1971 340's True HP?

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hux340

hux340

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Hi all,
I have a 71 H code Dodge Demon & they reckon it came with 275hp from the factory. I've heard a lot of Chrysler made their muscle cars hp underrated for insurance purposes. If that's true what would be a more accurate hp figure for the 340's.

Cheers,
Glenn.
 
Bob Lambeck (30 years ago, Camaro Craft did a actual 340 Dart restoration giveaway...) Got 315 horses through a a basic rebuild (most likely blueprinted....) through a stock 69 intake /carb & exhaust manifolds(. Camaro Craft giveaway Dart at the Street MachineNats,'85-'86..B5 blue, rump stripe.. Sweetness.)
 
hux340 said:
Hi all,
I have a 71 H code Dodge Demon & they reckon it came with 275hp from the factory. I've heard a lot of Chrysler made their muscle cars hp underrated for insurance purposes. If that's true what would be a more accurate hp figure for the 340's.

Cheers,
Glenn.
Click to expand...

NHRA rated the 340 for classification purposes at 310-320 hp, and there were some that said production engines of that era varied between 260 - 315 hp. 340 peak torque overall.
 
hux340 said:
Hi all,
I have a 71 H code Dodge Demon & they reckon it came with 275hp from the factory. I've heard a lot of Chrysler made their muscle cars hp underrated for insurance purposes. If that's true what would be a more accurate hp figure for the 340's.

Cheers,
Glenn.
Click to expand...

The NHRA re-factored the 340/275 HP to 310 HP back in the day.

But the 1971 version with the Carter Thermoquad Carburetor puts out
approximately {+8 HP} over the earlier {1968 thru 1970} 340's with
Carter AVS Carburetor

When we Dyno-Tested a couple of new 'stock' 1971 Duster's 340 back in 1971,
we were right in the {299 to 302 HP} range when dialed in.

Current Horsepower numbers are listed at >
1968 thru 1970 ~ 340/275 HP ....... 290 HP
1971 ~ 340/275 HP ...................... 297 HP
 
hux340 said:
Hi all,
I have a 71 H code Dodge Demon & they reckon it came with 275hp from the factory. I've heard a lot of Chrysler made their muscle cars hp underrated for insurance purposes. If that's true what would be a more accurate hp figure for the 340's.

Cheers,
Glenn.
Click to expand...

I don't know but here's my story, I'm stickin to it. In the 70's in the Navy when "the first gas crunch" got underway, an unfortunate series of events ended up I decided to put a 340 into my V code 70 RR. This was a low miles, junkyard 71 340, with Hedman headers, stock cam and intake. The car was a 70 RR, 4 speed, Dana 3.54, hang on "knee knocker" AC

THAT THING would get 17.5 mpg on the highway with "uncareful" driving, and would stay right with most any 383 RR. Some of them would just scratch their heads when I lifted the 440-6 hood and there was that little bitty SB in there.

Yup. I was broke. This was right after swapping it in, before headers or aluminum valve covers, and before the AC got re-installed.

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I've read a few dyno tests of stock early 340's and they are indeed around 275 - 280 hp
the early 340's had a small 535 or 585 cfm carb so if you add the larger thermoquad you can probably expect a bit more.
 
71's are the hottest of the 340's with exception of the 6 pack 340's. I wouldn't dought 295 to 315hp depending on how close to spec the deck hight and head cc's were. The carb and intake are quite a bit better than the earlier ones, and the exhaust manifold's from some testing that I have seen are only down about 2hp from the 70's.
 
ir3333 said:
I've read a few dyno tests of stock early 340's and they are indeed around 275 - 280 hp
the early 340's had a small 535 or 585 cfm carb so if you add the larger thermoquad you can probably expect a bit more.
Click to expand...

The Carter AVS Carburetor for the 1968 -thru- 1970 '340' was rated at 630 CFM's.
 
My understanding is NHRA immediately refactored the '68 to '70 340 to 310 HP when it came out in 68 and the '70 six pac to 325 and the '71 340 to 330 . The '71 was the hottest of the factory 340's with it's Thermo Quad ( listed as 800 but actually 737 cfm) and wonderfully designed TQ manifold. The '72 was pretty much the same engine except for the 360 intake valve 1.880 and about 1.5 points lower in CR. Those '72's were good performers also with actual HP numbers around 290 . The big valves worth about 20 HP. The '72's were about equal to the '68-'70 AFB 340's . JMHO.

Terry
 
krazykuda said:
What's the CFM of the 71 Thermoquad compared to the AVS?
Click to expand...

The Carter AVS {1968 -thru- 1970} that was found on both the 340 4-Barrel
and 383 4-Barrel was advertised at 625 CFMs for marketing purposes.

Primary .......... 1 7/16 {1.437"} ......... Venturi > 1.186 {1 3/16"}
Secondary .... 1 11/16" {1.686"} ......... Air-Vacuum Operated

But the Carter AVS was closer to a true 630 CFM rating.

John Bauman {Fuel Engineer} for Chrysler Racing had several articles stating
that the {above} Carter AVS Carburetors that he tested for CFM flow ranged from
618 to 635.

The best 'off-the-shelf' that he ever tested, flowed at 637 CFM's.
 
69 Cuda 440 said:
The Carter AVS {1968 -thru- 1970} that was found on both the 340 4-Barrel
and 383 4-Barrel was advertised at 625 CFMs for marketing purposes.

Primary .......... 1 7/16 {1.437"} ......... Venturi > 1.186 {1 3/16"}
Secondary .... 1 11/16" {1.686"} ......... Air-Vacuum Operated

But the Carter AVS was closer to a true 630 CFM rating.

John Bauman {Fuel Engineer} for Chrysler Racing had several articles stating
that the {above} Carter AVS Carburetors that he tested for CFM flow ranged from
618 to 635.

The best 'off-the-shelf' that he ever tested, flowed at 637 CFM's.
Click to expand...


Ok, now what are the CFM numbers for the 71 thermoquad?
 
krazykuda said:
Ok, now what are the CFM numbers for the 71 thermoquad?
Click to expand...


The Carter Thermoquad for the 1971 '340'.

Primary ........ 1 3/8" {1.375"} ..... Venturi > 1 1/16" {1.063"}
Secondary ..... 2 1/4" {2.250"} ...... Air-Vacuum Operated

Advertised at a Flow Rating between 750 and 800 CFM's.

True CFM Rating .......... 737 CFM's.
 
Vs29H1B said:
there were some that said production engines of that era varied between 260 - 315 hp.
Click to expand...

Given the mass production machining tolerances and assembly techniques of the day, I would say that wide 260-315hp range is probably about right!
 
EL5DEMON340 said:
t quads rated 800cfm for the small primary and 850cfm large.
Click to expand...

'Advertised'

* Small Primary {1 375"} ........ 750 to 800 CFM's
* Large Primary {1.500"} ........ 800 to 850 CFM's

Carter Carburetor, a division of ACF Industries 'never' released an exact CFM Flow number, for the 1971 and later Thermoquad's found on the Mopar
Engines.

The CFM flow-rates were 'estimated'.
 
69 Cuda 440 said:
The Carter Thermoquad for the 1971 '340'.

Primary ........ 1 3/8" {1.375"} ..... Venturi > 1 1/16" {1.063"}
Secondary ..... 2 1/4" {2.250"} ...... Air-Vacuum Operated

Advertised at a Flow Rating between 750 and 800 CFM's.

True CFM Rating .......... 737 CFM's.
Click to expand...


There you go! That's what I was looking for. :cheers:
 
Just for comparison do you know the primary sizes of the Carter 2 barrels on a 70 318?
 
toolmanmike said:
Just for comparison do you know the primary sizes of the Carter 2 barrels on a 70 318?
Click to expand...

Yes I would.

Carter BBD-4721S {M/T}
Carter BBD-4722S {A/T}

Primary ........ 1 7/16" {1.437"} ...... Venturi > 1 3/16" {1.186"}

Flow Rating .......... 285 CFM's

Without a doubt, the biggest 'draw-back' on the 318.
 
Thanks, no wonder why fuel mileage often improves when replacing the old 2 barrel with a t-quad. (as long as you drive it smart) tmm
 
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