[Bigbird]

I don't know much about Mopar big-block engines. How do you know if an engine is a B or RB and what is the differance between them?

 

[tv_larsen]

Basically, the difference is deck height. The RB's have a taller block to accomadate a longer stroke. Because of this, the intake is wider, and the distributor and push rods are longer. They also have larger main bearings.

383's and 400's are examples of B blocks, and 440's are RB blocks. Does that help?

 

[Bigbird]

Basically, the difference is deck height. The RB's have a taller block to accomadate a longer stroke. Because of this, the intake is wider, and the distributor and push rods are longer. They also have larger main bearings.

383's and 400's are examples of B blocks, and 440's are RB blocks. Does that help?

For the most part it does. Thanks.

 

[440Ramcharger]

There were a few RB 383's made. RB 383 engine 4.03" x 3.75" stroke.

 

[tv_larsen]

There were a few RB 383's made. RB 383 engine 4.03" x 3.75" stroke.

Are you sure? I've never heard of such an animal. Actually, that sounds like the bore and stroke of a Chevy 350 stroked to 383 cubes.

 

[Mala-Sangre]

Are you sure? I've never heard of such an animal. Actually, that sounds like the bore and stroke of a Chevy 350 stroked to 383 cubes.

Yes TV, he's correct. There was an RB 383 in the early years of RB production. It's as rare as a free 426 Hemi, or a 350ci B engine, but it was available nonetheless.............Los

 

[aepowell]

I believe all 383 road runner engines were rbs. They had 440 heads ,intakes and exhaust manifolds on them. Please correct me if I'm wrong.

 

[Evildriver-3]

The heads all interchange so does the exh, what doesn't just bolt up are the dist's and intakes,pushrods, cranks between the b/rb's

 

[Desert_Dog]

Anthony,

Only a short run one year for RB 383's. Mala can tell you what year. I think it is like 1961 or so.

All 383's after that were B's.

The ultimate big-block Chrysler wedge is a B block... MMMM... 451... (400 block and 440 crank)

Yeah, a 451 and a cross-ram... in an E-body of course...

OK, I am better now...

Mike

 

[440Ramcharger]

More info than you care to know. @ http://www.allpar.com/mopar/383.html

 

[ramcharger_blue02]

we've got a road runner 383 in the shop sittin in the corner. they go for about $6000 now. cool engine though. it still has the original color on it, too. It's just chillin, im trying to get my dad to GIVE IT TO ME!!!!!!! AHAHAHAHA!!!!!!!

 

[440Ramcharger]

The 383 was an excellent engine. Not too big so it got decent? mileage on the road compared to a 440. It had a shorter stroke and reved quick compaired to a 3.75" RB. We had one in an old '67 wagon. I did things that I would not want to admit to, and it took it in stride. 2bbl, dual exhaust wagon that had highway gears in an 8.75" with a 727 Torqueflite. I could see DC (Daimlar Chrysler) bringing back some of the older designs that were scrapped due to emissions. In fact they are!!! Look the hemi is back!! A smaller version, but is has the bow tie boys shaking and crying fowl! I would love to see the /6 come back. Technology makes things possible that were not even considered 5-10 years ago. How many know of the 265 6 cylinder hemi that Chrysler had in Australia? That is a kick butt engine. Light, more than 1 HP per cu.in. etc. I want one!!!!!!!!

 

[440Ramcharger]

In general. 3.38" vs. 3.75" and less rotating mass.

 

[Mala-Sangre]

we've got a road runner 383 in the shop sittin in the corner. they go for about $6000 now.

What exactly goes for $6,000.00 now, the Road Runner or the 383?.....................Los

 

[big10]

I believe all 383 road runner engines were rbs. They had 440 heads ,intakes and exhaust manifolds on them. Please correct me if I'm wrong.

While a 68 GTX and 68 Roadrunner both had "906" heads, the 383 is still a B block and the 440 is a RB block.
The intake manifolds don't interchange between B and RB.
383/440 exhaust manifolds are probably the same casting but the 69 1/2 thru 71 440+6 exhaust manifolds were different than the 4bbl engines.

 

[ratcharger]

That doesn't really answer my question, but I'll go ahead and throw this out for discussion.

I hear the "faster reving" argument quite a bit in reference to the 383 vs. 440, and 451 vs. 440. For all intents and purposes lets assume that the lighter reciprocating assembly has a similar effect of a lighter weight flywheel.........now in a stripped A body I can very well see that it's a desireable trait, especially in race conditions, however, in a heavy truck I can't hardly see how the lighter mass of internal parts has much bearing on how the truck runs (or more specifically launches), in fact, it can tend to be detrimental as it will take more throttle application to accelerate the truck than if you had the inertia from the additional reciprocating weight helping to get the rest of the drivetrain in motion. End result, it'll take fewer RPM to move the truck from rest with an RB than a B block, or even a low deck stroker. How "fast" an engine revs in a no-load situation is really a moot point, how fast it revs when under load is what counts and in that situation the RB will always outperform a B when similar builds are compared.
Jay

Jay, would'nt the additional mass of the RB pistons actually rob that energy from the drivetrain rather than contribute to it?

After all it will take more force to move the larger piston the same distance than with the 451.

 

[ratcharger]

Playing fast and loose here for a second the short answer is yes, the additional mass will effectively rob HP (using a 451 vs 440), and in a light weight car in a drag race situation it can make a difference. However lets make things more equal by using the same lightweight pistons in a 440 and the actual reciprocating weight difference is considerably less.

Continuing fast and loose... ;-)

That said, the HP required to spin an engine is far less than that required to accelerate a vehicle up to speed.......especially a heavy vehicle. Since the reciprocating assembly is in motion it's also in effect "storing" energy.....albeit not as efficiently as an actual flywheel. The effect of that extra mass rotating helps get the other drivetrain components in motion. Similar to a heavier flywheel, that stored energy is converted to motion once vehicle is accelerated.

A rather poor analogy (but apt) would be to compare a motorcycle engine to an automotive engine........the cycle engine can rev nearly instantaneously, while a stock automotive engine will seem rather sluggish in comparison.........but the cycle engine also drops back down to idle much quicker as well.....because it has little reciprocating mass. What that means in the real world is that it's considerably easier to stall upon launch unless the revs are up (using manual transmissions as comparison), whereas a large engine can nearly idle away since the rotating assembly helps by using it's stored energy initiate movement.

I am starting to see your point here but isn't the inertia of the crank maintained by good timing and combustion? That said, a lighter assembly should once again be superior because it would take less energy to keep in motion and quicker to respond to changes as well.

Also as far as bore and stroke these two engines are the same with the exception that the "B" engine can maintain the same bore, stroke, compression while using a smaller and lighter piston. This is redundant info but I repeat it only because I see it as a more accurate example than the motorcycle/car engine one. (Unless we are talking the "Boss Hoss", then there is no contest. ;-))

End result.......with a smaller stroke or lighter reciprocating mass engine it'll take more throttle, and more rpm to accelerate. Fine in a race car, but not as good in a heavy vehicle. Seat of the pants feel, and actual acceleration #'s will bear that theory out I believe.
Jay

I'm not sure I agree with that but I know you have had both so I will take your word for it....