Is 400 B-block inferior to 383?

[patrick66]

A 400 is nothing but a 383 with bigger bore holes. Plus, the 400 was a smog engine from the beginning, designed to work with the then-new emissions standards. As stated, the early 400s are more desireable than the early ones, because of perceived thinner cylinder walls - that has been disproven, along with the same alleged "weakness" in the '74 - '78 440 engines. You can build the 400 exactly the same way as you would any 383. Use earlier 383/440 factory exhaust manifolds, a Carter AFB or a T-Quad, a cam installed correctly and the timing set accordingly...you'll have a 400 every bit as capable as a 383 4-barrel from the factory. Plus, someone looking at the engine at a car show will NEVER know the difference.

 

[70bigblockdodge]

It is all in the camshaft and cam timing, re: cam needs to be degreed as quality control on crank keyway was lax at best, also any engine the you put closed chambered heads on will run better, they act much the same as the swirl castings 302&308 small block heads, more complete burn.

 

[polara66hardtop]

It is all in the camshaft and cam timing, re: cam needs to be degreed as quality control on crank keyway was lax at best, also any engine the you put closed chambered heads on will run better, they act much the same as the swirl castings 302&308 small block heads, more complete burn.

it sure helped the performance of the van it was in. I had a lot better luck with the comp cam in my 68' 383 than the original purple shaft. I want smooth reliability like I now have in the 68', so will that .455 lift OEM spec run well with the low compression and stock 77' heads?

 

[moper]

Like was said - the 400 is a 383 with a bigger bore. Instead of rebuilding it, do a compression test. If they are all over 110psi and within 5% just do some bolt-ons. Put in a small cam and timing set - the Summit Racing smaller cam is a great one. Stick on some basic performance valve springs with it. Replace the intake and carb with a dual plane modern (Edelbrock Performer or RPM is fine) and a 4bbl around 650cfm (I like Performers or Carters for milder setups). Last, replace the distributor and ignition with something tunable. Properly tuned a 400 built like that should get closer to 17mpg mixed driving, and feel like a 440. They are that good with 7.8:1 compression when properly set up.

 

[70bigblockdodge]

And with the low compression you can run any old regular swill you can find at any station that alone will save you $.

 

[polara66hardtop]

The engine has about 36k actual, good compression, and the 68' 383hp Intake, with an Edelbrock, and petronix Ignition. The car came with the heavy duty tow Pkg and 4 bbl with 3:21 ratio. it also has the 70 roadrunner exhaust system all the way back. It runs ok, is reliable, but it isn't my 68', anywhere near close.I Don't expect the 400 to run like a 10:0.1 engine, just better would be nice. Granted the car is a couple hundred pounds more. I think the cam as suggested is the next thing, as well as the 915 closed chamber heads. However, The parts book shows HD valve springs on the tow package engine. I ask because I have the .455 OEM in my 69' 383 with the 9:2.1, and the low end is Inferior. With the 400, if it weren't for the A/C working so well, I would put in a 440. But, in that year I would have to change the compressor brackets, Exhaust pipe height, etc. A bit of a Dilemma.

 

[1978 NYB]

I believe you can still get 1972 stock 400 pistons that raise the compression to almost 10:1 without any mods or machining. Add a Mopar performance cam and dual exhaust and it'll really wake up that 400.

 

[Henrius]

And with the low compression you can run any old regular swill you can find at any station that alone will save you $.

But my 1965 383 has 9.5:1 compression, and I can run it on regular with no knocking. I raised the compression to 9.5:1 in my 2.0L Pinto and also am able to run it on regular.

So what would be the penalty to raising the compression ratio to 9.5:1 on my 1972 400? I would think it would raise engine efficiency.

 

[polara66hardtop]

I have a 69' 340 with the OEM spec comp cam , and with 10:5.1 no pinging. The engine runs great. And I can say with a 7:9.1 compression 400, if I push it, it rattles like you wouldn't believe, with 91 octane in it. it's all about efficiency. I've got some work to do,,,,,

 

[copchaser]

I've built a ton of 383's and 400's. Both are very good engines. the 400 in factory trim was a little doggy just like the later 440's. Changing the degree of the cam installed centerline will wake up 400 big time. I'm not a believer in the theory that the later big blocks were thin walls. I sonic check every block I build. I've found that 400's are normally thin wall castings. Which is fine for a stock or mild engine. I just completed a 512 for a guy, the 13th block I checked was thick enough to support the power level we were after with out the risk of splitting a cylinder. Now the 383 castings are normally very thick.

 

[polara66hardtop]

Hey copchaser, good to see another mopar guy so close. my family is from Coon Rapids. I have a July 72' 400 that appears to been rebuilt in the 90's that I picked up on a trade. I forgot about it for a long time, traded it, and then got it back. The puzzling part is it has 70' 906 heads, Intake, and a forged crank. Can you Install a 383 crank in the 400? One of theses days I'm going to take it apart and see what was done.

 

[copchaser]

Yes, the crank is interchangable, make sure you keep the forged crank balancer with the forged crank. All 400's that came factory with a manaul trans had a forged crank. You should road trip up and check out the 65 Newport that is ready for delivery. When you say July engine, is that the casting or assembly date of July? A lot of the 72 castings had extra material in the main webs.

 

[polara66hardtop]

Assembly date, stamped by the Distributer. I have to go to Fort Dodge this week, I may stop by. PM your contact information