340 or 383 for 1968 Dart

[RustyRatRod]

this is the correct answer.

"lizard brain sez: vroom vroom big block"

Nice.

 

[RustyRatRod]

The 300 rating was not due to the exhaust manifolds, it was due to the camshaft profile. Camshaft in the 383 GTS was not the same as the 383 in the Roadrunner

Yes. There have been many magazine articles that have proven the big block manifolds did not restrict the factory power ratings.

 

[rmchrgr]

A 300hp 383 would be a little over 0.78hp/c.i.
A 275hp 340 would be almost 0.81hp/c.i. and was admittedly underrated, like you said.

Ha, I did the math backwards. I knew that didn't seem right!

 

[dart4forte]

The 1968 ~ 383/330 HP and 383/300 HP 'Super Commando' Camshaft

Lift............. 431"/.443"
Duration.... 256*/260* Duration
Overlap..... 32* Overlap

Valve Springs........ #134 lbs. Valve-Closed / #208 lbs. Valve-Open

Available in the........Barracuda, Belvedere, Satellite and Sport Satellite

-------------------------------------------------------------------------------------
The 1968 383/335 HP 'Road Runner' and 440/375 'Super Commando'
utilized the same Camshaft.

Lift............. 450"/.458"
Duration..... 268*/284*
Overlap....... 46*

Valve Spring Load-Rate....... #129 lbs. Valve-Closed / #250 lbs. Valve-Open

The Stock Valve Springs should be a 'dull' red in color.

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[rmchrgr]

The 300 rating was not due to the exhaust manifolds, it was due to the camshaft profile. Camshaft in the 383 GTS was not the same as the 383 in the Roadrunner

Based on the info provided in post # 54, the 300hp cam in the GTS 383 was in fact smaller than the 340 cam so maybe but the manifold was still restrictive.

 

[BSB67]

The 300 rating was not due to the exhaust manifolds, it was due to the camshaft profile. Camshaft in the 383 GTS was not the same as the 383 in the Roadrunner

Right. At the stock factory hp level, the driver side manifold was adequate with the small cam.

 

[Jeremiah (jd)]

You can make plenty of power with stock bb a body manifolds.

That said, I have to remove the #6 spark plug from under the car. It's no worse that a 70 C body with hp manifolds IMO.

 

[fishmens67]

You can make plenty of power with stock bb a body manifolds.

How much is plenty

 

[RustyRatRod]

How much is plenty

Enough to see air under them front tires.

 

[Jeremiah (jd)]

How much is plenty

Compression ratio and camshaft grind have a lot to do with it. 600+ hp is doable with enough cubes

 

[340six]

Just got home guys...lots of super responses! I screwed up and should have mentioned the gentleman actually has a 68 340 GTS, but the original 340 is gone. He has a 383 with the correct 383 K frame, motor mounts, exhaust manifolds and rebuilt big block rad! Also has a '70 340 with hi flow manifolds and correct rebuilt 340 rad.
A tough decision for sure. I think the 383 with the correct pieces may edge out the 340?

Real 340 car gets a 340

 

[LO23M8B]

Man o man. Lots of bs on here.

 

[fishmens67]

Compression ratio and camshaft grind have a lot to do with it. 600+ hp is doable with enough cubes

I know you'll never tell and I don't expect you to. we'll just say somewhere between 451 and 500 or so cubes.
It's hard to figure what flavor you have in there now.
Are you still running manifolds?

 

[Oldmanmopar]

On the 8th day God created the 340! My little small block is an elephant tamer.

 

[rumblefish360]

Icon 687. But you are stuck with the 1.094" wrist pin.

Not a horrible thing for a moderate to hot S-S car.

 

[matthon]

Original is no fun when one has the option to go bigger.

 

[LO23M8B]

Original is no fun when one has the option to go bigger.

View attachment 1716470617

Love the D mailbox.

 

[ir3333]

i don't think many 383 GTS's were made in '68 or 340's either. From the posts each have their following
with no real winner?

 

[BSB67]

i don't think many 383 GTS's were made in '68 or 340's either. From the posts each have their following
with no real winner?

It is a bit of a blond verses brunette thing.

 

[85glht]

Yep. Still debating this stuff in 2025 even though both engines have been obsolete for almost 55 years. Mopar or No Car.

Even in stock form the Gen III Hemi is better than all of them anyway!

That would be my suggestion. Just run A Gen. 3 Hemi and be done with it. There will be aftermarket and junkyard parts for years

 

[Mtrhead]

I got a stock bore 4.04... 1968 / 340 block still perfect crosshatch pattern on cylinders....also have forged crank and shot peened rods and 10.5/1 slugs....PM me

 

[Jeremiah (jd)]

The bb a body can be a challenge to maintain for sure.. I currently have the centerlink dropped and driver side header unbolted to r'n'r the starter. My next project is swapping in a CVR electric water pump which will require removal of the radiator :/ Nothing a hot cup of coffee and some patience cannot solve on a Saturday morning.

With so many choices out there for big and small block combinations it's hard to choose a direction if you are starting from scratch. Add the g3 hemi to your list of options if you really want to go down a rabbit hole.

If I had an original 340 car I'd build a 360 based 408+ cube engine. If you really want to go fast call Brett Miller.

 

[66fs]

Thanks. I was hoping for a similar comparison, with the aluminum bbm heads compared to a similarly equipped iron head small block.
I wouldn't consider a aluminum intake/head/water pump/ housing, header, comparison to an all iron (including intake and exhaust manifolds) small block fair. Would be informative, though.
I've always wondered how much, ACTUALLY, the supposed weight difference really "hurts handling"
Not one of my six mopars has power steering, so handling does not enter my conversation, normally.

BS on poor handling, I have an original 383 car and it handles fine, all cast heads, intake and exhaust manifolds. Nothing wrong with a 383, just swap carbs and a custom cam.

 

[matthon]

Mini starter and Schumacher headers.
Easy peasy to change spark plugs and starter.
Don't forget the Remflex gaskets.

 

[matthon]

Just run A Gen. 3 Hemi and be done with it.

They fit nicely, not cheap though.