Factory 68-71 340 puts 325HP on GM Dyno

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NHRA immediately refactored the '68 340 to 310 h.p. when it came out and the '70 3x2 six-pac 340 to 325 h.p. The '71 TQ equiped 340 was NHRA factored to 330 h.p. I believe the '71 was the best of the 340 series. It still had the high compression , the big valve heads and the wonderful and under rated TQ, with the well designed spread bore manifold. They were VERY strong performers indeed. And VERY under rated for sure. My '72 Duster 340 auto 727 stock convertor with 98,000 on the entire drivetrain , 340 with a port-o-sonic intake with the stock TQ and an alliance 292/.480 hyd. cam, 1970 340 2.020 heads , small tube 1 5/8 headers and 391 gears on street tires ran consistant 13.60/13.50's at 103 mph with a best of 13.53 @ 104 in 1/4. Absolutely true. Later went much quicker after .030 rebuild and other mods. The 340 is THE best small block EVER..!!

Terry
 
I'm really on the fence whether I should do a 340/416 or a 360 mag/408 for my next engine. I really like the roller cam action in the 360 mag. Its more expensive than LA to build and I know I can roller a 340 but that is also expensive. I have always had a thing for high revving engines.......On the other hand there is a lot to be said for a 400 block stroked to 500 plus. Because I am so cheap and want the biggest bang for the buck I will probably opt for a 400/500. Forged kits are now under 2k.
 
I used to work with a die-hard Mopar guy. He told me back in the day hime and some mechanic friends had a 68 bone stock 340 on the dyno and 325hp was the number it put out. He then told me that a 71 340 put out almost 10 more hp due to the thermoquad. He is a stand up honest guy so I don't doubt him at all.
 
great info guys, I didnt know a 327 made that much hp at one time, granted it had FI.

And I had heard a 340 made around 320-335ish, I believe I read that on allpar
 
I believe it about the TQ I put TQ from a 440 on my 340 and it really made a difference that I could feel . At least 10 HP plus . It was an 850 I believe , with headers the AVS was not enough , really woke up with the TQ .
 
without a doubt , the 340 was the hottest small block , even in its last in-car-nation in '72 / '73 ( cast crank and smaller intake valves , 240 h.p. rating ) .

one of the first cars I drove when I got my license ( Septembre 1989 ) was a 1973 Challenger Rallye in F6 Green , 340 , 727 , 3.55 / Sure Grip .
It was largely stock ( excepting its ThermoQuad was replaced with an AFB in the early 80's ) , original owner car .
That sucker was quick and fast !!

I used to work with someone whom had -- and hopefully still has -- a 1970 Swinger 340 , 4 speed , 3.23 / open . He bought it new in early 1970 ; he was still using it as his daily driver as recent as 2001 !

Here's a list of some of my favourite HOT small blocks from "the golden era" :

- 340
- 350 / 360 H.P. ( LT-1 )
- 351 "335 Series" Cleveland / Boss 351 ( 1971 )
- 360 / 390 / 401 AMC

If I could go back in time and order a 340-powered car from every year of its production :

- 1968 Dart GTS , 4 speed ( standard ) , 391's , AM-FM radio , fast ratio manual steering , manual disc brakes , triple black , including stripe .

- 1969 Swinger 340 , 4 speed , 3.23's / S.G. , a/c , fast ratio manual steering , manual disc brakes ( standard ) , AM-FM ,stripe delete , Green Mod Top / 999 Green Metallic

- 1970 Swinger 340 , 4 speed , 3.55's , power steering , manual discs , hood scoops , 1969 AM-FM radio ( no FM available in A-bodies again until 1972 ! ), B7 Blue on B7 Blue stripp-o interior

- 1971 Duster 340 , 727 , Super Perf Axle Pkg , power steering , manual discs , AM-Cassette , buckets / console , Tuff-Grip wheel ,999 Petty Blue / white interior

- 1972 Swinger Special ( Canadian ) , column T-Flite , 3.55's , AM-FM .
power steering , Tuff-Grip wheel , Hemi Orange

- 1973 Duster 340 , 4 speed , 3.55's , sunroof , AM-FM radio , power brake delete , power steering , white / B5 interior
 
340 HP numbers were correct for the RPM they were rated at, but made more HP as you kept revving them higher. My "71" 340, 4 speed Duster was still breaking into the 13's with 100,000 miles on it, with only headers and slicks. But most other 340's would not. I can't remember if they were Auto or stick. As for Chevrolets, I never ran against a 360 HP 327 but a friend of mine had a 375 HP 350, 4 speed in a Camaro and it was not as fast as the 340 Duster. Back in "the day" a lot had to do with how you tuned the engine and who was driving. In a small block Chevy or big block Chrysler you could lose a lot of power because of worn spark plugs. And it did not take long, 5,000 to 10,000 miles? You also usually had points in your distributor. Chevrolet was known for Dyno happy HP numbers, vetts in particular. All that said, the 327 is my favorite Chevy engine.
 
Thiink about it:
You go up from 318 to 340 cubes less shouding etc.
Up the size of the valves and ports
go to larger intake and exh manifolds
install dual ex
larger cam
8.8 to 10.5 compression
dual point distributor and other misc teeaks and then:

you claim only 45 more HP than a 318 2b ? Comon mine back in the day was factored at the track at 325 was the rating the NHRA gave a 340 for a stock car.

Chevy had many 320, 350 and a 370 hp 350, Also I can show you documents on the WAY under rated Z/28 302 in 69 and the cross ram versions that got only 290 hp ratings. All put out close to 400 hp and have been tested many times over the years to prove it.

I think it was several factors
1 insurance cost etc
2 try to fool the competition.

They did the same thing with a 426 hemi, tell you what it made at a certain RPM, but not the peak HP.

And by the way, I have an all origional documented 70 Cuda with a 340, it is a mean little go getter. Even with mild 3.23 posi will smoke the 255 60s 5-6 car lengths with no power braking and many I saw at the track back inthe day would pull a high 13 or low 14 stock with out slicks.
 
I had two of those 365 h.p. 327's in two 1964 Corvettes back in
the day. They were very powerful engines. High compression solid
lifter, alum. intakes and Holley four barrels. Very noisy valve train,
Gap on the solid lifters was .030 on the intake and exhaust. I believe
they were called Duntov 30-30 cams.

Great engines.....so were the 340's
 
Hey, I got a theory! The horses GM used were small ones! Because a 210HP 318 will pull harder in a truck than the 250HP 350.......... MAybe GM used shetland ponies for thier ratings???????

That said, dad had a 64 325 HP 327, idled fairly smooth, and would rev to 7500 any day, made more power than ANY Mopar SB, and it was EASY to get, hell, the HYD lifter 340 would float the valves before 7K...

MOPAR guy thrue and thrue, but I have learned one thing. DYNO's are for tuning, who cares what they say in real life. Example, why does my 300HP Cummins pull a hill with a heavier load harder than the 400 or whatever Dmax?

It's not the PEAK that matters, it's how LONG in the band you have the power.
 
327 had the best bore to rod ratio combo of that series of chevy sb's.

The heads were also their best heads they offered in factory stock condition.

None of this matters really though cause on the street the 327 bow'd to the 340....


as for 318's...yep, my stock 74 318 4 door dart would smoke my buddys 69 malibu w/ mildly built 350 though exhaust manifolds any day.

it's 340ft pounds of torque from that 318, great lil motor for what it is.
 
Here's the quote from the allpar page.

With reworked heads and a set of headers, the factory 275 horse animal (that the insurance companies at that time corrected to be 325 horsepower) becomes 330 according to Dodge and 380 horsepower according to the insurance companies.
Click to expand...

Insurance companies came in high because that is what they wanted, desired outcome.

----------------------------------------------

Dyno's have correction factors that can be adjusted to make an engine have pretty much whatever HP you like.
 
Thiink about it:
You go up from 318 to 340 cubes less shouding etc.
Up the size of the valves and ports
go to larger intake and exh manifolds
install dual ex
larger cam
8.8 to 10.5 compression
dual point distributor and other misc teeaks and then:
Click to expand...

BUT............

Here's something interesting.....

Having 318's and 340's in the same truck, the 318 with the single plane 2bbl would drag a trailer just as fast as the 340 up a hill when it came to what matters. A simple offy dual port manifold, and 600EB and he 318 would outrun the 340 up a hill. (I'm talking a 10K trailer, in a 3/4 ton truck)... They advertise the torque as the same, just the 318 makes it lower in the power band...

However, the 340 in the truck, light, would outrun the 318 by a bit........

So, IMO, the real difference isn't much, and none at all until over 3500RPM or so. I know, I know, the sacred 340 outran RB engines, ho hum....... BUT, if chrysler had made factory small valve big port 318's with all the goodies in the 340, and never MADE a 340, you all would be sitting here saying the same darn thing, the "Amazing" 318.... :)

Just something to ponder.

Because of my age, I missed most of the "stock" muscle cars, but the 340's built stock, and the ones untouched, really left something to be desired, and sure as hell weren't no 440.

And GM still used miniature horses for their dyno's....
 
gearing will get you faster up a hill than a simple cid change.

we had a guy pay us to put a 318 n his truck, he was thinking he'd pull the hill a lot faster...we said don't waste your time and just go big block or 360.
he insisted....

he ate crow later on.
 
Don't flame me, but I have never been impressed with the "overall" performance of the 340.................

If it ran strongish, it got **** mileage, just like the 400, bores too big. Sure, there are exceptions, but I too, think the solid cam 327's would outrun the 340, hell, for that matter, I think the commando, and the Hiippo 283's would outrin a 340, in a light car of the same weight.....

In stock form at least.



I wish I could spend a day in a parralell world where MOPAR never made a 340....... Wonder what it would be like??
 
A-BOMB360 said:
thats some strong smelling crap you just dumped.
I do believe a 64 chevyII would smoke any 340..
Not to mention the 69 302 Camaro Z/28 which
gave even HEMIs fits.
Click to expand...

yeah...like I said...


better get some slicks with that pos 302 cause I've driven a bone stock z28 and don't make beans till 5000 rpm!!!!!!!
 
learn how to tune.....my ported head built 340 in a 4spd car with gear gets 15+mpg

Ones experience does not dictate the final outcome for the rest of us.
 
I dont see the stock 302 whoopin' the 340 either wild. It seemed a littly hyped up to me.....

But the hey lasted longer than the newer chubbies until the roller ones too, I think......

Seen many ABUSED 283 power two ton trucks with the same little 283 they had since new running WOT 90% of it's life when I was a kid.


Never was interested who they got so poopooee in the later years, just wondered why they did it.
 
I know someone right now with a 69 z28 thats won all kinds of trophy's at shows for being correct and he even says the thing was meant for 4500+, hence why we built a 383 stroker and hid it under stock/correct appearing parts.
 
with a chevy, as the stroke went down, the rod ratio went up....283/327's were known to live a lil longer than the 350.

look at the parts that are in a 302 chevy....
 
1wild&crazyguy said:
learn how to tune.....my ported head built 340 in a 4spd car with gear gets 15+mpg

Ones experience does not dictate the final outcome for the rest of us.
Click to expand...





Read it again, I said there were exceptions, I had a 400 that would get over 20 in a cordoba........ And 400's in trucks, that wouldn't get 8MPG. Hell, my 390 will get 16 with 4.10 gears and four back tires.....
The Cummins will get 30 running half drain oil.......
472 Caddy's will get over 20mpg too........

But as a whole, 90% of the people in the world, didn't hit the sweet spot like you did, and are getting 10MPG with the same engine, close to same build.
 
1wild&crazyguy said:
with a chevy, as the stroke went down, the rod ratio went up....283/327's were known to live a lil longer than the 350.

look at the parts that are in a 302 chevy....
Click to expand...

Nah, I'll leave that for the chubby guys.......

Chev motors just don't intrest me, must be the first thing you run into when you pop the valve cover...... And it goes downhill from there,.
 
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