Is 400 B-block inferior to 383?

[Henrius]

I have got a 1965 Fury III with 383 that has never been rebuilt. It was my grandmother's car and always taken care of. The engine has always run smoothly like a champ. It now has 156,000 miles!

On the other hand, the 400 in my 1972 Chrysler Newport has never run as well. I realized that engine had a lowered compression ration for smog. It was rebuilt at 100,000, and doesn't run as smoothly or with as much power as the 383 in my Fury!

I contemplated doing another rebuild on the 400 and increasing the compression. But are the later 1970s engines just poorer quality? Would I do better swapping it out for a 383 or 440, or even a 360 A-Block, which I hear is more economical?

 

[commando1]

I'd rebuild that 383 into a super reliable nice mild engine. No C.R. increase. No rad cam. Just a sweet running no headaches trying to tune it engine. 550 RPM smooth idle and responsive acceleration with no bog, farts, or hiccups.
BEST bang for the buck by far.

 

[Badvert65]

Nothing wrong with a 400. I am building one myself. Compression ratio is the biggest handicap (a 72 is supposed to have 8.4:1 compression). I am building a 72 400 myself for a bracket car. Basic stock rebuild until I get the rest of the car sorted out. Main problem with the 65 383 is inferior heads (compared to the later ones).

 

[tallhair]

NO. The 400 is actually beefed up and esp early 72 400's are sought after for the heavier casting.

I wouldn't hesitate to build a 400 over a 383 and you can use a 440 crank to make it a 440 something if you are changing pistons anyway.

 

[mcmlvii]

The engine has always run smoothly like a champ.

As a kid in the 60s we had a '66 Fury with 383 2bbl. That motor was so smooth and quiet we could hardly tell it was running when sitting at a stop. The car was sold in the 90s with 150k+ on it, still running strong, engine never been touched (that I recall). I'd keep the 383 in that car if I were you, Henrius.

 

[commando1]

I have always maintained the 383-2's were the smoothest engines ever to go into a Mopar.

 

[tallhair]

because they had a very mild cam and as you've noted there's no extra set of carb secondary valves opening up to distract from your smooth consistant acceleration

 

[commando1]

Not simply that though.
The bore/stroke ratio and the con rod length have a big part in it.
The intake manifold design.
And it goes on.
That block and heads is theoretical engineering at it's best.
Increasing the 383 to 400 upsets the ultra delicate balance.

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[polara71]

Had a 72 400 HP in my 71 Polara once, it came from a 69 Polara, where that came from who knows but it was the best engine I had ever owned, to this day. It would run the speedometer through 140 easily. The 383? Even after the build it has less power than my 360 had at 140,000 miles. I have maintained this opinion throughout my tenure on FCBO and have taken plenty of abuse. The 383 is always my last engine choice

 

[LocuMob]

A 440 crank in a 400 gets you 451 cubes. The 383 is the 318 of the big blocks, nothing fancy but reliable.

 

[polara66hardtop]

I have a 400 in a 77', and it is a pooch beyond description. My 68 383 Hp will eat it up and spit it out, in stock form at least. A 400 is a good engine to modify, but in stock form it doesn't offer much. the 383 is the better of the two, in stock form, and outsold the 400 by leaps and bounds.

 

[Henrius]

As a kid in the 60s we had a '66 Fury with 383 2bbl. That motor was so smooth and quiet we could hardly tell it was running when sitting at a stop. The car was sold in the 90s with 150k+ on it, still running strong, engine never been touched (that I recall). I'd keep the 383 in that car if I were you, Henrius.

One time on the highway in the winter the heater core hose broke and ran the engine out of coolant. It overheated and stopped. I let it cool down, put water from Wendy's in the radiator, and got it home. No damage done to engine!

Never planned to swap out the Plymouth 383 engine. Trying to figure out what to do with the 400 in my Newport, which has never run that smoothly. White trash owned the Newport for the first 40,000 miles of its life, so no telling what the engine suffered in its youth. However, the stock rebuild at 100,000 miles should have made up for mistreatment!

 

[Henrius]

Nothing wrong with a 400. I am building one myself. Compression ratio is the biggest handicap (a 72 is supposed to have 8.4:1 compression). I am building a 72 400 myself for a bracket car. Basic stock rebuild until I get the rest of the car sorted out. Main problem with the 65 383 is inferior heads (compared to the later ones).

Can I increase compression to 9.5:1 on the 400? I am trying to get all the efficiency gain I can. Anything to get more than 16 mpg!

 

[Henrius]

I'd rebuild that 383 into a super reliable nice mild engine. No C.R. increase. No rad cam. Just a sweet running no headaches trying to tune it engine. 550 RPM smooth idle and responsive acceleration with no bog, farts, or hiccups.
BEST bang for the buck by far.

Fortunately, the 383 does not need rebuilding, it still runs well at 156,000 miles, although idle is not as good as formerly. It already had 9.5:1 compression, and I want to continue running on regular.

The debate is how to improve the 400 in my 72 Newport. I was thinking about swapping for ANOTHER 383. (Not the one in my 65 Fury.)

But you guys say I could modify that engine and make it better.

A friend said that if you drive it carefully, you can actually get better gas mileage with a 440. That is another possibility, if it fits. The whole idea is to get better efficiency, not hot-rod performance.

 

[polara71]

Are you using this car every day? The last thing I worry about when I drive the oldies is efficiency. Making it more durable and reliable is a different story.

Driving a few thousand miles a year is not worth the expense of a rebuild or swap. That being said you wanna save fuel put a 318 between the rails

 

[Henrius]

Are you using this car every day? The last thing I worry about when I drive the oldies is efficiency. Making it more durable and reliable is a different story.

Driving a few thousand miles a year is not worth the expense of a rebuild or swap. That being said you wanna save fuel put a 318 between the rails

Well, the 1965 Fury III is my second car and I try not to use it for long trips. My son will borrow it for short trips to the soccer field. Probably will total 8,000 miles per year. The plan is, when I get the Newport with the 400 running again, I will alternate driving the Fury and the Newport on alternate weeks.

Just remembered- I spent a good bit of money having a modern A/C compressor in the Newport, which I do not think would be easy to transfer to a small block. Better keep it a big block!

 

[polara71]

If you can save two to three miles a gallon.... Is it worth it

 

[Wildaugust]

The 400 had the same stroke as a 383, so , it should have the same rod ratio as a 383, unless you rebuild it as a stroker. If higher compression pistons are available as replacements for stock pistons, I would think they would be an improvement over the low compression slugs. If I'm not mistaken, and I could be, I believe that the 400 was built with deliberately retarded cam timing. So, I would think that installing a mild cam "straight up" instead of retarded, should help too.

 

[polara66hardtop]

In all fairness to the 400, the cam was a real retard for sure. My brother Installed a performer Intake, 915 heads, and a 440hp cam in his, and the 400 really came to life, and turned into a whole different engine. The 8:0.1 compression didn't do the engine any favors, either. The vote is still out on my 77' 400 Cordoba. I'm not happy with the 400, but it's a lot of trouble to change over to what I would like to put in the car.

 

[polara71]

And that's why the 400 gets a bad rap.... It was purposely built bad