]

This could be a good thread if people look for the information it contains. One thing I really dislike is imaginary horsepower. Guessing or hoping doesn't prove much. It's only been recently I've been really checking deck clearances, CC'ing heads etc. Not much I have measured lately matches what the factory tells you. I've never checked a stock 340, but I do have one. When it comes out, I'm betting that 10.5 to 1 compression is closer to 9.25 to 9.5. A point of compression is significant. Add a less than optimal factory ignition curve, lean jetting, crappy factory exhaust pipes, etc. I would bet that just as many stock 340's out there make less than 275 as there are ones that make more than 275 in stock form. The link to the MM article, and the origional posters results closely mirror each other, and show what mild modifications can do.

 

[65Vart]

275 was a joke for the 340. 68-71 340s made more like 350-375. The 275 was for the insurance guys. Same thing with street hemis , 425 was a joke. Actual hemi numbers were way higher.

 

[BBBCUDA]

275 was a joke for the 340. 68-71 340s made more like 350-375. The 275 was for the insurance guys. Same thing with street hemis , 425 was a joke. Actual hemi numbers were way higher.

Did you look at any of the dyno tests in here?

 

[65Vart]

Did you look at any of the dyno tests in here?

It's a fact, They measured factory HP below peak RPM.Ive seen a stock spec 340 make just over 325 thru stock HP exhaust manifolds, stock hydro 340 cam, stock heads, at 6000 rpm.

 

[BBBCUDA]

I thought they were 350-375? The origional posters didn't hit 375 with a cam, carb, and open headers. The stock one in the MM article, NON- blueprinted, made 281 with open exhaust off the manifolds. None of these were blueprinted from the factory, and were far from optimum. A carefully assembled one, with everything perfect? Sure, I can see more than the factory rating, but the average one I seriously doubt made much more. MM did a 383, and a 440 also, the 383 was very close, the 440 made a little less. I saw a trend in those builds, and that trend was that Mopar was pretty honest with their ratings. If stock 340's made 350-375 HP, they wouldn't have all run low 14's or high 13's.

 

['73red-duster]

I think some of us may be forgetting that the way horsepower was rated changed drastically in 1972. Gross hp (or brake hp) verses net hp. My '72 Duster, 318/150 hp, blew the doors off of several '70/'71 210 hp versions. Same motor/same specs/differant hp rating.

 

[65Vart]

I thought they were 350-375? The origional posters didn't hit 375 with a cam, carb, and open headers. The stock one in the MM article, NON- blueprinted, made 281 with open exhaust off the manifolds. None of these were blueprinted from the factory, and were far from optimum. A carefully assembled one, with everything perfect? Sure, I can see more than the factory rating, but the average one I seriously doubt made much more. MM did a 383, and a 440 also, the 383 was very close, the 440 made a little less. I saw a trend in those builds, and that trend was that Mopar was pretty honest with their ratings. If stock 340's made 350-375 HP, they wouldn't have all run low 14's or high 13's.

all I'm saying is 350 is easy with a tune. Then a bigger carb on a stock 340 intake can get you 25 plus HP, headers another 20, list gos on. You don't need to touch the bottom end on a 340 to get well over 350 (yes I was reaching a bit for 375 but with a cam you will get it +, still with stock X heads and a better spring). Best small block ever built.

 

[BBBCUDA]

We agree on one thing; BEST small block ever built. Way under rated? I say no, and the ET's and Mph from those cars stock jive perfectly with the factory rating. If we want to talk OVER rated, how does GM explain why the 340's ran with or beat their much higher "rated" small blocks?

 

[pishta]

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 heard those were like 600 at RPM...wow!

 

[604]

guess it really depends on if you got one with good or one with crappy factory machine work.

Boy do I hear that on the crappy factory work. In the last 6 months I have tore down 5 small blocks. 3 318's and 2 360's None of them has had the rods in the correct locations (numbers in the wrong hole) And the 360 I am taking down right now even has one or two rods with letters instead of numbers. I remember a "H" for sure. LOL

On the rating,
I had a guidance counselor in high school that had a restored panther pink 1970 TA 340 six pack, and a 4 speed. Do not remember what gear it was, but no way it was only 290 hp! That thing was crazy, and stock.

 

[cosgig]

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?[/QUOTE



Thats true that the 68 4 speed motor had a slightly more agressive cam than the automatic cars and after the 68 model year was over, they went to the automatic grind for all regular production 340's.

I don't know about the Wed/Fri battle, but I wouldn't doubt it. I worked at an auto parts manufacturing plant back in my younger years and the place was a ghost town on Friday, and whoever actually came back had been out drinking and smoking their lunch!!! Yep, me too!!!

Geof

 

[crackedback]

Stock 340's, even 68 4 speeds, no way, no how with factory carb, intake, exhaust make 350hp... ain't gonna happen. They were lucky to make 300 at the flywheel.

Put headers, carb, etc. on them and they wake up.

 

[Bill Dedman]

Put headers, carb, etc. on them and they wake up.

The '71 340 had a 750cfm Thermoquad...

Just what kind of a carb do you think might be an improvement?

 

[Bill Dedman]

I heard those were like 600 at RPM...wow!

The stock Boss 429 was a PIG.

The thing came with a mild hydraulic cam, and huge intake port sizes that only worked well at engine speeds over 6,000 rpm.
It wouldn't even TURN 6,000 rpm with the stock cam!

Horrible mismatch...

I had a good friend who bought a new one in 1970(?).... I think that was the year; might have been '69.

I wouldn't get out of its own way when it was stock.

Seriously...

From a Boss 429 web page: "One would think that the Boss 429 would have been a street terror- given its impressive specifications. At best, in stock form, it equaled the 428CJs performance. The usual after market bolt-on modifications were extremely effective on waking the engine up. But as far as Ford was concerned, there was no reason to promote this Mustang- it's only purpose for being was to get that monster engine homolugated."

They give 14.09 at 102.85 mph as Car Life's road test performance figures. My buddy's wasn't that fast...

 

[Rat Patrol]

Just for giggles - I ran a 340 68 manual cam thru DD2003.

.444" / .453"
276/284

I used the following X head flow figures off the Al West site.

.............................................................................. .600th

Int 32 58 125 172 208 221 210
Exh 22 45 95 122 135 140 142

Pretty darn close!!

 

[Rat Patrol]

....I'll add my 2c as well.....Crackedback has got it right.

If they were making 350 HP those cars would be running 13.2s at 3000lbs from the factory. Simple fact is...they didn't.

I'd buy 300HP on a good day...tops.

Or was the 250 HP 14.8 LT350 really making 300? LOL!!

 

[DusterKrazy]

The '71 340 had a 750cfm Thermoquad...

Just what kind of a carb do you think might be an improvement?

I'm pretty sure the '71 had an 850??
BTW, Can anyone speak out on '71 vs. '72 340 performance (as in seat of the pants power?)

 

[racerbob]

I'm pretty sure the '71 had an 850??
BTW, Can anyone speak out on '71 vs. '72 340 performance (as in seat of the pants power?)

'71 definately faster by a bunch.

The TQ's were changed in 1972 model year and later and are supposedly better. I dunno about that.

I had a '72 duster I bought wrecked (but it still was driveable) as a parts car. 340/auto with stock (3.23 open) rear. Car was actually pretty quick and fun to drive!, but not as fast as my friend's 1970 dart swinger 340/4 speed!!

I think having the TQ carb has helped '72-'73 340 cars stay competitive in class racing. Notice the fastest stock elimnator 340 car was a '71 duster at like 10.70's (at least that I have seen). '71 has the big TQ carb and the steel crank, high compression , big valves, etc.

I just bought a car with a 1968 340 / 4 speed powertrain in basically stock form. It runs real well, but not anywhere near as fast as my 360-400 hp 340 in the 73 dart sport racecar. 68 340 4 speed is around 300 maybe a bit more.

bob

 

[RustyRatRod]

Two basic sizes for the Thermoquad. 800 for small blocks and 850 for big blocks. The 71 Thermoquads might have made a tad more HP peak but where they were lacking was tunability. They were a beeotch to tune at part throttle/idle because they were air metered instead of fuel metered. That's why they were replaced under Chrysler TSBs back in the day with the 72 model.