Switched 68 Fury 383 to 76 Monaco 400

[Dave Fox]

I've got a 68 Sport Fury that had 3 broken pistons in the original 383 H.P. engine, so I put a 76 Dodge Monaco 400 H.P. in it till I get some pistons for my 383. I've got a vibe above 55 mph. I noticed the flex plates were different when I changed the engines, so I tried to keep the same plate with it's motor. Someone told me that I would need to use the 400 torque converter instead of the 383 convertor. They are both high performance engines. So, does anybody know for sure about this, and are there part numbers for each piece and how do I find out what they are? And it's not the u-joints. lol

 

[wes poloway]

you need the vibration damper and torque converter from the 400 as well. As it is externally balanced.

 

[Polara_500]

Yep, you'll need the 400 TQ with the 400 engine. You can tell the difference by the weights welded onto the back of the TQ on the 400's unit. 383 is internally balanced, 400 externally.

 

[Polara_500]

you need the vibration damper and torque converter from the 400 as well. As it is externally balanced.

I would assume(hope) you didn't swap the vibration damper also, it also needs to stay with the engine it came on.

 

[moper]

The engine is out of balance. You needed to retain the 400's torque convertor and swap it with the engine. However since it's in... Get this MP part number P4120241 and weld the right weight where the template tells you to.

 

[CBODY67]

If the engine is out of balance, the vibration will be RPM related and not specifically "road speed" related. How bad is the vibration? The 400s, being cast crank motors, are externally balanced, BUT Chrysler built 400HP steel crank motors if the car had a factory 4-speed trans, up until about '76 or so, according to the parts book.

55mph would probably be about 2000rpm in 3rd gear.

How did you adapt the late model engine mounts to the earlier motor's engine frame mounts? I believe the later model mounts are the "spool" type?

As for finding pistons that completely match what's in the '66 motor, I wish you luck in the aftermarket! Might end up with some forged items rather than cast pistons (factory OEM). Also plan on usually finding .030+ rather than "standard" size.

With any aftermarket piston, the weight of the piston varies from stock OEM pistons, so getting things "balanced" will be necessary. IF you find the correct factory OEM NOS piston, their weight should be the same through .030"+ size, but you can get it balanced for good measure. Compare the weights of the NOS piston to one of the good ones, on a digital postal scale (or similar).

Just some thoughts,
CBODY67

 

[Dave Fox]

If the engine is out of balance, the vibration will be RPM related and not specifically "road speed" related. How bad is the vibration? The 400s, being cast crank motors, are externally balanced, BUT Chrysler built 400HP steel crank motors if the car had a factory 4-speed trans, up until about '76 or so, according to the parts book.

55mph would probably be about 2000rpm in 3rd gear.

How did you adapt the late model engine mounts to the earlier motor's engine frame mounts? I believe the later model mounts are the "spool" type?

As for finding pistons that completely match what's in the '66 motor, I wish you luck in the aftermarket! Might end up with some forged items rather than cast pistons (factory OEM). Also plan on usually finding .030+ rather than "standard" size.

With any aftermarket piston, the weight of the piston varies from stock OEM pistons, so getting things "balanced" will be necessary. IF you find the correct factory OEM NOS piston, their weight should be the same through .030"+ size, but you can get it balanced for good measure. Compare the weights of the NOS piston to one of the good ones, on a digital postal scale (or similar).

Just some thoughts,
CBODY67

The 68 motor mounts bolted right up.

 

[Dave Fox]

I would assume(hope) you didn't swap the vibration damper also, it also needs to stay with the engine it came on.

yup. Kept the dampers with their respective engine. Never thought to look at the back of the convertor.

 

[Dave Fox]

The engine is out of balance. You needed to retain the 400's torque convertor and swap it with the engine. However since it's in... Get this MP part number P4120241 and weld the right weight where the template tells you to.

Thanks, but I'd rather swap out the convertor so I have the right one for my 383 when I put it back in.

 

[Dave Fox]

I would like to know if anybody has the flex plate numbers if they are marked, or maybe a photo of one or the other so I can make sure I get the right one back in.

 

[Ripinator]

I've got a 68 Sport Fury that had 3 broken pistons in the original 383 H.P. engine, so I put a 76 Dodge Monaco 400 H.P. in it till I get some pistons for my 383. I've got a vibe above 55 mph. . . And it's not the u-joints. lol

Didja check the thermostat?!?

 

[CBODY67]

yup. Kept the dampers with their respective engine. Never thought to look at the back of the convertor.

Mopar Perf used to have a "weight kit" to put the weights on a neutral balance converter. Similarly, knock off the external balance weights to use with an internal balance engine. One on each side of the drain plug (or where it used to be).

CBODY67

 

[moper]

You tack weld the weights on. If you need to remove them, you break them back off. We used to just break off the factory weights "as needed". Sure beats the transmission going in and out a few times.

 

[Dave Fox]

Okay. One other question. When you bolt the torque converter up to the flex plate how should it line up? An old friend of mine said to line the hole in the flex plate up on the opposite side of the converter's drain plug.

 

[Ripinator]

Okay. One other question. When you bolt the torque converter up to the flex plate how should it line up? An old friend of mine said to line the hole in the flex plate up on the opposite side of the converter's drain plug.

I don't know what this means, but I do know the flex plate only bolts up to the converter one way. The mounting holes in the flex plate are offset.

 

[moper]

I take the flexplate and lay it against the convertor. Rotate it til the bolt holes all align, then spray across that ear of the flexplate and convertor so the shadow is visible. Then you know that's the one way it will work.
I "think" the hole in the flex plate was supposed to go towards the drain plug... But that was a while ago. Someone with a FSM will be able to confirm that.

 

[Gerald Morris]

The 68 motor mounts bolted right up.

Yes, all the B and RB blocks have the same casting for mounts, so older style mounts will bolt right to later blocks. I'm planning to drop a 400 into Mathilda (my 1966 Newport) eventually. Yes, you should either keep all the rotating assembly stuff for the 400 w the 400, or get the appropriate weights, balancer & such added on if you bolted it to the older tranny. I learned a bit about how the internally balanced forged crank of the 383 requires NO external balance while the cast iron cranks of the 400 require a weighted, balanced torque converter and a weightier harmonic balancer up front. That was what made me opt to have the original 1966 edition 727 rebuilt for old Tilly so long as I run that 383. I plan to buy another 383 crank (or whole lower engine knowing how prices go for used parts) and after a bit of shop dressing, use the 383 crank in my 400. Forged steel cranks generally are more durable than cast nodular iron, period. When Uncle started castrating and lobotomizing Detroit in the early 70s, the corporate beancounters agitated for and got cheaper crankshafts, pistons and a plethora of other parts. Mind you, the 1970s BLOCKS for MoPar B/RB motors were the BEST of the run. The crank bearing support webbing in the 72 400 is the thickest Detroit ever made, and the later ones were still WELL endowed. I don't aspire to a hotrod, but want something that will LAST another 53 years with little fuss, though what folks will do for petrol then is quite conjectural!

 

[Moparwilks]

good read. nice to see some 400 love lots of guys treat 72 like Dracula treats garlic with the end of the 383 engine & the 300 model. guess the 400 gets a bad rap for the wimpy cam & the least non mopar sounding displacement.

 

[Gerald Morris]

good read. nice to see some 400 love lots of guys treat 72 like Dracula treats garlic with the end of the 383 engine & the 300 model. guess the 400 gets a bad rap for the wimpy cam & the least non mopar sounding displacement.

'Tis a real pity, for the superstitious. Me, I LOVE that super thick main crank bearing mount webbing, ESPECIALLY on the '72. Mine is a 77, so it won't be so massive as that, but its STILL the STRONGEST BLOCK MoPar ever cast for B/RBs. One can bolt whatever heads one wishes, for B blocks especially, tho the 452 seems most common for post 1970, and given that the valve seats are hardened, that makes for one less worry. I know an old duffer who does titanium seats, if one has the $$. I don't. God-willing, I can raise the bread to rebuild the 400 within the next 12 months, then do some surgery on the 383 Tilly currently runs while the 400 does its job.