390 vs 408

[Valleyant]

HI,
My '70 Duster needs one of these engines. I have a 1981 360 and a 1972 318 to choose from. The 318 is a known good running motor. The 360 hasn't run for years and is partially disassembled. Budget is a concern although if I do a build it will get aluminum heads. Ocassional strip ( 1/4 mile) outings but mainly a street car. Automatic for now but it will probably be converted to 4 or 5 speed down the road sometime. Planning sub-frame connectors and front disc brakes. Thats about as much as I have planned for the suspension/chassis. Need your take on these stroker engines for a nice full interior/resto mod Duster...Thanks

 

[70aarcuda]

if budget is concern...

the 360/408 had more pistons to choose from...rings are cheaper since they are based off a 4.00 bore..shares chevy and ford engines...

the 318/390 ...either diamonds pistons or KB pistons ...rings are more expensive..smaller bore ..less cubic inches...

you should write out on paper and compare prices between the two...and see which engine is in the best shape and it could save you money in machine work...

 

[dodgetkboy78]

18 cubic inches = 18 HP............

I built a 390 because I wanted a purpose built motor, and love 318's....... the 408 is cheaper.

 

[Oldmanmopar]

There is no replacement for displacement. No brainer. just make sure you internally balance that 360 so you can use a nuetral balance converter.

 

[rumblefish360]

There is no replacement for displacement. No brainer. just make sure you internally balance that 360 so you can use a nuetral balance converter.

Agreed. Internal balanced motors are beter. hough you can have it externally balanced, why you would is beyond me for a build like this. Ha ha ha.

The selection of balancers and converters are larger and cheper for a internal balanced engine. Quicker, easier, shorter down time / swap times.

 

[srduster340]

Go with the 360 block. No brainer.

 

[pettybludart]

408 Hands down :thumblef:

 

[dodgetkboy78]

390, by far. The old 318 block is more than likely a better block, the smaller combustion chamber is more efficient, has less chance of detonation, and will get more MPG's......

And you can tell everyone it is a 318.

 

[AdamR]

May as well use the 360 block if you have it. You can still tell everyone its a 318.

 

[Abodyman]

There is no replacement for displacement. No brainer. just make sure you internally balance that 360 so you can use a nuetral balance converter.

No disrespect, but from all the research I've done, the horsepower ratings between the two is very comparible..... Since you have both engines you should go with the360 because the kits for those are much cheaper. That would be the only reason I'd go that route.

 

[Demon 408]

... Budget is a concern although if I do a build it will get aluminum heads.

I understand the budget but wonder why you say it will have aluminum heads? Good cast iron heads are available that may save you $ in the long run depending on future plans for motor

... Ocassional strip ( 1/4 mile) outings but mainly a street car. Automatic for now but it will probably be converted to 4 or 5 speed down the road sometime. Planning sub-frame connectors and front disc brakes. ...Need your take on these stroker engines for a nice full interior/resto mod Duster

Very similar build to my Demon with stroker 408. With your goals I wouldn't worry about horsepower numbers as much as budget and parts selection. Either motor will get you in the ball park. I used a 360 and 308 heads because I already owned them (RHS heads were not yet available) and an old dual plane LD340 intake. I would do it all again, but change to RHS heads.

This of course is my opinion, and worth every penny. :thumblef:

 

[Valleyant]

I understand the budget but wonder why you say it will have aluminum heads? Good cast iron heads are available that may save you $ in the long run depending on future plans for motor

Well, I figured it would be worth the weight savings, and will tolerate more compression, and I just know I would progress to them eventually so no use in rebuilding the iron heads. I think I am leaning towards the 408...just need to cart the block to the machinist and start already! The 390 still sounds interesting though! Thanks guys for the replies